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. Author manuscript; available in PMC: 2026 Apr 25.
Published before final editing as: J Voice. 2025 Apr 25:S0892-1997(25)00152-3. doi: 10.1016/j.jvoice.2025.04.003

Effects of Sustained Semi-Occluded Vocal Tract Exercises in Non-Disordered Populations

Jakob R Holm 1, Owen P Wischhoff 1, Tomas K Gilvydis 1, Brady D Prosser 1, Ashmita Bhowmik 1, Grayson J Bienhold 1, Jack J Jiang 1
PMCID: PMC12353171  NIHMSID: NIHMS2074176  PMID: 40287308

Abstract

Introduction:

Semi-occluded vocal tract (SOVT) exercises, including straw phonation therapy, are effective for treating vocal disorders and increasing ease of phonation by decreasing phonation threshold pressure and increasing subglottic pressure. While the short-term effects of SOVT straw phonation therapy have been demonstrated, the sustained and lingering effects remain largely unexplored. This study aims to assess the effects of sustained daily SOVT exercises across three different straw lengths by evaluating aerodynamic parameters, including phonation threshold pressure (PTP), mean flow rate (MFR), subglottic pressure (PS), laryngeal resistance (RL), and phonation power (PW) to help guide optimized straw phonation usage and configurations.

Methods:

Twenty-two normophonic participants completed a four-week daily protocol of SOVT straw phonation exercise with a randomly assigned straw length (7.50, 15.00, or 30.00 cm). Aerodynamic measurements were recorded via mechanical interruption and electroglottography (EGG) at week zero (baseline), week two (mid-therapy), week four (post-therapy), and week five (post-therapy).

Results:

A significant main effect of time was observed for PTP with post hoc tests showing significant and gradual decreases in PTP from week zero to week four, with PTP returning to baseline at week five. All three straw lengths generated the same statistical results. No significant main effects of time and straw length were observed for MFR, PS, RL, or PW, indicating that these parameters did not change in non-disordered participants following four-week SOVT exercises.

Conclusion:

sustained SOVT straw phonation therapy in a non-disordered population significantly reduces PTP, demonstrating improvements in ease of phonation over time. Lingering effects of daily SOVT exercises lasted greater than one, and less than seven days in terms of PTP. No significant differences were observed between straw lengths, suggesting that straw lengths tested do not impact sustained phonatory outcomes in a non-disordered population.

Keywords: Semi-Occluded Vocal Tract (SOVT), straw phonation, phonation threshold pressure (PTP), mean flow rate (MFR), subglottal pressure (PS), laryngeal resistance (RL), phonation power (PW), electroglottography (EGG)

INTRODUCTION

The voice is an essential aspect of daily life, yet voice disorders are reported to affect one in eight Americans annually with this number increasing1. Semi-occluded vocal tract (SOVT) exercises have been extensively used to help patients improve vocal efficiency2. In particular, SOVT straw phonation exercises have been used as warm-ups for vocalists and therapeutic exercises for patients with dysphonia3. Studies have shown a direct link between SOVT exercises (SOVTEs) and the decrease in phonation threshold pressure (PTP), the minimum subglottal pressure required to initiate phonation4. Using straw phonation as a SOVTE provides a source of supraglottal pressure which supports phonation by reducing PTP5. Paramesh and Yeshoda examined the sustained effect of straw phonation exercises on patients with a hyperfunctional voice disorder (HFVD) by measuring airflow rate (AFR) and subglottal pressure (PS). Patients diagnosed with HFVDs usually require greater efforts to phonate, experience laryngeal tension, or possess any kind of vocal trauma6. Paramesh and Yeshoda revealed that the AFR and PS decreased during the weeks participants performed straw therapy, indicating a positive trend towards improved phonation. Additionally, there were no lingering effects of AFR and PS post-therapy a month after the cessation of straw phonation6.

Ohm’s law can be applied to understand the effects of various aerodynamic parameters on phonation. Voltage is the analog to pressure, current is compared to flow, and resistance is the analog to laryngeal resistance. Therefore, laryngeal resistance (RL) is approximated as PS divided by the MFR. RL can offer insights into the airway’s physical characteristics and the mechanical properties of laryngeal tissues. Increased RL has been shown in adductor spasmodic dysphonia, and therefore may be a valuable metric to speech-language pathologists7. Phonation power (PW), can be calculated as the product of PS and MFR. It represents aerodynamic energy conversion into acoustic energy during phonation8 and the mean airflow rate (MFR), which is defined as the airflow rate in the laryngeal column during sustained phonation, of normal-voiced participants, which have yet to be established9–11.

Straw phonation increases the acoustic impedance, which is the combination of resistance and reactance, or the difficulty of generating acoustics in the vocal tract12. Inertance is a positive component of impedance, a resistive force in phonation, which helps facilitate vocal phonation13. It can be represented as intraglottic pressure, pressure between the vocal folds, divided by a change in airflow in the vocal column14. SOVTEs are shown to increase patients’ supraglottal pressure, which is directly linked to increased intraglottal pressure15. Inertance is also directly proportional to the density of air in the vocal column (ρ) and the length of the column (L), while indirectly proportional to the cross-sectional area of the air column (A) since I = ρ L/A4.

SOVTEs have been shown to reduce the cross-sectional area of the distal part of the vocal tract during vocalization, which inversely increases the inertance4. The direct relationship that SOVT straw phonation exercises have on key factors that increase inertance supports the possibility of vocal improvement in patients who perform SOVT straw phonation exercises.

A study by Mills et al found that different straw lengths did not have significance on pressure and aerodynamic resistance parameters, despite suggesting its possibility16. However, another study by Tangney et al established that longer straws around 25 cm have a more pronounced effect on PTP than shorter straws around 5 cm17. Conroy et al also performed a study that showed a significant decrease in PTP when using a narrower or longer straw, at 6.5 mm constriction and 30 cm respectively18. Mills et al also demonstrated an overall short-term decrease in oral pressure and aerodynamic resistance for all straw lengths, which follows the trends toward better phonation. Yet, Mills et al found a short-term increase in MFR, contradicting previous studies establishing a long-term decrease in MFR16,19. Furthermore, Kaneko et al found that two groups, one with a history of singing and one without, showed an increase in MFR after 12 weeks of performing SOVTEs with a much greater increase in MFR in the group without any singing background19. This study explores these divergent conclusions by evaluating the effects of sustained straw phonation therapy on MFR to solidify its trends. Kang et al observed a decreased phonation threshold pressure due to short-term straw therapy4. Controlling the supraglottic pressure during straw phonation has shown improved aerodynamic and electroglottography (EGG) voice measurements12. It is known that straw phonation decreases the patient’s PTP by increasing their supraglottal pressure5. The continuous positive airway pressure (CPAP) machine mimics straw phonation therapy by sending out a constant airflow, establishing a constant supraglottal pressure that can be used to find the optimal supraglottal pressure for PTP reduction. Therefore, studying the aerodynamic effects of using a CPAP machine can provide potential insight into the effects of straw therapy. The observed trend was a decrease in PTP, with the decreasing amount growing faster as the supraglottal pressure generated by the CPAP machine increased12. Smereka et al utilized a CPAP device connected to a straw-like mouthpiece and found greater decreases in PTP at lower supraglottal pressures, which opposes the results from Silverman et al which found optimized supraglottic pressures of 4–6 cm H2O12,20. It was suggested that lower supraglottal pressure be used for longer periods for optimal results in phonation ease20. Despite the differences in the results of these studies, both suggest straw phonation therapy will reduce PTP by increasing the supraglottal pressure, making it easier for subjects to phonate. Tsai et al increased supraglottal pressure through water and found that after four weeks of straw phonation exercises, elderly participants had lower MFR, higher PS, and higher quality of life scores than before straw phonation21.

This study aims to quantify the aerodynamic changes, with three straw configurations to help guide sustained straw phonation usage and understand lingering effects in a normophonic population. Studying the sustained effects of straw phonation in a normophonic population provides a baseline for understanding its impact, independent of pathology-related changes. This baseline serves as a crucial reference for interpreting results in voice-disordered populations. Additionally, these findings are particularly relevant for professionals with high vocal demands, such as singers, teachers, and physicians, offering insights into voice optimization and prevention of vocal fatigue. The straw variations will allow configurations to be optimized in a healthy-voiced population. The effectiveness of the straw intervention will be measured in changes in PTP, MFR, RL, PS, and PW. While straw phonation has been widely studied, there is a lack of research on the sustained aerodynamic changes it produces, especially with intensive use. It is hypothesized that SOVT straw phonation exercises will decrease PTP, MFR, and PS when consistently done from weeks zero to four, with the most pronounced effects in the long straw due to the increased inertance changes. It is also hypothesized that the improvements in the aerodynamic data will be sustained for a week after cessation of the SOVT straw phonation exercises compared to pre-therapy measurements.

METHODS

Study Design

Twenty-seven healthy normophonic adult subjects were recruited with a UW-Madison campus-wide email sent through UW-Madison’s Research Email Services following IRB ID: 2015–1466 approval. Each participant was paid $150.00 upon successful completion of the study. The exclusion criteria for this study encompassed participants who self-reported a history of smoking, vocal disorders, or asthma. These self-reports were grounded in clinical diagnoses previously received by the participants. Additionally, prior experience with straw phonation or SOVT exercises was not used as a determinant for eligibility, allowing the inclusion of individuals regardless of their familiarity with these techniques. Although sex was determined to be an insignificant factor in evaluating the aerodynamic parameters tested, sex was balanced across treatment groups before the initiation of the study9.

To evaluate the effects of sustained SOVT exercises, participants performed a straw phonation SOVT task for four weeks, with sessions conducted six days per week. The six days of exercises per week were chosen because daily SOVTEs have been shown to increase maximum phonation time22. Participants did not perform SOVTEs on assessment days in the lab to ensure accurate data measurement. Therefore, participants trained six days per week between data collection periods to maintain a consistent exercise frequency The SOVT task consists of the participants repeating a short task eight times, with thirty-second breaks between each task. The short task consists of the participants phonating /a/ into the straw for 5 seconds, immediately followed by a 3-second break, repeated ten times consecutively. The vowel /a/ was used to ensure minimal vocal tract occlusion during the exercises, allowing supraglottic pressure buildup solely from the straw. The total time spent phonating into a straw for each exercise was 6 minutes and 40 seconds. The total duration of the task is 14 minutes and 40 seconds. Participants were instructed to record themselves performing the tasks when completing them without lab supervision to ensure compliance with the requirements of the study since these tasks were performed outside of the lab and free of supervision. These videos were transferred to a USB drive and submitted for review after the four weeks of daily SOVT exercises were completed to validate compliance with the protocol further. After the four weeks of SOVT exercises were completed, participants stopped completing the SOVT exercises for one week to assess the lingering effects of the exercises.

The effectiveness of sustained daily SOVT straw exercises was determined by aerodynamic measurements that were recorded using mechanical interruption. Mechanical interruption has higher intra-subject retest reliability compared to labial interruption9. Participants were required to visit the lab for benchmark aerodynamic measurements four times total: before initiating the daily SOVT task (week zero), after two weeks of performing daily SOVT tasks (week two), after four weeks of performing daily SOVT tasks (week four), and after five weeks of participation in the study and after one week of discontinuing daily SOVT tasks (week five). Aerodynamic measurements were recorded using a Glottal Enterprises 2-channel EEG and a Glottal Enterprises AeroViewPlus Phonatory Aerodynamic System (KayPENTAX, Montvale, NJ). EGG was used to identify the phonation cutoff needed to calculate PTP. Sound pressure level (SPL) was recorded using a microphone built into the interrupter, located 5 cm from the mouthpiece. Subjects wore a nose clip while using the interrupter to prevent air leakage during mechanical airflow interruption. During the participants’ sustained phonation of /a/ into the interrupter, the balloon valve was periodically filled for 150 ms, allowing the tube’s pressure to equilibrate with subglottal pressure (T4) (Figure 1). The pressure at T4 minus the pressure at T2 equaled PTP9. This mechanical interruption yielded EEG and audio data to record PTP phonation offset10, MFR, and PS. When multiple peaks yielded analyzable data, pressures were averaged. The mean flow rate was calculated during sustained vowel phonation. SPL was controlled for each participant between 60.0 and 70.0 dB.

FIGURE 1.

FIGURE 1.

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A: Audio (red) and EGG (green) analysis overlaid from a mechanical interruption. T1 represents the initiation of interruption. T2 represents the time that the audio fully stopped. T3 represents a 75 ms marker. T4 represents 150 ms, where supraglottal pressure is measured and equal to subglottal pressure (PS). The pressure at T4 minus the pressure at T2 equals PTP. B: EGG analysis from a mechanical interruption used to supplement the audio analysis. EGG data is used to determine the onset of mechanical interruption.

Straw Information

The straws were manufactured through 3D printing utilizing acrylonitrile butadiene styrene (ABS), a commonly used, non-toxic material in additive manufacturing processes. Participants were randomly assigned to one of three different straw treatment groups: short, medium, and long straws. The short, medium, and long straws were 7.50, 15.00, and 30.00 cm long, respectively. These straw lengths were chosen due to their large range and efficacy based on an efficacy study by Mills et al16. All other dimensions of the straws were identical between treatments. The diameter of the straws was 5.0 mm.

Statistical Analysis

Statistical analyses were conducted using RStudio (R Core Team, Vienna, Austria). Model assumptions were assessed, including sphericity, normality, and homogeneity of variance. Post hoc tests were used for models that met ANOVA assumptions. When assumptions were violated, Greenhouse-Geisser corrections were applied. Effect sizes were calculated using partial eta-squared (ηp2). To evaluate the effects of time and straw length on PTP, MFR, PS, RL, and PW, Type III two-way repeated measures ANOVA tests were performed to assess the main effects of time and straw length and their interaction.

When significant effects were identified in the repeated measures ANOVA tests, post hoc Tukey HSD tests were conducted for pairwise comparisons between conditions. Additionally, one-way repeated measures ANOVA tests were used to examine the effect of time, regardless of straw length. Significant results were followed by post hoc tests with Bonferroni corrections to reduce the risk of Type 1 statistical errors. All statistical analyses were conducted with a significance level of ɑ = 0.05.

RESULTS

Participant Information

Twenty-six participants initiated the study; however, four participants were removed from the study due to failure to complete the SOVT tasks according to the protocol, as self-indicated by the participant before the completion of the study. Therefore, twenty-two participants completed this study in compliance with the protocol. Eight males and fourteen females had suitable data for analysis. Due to removing study participants, sex balancing became less even across the groups. After reviewing the recordings of the participants completing the SOVT tasks, no additional participants were removed from the study. This resulted in seven participants assigned to the short straw treatment, six to the medium straw treatment, and nine to the long straw treatment. The average age of the twenty-three participants who completed the study was 32.86 ± 12.52 years old and ranged from 20 to 64 years old. The average days between data collections for weeks zero and two were 14.14 ± 2.32 days, weeks two and four were 13.95 ± 2.72 days, and weeks four and five were 7.50 ± 1.47 days.

PTP

PTP in all conditions ranged from 1.259 to 3.237 cm H2O. A two-way type III repeated measures ANOVA analyzing time and straw length showed significant main effects of time (F[2.35, 44.90] = 28.3, ηp2 = 0.06, P = 2.45 × 10−11) but no significant effects of straw length (F[2, 19] = 1.21, ηp2 = 0.02, P = 0.837). No significant interaction was observed between time and straw length (F[4.73, 44.90] = 1.21, ηp2 = 0.11, P = 0.313).

Type III repeated measures ANOVA analyzing PTP regardless of length found significant main effects of time (F[2.27, 47.59] = 28.43, P < 0.001). Significant differences in PTP were found for week zero versus week two (df = 19, t ratio = 6.252, P < 0.0001), week zero versus week four (df = 19, t ratio = 7.232, P < 0.0001), week two versus week four (df = 19, t ratio = 4.921, P = 0.0004), week four versus week five (df = 19, t ratio = −6.392, P < 0.0001). All other differences were insignificant.

Post hoc tests revealed significant differences in the average PTP for long straw week zero and long straw week two (df = 57, t ratio = 4.584, P = 0.0081), long straw week zero and long straw week four (df = 57, t ratio = 5.036, P = 0.0031), medium straw week zero and long straw week four (df = 57, t ratio = 4.259, P = 0.016), medium straw week zero and medium straw week four (df = 57, t ratio = 4.881, P = 0.0043), medium straw week zero and short straw week four (df = 57, t ratio = 3.856, P = 0.0365), medium straw week two and medium straw week four (df = 57, t ratio = 3.894, P = 0.0338), long straw week four and long straw week five (df = 57, t ratio = −3.979, 0.0285). All other post hoc tests revealed no statistically significant results (P > 0.05) (Figure 2).

FIGURE 2.

FIGURE 2.

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Bar graphs of phonation threshold pressure (PTP). A: Time comparison between straw length on PTP. B: Effects of time on PTP. P-values were obtained from post hoc tests with a significance level of ɑ = 0.05. ns = P > 0.05, * = P < 0.05, *** = P < 0.001, ***** = P < 0.0001. Error bars show standard error.

MFR

MFR in all conditions ranged from 5.447 to 31.229 L/min. A two-way type III repeated measures ANOVA analyzing time and straw length showed no significant main effects of time (F[57] = 1.6149, ηp2 = 0.04, P = 0.196) and straw length (F[57] = 0.3686, ηp2 = 0.08, P = 0.6966). No significant interaction was found between time and straw length (F[57] = 0.7537, ηp2 = 0.07, P = 0.6091). No post hoc tests revealed significant results between any straw length of time as indicated by ɑ = 0.05 (Figure 3).

FIGURE 3.

FIGURE 3.

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Bar graphs of mean flow rate (MFR). A: Time comparison between straw length on MFR. B: Effects of time on MFR. P-values were obtained from post hoc tests with a significance level of ɑ = 0.05. ns = P > 0.05, * = P < 0.05, *** = P < 0.001, ***** = P < 0.0001. standard error.

PS

PS in all conditions ranged from 6.633 to 15.031 cm H2O. A two-way type III repeated measures ANOVA analyzing time and straw length showed no significant main effects of time (F[3, 57] = 0.66, ηp2 = 0.08, P = 0.58) and straw length (F[2, 19] = 0.87, ηp2 = 0.03, P = 0.44). No significant interaction was found between time and straw length (F[6, 57] = 1.51, ηp2 = 0.14, P = 0.6091). No post hoc tests revealed significant results between any straw length of time as indicated by ɑ = 0.05 (Figure 4).

FIGURE 4.

FIGURE 4.

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Bar graphs of subglottal pressure (Ps). A: Time comparison between straw length on Ps. B: Effects of time on Ps. P-values were obtained from post hoc tests with a significance level of ɑ = 0.05. ns = P > 0.05, * = P < 0.05, *** = P < 0.001, ***** = P < 0.0001. standard error.

RL

RL in all conditions ranged from 0.246 to 1.243 cm H2O/L/min. A two-way type III repeated measures ANOVA analyzing time and straw length showed no significant main effects of time (F[3] = 1.24, ηp2 = 0.02, P = 0.31) and straw length (F[2] = 0.18, ηp2 = 0.06, P = 0.84). No significant interaction was found between time and straw length (F[6] = 0.46, ηp2 = 0.13, P = 0.21). Post hoc tests failed to reveal significant results between straw length and time (Figure 5).

FIGURE 5.

FIGURE 5.

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Bar graphs of laryngeal resistance (RL). A: Time comparison between straw length on RL. B: Effects of time on RL. P-values were obtained from post hoc tests with a significance level of ɑ = 0.05. ns = P > 0.05, * = P < 0.05, *** = P < 0.001, ***** = P < 0.0001. standard error.

PW

PW in all conditions ranged from 22.663 to 326.778 H2O ✕ L/min. A two-way type III repeated measures ANOVA analyzing time and straw length showed no significant main effects of time (F[3, 37] = 0.73, ηp2 = 0.07, P = 0.54) and straw length (F[2, 19] = 0.70, ηp2 = 0.04, P = 0.51). No significant interaction was found between time and straw length (F[6, 57] = 1.38, ηp2 = 0.13, P = 0.24). No post hoc tests revealed significant results between any straw length of time as indicated by ɑ = 0.05 (Figure 6).

FIGURE 6.

FIGURE 6.

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Bar graphs of phonation power (PW). A: Time comparison between straw length on PW. B: Effects of time on PW. P-values were obtained from post hoc tests with a significance level of ɑ = 0.05. ns = P > 0.05, * = P < 0.05, *** = P < 0.001, ***** = P < 0.0001. standard error.

DISCUSSION

To assess the effects of short, medium, and long straw length on sustained SOVT straw phonation exercises in healthy participants, aerodynamic measurements of PTP, MFR, PS, RL, and PW were measured using mechanical interruption over five weeks for twenty-two subjects. Optimizing the effectiveness of SOVT exercises requires analyzing these parameters. It was hypothesized that SOVT exercises would enhance phonation efficiency, as indicated by aerodynamic changes, with the most pronounced benefits observed in the longest straw condition. Additionally, the effects of the sustained SOVT straw phonation exercises were expected to persist one week after their cessation.

This study spanned five weeks, with participants performing SOVT straw phonation exercises for four weeks. Throughout this period, PTP decreased consistently each week regardless of straw length with no plateau observed before cessation of SOVT exercises (Figure 2B). This suggests potential benefits in exploring longer intervention durations to determine when a plateau in PTP reduction occurs. Participants completed SOVT tasks six days per week, totaling 160 minutes of phonation across four weeks (approximately 6 minutes and 40 seconds per session). Our findings align with the study by Paramesh and Yeshoda, who reported significant reductions in aerodynamic subglottic pressure and other vocal parameters in patients with hyperfunctional voice disorders after twelve 30-minute intensive sessions over three weeks6. The participants were instructed to conduct straw phonation therapy four times a week for three weeks with data collected pre-therapy, mid-therapy, post-therapy, and a one-month follow-up. Notably, they found no significant changes from pre-therapy to mid-therapy, suggesting that extended therapy duration and consistent practice may be necessary for optimal outcomes. The improvements observed in our study, with these findings in disordered populations, emphasize the importance of both session duration and overall intervention length in clinical and performance settings. Although PTP decreased during SOVT tasks, the relationship between exercise intensity, duration, and outcomes requires further investigation to determine how these variables influence PTP during and after exercise.

Our statistical analyses revealed significant main effects of time, indicating notable differences in PTP across weeks. Further analysis, independent of straw length, showed significant PTP reductions between weeks zero and two, zero and four, and two and four, aligning with our hypothesis that SOVT straw phonation exercises decrease PTP. However, a significant difference between weeks four and five, coupled with no difference between weeks zero and five, suggests that the effects of SOVT exercises do not persist one week after discontinuation. PTP progressively decreased during the four weeks of SOVT exercises but returned to baseline within a week of cessation, indicating that the lingering effects last beyond one day but dissipate within seven days. This helps guide care for speech-language pathologists (SLPs) prescribing straw phonation for voice weakness because differences in straw lengths yielded the same positive results and regression after the end of sustained straw phonation use may produce diminishing results for vocal economy. SLPs assess overall voice quality and speech production, and evaluating aerodynamic parameters like PTP is a practical metric for phonation improvement over time. Understanding the duration of sustained effects of straw phonation can help clinicians and voice users optimize therapy frequency and duration.

A two-way type III repeated measures ANOVA assessing time and straw length found no significant effect of straw length on PTP, contradicting our hypothesis that the longest straw would produce the greatest PTP reduction. Previous studies suggest that increasing the straw length extends the effective vocal tract length, which is directly proportional to inertive reactance, leading to increased vocal tract inertance and reduced PTP that facilitates phonation initiation13,16. However, our findings did not reveal significant differences in PTP across straw lengths. This could be attributed to our study having a limited number of participants assigned to each straw group; seven participants were assigned to the short straw group, six to the medium straw group, and nine to the long straw group. Increasing the number of participants in each treatment group may improve the statistical power of future analyses.

Insignificant differences in PTP across straw lengths may be influenced by introduced variability regarding differences in vocal tract length between men and women. In SOVT straw phonation exercises, the straw functions as an extension of the supraglottis, effectively increasing the total vocal tract length. The relative percentage increase in vocal tract length depends on the individual’s baseline vocal tract dimensions and the straw length used. Consequently, participants with shorter vocal tracts experience a proportionally greater increase in vocal tract length when using the same straw length as those with longer vocal tracts18. This disproportionate extension may contribute to a more pronounced reduction in PTP for individuals with shorter vocal tracts. Research indicates that the average adult female vocal tract measures approximately 14.0–14.5 cm, whereas the male vocal tract averages 17.0–18.0 cm15. Given these differences, female participants may experience a greater relative increase in vocal tract length during SOVT exercises, potentially leading to more significant decreases in PTP at a certain straw length compared to male participants at the same straw length.

Our analyses did not reveal significant main effects of time and straw length on MFR, PS, or RL. These aerodynamic parameters are key indicators of the effort required to initiate phonation and provide insight into laryngeal function23. Specifically, RL and MFR are sensitive to changes in glottal configuration, with MFR measured during sustained phonation as a function of glottal impedance and integrity24. While some studies have observed changes in glottal configuration during and after SOVT exercises, our study did not find such effects25. One possible explanation is that our participants were healthy individuals without voice disorders; therefore, their baseline laryngeal function may have limited the potential for measurable improvement. Generally, MFR serves as a valuable marker of laryngeal pathology and dysfunction, offering insight into conditions such as incomplete vocal fold closure or excessive airflow during sustained phonation24. Similarly, Zhuang et al demonstrated that phonation threshold flow (PTF) and MFR effectively distinguish normal from pathological voices due to their sensitivity to biomechanical laryngeal function26. However, while MFR is a useful diagnostic tool, it was not significantly altered during the five-week study, possibly due to the absence of underlying laryngeal pathology in the normophonic population tested in this study.

No significant main effects of time and straw length on PS were observed in our study, contrasting with previous research that reported an increase in subglottic pressure following straw phonation25,27,28. However, these studies measured aerodynamic parameters during or immediately after SOVT exercises. For instance, Guzman et al found that PS increased by 18% during straw phonation, but decreased to a 7% increase once the straw was removed, suggesting that the effects on PS are short-lived29. Similarly, Dargin and Searl measured PS immediately after SOVT and found no significant changes30. Since our study did not assess PS immediately post-exercise, the absence of significant differences may reflect the transient nature of SOVT’s effects on PS.

RL is a measurement derived by dividing PS by MFR and provides insight into airway structure and the mechanical properties of laryngeal tissues23,31. Since our study found no significant main effects of time or straw length on RL and MFR, both of which are influenced by glottal configuration, it suggests that SOVT straw phonation exercises do not produce lasting changes in glottal configuration. However, variability regarding RL may be attributed to individual differences in airway size, particularly between males and females, as females generally have a smaller larynx, which could influence the results31.

The data also showed no significant main effects of time and straw length on PW. PW, calculated as the product of subglottal pressure and airflow rate, represents the rate at which aerodynamic energy is converted into acoustic energy during phonation8. It serves as an indicator of the laryngeal efficiency in transforming airflow into sound. Previous studies have found that PW decreases significantly in individuals with disordered laryngeal biomechanics, particularly in conditions affecting vocal fold vibration patterns or glottal closure32,33. Since our study involved healthy participants with presumably optimal vocal biomechanics at baseline, the absence of significant PW changes aligns with prior findings. Additionally, while SOVT exercises influence supraglottal acoustic loading, they may not significantly alter vocal fold biomechanics in healthy individuals, explaining the unchanged energy transfer efficiency.

MFR, PS, RL, and PW are key measures of glottal configuration and have been shown to exhibit changes during or immediately after SOVT exercises28,32. However, our study did not observe significant effects on these parameters. In contrast, a sustained decrease in PTP was found, suggesting that the benefits of sustained SOVT straw phonation exercises may be more related to improved laryngeal aerodynamic efficiency than to persistent changes in glottal configuration.

CONCLUSION

This study examined the sustained and lingering effects of SOVT straw phonation with three different straw lengths on aerodynamic measurements of PTP, MFR, PS, RL, and PW. Prolonged straw phonation resulted in decreased PTP over four weeks of use. Daily SOVT exercise elicits lingering effects greater than one, and less than seven days in terms of PTP. For effective results, continued straw phonation is required to maintain benefits from SOVTEs. Flow is related to biomechanics, which stays relatively consistent in a healthy population. Therefore since the flow did not significantly change, neither did RL or PW. Elucidating increased specificity of lingering effects is of interest for future research.

ACKNOWLEDGEMENTS

This study was funded by the National Institutes of Health R01 grant 5R01DC015906-05.

Footnotes

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Declaration of Interest:

Authors have no conflicts to Declare.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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