Subglottic Pressure and Immersion Depth: Key Determinants of Voice Outcomes in Water Resistance Tube Exercise.

PURPOSE: The present study aimed to evaluate the effects of different immersion depth levels and subglottic pressure (Psub) levels on the oscillatory features of oral pressure (Poral; frequency, amplitude, and regularity), the degree of glottal adduction, and the subjective perception of phonatory ease when performing a water resistance tube (WRT) exercise. METHOD: Forty participants were recruited: 20 having normal voice and 20 diagnosed with functional dysphonia confirmed by laryngoscopic examination. Assessment protocol included (a) the self-assessment of ease of phonation and (b) the objective assessment of air pressure-related variables and electroglottographic (EGG) contact quotient (CQ). Participants in both groups were instructed to select and produce a sustained-vowel-like phonation into a tube immersed in a recipient filled with water at five different depths: 2, 4, 6, 8, and 10 cm (Experiment 1). Then, they were required to phonate into the tube with three different Psub targets (10, 15, and 20 cm H2O) while keeping a constant immersion level (Experiment 2). Participants were asked to self-assess the degree of ease of phonation. Objective measurements of air pressure-related variables and CQ were acquired during WRT exercises. RESULTS: Changes in depths and Psub levels showed significant effects on CQ and massage-like sensation in both groups. Poral oscillation variables (amplitude, frequency, jitter, and shimmer of oscillation) were significantly influenced by changes in the depth of immersion and Psub values. No significant differences were found for most variables when comparing both groups. CONCLUSIONS: Findings confirm that modifying immersion depth and Psub during WRT exercises induces measurable changes in vocal physiology. Across both experiments, higher loads (greater immersion or increased Psub) led to a progressive increase in CQ, accompanied by higher Poral instability and a significant reduction in perceived ease of phonation. Also, both Psub and immersion depth were shown to influence bubble characteristics, Poral oscillations, and potentially the massage-like sensation associated with WRT. Thus, careful control of these variables appears essential to optimize therapeutic outcomes in patients with voice disorders.