Evaluating the Influence of Targeted Air Flow on Sound Pressure Level and Closed Quotient

Purpose Measures of estimated subglottal air pressure and translaryngeal air flow enable the researcher or clinician to noninvasively assess aerodynamic features related to respiratory and phonatory function. Our goal was to examine the unique relationship between air flow with sound pressure level (SPL) during syllable production while attempting to hold fundamental frequency and subglottal air pressure relatively constant. Method We completed two studies. Study 1: During syllable production, resultant sound pressure level was measured under conditions of constant fundamental frequency and estimated subglottal air pressure while systematically varying translaryngeal air flow. Study 2: During syllable production, resultant sound pressure level and closed quotient (using laryngeal stroboscopy) were measured under conditions of constant fundamental frequency and estimated subglottal air pressure while systematically varying translaryngeal air flow. Results Study 1: Findings suggest a steady increase in sound pressure level with increases in air flow between 25 cc/s and 150 cc/s. Interestingly, relatively stable mean sound pressure level was maintained over a considerable range of air flow values between 225 and 450 cc/s, suggesting that air flow could be further increased without a marked loss of sound pressure level. Study 2: Findings suggest a systematic increase in mean sound pressure level as supraglottic activity subsided and as the closed quotient decreased from 0.80 to 0.58. Interestingly, sound pressure level was relatively stable as the closed quotient decreased from 0.58 to 0.35. Conclusions Our findings suggest that sound pressure level can be maintained over a considerable range of increasing translaryngeal air flow values and over a considerable range of decreasing closed quotient values. These results provide motivation for investigating the interaction between air flow, glottal closure, and sound pressure level among other measures of phonatory function, with important clinical implications for therapeutic approaches that emphasize increases in air flow and focus on reducing contact between the vocal folds.