Abstract

Introduction Semi-occluded vocal tract exercises are widely used in voice therapy and training. It is well known that longer and narrower tubes offer more resistance to the airflow due to frictional losses. Moreover, when a tube is submerged in water, an extra resistance is added due to hydrostatic pressure, which is dependent mainly on the depth of immersion. The purpose ofthis study was to investigate the effect of different artificial lengthening of the vocal tract (with the free end in water and in air) on air pressurevariables and vocal fold adduction in subjects with different voice conditions. Methods Forty-five participants were assessed. They were divided in four groups: normal voice without voice training (n=12), normal with voice training (n=9), functional dysphonia (n=14), and subjects with unilateral vocal fold paralysis (n=10). Participants were asked to produce a series of six semi-occluded vocal tract postures: base line, drinking straw, stirring straw, silicon tube with the free end in air (10 mm of inner diameter and 55 cm in length) silicon tube with the free end submerged 3 cm below the water surface, and silicon tube with 10 cm below the water surface. For each task was obtain the mean glottal contact quotient (CQ), mean fundamental frequency, mean subglottic pressure (Psub), mean oral pressure (Poral), and mean transglottal pressure. Maximum and minimum Poral were also measured during both silicon tube submerged 3 and 10 cm below the water surface. Numerical variables were described by median and interquartile range (IQR), and compared by phonatory task and vocal status separately using Kruskal-Wallis test. A generalized multivariable linear model to observe the joint influence of phonatory task and vocal status in vocal parameters was fitted. Separate subgroup analysis for minimal and maximal oral pressure was also performed. Finally, linear correlation analysis using Pearson coefficient for overall correlation was used. Results All semi-occluded postures produced an increase in Psub and Poral compared to the baseline condition (vowel phonation). Phonation with tube into the water (10 and 3 cm below the surface) and phonation into a stirring straw produced the three highest values for Poral. Interestingly, the same three phonatory tasks caused the highest values for Psub. The correlation analysis demonstrated a high correlation between these two dependent variables. No significant differences were observed between voice conditions. Multivariate linear regression model showed that all voice condition behaved similarly regarding air pressure variables. Tube 10 cm, tube 3 cm, and stirring straw presented the highest values in both, Psub and Psupra for all voice conditions. It seems that these variables are in general more dependent on the degree of airflow resistance than vocal status of participants.