Phonation Threshold Pressure Revisited: Effects of Intrinsic Laryngeal Muscle Activation.

Abstract

Phonation threshold pressure (P_th ) is the minimum subglottic pressure required to reach phonation onset and is considered a marker for vocal efficiency and health. We investigated the effects of intrinsic laryngeal muscle (ILM) activation on P_th . In vivo animal study. In an in vivo canine phonation model, laryngeal adductor muscles were activated together by stimulation of the recurrent laryngeal nerves (RLNs) and individually via stimulation of respective terminal nerve branches. Cricothyroid (CT) muscles were activated via stimulation of the superior laryngeal nerves. ILMs were activated in a graded manner at various combinations as transglottal airflow was gradually increased. Aerodynamic and glottal posture parameters were measured at phonation onset. Graded RLN stimulation decreased glottal distance and increased P_th . Thyroarytenoid (TA) muscle activation alone increased P_th . Lateral cricoarytenoid (LCA) muscle activation alone had minimal effects. However, graded TA activation as a function of LCA activation level revealed a synergistic relationship between the two muscles in increasing P_th . Effects of CT activation were dependent on adductor stimulation level: CT activation increased P_th at low RLN stimulation levels and decreased P_th at high RLN levels. The effects of ILM activation on P_th were consistent with their expected effects on vocal fold stiffness and tension. TA was the primary adductor controlling P_th . While LCA alone had minimal effects on P_th , it enhanced the role of TA in controlling P_th . TA and CT have antagonistic roles in controlling P_th . These relationships should be considered in clinical efforts to improve ease of phonation and vocal efficiency. NA, basic science Laryngoscope, 132:1427-1432, 2022.