Abstract
Dysphagia leads to poor swallowing function and high risk of aspiration; swallowing rehabilitative therapies including jaw exercises, tongue exercises, chin tuck against resistance (CTAR), Shaker exercises, effortful swallow training (EST), traditional dysphagia therapy (TDT), and respiratory muscle training (RMT) including inspiratory muscle strength training (IMST) and expiratory muscle strength training (EMST) are a crucial part of dysphagia rehabilitation. However, limited evidence exists on the comparative efficacy of swallowing rehabilitative therapies in adults with dysphagia. This is the first network meta-analysis (NMA) to investigate the comparative efficacy of swallowing rehabilitative therapies for adults with dysphagia. Web of Science, Embase, CINAHL, Cochrane Library, and PubMed were comprehensively searched until September, 2024. The Frequentist NMA model was performed in R-Software presenting standardized mean differences with corresponding 95% confidence interval (95% CI) for swallowing function and aspiration. Cochrane Q, τ2, and I2 statistics estimated heterogeneity and full design-by-treatment interaction random-effects and node-splitting models determined transitivity. Ranking of the swallowing rehabilitative therapies used the netrank function. The search yielded 7697 studies from which 25 randomized controlled trials with 1020 adults with dysphagia were included. The study findings revealed that CTAR + TDT (SMD = 3.44 [95% CI 2.42, 4.47]), EMST + TDT (SMD = 2.92 [95% CI 1.59, 4.25]), Shaker + TDT (SMD = 2.83 [95% CI 1.81, 3.84]), JE + TDT (SMD = 2.52 [95% CI 1.21, 3.83]), TE + TDT (SMD = 2.19 [95% CI 1.26, 3.12]), RMT + TDT (SMD = 2.14 [95% CI 1.36, 2.93]), and TDT (SMD = 1.92 [95% CI 1.42, 2.42]) showed very-large to huge effect in improving swallowing function. CTAR + TDT (0.93) demonstrated superior improvements for better swallowing function. Additionally, CTAR + TDT (SMD = − 1.82 [95% CI − 2.89, − 0.75]), Shaker + TDT (SMD = − 1.32 [95% CI − 2.36, − 0.27]), EMST (SMD = − 1.23 [95% CI, − 2.01, − 0.45]), and EMST + TDT (SMD = − 1.10 [95% CI − 2.15, − 0.04]) revealed very-large to large effect in preventing aspiration. CTAR + TDT (0.96) and Shaker + TDT (0.76) demonstrated superior improvements for reduced aspiration. The combination of swallowing rehabilitative therapies including CTAR + TDT and Shaker + TDT offers a more comprehensive approach for dysphagia management in adults. Study registration is PROSPERO: CRD42022321345.
Supplementary Information
The online version contains supplementary material available at 10.1007/s11357-024-01389-5.
Keywords: Adults, Dysphagia, Swallowing rehabilitative therapies, Network meta-analysis
Introduction
Dysphagia occurs as a result of progressive structural and physiological due to normal aging process known as presbyphagia and comorbidities including head and neck cancer (HNC), esophageal cancer, stroke, multiple sclerosis, Parkinson’s disease, and dementia [1–4]. In addition, sarcopenia, age-related loss of muscle mass and function, weakens the swallowing muscles in the oral cavity, pharynx, and esophagus and respiratory muscles significantly exacerbating dysphagia in adults [5, 6]. Moreover, the decline in muscle mass and function as a result of normal aging, sarcopenia, and comorbidities leads to reduced strength and poor coordination of swallowing and respiratory muscles impairing the swallowing process [5, 6]. This increases the risk of potentially life-threatening complications including aspiration pneumonia, malnutrition, decreased quality of life, and increased mortality rates among adults. As such, strengthening of the swallowing and respiratory muscles using targeted swallowing rehabilitative therapies is crucial in dysphagia management to increase muscle function, thereby improving swallowing efficiency and safety reducing dysphagia-related complications.
Dysphagia management can be categorized into four distinct therapeutic approaches including (1) swallowing compensatory therapies, (2) swallowing rehabilitative therapies, (3) swallowing adjunctive therapies, and (4) swallowing preventive therapies [7–10]. (1) Swallowing compensatory therapies are strategies that facilitate improved swallowing safety but have no lasting effect on the swallowing physiology, such as postural techniques, sensory techniques, pacing and feeding techniques, and intraoral prosthetics. (2) Swallowing rehabilitative therapies are strategies that improve swallowing physiology and enact lasting changes on the swallowing mechanism resulting from specific impairments in the swallowing phases. (3) Swallowing adjunctive therapies are non-swallowing strategies that are used to complement swallowing rehabilitative therapies by targeting different areas of the swallowing mechanism, such as biofeedback and neurostimulation therapies. (4) Swallowing preventive therapies are strategies that focus on avoiding dysphagia negative outcomes including food restrictions, nutrition and hydration deficits, or infections and prevention of dysphagia in high-risk populations and these include diet modification and prophylactic swallowing exercises. These dysphagia management therapies represent a comprehensive approach to improving swallowing efficiency and safety addressing short-term and long-term needs for adults with dysphagia.
Swallowing rehabilitative therapies are strategies that focus on improving and enhancing the swallowing physiology in the oral-preparatory, oral, and pharyngeal phases of the swallowing process [7–10]. Swallowing rehabilitative therapies comprise of oral motor control and range of motion exercises, pharyngeal range of motion exercises, swallowing maneuvers (supraglottic maneuver, super-supraglottic maneuver, Mendelsohn maneuver, effortful swallow maneuver, Masako (tongue-hold) maneuver), respiratory muscle strength training (inspiratory and expiratory muscle strength training), shaker exercise, chin tuck against resistance (CTAR) exercise, and respiratory muscle strength training (inspiratory and expiratory muscle strength training). In addition, traditional dysphagia therapy (TDT) is a strategy that involves performing swallowing exercises and maneuvers focused on improving swallowing safety and efficiency. Moreover, swallowing rehabilitative therapies present as low-cost non-pharmacological interventions that improve dysphagia-related complications and quality of life for adults with dysphagia. As such, identifying the most effective swallowing rehabilitative therapies also allows for personalized and targeted approach improving the management of dysphagia-related complications among adults.
Swallowing rehabilitative therapies integration into clinical practice represent a comprehensive approach to managing dysphagia [7–10]. As such, evidence-based practices for dysphagia could help to improve swallowing rehabilitative therapies protocols, leading to improved outcomes for adults with dysphagia across diverse populations. Recent evidence from pairwise meta-analyses has shown that swallowing exercises improve swallowing function in HNC patients [12], traditional dysphagia therapy effectively improves swallowing function in post-stroke dysphagia [14], and swallowing exercise therapy is beneficial in enhancing swallowing ability in stroke patients [15]. However, despite previous pairwise meta-analyses reporting positive outcomes, (1) there is lack of comprehensive evidence on the comparative efficacy of various swallowing rehabilitative therapies [12, 14, 15], (2) previous pairwise meta-analysis could only assess the effectiveness of single and combined swallowing rehabilitative therapies alone [12, 15], and (3) no simultaneous comparison and ranking of swallowing rehabilitative therapies from previous pairwise meta-analyses could be performed [12, 15]. Thus, significant gap in dysphagia research exists necessitating further investigation using a network meta-analysis (NMA). Incorporating these swallowing rehabilitative therapies into rehabilitation programs provides an opportunity to expand access to dysphagia management and continuously monitoring of patients’ progress.
Network meta-analysis is an advanced statistical approach that extends the traditional pairwise meta-analysis through simultaneous comparison of multiple interventions with a common comparator and interventions that have not been directly compared within individual trials providing a comprehensive overview for a particular outcome in a given population [16, 17]. As such, conducting an NMA presents several advantages over previous pairwise meta-analysis by (1) providing valuable insights on the comparative efficacy of swallowing rehabilitative therapies, informing evidence-based practice, and improving dysphagia management in adults. (2) An NMA will enhance the precision of effect estimates of the previous pairwise comparisons and offer a broader context of the swallowing rehabilitative therapies. (3) An NMA will identify the most effective and rank swallowing rehabilitative therapies. The integration of swallowing rehabilitative therapies into rehabilitation programs can further facilitate the implementation of the most efficacious interventions, enhancing patient outcomes, and accessibility of care. Therefore, to extend evidence and address the gap in previous research, the first NMA of randomized controlled trials (RCTs) was performed to explore the comparative efficacy of swallowing rehabilitative therapies in adults with dysphagia.
Methods
Search strategy
The reporting of the current NMA study followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses–Network Meta-analyses (PRISMA-NMA) statement and the study protocol was registered with PROSPERO: CRD42022321345 [18]. Web of Science, Embase, PubMed, CINAHL, and Cochrane Library and reference lists of published systematic reviews and meta-analyses were comprehensively searched until September, 2024. The following keywords were used with a detailed search strategy in Supplementary Material 1: dysphagia OR swallowing disorder OR deglutition disorder OR oropharyngeal dysphagia OR swallowing difficulty AND elderly OR aged OR old age OR adults OR older adults OR old people AND Oral Motor Control and Range of Motion Exercises OR Lip Exercises OR Tongue Exercises OR Tongue Range of Motion OR Tongue Resistance and Strengthening Exercises OR Jaw Range of Motion OR Jaw Exercises OR Pharyngeal Range of Motion Exercises OR Vocal Fold Adduction Exercises OR Tongue Base Exercises OR Laryngeal Elevation Exercise OR The Falsetto Exercise OR Shaker Exercise OR Chin Tuck Against Resistance OR CTAR OR Respiratory muscle strength training OR Expiratory Muscle Strength Training OR EMST OR Inspiratory Muscle Strength Training OR IMST OR Swallowing Maneuvers OR Supraglottic Swallow Maneuver OR Super-Supraglottic Swallow Maneuver OR Effortful Swallow Maneuver OR Mendelsohn Maneuver OR Masako Maneuver OR Tongue-Hold Maneuver. Corresponding authors were contacted through emails for additional or missing data to ensure that all potential studies were included and studies were excluded when no reply was received at the time of the analysis.
Study selection
The eligible studies had to meet the following inclusion criteria: (1) RCTs assessing efficacy of swallowing rehabilitative therapies; (2) adults ≥ 18 years old with dysphagia; (3) comparison groups were traditional dysphagia therapy, sham therapy, and standard care; and (4) no language restrictions. The exclusion criteria for eligible studies included the following: (1) non-RCTs, (2) non-relevant population studies, (3) duplicate studies, (4) unrelated to topic studies, (5) systematic review or meta-analysis studies, (6) insufficient data studies, and (7) studies that compared similar swallowing rehabilitative therapies (Fig. 1).
Fig. 1.
PRISMA flowchart for study selection
Data extraction and study outcomes
The following data was extracted by two independent reviewers (CLL and KJB); (1) author and year of publication, (2) intervention comparison, (3) age, (4) gender, (5) cause of dysphagia, (6) sample size, (7) protocol of including swallowing rehabilitative therapies, (8) study outcomes, and (9) outcome assessment time. The primary outcome was swallowing function with higher scores in the intervention group demonstrating to be better than lower scores in the control group. The secondary outcome was aspiration with lower scores in the intervention group demonstrating to be better than higher scores in the control group (Table 1).
Table 1.
Study demographic and interventional characteristics for included studies
| Author (year) Diagnosis |
Intervention comparison Age (mean (SD) |
Gender Sample size |
Protocol of intervention | Study outcomes | Outcome assessment |
|---|---|---|---|---|---|
| Balbinot et al., 2020 | TDT vs SC | Male: 25 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 5 | Total sessions: 20 | FOIS | |||
| Duration: 45 min/day | 4 weeks | ||||
| HNC | EG: 60.3 (6.7) | Total: 30 | Total hours: 7.5 | Aspiration | |
| CG: 59.4 (10.1) | EG: 15 | Total days: 20 | NA | ||
| CG: 15 | |||||
| Chen et al., 2018 | TDT vs SC | Male: 73 | Frequency: 2 times/week | Swallowing function | Baseline |
| Female: 3 | Total sessions: 48 | SSQ | |||
| HNC | EG: 53.0 (8.7) | Duration: 40 min/day | 24 weeks | ||
| CG: 51.1 (7.9) | Total: 76 | Total hours: 4.3 | Aspiration | ||
| EG: 38 | Total days: 48 | NA | |||
| CG: 38 | |||||
| Kotz et al., 2012 | TDT vs SC | Male: 20 | Frequency: 3 times/week | Swallowing function | Baseline |
| Female: 6 | Total sessions: 36 | FOIS | |||
| HNC | EG: 57.0 (10.0) | Duration: 30 min/day | 12 weeks | ||
| CG: 62.0 (11.0) | Total: 26 | Total hours: 30 | Aspiration | ||
| EG: 13 | Total days: 36 | NA | |||
| CG: 13 | |||||
| Tarameshlu et al., 2019 | TDT vs SC | Male: 7 | Frequency: 3 times/week | Swallowing function | Baseline |
| Female: 13 | Total sessions: 18 | MASA | |||
| EG: 47.5 (12.9) | Duration: 30 min/day | 6 weeks | |||
| Multiple sclerosis | CG: 39.9 (9.7) | Total: 20 | Total hours: 9 | Aspiration | |
| EG: 10 | Total days:18 | PAS | |||
| CG: 10 | |||||
| Turra et al., 2021 | TDT vs SC | Male: 13 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 19 | Total sessions: 10 | FOIS | |||
| Post-intubation dysphagia | EG: 56.3 (5.8) | Duration: 30 min/day | 2 weeks | ||
| CG: 68.5 (6.9) | Total: 32 | Total hours: 5 | Aspiration | ||
| EG: 17 | Total days: 10 | PAS | |||
| CG: 15 | |||||
| CG: 15 | |||||
| Hsiang et al., 2019 | TDT vs SC | Male: 48 | Frequency: 3 times/week | Swallowing function | Baseline |
| Female: 2 | Total sessions: 36 | NA | |||
| HNC | EG: 55.6 (8.6) | Duration: 20 min/day | 12 weeks | ||
| CG: 56.7 (9.0) | Total: 50 | Total hours: 12 | Aspiration | ||
| EG: 25 | Total days: 36 | PAS | |||
| CG: 25 | |||||
| Troche et al., 2010 | EMST vs SC | Male: 47 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 13 | Total sessions: 20 | NA | |||
| Parkinson’s disease | EG: 66.7 (8.9) | Duration: 20 min/day | 4 weeks | ||
| CG: 68.5 (10.3) | Total: 60 | Total hours: 12 | Aspiration | ||
| EG: 30 | Total days: 20 | PAS | |||
| CG: 30 | CG: Standard care | ||||
| Park et al., 2019 | EST + TDT vs TDT | Male: 42 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 26 | Total sessions: 20 | NA | |||
| Stroke | EG: 61.3 (8.5) | Duration | 4 weeks | ||
| CG: 61.9 (9.2) | Total: 68 | EST: 30 min/day | Aspiration | ||
| EG: 34 | TDT: 30 min/day | PAS | |||
| CG: 34 | Total hours | ||||
| EST + TDT: 20 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Choi et al., 2017 | Shaker + TDT vs TDT | Male: 19 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 12 | Total sessions: 20 | FOIS | |||
| Stroke | EG: 60.8 (10.9) | Duration: | 4 weeks | ||
| CG: 60.4 (10.5) | Total: 31 | Shaker + TDT: 46 min/day | Aspiration | ||
| EG: 16 | TDT: 30 min/day | PAS | |||
| CG: 15 | Total hours: | ||||
| Shaker + TDT: 25.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Dotevall et al., 2023 | Shaker + TDT vs TDT | Male: 35 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 12 | Total sessions: 40 | NA | |||
| EG: 63.0 (8.2) | Duration: | Aspiration | 8 weeks | ||
| HNC | CG: 62.7 (6.4) | Total: 47 | Shaker + TDT: 46 min/day | PAS | |
| EG: 23 | TDT: 30 min/day | ||||
| CG: 24 | Total hours: | ||||
| Shaker + TDT: 30.6 | |||||
| TDT: 20 | |||||
| Total days: 40 | |||||
| Park et al., 2017 | Shaker + TDT vs TDT | Male: 17 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 10 | Total sessions: 20 | NA | |||
| Stroke | EG: 59.3 (11.9) | Duration: | 4 weeks | ||
| CG: 61.6 (13.6) | Total: 27 | Shaker + TDT: 46 min/day | Aspiration | ||
| EG: 13 | TDT: 30 min/day | PAS | |||
| CG: 14 | Total hours: | ||||
| Shaker + TDT: 25.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Tuomi et al., 2022 | Shaker + TDT vs TDT | Male: 39 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 13 | Total sessions: 40 | NA | |||
| HNC | EG: 63.7 (8.4) | Duration: | 8 weeks | ||
| CG: 63.7 (6.7) | Total: 52 | Shaker + TDT: 46 min/day | Aspiration | ||
| EG: 25 | TDT: 30 min/day | PAS | |||
| CG: 27 | Total hours: | ||||
| Shaker + TDT: 30.6 | |||||
| TDT: 20 | |||||
| Total days: 40 | |||||
| Kim and Park, 2019 | CTAR + TDT vs TDT | Male: 12 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 13 | Total sessions: 30 | FOIS | |||
| EG: 63.5 (5.5) | Duration: | 6 weeks | |||
| Stroke | CG: 65.2 (6.2) | Total: 25 | CTAR + TDT: 43 min/day | Aspiration | |
| EG: 12 | TDT: 30 min/day | PAS | |||
| CG: 13 | Total hours: | ||||
| CTAR + TDT: 21.5 | |||||
| TDT: 15 | |||||
| Total days: 30 | |||||
| Park et al., 2018 | CTAR + TDT vs TDT | Male: 10 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 12 | Total sessions: 20 | NA | |||
| Stroke | EG: 62.2 (17.3) | Duration: | 4 weeks | ||
| CG: 58.4 (12.5) | Total: 22 | CTAR + TDT: 43 min/day | Aspiration | ||
| EG: 11 | TDT: 30 min/day | PAS | |||
| CG: 11 | Total hours: | ||||
| CTAR + TDT: 14.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Park et al., 2020 | JE + TDT vs TDT | Male: 17 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 12 | Total sessions: 20 | FOIS | |||
| Stroke | EG: 62.1 (10.1) | Duration: | 4 weeks | ||
| CG: 61.8 (12.1) | Total: 29 | CTAR + TDT: 43 min/day | Aspiration | ||
| EG: 15 | TDT: 30 min/day | PAS | |||
| CG: 14 | Total hours: | ||||
| CTAR + TDT: 14.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Kim et al., 2017 | TE + TDT vs TDT | Male: 19 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 16 | Total sessions: 20 | NA | |||
| Stroke | EG: 62.2 (11.0) | Duration: | 4 weeks | ||
| CG: 59.3 (10.2) | Total: 35 | TE + TDT: 40 min/day | Aspiration | ||
| EG: 18 | TDT: 30 min/day | PAS | |||
| CG: 17 | Total hours: | ||||
| TE + TDT: 13.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Moon et al., 2018 | TE + TDT vs TDT | Male: 7 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 9 | Total sessions: 40 | MASA | |||
| Stroke | EG: 62.0 (4.2) | Duration: | 8 weeks | ||
| CG: 63.5 (6.1) | Total: 16 | Shaker + TDT: 60 min/day | Aspiration | ||
| EG: 8 | TDT: 60 min/day | NA | |||
| CG: 8 | Total hours: | ||||
| Shaker + TDT: 40 | |||||
| TDT: 40 | |||||
| Total days: 40 | |||||
| Plaza et al., 2022 | TE + TDT vs TDT | Male: 34 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 26 | Total sessions: 40 | FOIS | |||
| Parkinson’s Disease | EG: 71.2 (7.6) | Duration: | 8 weeks | ||
| CG: 67.5 (6.9) | Total: 60 | TE + TDT: 45 min/day | Aspiration | ||
| EG: 30 | TDT: 30 min/day | NA | |||
| CG: 30 | Total hours | ||||
| TE + TDT: 30 | |||||
| TDT: 20 | |||||
| Total days: 40 | |||||
| Jang et al., 2019 | RMT + TDT vs TDT | Male: 19 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 17 | Total sessions: 10 | ASHA-NOMS | |||
| Stroke | EG: 67.3 (9.5) | Duration: | 2 weeks | ||
| CG: 71.2 (8.6) | Total: 36 | RMT + TDT: 90 min/day | Aspiration | ||
| EG: 18 | TDT: 60 min/day | PAS | |||
| CG: 18 | Total hours: | ||||
| RMT + TDT: 15 | |||||
| TDT: 10 | |||||
| Total days: 10 | |||||
| Maki et al., 2018 | RMT + TDT vs TDT | Male: 20 | Frequency: 2 times/week | Swallowing function | Baseline |
| Female: 47 | Total sessions: 12 | RSST | |||
| Oral frailty | EG: 83.1 (7.7) | Duration: | 6 weeks | ||
| CG: 81.8 (8.4) | Total: 67 | EMST + TDT: 20 min/day | Aspiration | ||
| EG: 33 | TDT: 10 min/day | NA | |||
| CG: 34 | Total hours: | ||||
| EMST + TDT: 4 | |||||
| TDT: 2 | |||||
| Total days: 12 | |||||
| Liaw et al., 2020 | RMT + TDT vs TDT | Male: 19 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 12 | Total sessions: 30 | FOIS | |||
| Stroke | EG: 65.4 (11.5) | Duration: | 6 weeks | ||
| CG: 60.4 (10.7) | Total: 31 | EMST + TDT: 40 min/day | Aspiration | ||
| EG: 15 | TDT: 20 min/day | NA | |||
| CG: 16 | Total hours: | ||||
| EMST + TDT: 40 | |||||
| TDT: 20 | |||||
| Total days: 30 | |||||
| Eom et al., 2017 | EMST + TDT vs TDT | Male: 11 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 15 | Total sessions: 20 | NA | |||
| Stroke | EG: 69.2 (4.1) | Total: 23 | Duration: | 4 weeks | |
| CG: 70.2 (3.6) | EG: 12 | EMST + TDT: 40 min/day | Aspiration | ||
| CG: 11 | TDT: 20 min/day | PAS | |||
| Total hours: | |||||
| EMST + TDT: 20 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Park et al., 2016 | EMST + TDT vs TDT | Male: 12 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 15 | Total sessions: 20 | FOIS | |||
| Stroke | EG: 64.3 (10.7) | Duration: | 4 weeks | ||
| CG: 65.8 (11.3) | Total: 27 | EMST + TDT: 40 min/day | Aspiration | ||
| EG: 14 | TDT: 20 min/day | PAS | |||
| CG: 13 | Total hours: | ||||
| EMST + TDT: 20 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Gao & Huang, 2014 | EG1: CTAR + TDT vs TDT | Male: 42 | Frequency: 5 times/week | Swallowing function | Baseline |
| Female: 48 | Total sessions: 20 | NA | |||
| EG2: Shaker + TDT vs TDT | Duration: | 4 weeks | |||
| Stroke | Total: 90 | CTAR + TDT: 46 min/day | Aspiration | ||
| EG1: 30 | Shaker + TDT: 46 min/day | PAS | |||
| EG1: 70.9 (6.6) | EG2: 30 | TDT: 30 min/day | |||
| EG2: 71.1 (7.1) | CG: 30 | Total hours: | |||
| CG: 71.1 (6.4) | CTAR + TDT: 15.3 | ||||
| Shaker + TDT: 15.3 | |||||
| TDT: 10 | |||||
| Total days: 20 | |||||
| Park et al., 2019 | CTAR + TDT vs | Male: 23 | Frequency: 5 times/week | Swallowing function | Baseline |
| Shaker + TDT | Female: 17 | Total sessions: 20 | FOIS | ||
| Stroke | EG: 60.9 (11.2) | Duration: | 4 weeks | ||
| CG: 59.5 (9.3) | Total: 40 | CTAR + TDT: 46 min/day | Aspiration | ||
| EG: 20 | Shaker + TDT: 46 min/day | PAS | |||
| CG: 20 | TDT: 30 min/day | ||||
| Total hours: | |||||
| CTAR + TDT: 15.3 | |||||
| Shaker + TDT: 15.3 | |||||
| TDT: 10 | |||||
| Total days: 20 |
ASHA-NOMS American Speech-Language-Hearing Association-National Outcome Measurement System Swallowing scale, CG control group, CTAR Chin Tuck Against Resistance, EG experimental group, EMST Expiratory Muscle Training, EST Effortful Swallowing Training, FOIS Functional Oral Intake Scale, JE jaw exercises, MBS Modified Barium Swallow, mins minutes, NA not available, PAS Penetration Aspiration Scale, RMT Respiratory Muscle Training, RSST Repetitive Saliva Swallowing Test, SC Standard Care, SSQ Sydney Swallowing Questionnaire, TDT Traditional Dysphagia Therapy, TE tongue exercises
Quality assessment of included studies
Two independent reviewers (CLL and KJB) assessed the quality of the included studies using Cochrane Handbook for Systematic Reviews of Interventions Version 2.0 [19]. The risk of bias has five domains of bias including (1) missing outcome data, (2) selection of the reported results, (3) measurement of the outcome, (4) randomization process, and (5) deviations from intended interventions. The overall quality of each RCT was rated as low, some concerns, or high risk of bias by checking and summing the five domains of risk of bias (Supplementary Material 10). A third expert reviewer (KRC) resolved discrepancies between the reviewers through discussions.
Data synthesis and analysis
The netmeta package in R-Software was used to perform the network meta-analysis presenting standardized mean differences (SMDs) using post-treatment mean and standard deviation (SD) for swallowing function and aspiration [16, 17]. The Frequentist NMA model was used to determine the comparative relative efficacy of swallowing rehabilitative therapies [16, 17]. Standardized mean differences (SMDs) and corresponding 95% confidence interval (95% CI) for the direct, indirect, and network evidence of swallowing function and aspiration for pairwise intervention comparisons were generated with network maps from the post-treatment mean and SD.
The Cochrane Q, τ2, and I2 statistics as a measure of heterogeneity for swallowing function and aspiration were estimated by the generalized DerSimmonian-Laird method [16, 17]. The effect sizes of the standardized mean differences for the direct, indirect, and network evidence were interpreted as very small, 0.1; small, 0.2; medium, 0.5; large, 0.8; very large, 1.2; and huge, 2.0 [20]. The global consistency and inconsistency was examined by the full design-by-treatment interaction random-effects model while the local consistency and inconsistency examined by the network node-splitting model determined the transitivity assumption for the current NMA, respectively [16, 17]. The Egger’s regression method and the comparison-adjusted funnel plots were used to assess publication bias of the pairwise intervention comparisons [16, 17].
Treatment ranking of swallowing rehabilitative therapies
Treatment ranking among swallowing rehabilitative therapies from the best to the least effective intervention was estimated by the netrank function [21]. The swallowing rehabilitative therapies were categorized as (1) first-ranked intervention: P-score ≥ 0.75–1.00 (definitely superior); (2) second-ranked intervention: P-score ≥ 0.50– < 0.75 (probably superior); (3) third-ranked intervention: P-score ≥ 0.25– < 0·50 (probably inferior); and (4) least-ranked intervention: P-score 0– < 0.25 (definitely inferior) (Tables 2 and 3).
Table 2.
Summary of findings for swallowing function
Table 3.
Summary of findings for aspiration
Moderator analysis
Moderator analysis was performed with the Bayesian network-meta-analysis model for swallowing function and aspiration [22]. The deviance information criterion (DIC) was estimated for the initial unadjusted NMA model, which was compared with the adjusted NMA model using the study demographic and interventional characteristics. The demographic variables included (1) age, (2) gender, and (3) sample size while interventional variables included (1) frequency, (2) sessions, and (3) duration. Significant intervention estimate suggested significant moderating effect of a given study variable (Supplementary 9–10).
Confidence rating of the estimated evidence
The confidence rating of the estimated evidence in the current network meta-analysis (NMA) were evaluated using the confidence in network meta-analysis (CINeMA) guideline [23]. The CINeMA guideline comprises of six domains: (1) within-study bias—assesses each study’s contribution matrix based on its individual risk of bias, categorized as low, moderate, or high risk; (2) reporting bias—examines suppression of negative study findings, publication bias, time-lag bias, and omission of unfavorable results; (3) indirectness—scrutinizes the representativeness of study settings, populations, interventions, and outcomes among included studies; (4) imprecision—reflects the clinical significance difference based on treatment effect and the 95% confidence interval (CI) of the intervention comparison; (5) heterogeneity—measured by Cochrane Q, τ2, and I2 statistics, shows true variation among the included studies; (6) incoherence—refers to statistical intransitivity when direct and indirect evidence do not align. Each domain is categorized as no concerns, some concerns, or major concerns while the overall CINeMA confidence rating is classified as very low, low, moderate, or high confidence (Supplementary Material 11–14).
Results
Study characteristics
The search strategy of the electronic databases and reference lists yielded 7697 studies from which 25 RCTs [23–48] published between 2012 and 2023 were included (Fig. 1; Table 1) with 1020 adults with dysphagia. The sample size ranged from 20 to 90 in the included studies with 61.8% (630) of the participants being males and 38.2% (390) being females. The mean age in the experimental groups ranged from 47.5 to 83.1 years and ranged from 39.9 to 81.8 years in the control groups. The cause of dysphagia among the included studies were stroke (14 studies), HNC (6 studies), Parkinson’s Disease (2 studies), post-intubation dysphagia (1 study), oral frailty (1 study), and multiple sclerosis (1 study) (Table 1). The results of the study quality showed seven low risk of bias studies and 19 some concerns risk of bias studies (Supplementary Material 6).
Interventional characteristics
The following swallowing rehabilitative therapies were identified including Chin Tuck Against Resistance and Traditional Dysphagia Therapy (CTAR + TDT), Shaker and Traditional Dysphagia Therapy (Shaker + TDT), Expiratory Muscle Strength Training and Traditional Dysphagia Therapy (EMST + TDT), Jaw Exercises and Traditional Dysphagia Therapy (JE + TDT), Tongue Exercises and Traditional Dysphagia Therapy (TE + TDT), Effortful Swallow and Traditional Dysphagia Therapy (EST + TDT), Respiratory Muscle Training and Traditional Dysphagia Therapy (RMT + TDT), Traditional Dysphagia Therapy (TDT), and Standard Care (SC). The protocol of combined swallowing rehabilitative therapies including CTAR + TDT, Shaker + TDT, EMST + TDT, JE + TDT, TE + TDT, EST + TDT, and RMT + TDT included frequency of the intervention per week ranging from two to ten times; the total duration of the interventions per day ranged from 20 to 60 min, the total number of hours ranged from 4 to 60 h, and the number of sessions ranged from 12 to 80 sessions. The study period for combined swallowing rehabilitative therapies ranged from 2 to 12 weeks. The protocol of single swallowing rehabilitative therapies including EMST, TDT, and standard care included frequency of the intervention per week ranging from two to ten times; the total duration of the intervention per day ranged from 10 to 60 min, the number of sessions ranged from 16 to 80 sessions, and the total number of hours ranged from 2 to 40 h. The study period for single swallowing rehabilitative therapies ranged from 2 to 12 weeks (Table 1).
Assessment of NMA assumptions
The results for the global inconsistency and consistency models from the full design-by-treatment interaction random-effects model revealed consistency and homogeneity of the included pairwise interventions comparisons for swallowing function (Q-statistic = 0.12, τ2 = 0.17, P = 0.73) and aspiration (Q-statistic: 1.32, τ2 = 0.000, P = 0.72). Similarly, the results of the local inconsistency and consistency models from the network node splitting models showed consistency and homogeneity (P > 0.05) of the included pairwise interventions comparisons for swallowing function (Supplementary Material 4) and aspiration (Supplementary Material 5).
Relative efficacy and ranking of swallowing rehabilitative therapies on primary outcome: swallowing function
CTAR + TDT (SMD = 3.44 [95% CI 2.42, 4.47]), EMST + TDT (SMD = 2.92 [95% CI, 1.59, 4.25]), Shaker + TDT (SMD = 2.83 [95% CI 1.81, 3.84]), JE + TDT (SMD = 2.52 [95% CI 1.21, 3.83]), TE + TDT (SMD = 2.19 [95% CI 1.26, 3.12), RMT + TDT (SMD = 2.14 [95% CI, 1.36, 2.93]), and TDT (SMD = 1.92 [95% CI 1.42, 2.42]) demonstrated very large to huge significant effect in improving swallowing function compared to standard care (Tables 2 and 4). We observed low heterogeneity: Q-statistic: 16.8, I2 = 46%, τ2 = 0.14, and P = 0.05. There was no evidence of publication bias for swallowing function (P = 0.09) (Supplementary Material 6). The overall confidence rating of the direct, indirect, and network evidence for swallowing function ranged from high to moderate confidence (Supplementary Material 11–12).
Table 4.
League table for network evidence of swallowing function (upper triangle) and aspiration (lower triangle)
*Significant intervention comparison
CTAR Chin Tuck Against Resistance, EMST Expiratory Muscle Training, JE jaw exercises, EST Effortful Swallow Training, RMT Respiratory Muscle Training, SC standard care, TDT Traditional Dysphagia Therapy, TE tongue exercises
The results of the netrank for the swallowing rehabilitative therapies revealed that CTAR + TDT (0.93) were the highest-ranked; the second-ranked were EMST + TDT (0.73) and Shaker + TDT (0.70); the third-ranked were TE + TDT (0.57), JE + TDT (0.42), and RMT + TDT (0.39); and the least-ranked were TDT (0.25) and standard care (0.00) for swallowing function (Table 2). The current NMA findings reveal that CTAR + TDT demonstrate superior improvements for better swallowing function.
Relative efficacy and ranking of swallowing rehabilitative therapies on secondary outcome: aspiration
CTAR + TDT (SMD = − 1.82 [95% CI − 2.89, − 0.75]), Shaker + TDT (SMD = − 1.32 [95% CI − 2.36, − 0.27]), EMST (SMD = − 1.23 [95% CI, − 2.01, − 0.45]), and EMST + TDT (SMD = − 1.10 [95% CI − 2.15, − 0.04]) demonstrated large to very large significant effect in preventing aspiration compared to standard care. We found no significant intervention comparison differences for EST + TDT (SMD = − 1.26 [95% CI − 2.80, 0.27]), JE + TDT (SMD = − 0.77 [95% CI − 1.86, 0.33]), RMT + TDT (SMD = − 0.76 [95% CI − 1.81, 0.28]), TE + TDT (SMD = − 0.73 [95% CI − 1.98, 0.52]), and TDT (SMD = − 0.47 [95% CI − 1.47, 0.52]) (Tables 3 and 4). We observed low heterogeneity: Q-statistic, 8.86; I2, 0%; τ2, 0.000; and p = 0.72. There was no evidence of publication bias for aspiration (p = 0.67) (Supplementary Material 7). The overall confidence rating of the direct, indirect, and network evidence for aspiration ranged from high to moderate confidence (Supplementary Material 13–14).
Regarding the ranking of the swallowing rehabilitative therapies, the results of the netrank revealed that CTAR + TDT (0.96) and Shaker + TDT (0.76) were the highest-ranked; the second-ranked were EST + TDT (0.66), EMST (0.65), and EMST + TDT (0.62); the third-ranked swallowing rehabilitative therapies were JE + TDT (0.39), RMT + TDT (0.38), and TE + TDT (0.37); and the least-ranked were TDT (0.16) and standard care (0.06) for aspiration (Table 3). The current NMA findings reveal that CTAR + TDT and Shaker + TDT demonstrated superior improvements for preventing aspiration.
Results of moderator analysis for swallowing function and aspiration
Regarding swallowing function, swallowing rehabilitative therapies demonstrated relatively strong model fits with unadjusted DIC value of 68.2 and SMDs ranging between 1.9 and 3.6, respectively. Among the interventions, the meta-regression results revealed significant improvements across swallowing rehabilitative therapies especially therapies with high frequency and sessions showing that these variables are critical predictors of swallowing improvement. CTAR + TDT (SMD = 3.4 [95% CI 2.5, 5.0]) showed significant improvement with increased frequency leading to better swallowing outcomes. Similarly, longer sessions contributed positively to better swallowing outcomes, with CTAR + TDT (SMD = 4.5 [95% CI 1.7, 52.0]) reporting a significant improvement indicating that adults with dysphagia who engaged in more frequent or longer sessions experienced greater improvements in swallowing function. However, age, sex, duration, and sample size did not demonstrate influence on improving swallowing function (Supplementary Material 8).
Regarding aspiration, swallowing rehabilitative therapies demonstrated relatively strong model fits with unadjusted DIC value of 68.3 and SMDs ranging between − 0.5 and − 1.9. CTAR + TDT (SMD = − 1.9 [95% CI − 3.1, − 0.5]) demonstrated the most pronounced improvement suggesting a significant reduction in aspiration. Shaker + TDT (SMD = − 1.4, 95% CI − 2.6, − 0.3]) and EMST + TDT (SMD = − 1.2 [95% CI − 2.4, − 0.1]) also revealed notable reductions in aspiration further emphasizing their efficacy in reducing aspiration. The moderator analysis demonstrated the influence of sex, frequency, session, and sample size on aspiration. However, age and duration did not reveal influence on reducing aspiration. Male participants revealed significant reduction in the aspiration with CTAR + TDT (SMD = − 2.1 [95% CI − 3.3, − 0.8]), Shaker + TDT (SMD = − 1.6 [95% CI − 2.8, − 0.3]), EMST (SMD = − 1.5 [95% CI − 2.6, − 0.5]), and EMST + TDT (SMD = − 1.4 [95% CI − 2.6, − 0.1]). These findings suggest swallowing rehabilitative therapies may have a stronger response in male participants. Furthermore, increasing the frequency and sessions of swallowing rehabilitative therapies was positively related with reduced aspiration especially for CTAR + TDT (SMD = − 1.9 [95% CI − 3.4, − 0.7]) and Shaker + TDT (SMD = − 1.4 [95% CI − 2.8, − 0.2), underscoring the importance of frequency and sessions in reducing aspiration (Supplementary Material 9).
Discussion
Principal findings
To our knowledge, this is the first NMA to compare the efficacy of various swallowing rehabilitative therapies including CTAR + TDT, Shaker + TDT, EMST + TDT, JE + TDT, TE + TDT, EST + TDT, RMT + TDT, EMST, TDT, and SC in adults with dysphagia. The combined swallowing rehabilitative therapies of CTAR + TDT demonstrated significant improvements and the highest efficacy in improving swallowing function compared to standard care. Other swallowing rehabilitative therapies including EMST + TDT, Shaker + TDT, JE + TDT, TE + TDT, RMT + TDT, and TDT also revealed positive effects with TDT ranking lower than other swallowing rehabilitative therapies but still outperformed standard care. In terms of ranking for swallowing function improvements, the netrank analysis supported the superiority of CTAR + TDT ranking as the definite superior swallowing rehabilitative therapies. As regards prevention of aspiration, CTAR + TDT, Shaker + TDT, EMST, and EMST + TDT demonstrated significant improvements compared to standard care. Other swallowing rehabilitative therapies did not demonstrate significant differences compared to standard care, and CTAR + TDT and Shaker + TDT had the highest efficacy highlighting the importance of specific swallowing rehabilitative therapies in reducing the risk of aspiration. The netrank analysis corroborated these findings, ranking CTAR + TDT and Shaker + TDT as the definite superior swallowing rehabilitative therapies reflecting their superior ability to enhance crucial muscles involved in airway protection during swallowing.
Efficacy of swallowing rehabilitative therapies on swallowing function
The current NMA findings suggest that the combination of swallowing rehabilitative therapies with traditional dysphagia therapy has more profound effect on oropharyngeal muscles leading to better swallowing function in adults with dysphagia. These results align with previous research findings from systematic reviews, pairwise meta-analyses, and other NMAs [12, 14]. Banda et al. (2021) [12] using a pairwise meta-analysis revealed that swallowing exercises for head and cancer patients were effective in improving swallowing function. Similarly, Banda et al. (2023) [14] through an NMA demonstrated that traditional dysphagia therapy was also effective in improving swallowing function in patients with post-stroke dysphagia. However, the previous NMA focused on post-stroke dysphagia and specific swallowing rehabilitative therapies including oral motor control and range of motion exercises, pharyngeal range of motion exercises, swallowing maneuvers (supraglottic maneuver, super-supraglottic maneuver, Mendelsohn maneuver, effortful swallow maneuver, Masako (tongue-hold) maneuver), respiratory muscle strength training (inspiratory and expiratory muscle strength training), shaker exercise, chin tuck against resistance (CTAR) exercise, and respiratory muscle strength training (inspiratory and expiratory muscle strength training) were not evaluated.
Previous studies have revealed that CTAR exercise activates the suprahyoid muscle leading to improved propulsion of the food bolus from the pharyngeal phase into the esophageal phase [7, 8]. The possible explanation for superior improvement in swallowing function is that CTAR combined with TDT targets strengthening key muscles involved in the swallowing process including the suprahyoid muscles, which are crucial for elevating the hyoid bone and larynx during swallowing. This elevation is essential for protecting the airway and opening the upper esophageal sphincter (UES), allowing food and liquids to pass safely into the esophagus while minimizing the risk of aspiration. Moreover, CTAR + TDT addresses both muscle strength and neuromuscular coordination, providing a comprehensive intervention that improves the mechanics of swallowing, reduces the risk of residue in the throat, and enhances airway protection. Furthermore, RMT including IMST improves the responsiveness of the swallowing reflex leading to efficient activation of neural pathways involved in swallowing, thereby improving the coordination swallowing [49] while EMST activates the submental muscle complex facilitating hyolaryngeal excursion and eventually opening of the upper esophageal sphincter (UES) [50]. Jaw and tongue exercises are crucial for preparing, masticating, and propelling the food bolus from the oral-preparatory and oral phases into the pharyngeal phase [7–9]. TDT maintains the tone, amplitude, and power of the oropharyngeal swallowing muscles, ensuring successful transportation of the food bolus through all four phases of the swallowing process [7–9].
The integration of swallowing rehabilitative therapies results in significant improvements in swallowing function, as evidenced by the high ranks of CTAR + TDT, EMST + TDT, and Shaker + TDT in the current NMA. Moreover, combining swallowing rehabilitative therapies with traditional dysphagia therapy targets and addresses multiple components of the swallowing anatomy and physiology, making them more effective compared to other rehabilitative strategies. Significant improvements in swallowing function were observed when administered with higher frequency and longer sessions attributable to enhanced neuromuscular adaptation these therapies promote. The possible explanation for the observed improvements is that frequent swallowing rehabilitative therapies sessions provide repeated stimulation, which leads to better muscle memory and coordination over time. Moreover, continuous reinforcement with longer sessions of swallowing rehabilitative therapies give patients more time to practice these complex motor tasks, reinforcing neuromuscular pathways involved in swallowing. Thus, intensity of swallowing rehabilitative therapies might be more important in improving swallowing function for adults with dysphagia rather than demographic variables such as factors age, sex, and sample size.
The current NMA findings also highlight the reliability of these results across different populations and settings, evidenced the absence of publication bias, suggesting that the observed effects are robust. Moreover, the combination of swallowing rehabilitative therapies with traditional dysphagia therapy offers a comprehensive approach for better swallowing function by improving the strength and coordination of the swallowing muscles and also supporting the improvement of respiratory function, which are crucial for effective swallowing. Additionally, incorporating swallowing rehabilitative therapies into dysphagia rehabilitation programs can help to optimize the use of healthcare resources by allowing therapists to manage more patients and reduce associated costs. By leveraging the strengths of dysphagia rehabilitation programs, healthcare professionals can deliver swallowing rehabilitative therapies to a wider range of patients resulting in improved patient outcomes ensuring that high-quality dysphagia care is available.
Efficacy of swallowing rehabilitative therapies on aspiration
Regarding aspiration, the current NMA findings suggest that CTAR + TDT, Shaker + TDT, EMST, and EMST + TDT demonstrate superior effects, leading to reduction in the risk of aspiration in adults with dysphagia. The results of the current NMA are consistent with results of previous research findings from systematic reviews and pairwise meta-analyses [50]. Previous systematic reviews and meta-analyses have demonstrated that CTAR and Shaker exercises significantly improve hyolaryngeal excursion and UES opening and enhance suprahyoid muscle strength, contributing to better airway protection. Evidence also reveals that muscle atrophy in adults with dysphagia leads to diminished force and coordination, increasing pharyngeal residues resulting in high risk of aspiration and complications such as aspiration pneumonia. The current NMA findings demonstrate the superior efficacy of combining CTAR and Shaker exercises with traditional dysphagia therapy (TDT), ranking as definite superior swallowing rehabilitative therapies and demonstrating their substantial impact on reducing aspiration compared to other rehabilitative strategies. As such, combined therapies provide a comprehensive rehabilitation strategy that targets both muscle strength and coordination, leading to significant improvements in swallowing safety, highlighting their potential impact in ensuring effective and comprehensive dysphagia management. Significant improvements and greater reductions in aspiration were experienced by male participants. The possible explanation is that male participants may have better baseline muscle strength compared to females leading to better performance of swallowing rehabilitative therapies and outcomes. In addition, significant improvements in the reduction of aspiration were observed with increased frequency and number of sessions. However, age, sample size, and duration did not influence aspiration, suggesting that the intensity and repetition of swallowing rehabilitative therapies play important role in improving aspiration. As such, these findings suggest that swallowing rehabilitative therapies could be effective across different age groups when delivered with sufficient frequency and increased sessions and incorporating these combined swallowing rehabilitative therapies with traditional dysphagia therapy into rehabilitation programs could be essential for prevention of aspiration.
Study strengths and limitations
The current NMA study has several strengths to be considered. Firstly, the current NMA study is the first to explore and provide comprehensive evidence on the comparative efficacy of swallowing rehabilitative therapies including CTAR + TDT, Shaker + TDT, EMST + TDT, JE + TDT, TE + TDT, EST + TDT, RMT + TDT, EMST, TDT, and standard care using findings from 25 RCTs with 1020 adults with dysphagia. Secondly, strict and rigorous scientific methods using the PRISMA-NMA guidelines were followed and did not have any language restrictions for the inclusion criteria of the eligible RCTs in the current NMA. Thirdly, confidence of the estimated direct, indirect, and network effect estimates was determined for quality of the evidence. Some limitations need to be taken into consideration when interpreting the findings of the current NMA. First, limited number of studies in the adults with post-extubation dysphagia, oral frailty, and multiple sclerosis could limit the generalizability of the study findings in these population in the study outcomes. Second, limited studies with follow-up size periods makes it hard to determine carry-over effects of swallowing rehabilitative therapies.
Conclusions
The NMA findings suggest that CTAR + TDT for swallowing function while CTAR + TDT and Shaker + TDT for aspiration were the definite superior swallowing rehabilitative therapies for adults with dysphagia. EMST + TDT, TE + TDT, JE + TDT, RMT + TDT, EMST, and TDT also demonstrated significant benefits but to a lesser extent for both swallowing function and aspiration. In contrast, standard care appeared to produce the least effect for both swallowing function and aspiration. Thus, the use of swallowing rehabilitative therapies combined with traditional dysphagia therapy with increased frequency and sessions suggest to offer a comprehensive approach for improved outcomes in dysphagia rehabilitation. Additionally, implementing these combined therapies provides a more holistic and effective treatment strategy for adults with dysphagia, ultimately enhancing their quality of life for adults with dysphagia. The integration of swallowing rehabilitative therapies into rehabilitation programs can also enhance accessibility and adherence to therapy, ensuring that a broader range of patients benefit from these therapies. Future rigorous randomized controlled trials (RCTs) with larger sample sizes and extended follow-up periods are needed to further determine the efficacy and carry-over effects of these interventions and provide improved clinical guidelines for the management of dysphagia.
Supplementary Information
Below is the link to the electronic supplementary material.
Acknowledgements
The findings and conclusions are those of the authors, who are responsible for its contents.
Author contribution
CLL, KJB, and KRC contributed to the literature search. CLL and KJB contributed to data collection, data analysis, and visualization. KJB and KRC wrote the original draft. KRC contributed to validation and editing of the manuscript. YHC, DL, CKL, CMS, and HA contributed to validation and review of the manuscript. KRC contributed to conceptualization and supervision.
Data availability
All the data related to the manuscript have been provided in the tables, figures, and Supplementary Information.
Declarations
Competing interests
The authors declare no competing interests.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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