Effects of Increasing Vocal Tract Insertion Depth in Semi-Occluded Vocal Tract Exercises on an Excised Canine Model

Straw phonation therapy, a form of semi-occluded vocal tract (SOVT) exercise, is commonly used to help treat various voice disorders. Although straw phonation therapy has been studied extensively for decades, the impact of straw depth on vocal function remains unexplored. This study aims to quantify the effects of various straw vocal tract insertion depths (VTID) into the vocal tract on common aerodynamic parameters such as phonation threshold pressure (PTP), phonation threshold flow (PTF), and phonation threshold power (PTW) in an ex vivo canine model. It was hypothesized that increasing the VTID of the straw would reduce the PTP, PTF, and PTW.

Five excised canine larynges were mounted on a pseudolung apparatus and attached to a simulated vocal tract in an acoustic sound booth. Two straw depths (20.0 and 60.0 mm) were tested to determine the effect of VTID on ease of phonation as indicated by the aerodynamic parameters of PTP, PTF, and PTW. The control had no straw and a VTID of 0.0 mm. The straw diameter and length above the simulated vocal tract were consistent between the straws. Sustained phonation was achieved, and aerodynamic data was collected and analyzed.

Both straw treatment groups exhibited significant reductions in PTP and PTW compared to the control. However, there were no significant differences between the 20.0 or 60.0 mm straw depths in PTP, PTF, or PTW.

The presence of a straw significantly reduced PTP and PTW, but VTID did not appear to influence these outcomes. This supports previous straw phonation therapy research suggesting that straw phonation therapy is beneficial primarily due to the presence of the straw rather than the depth of insertion. Future studies should explore the combined effects of varying straw diameters, lengths, and depths to optimize SOVT therapy for clinical use.