Abstract
Purpose:
This scoping review aimed to explore the use of volitional voice tasks in assessing swallowing-related outcomes and to evaluate their therapeutic impact on swallowing disorders, including their effects on swallowing biomechanics.
Method:
This scoping review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews guidelines. A literature search was performed across multiple databases (PubMed, Web of Science, and Scopus), and additional records were identified through manual searches. After screening and eligibility assessment, 36 studies were included for data extraction and analysis. The Effective Public Health Practice Project Quality Assessment Tool for Quantitative Studies was employed to evaluate the quality of the included studies.
Results:
The review identified various volitional voice tasks, such as maximum phonation time and pitch glides, as potential assessment tools for predicting swallowing-related outcomes. Additionally, voice tasks targeting pitch modulation, increased vocal loudness, and squeezed voice quality showed promising therapeutic benefits for swallowing disorders across different populations, especially individuals with neurological conditions and head and neck cancer.
Conclusions:
While methodological limitations were found in current literature, volitional voice tasks demonstrate potential as complementary tools for assessing and treating swallowing disorders, leveraging their interconnected neurological and biomechanical mechanisms underlying functions. Further research with more robust methodologies is needed to establish the efficacy of these integrated interventions, facilitate their translation into clinical practice, and test new possibilities.
Swallowing and phonation are critical functions of the upper aerodigestive tract that are complexly intertwined through laryngeal mechanisms, extending beyond mere anatomical links to shared neurobiological control systems. Central to these functions are the vocal folds, which are primarily responsible for protecting the airway during swallowing, with secondary functions such as thoracic fixation and facilitating vocal demands (Kim & Dewan, 2021; Onwordi & Al Yaghchi, 2022).
Explorations into the neurobiological foundations of voice production and swallowing reveal an integrated control system within the central nervous system. Ludlow (2011, 2015) advocates for a unified neural framework, emphasizing intertwined processing mechanisms. These studies conclude that integrative neural mechanisms between vocalization for speech and upper airway protective mechanisms are present at both the brainstem and cerebral network levels. Furthermore, the nucleus ambiguus plays a central role in coordinating motor outputs that are necessary for voice production and swallowing. Prior research also underscores this integrated control involving multiple brain regions, including the cortex and brainstem (Ludlow, 2005).
Recent studies explore the detailed neuroanatomy and functional connectivity within these integrated systems. Li-Jessen and Ridgway (2020) emphasize the sensorimotor integration of vocalization and swallowing, highlighting the precise coordination required between the central and peripheral nervous systems. They detail how the laryngeal motor cortex within the primary motor cortex controls the movements of laryngeal musculature for both voice and swallowing through direct neural pathways that facilitate complex sensorimotor integration. Similarly, Belyk et al. (2021) discuss the coordinated role of the laryngeal motor cortices in respiration, phonation, and airway protection, reinforcing the concept of shared neural control mechanisms (LaGorio et al., 2008; McFarland & Tremblay, 2006).
Moreover, voice and swallowing share not only proximate physiology and neuromuscular control but also clinical outcomes. The coexistence of voice and swallowing impairments is prevalent among various patient populations, including individuals with neurological conditions such as Parkinson's disease (PD) and stroke, head and neck cancer, and conditions leading to glottal insufficiency (e.g., vocal fold paralysis, paresis, or prolonged intubation) and those who may experience presbylarynx (Barnett et al., 2019; Beton et al., 2022; de Bruijn et al., 2013; Giraldez-Rodriguez & Johns, 2013; Heman-Ackah et al., 2023; Wallace & McGrath, 2021). This overlap creates a potential opportunity to approach both functions together, enhancing treatment efficacy.
Empirical studies support that interventions designed with a cross-system perspective can significantly improve patient outcomes related to voice and swallowing (de Queiroz et al., 2022; LaGorio et al., 2008; Niu et al., 2023). This body of work lays a scientific foundation for cross-system therapeutic approaches, leveraging the concept of neuroplasticity and neural transference, where enhancing one motor domain may secondarily benefit a related system (Guedes et al., 2017; McFarland & Tremblay, 2006; Miloro et al., 2014).
Cross-system interaction implies that certain interventions proposed for a particular function could simultaneously transfer their gains to another motor behavior (LaGorio et al., 2008; McFarland & Tremblay, 2006). For example, the Shaker exercise, initially designed to enhance swallowing function, has also been observed to improve the Dysphonia Severity Index, demonstrating the bidirectional nature of this therapeutic transference (Easterling, 2008). Similarly, it has been documented that expiratory muscle strength training, primarily targeted at improving cough strength, also positively influences swallowing functions and enhances voice quality across diverse patient groups (Darling-White & Huber, 2017; Desjardins et al., 2022; Pitts et al., 2013; Reyes et al., 2020). These examples show the versatility of the transference principle, revealing its capacity to facilitate improvements across related motor behaviors, whether the initial therapeutic intent was to address voice, swallowing, or respiratory functions. By focusing on enhancing voice and swallowing capabilities simultaneously, these interventions have the potential to streamline therapeutic efforts, yielding time- and cost-saving efficiencies while potentially improving patients' quality of life.
Despite the demonstrated connections between these functions, our understanding of how voice therapy impacts swallowing-related kinematics remains limited. Current evidence broadly addresses the effects of voice training on swallowing outcomes but does not specify which attributes of the therapy are most beneficial or transferable. Additionally, while volitional voice tasks have been used in some research to predict swallowing-related outcomes, these studies have not been systematically reported before. The specific ways in which different vocal tasks and their attributes contribute to the effectiveness of volitional voice tasks in both assessment and therapy have not been thoroughly explored or clearly explained. These gaps hinder the development of optimized, evidence-based therapeutic protocols.
For example, Niu et al. (2023) and de Queiroz et al. (2022) conducted reviews that found voice therapy and training interventions to be beneficial for improving swallowing function in people with dysphagia. However, both reviews emphasized the need for further research to refine these protocols and assess long-term effects. Notably, neither review linked specific vocal attributes directly to swallowing outcomes, suggesting that the observed benefits might result from a combination of factors rather than isolated elements.
To address this gap, this scoping review has two purposes: (a) to explore the use of volitional voice tasks in assessing swallowing-related outcomes and (b) to evaluate the therapeutic impact of these tasks on swallowing disorders, including their effects on swallowing-related biomechanics. The outcomes of this review shed light on the clinical implications and elaborate on the anatomical and physiological connections, particularly focusing on the role of the laryngeal system.
Method
This scoping review was conducted in alignment with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for Scoping Reviews guidelines (Tricco et al., 2018). Swallowing outcomes in this study refer to the specific, measurable effects of swallowing function, such as aspiration risk, bolus transit times, pharyngeal residue, laryngeal elevation, airway protection, and laryngeal biomechanics. These outcomes focus on improvements following therapeutic interventions and the predictive ability of voice tasks for these swallowing-related measures. The Effective Public Health Practice Project (EPHPP) Quality Assessment Tool for Quantitative Studies was employed to assess the risk of bias in the included studies, even though quality assessment is not typically required for scoping reviews (Thomas et al., 2004).
Eligibility Criteria
The inclusion criteria included original studies involving adult human subjects (e.g., 18 years of age and above) that investigated the connections between swallowing and volitional voice tasks, which are defined as intentional, voluntary vocal exercises or activities such as pitch elevation, prolonged phonation, and vocal intensity modulation (including speech and singing) and specific phonatory exercises designed to assess or improve swallowing-related outcomes. The measured outcomes related to both voice and swallowing functions, including but not limited to swallowing safety and efficiency. Research designs of interest included peer-reviewed articles encompassing various study designs, including experimental, observational, and cross-sectional approaches. Studies involving healthy adults were included when the experiments involved voice tasks with outcomes related to swallowing-related kinematics, regardless of the absence of swallowing dysfunctions.
Excluded from this scoping review were reviews, reflective articles, single-case studies, nonhuman studies, articles not written in English, medical intervention studies, and studies focusing solely on postswallow voice changes such as “wet voice” assessments. Populations with tracheostomy were also excluded as their voice tasks typically involve different occlusion techniques (e.g., phonation valves, Passy Muir valves, total occlusion) that focus on voice restoration through mechanisms not exclusively dependent on volitional voice tasks. Similarly, while respiratory training exercises such as those targeting respiratory strength or cough effectiveness have demonstrated benefits for both voice and swallowing, these were excluded as they do not specifically involve the intentional use of voicing required to meet the definition of volitional voice tasks.
Information Sources and Search Strategy
To ensure a comprehensive collection of studies related to voice and swallowing cross-system dynamics, a thorough literature search was conducted through the electronic databases PubMed, Web of Science, and Scopus using a combination of tailored key words and MeSH terms to account for the unique indexing and terminology of each database (e.g., “cross-system interaction,” “assessment,” “therapy,” “voice disorders,” and “swallowing disorders”). The search was comprehensive and did not use date restrictions (from each database's inception until the collection date on May 4, 2024) and was peer-reviewed by the team before implementation. The peer review involved multiple team members cross-checking the search terms and criteria to ensure they were comprehensive and aligned with the study's aims (McGowan et al., 2016). The specific search queries used for this review are detailed in the Appendix for reference.
To further broaden the search scope, manual searches were performed on the reference lists of identified articles and relevant review papers, ensuring the inclusion of potential studies that did not appear in the databases. The research team also conducted a final check (July 9, 2024) for new literature through Google Scholar to incorporate the most recent findings. Search results were systematically exported into an Excel spreadsheet detailing titles, abstracts, authors, and key words to facilitate the subsequent screening and eligibility assessment process.
Study Selection and Data Extraction
The initial screening of titles and abstracts was conducted independently by a single reviewer, the main author (A.C.-A.), who applied predefined eligibility criteria outlined in the Eligibility Criteria section. This section details the specific inclusion and exclusion parameters. Subsequently, a pair of coauthors (J.V. and N.B.) performed the full-text evaluation of potential studies. A standardized form was developed to guide the selection process, ensuring consistency. Calibration exercises were performed to align the reviewers' assessments. In the event of discrepancies, a third member (A.C.-A.) was consulted to reach a consensus.
Data extraction was conducted using a form collaboratively developed by the research team to capture critical details of each study systematically. Two team members independently charted data from the selected studies (A.C.-A. and J.V.). The form, piloted for accuracy, was refined through iterative discussions to ensure the consistent extraction of information. Key categories extracted from each study included study characteristics (target population, age, sample size, sex distribution, and study design), interventions or experiments conducted (main methods and procedures), primary outcome measures and results (significant findings and statistical outcomes), potential voice–swallowing therapy applications, and specific vocal tasks or approaches used. Additionally, insights into using volitional voice tasks for assessing and improving swallowing-related outcomes were also documented.
Quality Assessment of Individual Sources
The EPHPP Quality Assessment Tool for Quantitative Studies was applied to appraise the risk of bias in included studies (Jackson & Waters, 2005). This appraisal covered key areas such as selection bias, study design, confounders, blinding, data collection methods, and dropouts/withdrawals, which are inherent to the tool's comprehensive evaluation framework (Armijo-Olivo et al., 2012).
Each study underwent an evaluation in several key domains and was subsequently rated as “strong,” “moderate,” or “weak.” A study was deemed “strong” if it did not receive any “weak” ratings across the domains, “moderate” if it received one “weak” rating, and “weak” if it had two or more “weak” ratings. The quality assessment process was rigorously and independently carried out by another pair of coauthors (S.E. and N.B.). In instances of initial assessment discrepancies, a third author was consulted to achieve consensus (A.C.-A.), enhancing the reliability and accuracy of the evaluation process. Visualization of the quality assessment was conducted using the robvis (Risk-of-bias VISualization) Shiny web app, a tool designed for the easy creation of high-quality figures summarizing risk-of-bias assessments in systematic reviews and research synthesis projects (McGuinness & Higgins, 2021).
Synthesis of Results
A PRISMA 2020–compliant flow diagram of the study selection process was generated using a specialized Shiny app (Haddaway et al., 2022). Additionally, data analysis and visualization were performed using RStudio (Version 2023.12.1+402; https://www.rstudio.com/) and the diagramming app draw.io (https://www.drawio.com/).
Results
As detailed in the adapted PRISMA flowchart (see Figure 1), the search across PubMed, Scopus, and Web of Science yielded 616 records. An additional 29 articles from the authors' personal collections, which were also subject to the same screening and eligibility criteria as the other records, were incorporated, bringing the total to 645 records. After deduplication, 517 records were screened for relevance through title and abstract review, excluding 456 records. The remaining 61 full-text articles were retrieved and assessed for eligibility, achieving a high interrater agreement of 96.5%. Ultimately, 36 studies met the inclusion criteria and were included in the final review.
Figure 1.
Process of identifying studies for inclusion in the review. Flowchart created using the Shiny app to produce Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020–compliant flowcharts.
Characteristics of Sources of Evidence
Published study characteristics, as detailed in Table 1, reveal a diverse array of research designs within the data set. Observational studies, including cross-sectional, case–control, case series, and prospective cohort studies, comprised approximately 69% of all studies. Within these, prospective cohort studies alone constituted about 19% of the total.
Table 1.
Characteristics of included studies.
| Study | Target population | Age (years) |
n (M, F) | Study design | |
|---|---|---|---|---|---|
| Range | M ± SD | ||||
| Balou et al. (2019) | Individuals with dysphagia (varied etiologies) | 67–86 | 75.3 ± 5.3 | 9 (3, 6) | Prospective single-arm intervention |
| Castillo et al. (2020) | Individuals with idiopathic PD | — | 67.75 ± 11.39 | 42 (22, 20) | Cross-sectional |
| de Fraga et al. (2018) | Poststroke individuals with neurogenic oropharyngeal dysphagia | — | IG: 73.2 ± 7.6 CG: 63.8 ± 12.9 |
IG: 5 (3, 2) CG: 5 (3, 2) |
Randomized controlled trial: pilot |
| El Sharkawi et al. (2002) | Individuals with idiopathic PD | 48–77 | 69.8 | 8 (6, 2) | Prospective single-arm intervention: pilot |
| Fujimaki et al. (2017) | OAs with dysphonia caused by glottal incompetence | 60–91 | IG: 73.8 ± 7.26 CG: 73.3 ± 6.66 |
IG: 199 (115, 84) CG: 216 (106, 110) |
Randomized controlled trial |
| Fuller et al. (2009) | Individuals with dysphagia (varied etiologies) | — | 56.2 ± 20 | 28 (—) | Prospective: case series |
| Jiang et al. (2015) | Healthy individuals | 21–28 | 24.86 ± 2.12 | 30 (20, 18) | Cross-sectional |
| Jo et al. (2021) | HNC patients with dysphagia | — | IG: 50.87 ± 3.68 CG: 59.15 ± 4.22 |
IG: 15 (9, 6) CG: 13 (10, 3) |
Randomized controlled trial |
| Kennedy et al. (2020) | Individuals with dysphagia (varied etiologies) | — | 57.61 ± 13.94 | 41 (17, 24) | Cross-sectional |
| Ko et al. (2018) | Individuals with PD and PS | — | PD: 72.1 ± 9.4 PS: 67.4 ± 11.6 |
PD: 10 (5, 5) PS: 20 (11, 9) |
Cross-sectional |
| Ku et al. (2021) | Individuals with dysphagia after radiotherapy for nasopharyngeal cancer | 44–78 | IG: 59.55 ± 8.05 CG: 59.8 ± 9.84 |
IG: 62 (46, 16) CG: 15 (7, 8) |
Prospective cohort: multicentric |
| Lim et al. (2020) | Poststroke individuals | 30–82 | 68.43 ± 13.26 | 106 (44, 62) | Prospective cohort |
| Malandraki et al. (2011) | Individuals with dysphagia (varied etiologies) | 31–92 | 68 ± — | 40 (16, 24) | Prospective cohort: pilot |
| Marques et al. (2023) | Individuals with PD | — | IG: 68.7 ± 9.7 CG: 60.7 ± 11.81 |
IG: 20 (13, 7) CG: 10 (5, 5) |
Cross-sectional: comparative |
| Mavrea & Regan (2019) | Individuals with dysphagia and respiratory diseases | — | 75 ± 8.98 | 17 (9, 8) | Prospective cohort: pilot |
| McCulloch et al. (1996) | Healthy individuals | 23–26 | — | 7 (6, 1) | Cross-sectional |
| Miles & Hunting (2023) | Individuals with suspected dysphagia | 17–97 | 66 ± 16 | 222 (147, 75) | Prospective cohort |
| Miles et al. (2017) | Individuals with PD | 49–83 | 68 ± 3.5 | 20 (14, 6) | Prospective single-arm intervention: pilot |
| Miloro et al. (2014) | Healthy individuals | 22–30 | 25 | 10 (6, 5) | Cross-sectional |
| Nozaki et al. (2021) | Individuals with progressive supranuclear palsy | 59–96 | — | 7 (4, 3) | Prospective single-arm intervention: pilot |
| Ozawa et al. (2022) | Individuals undergoing esophagectomy for esophageal cancer | — | 64.3 ± 8.4 | 137 (109, 28) | Retrospective study |
| Park et al. (2022) | Individuals with Parkinsonism, specifically IPD and MSA-C | — | IPD: 67 ± 7.12 MSA-C: 63.86 ± 4.91 |
IPD: 6 (—) MSA-C: 7 (—) |
Prospective single-arm intervention |
| Pearson et al. (2013) | Healthy individuals | 22–30 | 25 | 11 (6, 5) | Cross-sectional |
| Perera et al. (2008) | Healthy individuals | 18–40 | — | 17 (7, 10) | Cross-sectional |
| Rajappa et al. (2017) | Poststroke individuals | 43–94 | 71.5 ± 13.58 | 45 (22, 23) | Prospective cohort |
| Ren et al. (2022) | Poststroke individuals | 50–75 | IG: 52.5 ± 6.3 CG: 53.8 ± 7.2 |
IG: 45 (29, 16) CG: 45 (27, 18) |
Retrospective (interventional intent) |
| Sayaca et al. (2020) | Poststroke individuals with hemiplegia (RH and LH stroke) | — | RH: 73.54 ± 7.28 years LH: 73.15 ± 6.94 |
RH: 37 (18, 19) LH: 20 (11, 9) |
Cross-sectional |
| Shaker et al. (2002) | Healthy individuals | — | 41 ± 2 | 11 (—) | Cross-sectional |
| Song et al. (2023) | Poststroke individuals | 43–77 | 57.70 | 40 (27, 13) | Cross-sectional with predictive modeling: pilot |
| Stegemöller et al. (2017) | Individuals with Parkinson's disease (LD and HD singing group) | — | LD: 69 ± 7 HD: 65 ± 11 |
LD: 18 (6, 12) HD: 6 (2, 4) |
Controlled trial with a nonconcurrent comparison group |
| Tabor Gray et al. (2023) | Individuals with amyotrophic lateral sclerosis | — | 63.14 ± 10.95 | 62 (32, 30) | Prospective (longitudinal natural history study) |
| Tawada et al. (2023) | Individuals undergoing esophagectomy for esophageal cancer | — | — | 409 (333, 76) | Prospective cohort |
| Vaiano et al. (2021) | Healthy individuals | 21–36 | 27 | 12 (6, 6) | Cross-sectional |
| Venkatraman et al. (2020) | Healthy YAs and OAs | — | YAs: 72.85 ± 5.59 OAs: 72.85 ± 5.59 |
YAs: 10 (5, 5) OAs: 8 (4, 4) |
Cross-sectional |
| Yamaguchi et al. (2018) | Individuals with dysphagia (varied etiologies) | — | 77.0 ± 14.6 | 30 (22, 8) | Cross-sectional |
| Yeo et al. (2021) | Individuals with dysphagia due to neurological impairments (PD, multiple system atrophy) and HNC (tongue cancer, mandibular gland cancer) | 54–77 | 65.8 | 4 (2, 2) | Prospective single-arm intervention (case study) |
Note. Em dashes indicate data not reported. M = male; F = female; PD = Parkinson's disease; IG = intervention group; CG = control group; HNC = head and neck cancer; PS = Parkinsonian syndrome; IPD = idiopathic PD; MSA-C = multiple system atrophy–cerebellar type; RH = right hemisphere; LH = left hemisphere; LD = low dosage; HD = high dosage; YAs = young adults; OAs = older adults.
Interventional studies featuring randomized controlled trials, prospective single-arm interventions, a retrospective study with interventional intent, and a controlled trial with a nonconcurrent comparison group made up about 31% of the studies. Notably, prospective single-arm intervention studies, which include several pilot studies, accounted for roughly 16% of the total.
Pilot studies, as designated by the original authors, were used to test feasibility and refine research protocols across various designs. These comprised about 22% of all articles reviewed. Within this category, prospective single-arm intervention pilot studies alone represented approximately 9% of the entire data set.
Across all reviewed research articles, participant ages ranged from 18 to 92 years. Demographic details reveal a generally balanced distribution between biological male and female participants across the data set, with some studies noting a slight male predominance in conditions such as PD and stroke. The scale of the studies showed substantial variability, with smaller pilot studies contrasting with larger studies conducted by Fujimaki et al. (2017) and Miles and Hunting (2023). These larger studies involved cohorts of several hundred participants, specifically 415 and 222, respectively.
Regarding target populations, approximately 44% of the studies concentrated on neurodegenerative disorders such as PD, multiple system atrophy, progressive supranuclear palsy (PSP), and stroke patients. Another 14% of the studies targeted individuals with dysphagia described by the authors as resulting from various causes. Healthy subjects comprised 22% of the studies. Head and neck cancer patients accounted for 11% of the findings. The remaining studies focused on individuals with dysphagia and respiratory diseases, those suspected of having dysphagia, and older adults experiencing dysphonia due to glottal incompetence.
Publication Trends
The review of 36 selected studies spanning from 1996 to 2023 shows an increase in published research on the use of volitional voice tasks and their therapeutic impacts on swallowing-related outcomes. In the decade of the 1990s, only one study was published, increasing to four studies in the 2000s. The 2010s saw a more substantial rise with 13 studies, and the current decade, the 2020s, has already produced 18 studies. As illustrated in Figure 2, this upward trend in the 2020s indicates a notable rise in the number of studies compared to previous decades, based on the selected studies and search criteria of this review.
Figure 2.
Publication trends in selected studies on voice- and swallowing-related research (1990s–2020s).
Quality Assessment of Individual Sources
The EPHPP Quality Assessment Tool was applied to evaluate the selected studies, revealing varied levels of methodological quality. Figure 3 synthesizes these evaluations, displaying the frequency of “strong,” “moderate,” or “weak” ratings within each domain via proportional bar graphs and provides a comparative perspective on the methodological rigor within each domain. It is important to note that a “weak” rating does not necessarily imply that the study is of low value or quality but rather that certain study components either were not fully described or did not align with the specific criteria outlined by the EPHPP tool.
Figure 3.
Bar graphs (color blind–friendly) summarize the overall quality of the assessed studies, showcasing the distribution of “weak,” “strong,” and “moderate” ratings within the methodological domains as per the Effective Public Health Practice Project Quality Assessment criteria.
Overall, the assessment of EPHPP domains indicated that approximately half of the studies (50%) were rated as “weak,” while 36% were classified as “moderate,” and only 14% were deemed “strong.” Figure 4 further delineates these ratings for individual studies. Studies by Fujimaki et al. (2017), Miles et al. (2017), de Fraga et al. (2018), Jo et al. (2021), and Tabor Gray et al. (2023) demonstrate methodological strengths, specifically in study design and confounder management, achieving an overall “strong” rating. Despite consistent strong performance in data collection across all studies, weaknesses were evident in study design, blinding, and selection bias, leading to lower methodological ratings in these domains.
Figure 4.
A traffic light plot (color blind–friendly) indicating the quality in specific component ratings and an overall quality assessment per study, as defined by the Effective Public Health Practice Project criteria.
Many studies within this review were cross-sectional, which inherently led to lower ratings in study design. Additionally, for cross-sectional and retrospective studies, criteria such as blinding and dropouts were often marked as “not applicable,” reflecting the limitations of these study designs. Notably, studies published since 2017 have shown overall improvements, particularly in study design, which have contributed to the enhancement of methodological quality and addressed some of these weaker domains.
Results of Individual Sources of Evidence
Table 2 presents a detailed summary of interventions, outcomes, and key results. Maximum phonation time (MPT) accounted for approximately 28% of the findings. This was followed closely by vocal pitch glides and pitch elevation in about 25% of the studies. Lee Silverman Voice Treatment LOUD (LSVT-LOUD) was the focus of about 11% of the reviewed literature. Furthermore, Table 2 catalogs a diverse array of other volitional voice tasks identified in the literature, such as effortful pitch glide (EPG), therapeutic singing, and loud/effortful vocalizations. Subsequent sections of this review systematically categorize the findings based on the application of these vocal tasks for assessment, for therapeutic interventions, or for both assessment and therapy. Correspondingly, Figure 5 shows the distribution and intersection of the identified volitional voice tasks across the assessment and therapy domains in the management of swallowing disorders.
Table 2.
Study intervention and main results.
| Study | Intervention/experiment | Main outcome measures | Main results | Potential voice–swallowing therapy insights | Identified vocal task/vocal approach |
|---|---|---|---|---|---|
| Balou et al. (2019) | Implemented an 8-week high-intensity swallowing exercise regimen, including varied techniques and pitch glides in individuals with dysphagia |
|
Improvements in MBSImP oral and pharyngeal composite scores; specific improvements in initiation of pharyngeal swallow, laryngeal elevation, and pharyngeal residue. Nonsignificant reduction in median PAS scores. | Effortful pitch glides could strengthen muscles involved in both voice and swallowing, indicating their potential utility in swallowing therapy. |
|
| Castillo et al. (2020) | Correlated peak SGP and key pulmonary function parameters in PD individuals |
|
Peak SGP has a moderate but significant linear association with MEP, voluntary, and reflex PCF, but not with MIP in individuals with PD. | Loud vocal tasks improving subglottic pressure could contribute to swallowing safety by enhancing glottic closure and SGP. |
|
| de Fraga et al. (2018) | Compared myofunctional therapy alone to its combination with vocal exercises in stroke rehabilitation |
|
The experimental group (myofunctional + vocal exercises) showed a significant increase in FOIS from 4 to 7, whereas the control group (only myofunctional exercises) had a smaller increase from 5 to 6. No significant difference between groups posttherapy. | Vocal exercises, particularly pitch glides and glottal closure tasks, could significantly improve swallowing function in stroke survivors. |
|
| El Sharkawi et al. (2002) | Conducted 16 LSVT-LOUD sessions over 4 weeks, focusing on enhancing vocal loudness and intensity in PD individuals |
|
LSVT-LOUD improved oral residue and tongue base function and significantly enhanced vocal intensity. | LSVT-LOUD would indirectly enhance swallowing function through improved vocal fold adduction and respiratory support. |
|
| Fujimaki et al. (2017) | Tested a self-administered vocal exercise focusing on glottal closure for elderly people with glottal incompetence |
|
Self-controlled vocal exercise improved glottal closure and reduced hospitalizations for pneumonia in the intervention group compared to control. | Pull-up voice exercise demonstrates clinical effectiveness in enhancing glottal closure, underscoring the pivotal role of vocal cord adduction in preventing aspiration pneumonia. MPT is a good metric to track therapy improvements. |
|
| Fuller et al. (2009) | Validated the PSM through simultaneous endoscopic and fluoroscopic evaluations in individuals with dysphagia |
|
The PSM is a valid surrogate measure of pharyngeal motor integrity. | PSM, triggered by pitch glides, could serve as a valuable tool for assessing pharyngeal muscle strength and swallowing safety. |
|
| Jiang et al. (2015) | Analyzed velopharyngeal function changes at varied sound intensities in a healthy cohort |
|
Significantly greater angular parameter values and velopharyngeal closure width at high sound intensity. Angular and linear measurements indicated a more significant velopharyngeal closure at high sound intensities. Higher sound intensity led to greater velopharyngeal constriction, evidenced by increased angular parameters and specific linear measurements excluding effective velopharyngeal length and vertical velopharyngeal length. |
Adjusting vocal intensity through pitch glides could affect velopharyngeal closure, with potential applications in voice and swallowing therapy. |
|
| Jo et al. (2021) | Explored therapeutic singing as an intervention to improve swallowing functions over a 4-week period in individuals with head and neck cancer |
|
L-DDK significantly increased in the intervention group. Swallowing functions improved as shown by significant improvements in VDS and DIGEST scores, especially in the pharyngeal phase. | Therapeutic singing, integrating pitch glides, could improve laryngeal elevation and the pharyngeal phase of swallowing, emphasizing the role of vocal exercises in swallowing mechanics. |
|
| Kennedy et al. (2020) | Investigated the differential effects of pitch glides on laryngeal lift in dysphagia patients |
|
The larynx lifted significantly less during a pitch glide than during a swallow, indicating that pitch glide is not an ideal task to predict laryngeal lift during swallowing. | Pitch glides might not mimic the extent of laryngeal lift observed during swallowing as effectively as hoped, suggesting a more nuanced approach to their use in dysphagia assessment. |
|
| Ko et al. (2018) | Assessed the relationship between MPT and swallowing function in Parkinsonism |
|
Significant correlations found between MPT and VDS, especially in bolus formation, oral transit time, pharyngeal swallow triggering, and laryngeal elevation. MPT was moderately correlated with NIH-SSS and VDS but not with PAS. | MPT could offer insights into phonatory function's influence on swallowing efficiency, particularly in tasks requiring precise laryngeal control. |
|
| Ku et al. (2021) | Examined pharyngeal motor function using VPSM and endoscopic grading in dysphagia postradiotherapy |
|
VPSM showed high intrarater and interrater reliability, predictive of EPCG scale ratings. EPCG correlated with PCR and was predictive of aspiration. VPSM presence indicated good pharyngeal motor function. | VPSM could be a promising therapeutic exercise to enhance pharyngeal contraction and coordination. |
|
| Lim et al. (2020) | Evaluated MPT as a screening tool for dysphagia risk in acute stroke patients |
|
MPT was significantly different and correlated with PAS, ASHA NOMS, and FDS scores. MPT differed significantly among normal, penetration, and aspiration groups. | MPT may serve as a simple, noninvasive indicator for dysphagia risk, highlighting the integral role of vocal cord activity in swallowing safety. |
|
| Malandraki et al. (2011) | Explored the predictive value of pitch glides for swallowing safety and efficiency in individuals with dysphagia |
|
Both maximum F0 and perceptual evaluation of pitch elevation significantly predicted PAS scores for thin liquid swallows, indicating that reduced pitch elevation may signify airway protection issues. | Pitch glide tasks could be predictive of dysphagia severity. |
|
| Marques et al. (2023) | Studied UES function and vocal tests using high-resolution manometry in PD patients |
|
The tests of high pitch /a/, /a/ with tongue protrusion, high pitch /i/, and /i/ with tongue protrusion significantly increased laryngeal elevation; however, an increase in the size and pressure of the UES was also observed. | Vocal tasks, especially high pitch glides, could impact UES function and laryngeal movement, potentially improving dysphagia rehabilitation outcomes. |
|
| Mavrea & Regan (2019) | Analyzed pitch glides' diagnostic accuracy for detecting aspiration in respiratory disease patients |
|
Maximum F0 of sound /a/ had high sensitivity and specificity in identifying aspiration on 10 ml of liquids during VFSS. Both pitch glides (/a/ and /i/) had moderate sensitivity and specificity in predicting aspiration on a sip of liquids. Pitch glide measures had low accuracy in predicting pharyngeal residue and hyolaryngeal excursion. | Pitch glide tasks could serve as an initial screening tool for aspiration risk, linking control of vocal folds to swallowing safety. |
|
| McCulloch et al. (1996) | Examined TA and IA muscle activity during various vocal and swallowing tasks in healthy individuals |
|
The study found that the TA and IA muscles showed the greatest magnitude of EMG activity during swallowing tasks, suggesting their primary role in protecting the airway during swallow. Phonatory tasks also showed increased EMG activity with higher pitch. | Focused exercises on the TA and IA muscles might offer targeted therapeutic interventions, enhancing voice and swallowing functions by improving airway protection. |
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| Miles & Hunting (2023) | Assessed the PSM's relationship with swallowing safety and efficiency in acute care patients |
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PSM impairment observed in 46% of patients correlated with accumulated secretions, penetration–aspiration, and postswallow residue. PSM reliability agreed with pharyngeal constriction ratio on videofluoroscopy. Abnormal PSM was associated with vocal cord immobility, reduced peak cough flow, reduced swallow frequency, and restricted diet at hospital discharge. | PSM during endoscopic assessment could predict swallowing safety and efficiency, emphasizing its role in dysphagia management strategies. |
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| Miles et al. (2017) | Investigated the impact of LSVT-LOUD on swallowing and cough functions in PD patients |
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Significant gains in SPL, reduction in pharyngeal residue, increased PES opening duration, and improvement in involuntary cough peak expiratory flow rate and rise time, sustained at 6 months | LSVT-LOUD may have a beneficial effect on swallowing safety and efficiency by improving pharyngeal muscle function and cough effectiveness in Parkinson's disease patients. |
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| Miloro et al. (2014) | Compared EPG exercise effects to swallowing mechanics using dynamic MRI in healthy individuals |
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Except for superior hyoid movement (greater in swallowing), no significant differences in biomechanics between EPG and swallowing were observed, suggesting that EPG mimics key swallowing mechanics closely. | EPG exercises could be effective in targeting muscles involved in swallowing. |
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| Nozaki et al. (2021) | Evaluated LSVT-LOUD's impact on swallowing functions in PSP patients |
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LSVT-LOUD significantly shortened the median duration of upper esophageal sphincter opening in videofluoroscopy, suggesting improved swallowing function. However, voice changes, including increases in voice intensity and sustained duration, were noted but not statistically significant. | LSVT-LOUD could potentially enhance swallowing function in PSP patients through improved neuromuscular coordination. |
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| Ozawa et al. (2022) | Evaluation of preoperative MPT as a predictor of postoperative pneumonia in patients undergoing esophagectomy |
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Shorter preoperative MPT was significantly associated with a higher incidence of postoperative pneumonia, particularly in male patients. | Underscores the importance of preoperative respiratory and phonatory assessments, particularly MPT in identifying patients at risk for postoperative complications. |
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| Park et al. (2022) | Assessed LSVT-LOUD's effects on swallowing functions in neurodegenerative disorders |
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Significant improvements in overall voice and swallowing measures, especially in the pharyngeal phase score and total score of the VDS, were observed after LSVT-LOUD in both groups. | LSVT-LOUD's focus on increasing vocal loudness has shown potential posttreatment benefits for swallowing functions, indicating its efficacy in neurodegenerative disorders. | - LSVT-LOUD |
| Pearson et al. (2013) | Measured muscle activation during swallowing and specific exercises using functional MRI in healthy individuals |
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Significant activation observed in the geniohyoid, mylohyoid, palatopharyngeus, and stylopharyngeus during swallowing and exercises, indicating their crucial role in hyolaryngeal elevation. The Mendelsohn maneuver and effortful pitch glide effectively targeted these muscles. | EPG could effectively target muscles involved in hyolaryngeal elevation, supporting their application in dysphagia therapy. |
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| Perera et al. (2008) | Explored phonation's effect on UES pressures and related movements in healthy individuals |
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Phonation induces a significant increase in UES pressure, suggesting the existence of a phonation-induced UES contractile reflex. This increase in UES pressure is significantly higher than that of the distal esophagus, LES, and stomach. | Phonation-induced UES contractile reflex during pitch glides suggests a unique mechanism for airway protection, indicating the potential of vocal tasks in therapeutic or diagnostic applications. |
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| Rajappa et al. (2017) | Investigated pitch elevation's ability to predict silent aspiration in stroke patients |
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Reduced maximum pitch elevation measured acoustically (max F0) significantly predicts silent aspiration of small liquid volumes in stroke patients, with 80% sensitivity and 65% specificity. The study found that max F0 did not predict nonsilent aspiration or penetration and did not significantly correlate with MBSImP variables. | Reduced pitch glide ability might indicate a risk of silent aspiration in stroke patients, pointing to a shared neurophysiological substrate between voice and swallowing functions. |
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| Ren et al. (2022) | Combined systematic voice training with swallowing exercises in stroke patient rehabilitation |
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Systematic voice training combined with swallowing function exercise was found to effectively prevent swallowing dysfunction in stroke patients and improve their quality of life. This approach resulted in lower incidences of swallowing dysfunction, aspiration pneumonia, and malnutrition compared to the group that received only single swallowing exercise. Furthermore, it led to higher scores in psychological, physical, social adaptation and overall quality of life dimensions. | Combining systematic voice training with swallowing exercises could effectively prevent swallowing dysfunction and improve quality of life in stroke patients. |
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| Sayaca et al. (2020) | Assessed the impact of unilateral stroke on swallowing and laryngeal function in stroke patient rehabilitation |
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No significant differences in swallowing difficulty or MPT between groups. Better neck flexor muscle endurance observed in the left hemisphere group. Significant relationships were found between MPT and muscle endurance and swallowing difficulty in the right hemisphere group. | MPT would provide insights into swallowing performance in hemiplegic stroke patients, suggesting a potential avenue for assessing laryngeal function in stroke rehabilitation. |
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| Shaker et al. (2002) | Measured vocal cord closure and intratracheal pressures across various tasks in healthy individuals |
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Vocal cord closure pressure varies depending on the performed function, with significantly higher pressures during tasks such as swallowing, coughing, straining, and phonation compared to intratracheal pressures. | Task-dependent variations in vocal cord closure pressure indicate the potential of vocal exercises, especially those enhancing closure. |
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| Song et al. (2023) | Employed voice parameters to identify risk of aspiration in poststroke individuals |
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The study's model combined MPT, F2 /u/, and ΔF0 as voice parameters to successfully identify the risk of aspiration with 87.5% accuracy and a sensitivity of 100% for high-risk cases. | Utilizing vocal parameters such as MPT and acoustic speech assessment offers a novel, noninvasive model for predicting aspiration risk in dysphagia patients. |
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| Stegemöller et al. (2017) | Examined the effects of therapeutic singing on swallowing and motor symptoms in PD |
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Therapeutic group singing resulted in significant increases in EMG timing measures, indicating prolonged laryngeal elevation during swallowing, as well as improvements in clinical symptoms (UPDRS scores). | Therapeutic singing, prolonging laryngeal elevation, could offer a novel early intervention strategy for oropharyngeal dysphagia in Parkinson's disease. |
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| Tawada et al. (2023) | Evaluation of preoperative MPT as a predictive tool for postoperative aspiration pneumonia in patients undergoing esophagectomy for esophageal cancer |
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Short MPT was found to be significantly associated with a higher incidence of late-onset pneumonia. Multivariate analysis showed that short MPT was an independent risk factor for late-onset pneumonia. | MPT could serve as a noninvasive, predictive screening tool for assessing the risk of aspiration pneumonia post-esophagectomy, indicating its potential utility in preoperative assessments. |
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| Tabor Gray et al. (2023) | Evaluate MPT as a potential home-based marker for respiratory decline in ALS |
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MPT was a significant predictor of FVC and PCF impairments. The discriminant ability of MPT was excellent for PCF and acceptable for FVC. | MPT can serve as a noninvasive, telehealth-compatible surrogate marker for important respiratory and airway clearance indices in ALS. |
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| Vaiano et al. (2021) | Investigated pharyngeal, esophageal, and UES pressures during vocal tasks using HRM in healthy individuals |
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The study found that esophageal pressures are higher during vocalization than at rest, and these pressures increase with vocal loudness. Pharyngeal and UES pressures did not significantly differ from rest. | Specific vocal tasks employed at varying intensities offer a practical approach to evaluate and potentially enhance UES and pharyngeal function through vocal exercises. |
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| Venkatraman et al. (2020) | Compared hyoid kinematics between swallowing and maximum vocal pitch elevation tasks in healthy young and older adults |
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Superior hyoid excursion was significantly greater during liquid and pudding swallows compared to vocal pitch elevation tasks. No significant difference in anterior hyoid excursion between swallowing and vocal tasks, although overall reduced in older adults. Moderate positive correlation between superior hyoid excursion during liquid swallows and maximum pitch elevation in young adults. | Pitch glides offer potential utility in evaluating and training the swallowing mechanism especially when considering age-related adaptations in therapeutic approaches. |
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| Yamaguchi et al. (2018) | Studied the relationship between swallowing function and respiratory/phonatory functions in individuals with dysphagia |
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Chest expansion scores at the 10th rib level and MPT were significantly shorter in patients with aspiration than without. A positive correlation was noted between the distance of laryngeal elevation and both chest expansion score and MPT. | A decline in respiratory and phonatory functions, including diminished MPT values and reduced chest expansion scores, directly impacts laryngeal elevation, thereby increasing the risk of aspiration. |
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| Yeo et al. (2021) | Investigation of a singing-enhanced swallowing protocol to improve swallowing function in patients with neurological impairments and head and neck cancer |
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Singing exercises improved VDS scores, indicating enhanced swallowing function across the board. Improvements in L-DDK and SWAL-QOL scores were also observed. MPT outcomes varied, with increases in neurological patients and decreases in those with head and neck cancer. | The study validated the effectiveness of singing exercises in treating swallowing disorders, emphasizing the importance of customized therapeutic approaches that consider the underlying cause of dysphagia. |
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Note. MBSImP = Modified Impairment Swallowing Profile; PAS = Penetration–Aspiration Scale; VPSM = velopharyngeal squeeze maneuver; EPG = effortful pitch glide; SGP = subglottic pressure; PD = Parkinson's disease; MIP = maximal inspiratory pressure; MEP = maximal expiratory pressure; PCFr = reflex peak cough flow; PCFv = voluntary peak cough flow; PCF = peak cough flow; FOIS = Functional Oral Intake Scale; GRBAS = Grade or overall severity of dysphonia, Roughness, Breathiness, Aesthenia, and Strain voice quality assessment; LSVT = Lee Silverman Voice Treatment; MBS = modified barium swallow; F0 = fundamental frequency; MPT = maximum phonation time; FEES = flexible endoscopic evaluation of swallowing; PSM = pharyngeal squeeze maneuver; dB = decibels; SPL = sound pressure level; VFSS = videofluoroscopic swallowing study; HNR = harmonics-to-noise ratio; L-DDK = laryngeal diadochokinesis; DIGEST = Dynamic Imaging Grade of Swallowing Toxicity; VDS = Videofluoroscopic Dysphagia Scale; NIH-SSS = National Institutes of Health Swallowing Safety Scale; EPCG = endoscopic pharyngeal contraction grade; PCR = pharyngeal constriction ratio; FDS = Functional Dysphagia Scale; ASHA NOMS = American Speech-Language-Hearing Association National Outcomes Measurement System swallowing scale; UES = upper esophageal sphincter; HRM = high-resolution manometry; TA = thyroarytenoid muscle; IA = interarytenoid muscle; EMG = electromyographic analysis of TA and IA muscles; PES = pharyngoesophageal segment; PEFR = peak expiratory flow rate; PEFRT = peak expiratory flow rise time; MRI = magnetic resonance imaging; PSP = progressive supranuclear palsy; SHI-15 = Speech Handicap Index-15; SWAL-QOL = Swallowing Quality of Life; LES = lower esophageal sphincter; EAT-10 = Eating Assessment Tool; UPDRS = Unified Parkinson's Disease Rating Scale; ALS = amyotrophic lateral sclerosis; FVC = forced vital capacity.
Figure 5.
Venn diagram illustrating the distribution of volitional voice tasks/approaches in the domains of assessment, therapy, and their intersection for swallowing disorder management.
Key Findings
The key findings of this scoping review are presented in three subsections: The first examines the use of volitional voice tasks in assessing swallowing-related outcomes, the second evaluates their therapeutic impact on swallowing disorders and biomechanics, and the third discusses dual-purpose vocal tasks used in both assessment and therapy. Each section specifies the voice tasks discussed, defining and contextualizing terms to ensure the findings are directly tied to the study aims. For detailed outcomes of each study, including main outcome measures and potential voice–swallowing therapy insights, please refer to Table 2.
Volitional Voice Tasks in Assessing Swallowing-Related Outcomes
This section explores the use of volitional voice tasks as predictive tools for swallowing-related outcomes. By evaluating these tasks, we aim to determine their utility as noninvasive indicators of swallowing function, aligned with our objective to assess their role in swallowing assessment.
MPT. MPT measures the maximum duration an individual can sustain a vowel sound (/a:/) on one deep breath at a comfortable pitch and loudness, indirectly evaluating laryngeal function and vocal cord vibration. Subjects receive standardized instructions and perform at least three trials; the highest measured value is used as the final MPT measurement (Ko et al., 2018; Ozawa et al., 2022; Speyer et al., 2010). Fujimaki et al. (2017) specifically investigated the therapeutic benefits of MPT-related voice exercises in elderly individuals (> 60 years old), focusing on improving vocal function and glottal closure efficiency. Their study also explored MPT's potential as an early indicator of swallowing dysfunction.
Ko et al. (2018) examined its relevance in individuals with Parkinsonism, linking MPT measurements to specific swallowing mechanics such as bolus formation and laryngeal elevation. Also, in the neurological population, research has been conducted on stroke survivors. Lim et al. (2020) correlated MPT with dysphagia severity, while Sayaca et al. (2020) identified significant relationships between MPT, muscle endurance, and swallowing difficulty, suggesting MPT's potential for assessing laryngeal function in patients who have had a stroke.
Yamaguchi et al. (2018) explored the relationship between MPT and swallowing function in individuals with dysphagia, finding that an MPT of 6.10 s or less, as assessed by videofluoroscopic swallowing study, may indicate increased aspiration risk. They also investigated chest expansion measures, demonstrating that reduced respiratory function, with a chest expansion of 2.95 cm or lower at the 10th rib level, significantly exacerbates the risks of swallowing dysfunctions. Song et al. (2023) expanded the application of MPT within a multiparametric model to predict aspiration risk in a mixed clinical cohort. Their study demonstrated that MPT, when combined with other speech-related parameters, such as the second formant frequency at /u:/ and the fundamental frequency difference before and after swallowing, can significantly enhance the accuracy of aspiration risk assessment. This approach, which offers high sensitivity and specificity, suggests that MPT could serve as a valuable component in a comprehensive and noninvasive dysphagia screening protocol.
Studies by Ozawa et al. (2022) and Tawada et al. (2023) evaluated the role of preoperative MPT task in predicting postoperative pneumonia in esophageal cancer patients. Ozawa et al. found that an abnormal MPT, defined as less than 15.0 s for men and 14.3 s for women, was associated with a higher incidence of pneumonia, particularly in male patients. Similarly, Tawada et al. classified patients into short MPT (< 15 s for men and < 10 s for women) and normal MPT groups, revealing that those with short MPT had a significantly higher incidence of late-onset pneumonia. Multivariate analysis confirmed short MPT as an independent and statistically significant risk factor for late-onset pneumonia, underscoring its utility as a predictive tool in preoperative assessments.
Recently, Tabor Gray et al. (2023) demonstrated that MPT, along with forced vital capacity (FVC) and peak cough flow (PCF), serves as a valuable indicator of swallowing safety in patients with amyotrophic lateral sclerosis (ALS). Lower MPT values were closely associated with increased risks of aspiration, reduced airway clearance capacity, and compromised pulmonary function, which elevate the risk of respiratory infections and pneumonia. Specifically, an MPT of less than 9.5 s was found to predict impaired PCF, essential for effective airway clearance significantly. The study emphasized that MPT could serve as a low-cost, pragmatic surrogate marker for FVC and PCF, particularly useful in telehealth settings. This approach could facilitate remote monitoring and management of ALS patients, providing critical assessments for those with limited mobility or access to in-person care.
Maximum pitch elevation. Maximum pitch elevation (MPE), or pitch glide, involves raising the pitch of the voice (F0) while producing sounds such as /i:/ or /a:/. The task starts with the individual taking a deep breath, then saying the vowel sound in their comfortable voice, and gradually gliding their voice to the highest possible pitch, holding it for 3–4 s. This exercise is typically modeled by the clinician, practiced by the participant, and repeated multiple times for accuracy (Malandraki et al., 2011; Mavrea & Regan, 2019; Rajappa et al., 2017). Malandraki et al. (2011) and Rajappa et al. (2017) utilized MPE tasks to assess silent aspiration risk in patients with upper aerodigestive tract dysfunctions. Malandraki et al. found that lower MPE, both acoustically measured and perceptually rated, was significantly associated with higher Penetration–Aspiration Scale scores for thin liquid swallows, indicating a greater risk of silent aspiration. Rajappa et al. demonstrated that reduced MPE in poststroke patients predicted silent aspiration of small liquid volumes with 80% sensitivity and 65% specificity. Mavrea and Regan (2019) explored the accuracy of MPE in predicting aspiration in patients with respiratory diseases. They found that the acoustic analysis of the /a:/ sound during pitch glide had high sensitivity and specificity for detecting aspiration on 10-ml liquid swallows. However, MPE tasks were less accurate in predicting pharyngeal residue and hyolaryngeal excursion.
Venkatraman et al. (2020) investigated the biomechanical relationship between swallowing and vocal pitch elevation in older adults. Their study revealed that anterior hyoid excursion was similar during both swallowing and pitch elevation tasks, indicating that this aspect of hyoid movement is consistent across these functions. However, superior hyoid excursion was significantly greater during liquid swallows compared to pitch tasks, highlighting a key difference in the biomechanical demands of these activities. Additionally, the study found that older adults exhibited reduced anterior hyoid excursion overall, suggesting that age-related muscle changes may impact the biomechanics of both swallowing and pitch elevation. Building on this exploration of the biomechanical connections, Kennedy et al. (2020) critically evaluated the efficacy of pitch glides as a diagnostic tool for dysphagia by comparing laryngeal lift during pitch glide to that during bolus swallows in dysphagic patients. Their findings revealed that laryngeal lift was significantly less during pitch glide than during swallowing, suggesting that pitch glides might not accurately mimic the laryngeal elevation required for effective swallowing.
Pharyngeal squeeze maneuver. The pharyngeal squeeze maneuver (PSM) involves asking the patient to make a strong, high-pitched /e:/ sound to assess pharyngeal constriction and narrowing of the hypopharynx and piriform sinuses. In a study by Fuller et al. (2009), simultaneous endoscopic and fluoroscopic evaluations were conducted to compare the PSM with the pharyngeal constriction ratio (PCR). It was found that an absent PSM corresponded to a higher PCR, indicating a weaker pharynx, suggesting that the PSM is a valid surrogate measure of pharyngeal motor integrity. Building on this concept, Ku et al. (2021) introduced the velopharyngeal squeeze maneuver (VPSM), a variant of PSM specifically designed for Chinese speakers who have undergone radiotherapy for nasopharyngeal carcinoma. This study employed both the VPSM and a novel endoscopic pharyngeal contraction grade (EPCG) scale during endoscopic examinations to assess pharyngeal motor function. The VPSM showed strong reliability and was closely associated with pharyngeal motor function, correlating well with the EPCG scale and PCR. Furthermore, the VPSM and EPCG scale were effective in predicting aspiration risk, reinforcing their utility as tools for evaluating pharyngeal function in this patient population.
Loud voice tasks. Castillo et al. (2020) examined the association between subglottic pressure (SGP) and pulmonary function in individuals with PD. In this study, SGP was indirectly assessed through intraoral pressure during loud voice tasks, specifically the production of the plosive /pa:/ at maximum loudness. The findings revealed that higher SGP values were directly associated with increased expiratory muscle strength and improved PCF. Castillo et al. suggested that gains in SGP through loud voice tasks, while primarily enhancing voice intensity, may also translate into better outcomes for airway protection and swallowing safety in PD patients.
Therapeutic Impact of Volitional Voice Tasks on Swallowing Disorders and Biomechanics
This section focuses on the therapeutic impact of volitional voice tasks, whether implemented as part of a structured therapy program, training regimen, or isolated exercises. These tasks, originally designed for voice improvement or specifically for swallowing therapy, were analyzed for their ability to enhance swallowing safety and biomechanics, aligning with our objective to evaluate their therapeutic benefits on swallowing disorders.
LSVT-LOUD. Results from the scoping review indicate that several types of voice tasks have demonstrated therapeutic benefits across various populations and conditions. LSVT-LOUD, initially developed for hypokinetic dysarthria in PD and currently applied to other neurological conditions, focuses on improving vocal loudness through high-effort vocalization (Pu et al., 2021; Ramig et al., 2018; Saffarian et al., 2019). It incorporates volitional voice and speech tasks as a core component of its intervention strategy and emerged as one of the most frequently applied voice therapy approaches in the studies included for full review. Research led by El Sharkawi et al. (2002) was among the first to demonstrate the efficacy of LSVT-LOUD in enhancing both vocal loudness and swallowing dynamics, reporting a 51% reduction in swallowing motility disorders. The study highlighted improvements in tongue control and strength, reduced oral and pharyngeal transit times, and significant increases in vocal intensity. Follow-up investigations, including those by Miles et al. (2017), Nozaki et al. (2021), and Park et al. (2022), extended these findings, reporting significant therapeutic outcomes in PD and other neurodegenerative conditions. Miles et al. focusing on PD patients, observed significant improvements in pharyngeal residue reduction, pharyngoesophageal segment opening, and cough effectiveness, with benefits maintained at 6 months. Nozaki et al. studied patients with PSP and found a significant reduction in upper esophageal sphincter (UES) opening duration on videofluoroscopy, with improved voice intensity. Park et al. reported significant enhancements in the pharyngeal phase of swallowing and overall swallowing function in patients with idiopathic PD and multiple system atrophy–cerebellar type (MSA-C), demonstrating LSVT-LOUD's efficacy across these populations
Moreover, Jiang et al. (2015) conducted a study to examine the effect of sound intensity on velopharyngeal function in normal individuals. The study utilized lateral cephalograms to evaluate velopharyngeal closure during the phonation of the vowel /i:/ at both high and low sound intensities. The findings revealed that higher sound intensity during phonation significantly enhanced velopharyngeal closure, as indicated by greater angular and linear parameter values. Specifically, the study found that the width of velopharyngeal closure increased at higher sound intensities, which is crucial for preventing nasal regurgitation during swallowing. This suggests that increasing vocal loudness could potentially improve the efficacy of velopharyngeal closure, thereby enhancing swallowing safety by reducing the risk of nasal regurgitation and improving bolus propulsion through the pharynx.
EPGs. EPG is a combined exercise that merges pitch glide and the PSM to target both laryngeal and pharyngeal muscles. The exercise involves gliding up in pitch to a high, squeaky voice and sustaining it effortlessly, aiming to improve laryngeal elevation and pharyngeal strength (Miloro et al., 2014). This voice task has been identified as a potential intervention for enhancing swallowing physiology (Balou et al., 2019; Miloro et al., 2014; Pearson et al., 2013). These studies found that EPG replicated certain swallowing biomechanics, specifically targeting and strengthening the musculature critical for swallowing efficiency. Specifically, Pearson et al. (2013) measured muscle activation during swallowing and specific exercises using functional magnetic resonance imaging in healthy individuals. They observed significant activation in the geniohyoid, mylohyoid, palatopharyngeus, and stylopharyngeus during swallowing and exercises, indicating the crucial role of these muscles in hyolaryngeal elevation.
Complementing this, McCulloch et al. (1996) conducted an electromyographic study on the thyroarytenoid and interarytenoid muscles during pitch modulation, swallowing, and the Valsalva maneuver. They observed similar activation patterns across these tasks and noted a correlation between increased vocal pitch and larger bolus volumes during swallowing. McCulloch et al. also suggested that these data could be utilized in designing therapies for both voice disorders and pharyngeal dysphagia. Moreover, Shaker et al. (2002) explored vocal cord closure pressures during volitional swallowing and other voluntary tasks, finding the highest pressures during Valsalva/straining, followed by swallowing, coughing, and phonation. While phonation exhibited the lowest sustained pressures, its initial spike in pressure may mimic swallowing conditions.
Pull-up exercise. Fujimaki et al. (2017) investigated the “pull-up” vocal exercise to improve glottic closure in elderly individuals with glottal insufficiency due to vocal cord atrophy. This exercise involved participants sitting on a chair, gripping the sides, and vocalizing numbers from 1 to 10 while pulling up on the seat. The exercise was performed in two sets, both in the morning and the evening. The study found that this vocal task significantly extended the MPT, an indicator of improved glottic closure. Additionally, the intervention group experienced a markedly lower rate of hospitalization for pneumonia compared to the control group, highlighting the exercise's potential in preventing aspiration pneumonia. The authors emphasized the importance of maintaining vocal function to prevent aspiration and associated pneumonia, thereby improving patient quality of life and reducing health care costs.
Voice exercise set. Voice therapy approaches incorporating multiple exercises have been studied as a means of dysphagia management. Results from Ren et al. (2022) and de Fraga et al. (2018) indicate that combining voice training with traditional swallowing exercises can facilitate dysphagia rehabilitation. These studies revealed that this integrated approach can significantly reduce swallowing dysfunction and improve the overall quality of life for stroke patients. The inclusion of specific vocal exercises, such as semi-occluded vocal tract exercises and vocal fry, has been shown to enhance swallowing outcomes, indicating the beneficial synergy of these modalities in therapy.
Ren et al. (2022) implemented a three-stage systematic voice training program: relaxation training of articulatory organs; muscle function improvement; and vocal cord movement enhancement, including semi-occluded vocal tract exercises, throat relaxation, and resonant vocalizations. De Fraga et al. (2018) utilized a combination of plosive sounds, effort/thrust, semi-occluded vocal tract with glottal firmness, MPT, and vocal fry. Techniques for laryngeal raising and lowering included musical scale elevation alternated with voiced postalveolar fricative or tongue snapping associated with nasal sound along with yawning–sighing for lowering.
Further enriching this therapeutic landscape, additional insights from Perera et al. (2008), Vaiano et al. (2021), and Marques et al. (2023) explored the physiological mechanisms underlying the impact of various voice tasks. Perera et al. identified a phonation-induced contractile reflex in the UES, which suggests a protective mechanism against aspiration and highlights the potential of vocal tasks for therapeutic or diagnostic applications. Vaiano et al. found that esophageal pressures rise with increased vocal loudness, indicating that vocal exercises could enhance UES and pharyngeal function, thereby supporting swallowing safety. Marques et al. demonstrated that high-pitch vocal tasks increased laryngeal elevation and UES pressure, underscoring their potential to improve dysphagia rehabilitation outcomes.
Therapeutic singing. This approach has also been studied for its potential therapeutic benefits for swallowing. Jo et al. (2021) introduced a novel intervention for head and neck cancer survivors, emphasizing improvements in vocal function and the pharyngeal phase of swallowing. This approach not only aided the physical rehabilitation process but also offered psychological benefits, leveraging the intrinsic joy of music and singing. Complementary findings by Stegemöller et al. (2017) suggested the utility of therapeutic singing in early PD, where even minimal initial difficulty with swallowing was mitigated, supporting the inclusion of singing exercises in therapeutic regimens. Similarly, Yeo et al. (2021) investigated the effects of a singing-enhanced swallowing protocol for patients with neurological impairments versus head and neck cancer. Their study found that targeted singing exercises facilitated improved swallowing function, laryngeal diadochokinesis, and quality of life measurements.
Voice Tasks With Dual Roles in Assessment and Therapy
Some of the previously discussed voice tasks reviewed in this study serve dual purposes, functioning as both assessment tools and therapeutic exercises. As mentioned by the authors of the selected studies, these tasks could be valuable additions to both assessment and therapy programs.
MPT, as discussed earlier, is commonly used to assess swallowing function by predicting aspiration risk and other swallowing dysfunctions (Ko et al., 2018; Yamaguchi et al., 2018). As a task focused on sustained glottic closure, MPT not only serves as a predictive tool but also has therapeutic value. Exercises targeting sustained phonation such as MPT help improve glottic function and respiratory support. This dual-purpose nature makes MPT a useful tool for both assessing swallowing and improving vocal function, particularly in individuals with glottic closure inefficiencies (Fujimaki et al., 2017). Additionally, sustained vowel production, as seen in singing therapy, has similar benefits, promoting prolonged phonation to improve both voice and swallowing outcomes (Jo et al., 2021; Stegemöller et al., 2017).
As previously discussed, tasks aimed at high-pitch production, such as pitch glides and EPG, are widely used to assess laryngeal elevation and pharyngeal wall constriction, both key indicators of swallowing function (Fuller et al., 2009; Miloro et al., 2014). These tasks have also been explored as therapeutic interventions to enhance hyolaryngeal range of motion, which contributes to swallowing rehabilitation. While valuable for assessment, pitch elevation tasks may also be beneficial for patients with reduced hyolaryngeal excursion (Malandraki et al., 2011; Miloro et al., 2014). Similarly, Miloro et al. (2014) emphasized the potential therapeutic benefits of EPG for swallowing rehabilitation, as these tasks replicate key swallowing biomechanics. Pitch glides are commonly used in both evaluation and therapy during swallowing management, as noted by Venkatraman et al. (2020).
Loud voice exercises, such as those assessing SGP through high-intensity tasks like /pa:/ production (Castillo et al., 2020) and those used in LSVT-LOUD, also serve dual purposes. These tasks assess glottic closure and SGP, which are critical for both voice and airway protection. In therapy, they improve glottic contact and respiratory support. While Castillo et al. (2020) found a correlation between loud voice tasks and SGP, suggesting their potential for assessing airway protection, the therapeutic use of these tasks, as seen in LSVT-LOUD, has been shown to improve both vocal intensity and pharyngeal function, contributing to safer swallowing (Miles et al., 2017).
Finally, the PSM, primarily used as an assessment tool to evaluate pharyngeal strength and constriction, may also have therapeutic potential. While Fuller et al. (2009) and Ku et al. (2021) demonstrated that PSM is a valid surrogate measure of pharyngeal muscle integrity, it could also be considered as a therapeutic exercise to strengthen the very muscles it assesses. Although this has not been directly confirmed in the literature, its consistent targeting of pharyngeal muscles suggests that it could be considered for future therapeutic applications aimed at strengthening these muscles in dysphagia management.
Discussion
This scoping review delved into the potential of volitional voice tasks for assessing and treating swallowing disorders, focusing on their impact on swallowing-related biomechanics. The findings reveal a growing body of research on these topics in recent years, highlighting the value of vocal tasks in predicting swallowing-related outcomes from both diagnostic/screening and therapeutic perspectives. Furthermore, the evidence gathered supports the beneficial effects of voice therapy and training in enhancing swallowing function and efficiency.
For assessment purposes, the evidence suggests that using MPT and high-pitched vocal tasks could effectively predict swallowing outcomes, particularly in assessing the risk of aspiration. This conclusion is tentatively supported by high-quality studies, including Fujimaki et al. (2017), which indicated that MPT is a good metric for tracking therapy improvements related to glottic closure in elderly populations, and Tabor Gray et al. (2023), which demonstrated MPT's utility in predicting respiratory function, including FVC and PCF, in individuals with ALS. Both studies received an overall “strong” rating, reflecting their rigorous study designs, effective management of confounders, and reliable data collection. The methodological quality of these studies supports the potential of MPT as a noninvasive, low-cost, and straightforward tool for early detection and evaluation of swallowing disorders across various etiologies.
Regarding therapy, the LSVT-LOUD emerges as a notable intervention. High-quality studies, such as those conducted by Miles et al. (2017), demonstrate its effectiveness in not only enhancing vocal loudness and speech intelligibility in people with PD but also improving swallowing outcomes. These improvements include reduced pharyngeal residue, increased pharyngoesophageal segment opening duration, and enhanced involuntary cough peak expiratory flow rate and rise time, indicating LSVT-LOUD's potential as a complementary approach in dysphagia management.
Overall, cumulative findings suggest that various vocal tasks can serve as complementary tools for swallowing therapy, with their utility primarily rooted in the biomechanical processes of the pharyngeal stage of swallowing. The consistent activation patterns observed in vocal fold behavior and intrinsic muscle activity during both voice tasks and swallowing highlight the therapeutic potential of these tasks in dysphagia management (McCulloch et al., 1996; Shaker et al., 2002). Shared actions between voice production and swallowing, such as vocal fold activity, glottic closure, and pharyngeal adjustments during pitch elevation, provide a platform for analogous therapeutic applications (Jo et al., 2021; Miles et al., 2017; Nozaki et al., 2021; Park et al., 2022; Stegemöller et al., 2017; Yeo et al., 2021). Biomechanical and physiological correlations between voice and swallowing are interpreted using vocal attributes such as pitch, loudness, duration, and voice quality to discuss the key findings related to our aims. See Figure 6 for a visual representation of various vocal tasks organized by voice attributes that impacted swallowing-related outcomes.
Figure 6.
Categorization of vocal tasks by voice (sound) attributes.
Attribute-Specific Impacts on Swallowing
Pitch-Related Tasks and Laryngeal Dynamics
The reviewed studies primarily explored the predictive value of pitch-related tasks on swallowing outcomes, focusing on the correlation between high-pitch vocalizations, hyoid movement, and muscle activity (Malandraki et al., 2011; Rajappa et al., 2017; Venkatraman et al., 2020). Tasks such as pitch glides, whether performed during singing or as effortful exercises, have shown beneficial effects on swallowing kinematics. These exercises engage critical muscles involved in both voice modulation and swallowing safety, highlighting their potential to enhance swallowing function, airway protection, and quality of life across various patient populations (Jo et al., 2021; Marques et al., 2023; Stegemöller et al., 2017; Yeo et al., 2021).
Pitch elevation and swallowing share significant anatomical and physiological pathways. The superior laryngeal nerve's internal and external branches (ISLN and ESLN) play crucial roles in both processes. The ISLN transmits sensory information from laryngeal and pharyngeal regions, essential for detecting penetration or aspiration, while the ESLN innervates the cricothyroid muscle, which is key for pitch elevation and contributes to the UES function. Disruptions in these nerves can impair both pitch elevation and swallowing, potentially leading to increased pharyngeal residue. Both functions also involve the anterior and superior displacement of the hyolaryngeal complex through the contraction of extrinsic laryngeal and suprahyoid muscles (Malandraki et al., 2011; McCulloch et al., 1996; Perera et al., 2008; Venkatraman et al., 2020)
Studies suggest an inverse correlation between the highest pitch reached and penetration–aspiration risks, emphasizing the importance of efficient hyoid movement and laryngeal elevation for swallowing safety (Fujiki et al., 2019; Rajappa et al., 2017). Also, the cricothyroid muscle, which modulates vocal fold tension and adduction, is notably involved in both phonation and airway protection during swallowing (Thakar et al., 2011). This overlap between pitch modulation and swallowing function highlights the potential of high-pitch tasks not only as predictive tools but also as exercises to improve swallowing biomechanics (McCulloch et al., 1996).
While studies by Malandraki et al. (2011), Rajappa et al. (2017), and Venkatraman et al. (2020) focus on high-pitch tasks, they are generally rated as weak to moderate in overall quality due to their research designs, despite showing some methodological rigor in specific aspects. Similarly, while Jo et al.'s (2021) study on therapeutic singing provides robust evidence, complementary findings by Stegemöller et al. (2017) and Yeo et al. (2021) show potential benefits but are rated as moderate to weak in quality. These findings indicate a need for further research to validate and expand upon these results across diverse study designs and populations.
Prolonged Duration and Glottic Closure
Vocal exercises emphasizing prolonged duration, such as those that enhance MPT, are linked to improvements in glottic closure. Similar benefits are observed with exercises that promote increased vocal fold adduction through sustained isometric efforts, such as the pull-up exercise (Van Stan et al., 2015). These exercises also have a positive impact on SGP and laryngeal excursion, which are key factors for vocal and swallowing efficiency.
MPT can be clinically significant as an indicator of glottic function and aspiration risk, with evidence supporting its use across various patient populations. Fujimaki et al. (2017) provided compelling evidence that targeted vocal exercises improving MPT can significantly reduce the risk of aspiration pneumonia in elderly patients, positioning MPT as a valuable tool not only for diagnosis but also as a therapeutic outcome measure. Additionally, studies have demonstrated that shorter preoperative MPT correlates with higher risks of postoperative pneumonia, underscoring the importance of maintaining efficient glottic function for airway protection (Ozawa et al., 2022; Tawada et al., 2023). These findings highlight the need for further research involving larger, more diverse populations to validate these results and optimize MPT's use in clinical practice.
Maintaining vocal fold integrity is crucial for both effective voice production and airway protection (Amin & Belafsky, 2010; Hunter et al., 2020; Onwordi & Al Yaghchi, 2022; Tabor Gray et al., 2023). Glottic insufficiency can lead to compensatory increases in cricothyroid muscle activity and respiratory effort, adding strain to the laryngeal and respiratory systems. Such adaptations exacerbate the risk of aspiration and contribute to pharyngeal weakness (Domer et al., 2014; Zhang, 2019). Furthermore, the interaction between effective glottic closure and factors such as pulmonary lung volumes and expiratory muscle strength is critical for sustaining respiratory function and ensuring protective laryngeal responses (Castillo et al., 2020; Eibling & Gross, 1996; Tabor Gray et al., 2023). This necessitates comprehensive structural and functional assessments, particularly in populations prone to glottic closure defects (Enver et al., 2021; Thakar et al., 2011; Yiu et al., 2020). Given these needs, MPT measurement has become an increasingly valued tool for assessing glottic efficiency and respiratory function, recognized for its effectiveness, ease of administration, and straightforward implementation in clinical settings.
Regarding intervention, prolonged vocal exercises not only strengthen laryngeal mechanics but also support comprehensive voice therapy programs aimed at improving vocal function, such as glottal contact and pitch modification (Van Stan et al., 2015). These therapies offer a dual benefit, enhancing both vocal and swallowing functions, making them effective treatment options for individuals with voice and swallowing disorders.
Loudness and Aerodynamic Considerations
Vocal tasks that emphasize loudness engage both respiratory and laryngeal structures, enhancing glottic closure and increasing SGP—key mechanisms for swallowing efficiency and effective cough (Castillo et al., 2020; Eibling & Gross, 1996; Park et al., 2022). Efficient swallowing relies on positive SGP, which is crucial for laryngeal elevation and airway protection (Eibling & Gross, 1996; Gross et al., 2006, 2012). Studies show that high SGP stimulates subglottic mechanoreceptors, essential for initiating and maintaining the coordinated motor activity necessary for laryngeal elevation and airway protection (Gross et al., 2003, 2012; Han et al., 2023).
The relationship between voluntary cough airflow and SGP highlights the clinical utility of voluntary cough in managing dysphagia. Effective cough airflow is vital for clearing aspirated material from the subglottis, making it a valuable target for compensatory strategies and exercise-based dysphagia management (Borders & Troche, 2022). The synergistic relationship between SGP and glottic closure underscores the potential of vocal tasks to enhance both voice and swallowing functions (Castillo et al., 2020; Giraldez-Rodriguez & Johns, 2013; Pitts et al., 2013).
Treatments such as LSVT-LOUD, which are well established for increasing vocal loudness, also enhance neuromuscular coordination and improve swallowing function across several neurodegenerative diseases. This dual benefit suggests that refining speech and swallowing therapy protocols through vocal loudness adjustments could lead to more effective interventions. In addition to LSVT-LOUD, other approaches such as Speak Out!, Phonation Resistance Training Exercises, and Pitch Limiting Voice Treatment (Belsky et al., 2023; Boutsen et al., 2018; de Swart et al., 2003) may also improve glottic closure and SGP. Exploring the potential of these interventions to improve swallowing safety is a worthwhile endeavor, given their impact on glottic efficiency and SGP, both critical for effective swallowing and airway protection.
The role of SGP in the realms of voice and swallowing research is widely acknowledged, with implications that go beyond standard traditional communication, especially for individuals with tracheostomies. Techniques such as above-cuff vocalization have been identified not only to facilitate communicative abilities but also to potentially augment swallowing mechanisms (e.g., spontaneous swallowing frequency and accumulated oropharyngeal secretions) and minimize the risk of aspiration (McGrath et al., 2019). Furthermore, the use of the Passy Muir valve has demonstrated improvements in swallowing biomechanics, contributing to the reduction of aspiration risks among tracheostomized patients (Han et al., 2022).
The study by Castillo et al. (2020) demonstrated moderate-quality evidence for the role of vocal tasks in improving SGP, while Jiang et al. (2015) offers weak-quality insights on velopharyngeal function. Regarding LSVT-LOUD, evidence quality varied. Park et al. (2022) present weak findings, whereas Miles et al. (2017) provide strong evidence of its efficacy across neurological conditions. This highlights the need for rigorous research and larger, more diverse sample sizes to validate these findings and enhance clinical applicability.
Voice Quality–Focused Tasks and Pharyngeal Strength
Voice quality–focused tasks, including the PSM, show promise as both diagnostic tools and complementary approaches for swallowing therapy. The PSM effectively targets the pharyngolaryngeal muscles, which are crucial for synchronized swallowing movements (Balou et al., 2019; Fuller et al., 2009). These tasks serve as noninvasive methods for assessing pharyngeal strength and coordination, as confirmed by recent studies (Miles & Hunting, 2023; Vergara & Miles, 2023). Additionally, research on voice quality modifications, such as twang, which considers pharyngeal constriction, has shown improvements in voice outcomes for conditions such as hypophonia (Lombard & Steinhauer, 2007; Saldías et al., 2021). Although these tasks have demonstrated potential benefits across various populations, the supporting evidence primarily comes from studies of moderate-to-weak quality, requiring further high-quality research to validate their efficacy.
Therapeutic Transference Across Systems
The principle of transference, where training in one domain enhances performance in another, is key to integrating voice, swallowing, and respiratory functions (Kleim & Jones, 2008). Cross-system interventions have been shown to significantly improve outcomes in both voice and swallowing. For instance, exercises that enhance vocal fold adduction not only improve glottic closure but also support airway protection during swallowing. This integrated approach targets multiple physiological systems, providing a comprehensive treatment strategy for individuals with co-occurring voice and swallowing disorders.
Miloro et al. (2014) highlight how phonation-related exercises, such as EPGs, can improve swallowing function, demonstrating the potential of these interventions. Additionally, specific voice tasks have been shown to predict swallowing-related outcomes. Measures such as MPT and high-pitched vocal tasks can effectively predict aspiration risk, offering valuable insights for early intervention and tailored treatment plans (Fujimaki et al., 2017; Tabor Gray et al., 2023). This predictive capability demonstrates the importance of incorporating voice assessments into dysphagia management.
The concept of neuroplasticity and neural transference further supports incorporating voice tasks into dysphagia management, as enhancing one motor domain can positively influence related systems through shared pathways. This approach is particularly beneficial for individuals with overlapping impairments, offering an efficient therapeutic strategy that can lead to overall health improvements and enhanced quality of life.
Limitations and Future Directions
As with any study, this work has its limitations, beginning with the variations in search terms across different databases due to each database's unique indexing and terminology. Although these tailored searches were essential for a thorough review, they introduced inconsistencies in query formulation. A comprehensive review confirmed that these variations did not lead to the omission of relevant studies or the inclusion of irrelevant ones, but adjustments such as population age filters may affect reproducibility. Future work could benefit from standardized search terms across databases and increased topic focus and search engine consistency.
Another limitation is the potential bias from relying on a single reviewer for the initial title and abstract screening. Although subsequent cross-checks by other team members mitigated this risk, subjectivity could still be introduced despite the care taken. Future studies, especially those involving larger volumes of initial database results, should employ multiple reviewers in the initial screening stages to minimize bias.
Excluding non-English studies due to limited translational resources may have limited the comprehensiveness of this review. Future reviews could provide a broader perspective by including studies in multiple languages, although this could introduce additional variability. Moreover, the small sample sizes, limited study designs, and weak methodological quality of many included studies limit the strength of our conclusions. This is partly due to the emerging nature of the research topic. Nonetheless, future research should prioritize well-designed studies with larger sample sizes to strengthen the evidence base.
Our review finds that many studies are categorized as “weak” in methodological quality, but this does not diminish their value or relevance, particularly in the early stages of integrating voice and swallowing interventions. Despite this, the field is growing, as evidenced by recent publication trends. Notably, studies published since 2017 indicate a trend toward improved quality, with a higher proportion receiving “strong” or “moderate” ratings than earlier studies. This mirrors challenges in related fields, such as swallowing therapy, where reviews like that by Langmore and Pisegna (2015) highlight that many prescribed exercises lack robust evidence for efficacy but remain crucial for clinical practice due to their potential benefits. Enhancing research in voice and swallowing disorders should prioritize randomized controlled trials, rigorous blinding, diversity in participant groups, and methodological transparency. These steps will strengthen the evidence base and facilitate the development of more effective integrated treatments.
To advance the field further, future studies should focus on designing and testing specific voice exercises that enhance oropharyngeal strength and swallowing kinematics. Targeted interventions in populations with neurological conditions or the elderly population, which address physiological deficits while enhancing both voice and swallowing functions, could significantly improve health and quality of life. Such treatments offer long-term benefits and substantial returns in patient outcomes and health care efficiency.
Research into the clinimetric properties of voice assessment tools shows promise as a noninvasive, cost-effective approach for predicting swallowing-related outcomes (Fava et al., 2012; Zaga et al., 2022). Validating these tools' sensitivity, specificity, and predictive values could streamline the identification of swallowing disorders and facilitate early intervention strategies.
Assessing clinicians' perceptions of cross-system approaches is crucial for evidence-based practice. Evaluating these perspectives would provide insights into the applicability and potential barriers to implementing integrated therapeutic strategies, ensuring that emerging interventions are scientifically robust and clinically translatable. Understanding the clinical perspective will help refine these approaches to meet patient needs better, enhancing the quality of care and outcomes in dysphagia management.
Conclusions
This scoping review systematically analyzed the utilization of voluntary vocal tasks for evaluating and treating swallowing disorders. It illuminates promising areas and gaps within the existing literature, illustrating multiple impact opportunities. Tasks such as MPT and pitch glides have been shown to offer predictive value for swallowing-related outcomes, suggesting their utility as complementary tools for swallowing assessment. Similarly, voice training approaches involving pitch modulation, such as singing or targeting increased vocal loudness, have demonstrated potential benefits in cross-system treatment strategies.
Voluntary vocal tasks are typically noninvasive, cost-effective, and safe methods poised for integration into evidence-based practice. However, future research must prioritize methodological rigor and detailed transparency to advance the clinical integration of vocal tasks for swallowing assessment and treatment. The integration of vocal tasks into dysphagia clinical practice has the potential to provide a holistic and scientifically robust complementary approach to treating patients with both voice and swallowing disorders. This approach can potentially improve outcomes by simultaneously targeting multiple physiological systems, thereby offering comprehensive health improvements and enhancing the overall quality of life related to communication and feeding for patients.
Data Availability Statement
All data generated or analyzed during this study are included in this published review article. Spreadsheets utilized during the current study are available from the corresponding author on reasonable request.
Acknowledgments
This project was partly funded by the Chilean National Agency for Research and Development (ANID) through the BIO Fulbright-ANID Scholarship for doctoral studies (Scholarship ID 56170003), associated with Adrián Castillo-Allendes. Also, it was supported, in part, by National Institute on Deafness and Other Communication Disorders Award R01DC012315, with Eric J. Hunter serving as the principal investigator. Anaïs Rameau was supported by a Paul B. Beeson Emerging Leaders Career Development Award in Aging (K76 AG079040) from the National Institute on Aging and by a Bridge2AI award (OT2 OD032720) from the National Institutes of Health Common Fund. The first author (Adrián Castillo-Allendes) would like to express his sincere gratitude to his wife, Javiera Castillo, a speech-language pathologist, for her invaluable insights and continuous support throughout the development of this review article. Her vision and thoughtful contributions have significantly enriched his understanding of and approach to the topic. He also deeply appreciates Lady Cantor-Cutiva's methodological guidance and valuable input.
Appendix
Database Search Strategies
| Database | Filters | Search strategy | Results |
|---|---|---|---|
| PubMed | Clinical Trial, Randomized Controlled Trial, Humans, English | ((((((voice[Title/Abstract]) OR (phonation[Title/Abstract])) OR (pitch[Title/Abstract])) OR (vocal[Title/Abstract])) AND (swallowing[Title/Abstract])) OR (deglutition[Title/Abstract])) AND (((((biomechanics[Title/Abstract]) OR (relationship[Title/Abstract])) OR (physiological[Title/Abstract])) OR (therapy[Title/Abstract])) OR (assessment[Title/Abstract]))) AND (adults [Title/Abstract] OR adult [Title/Abstract] OR aged [Title/Abstract] OR elderly) | 68 |
| Scopus | Article, English | ( ( TITLE-ABS-KEY ( voice ) OR TITLE-ABS-KEY ( phonation ) OR TITLE-ABS-KEY ( pitch ) OR TITLE-ABS-KEY ( vocal ) AND TITLE-ABS-KEY ( swallowing ) OR TITLE-ABS-KEY ( deglutition ) AND TITLE-ABS-KEY ( biomechanics ) OR TITLE-ABS-KEY ( relationship ) OR TITLE-ABS-KEY ( physiological ) ) ) AND ( LIMIT-TO ( DOCTYPE , "ar" ) ) AND ( LIMIT-TO ( LANGUAGE , "English" ) ) | 278 |
| Web of Science (all databases) | Article, English | Search #1 (TS=(voice) OR TS=(voicing) OR TS=(pitch) OR TS=(phonation) OR TS=(loudness)) AND (TS=(swallowing) OR TS=(deglutition )) and Search #2 (TS=(biomechanics) OR (TS=relationships) OR (TS=Physiological) OR (TS=Physiologic)) |
270 |
Funding Statement
This project was partly funded by the Chilean National Agency for Research and Development (ANID) through the BIO Fulbright-ANID Scholarship for doctoral studies (Scholarship ID 56170003), associated with Adrián Castillo-Allendes. Also, it was supported, in part, by National Institute on Deafness and Other Communication Disorders Award R01DC012315, with Eric J. Hunter serving as the principal investigator. Anaïs Rameau was supported by a Paul B. Beeson Emerging Leaders Career Development Award in Aging (K76 AG079040) from the National Institute on Aging and by a Bridge2AI award (OT2 OD032720) from the National Institutes of Health Common Fund.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All data generated or analyzed during this study are included in this published review article. Spreadsheets utilized during the current study are available from the corresponding author on reasonable request.