Phonation Threshold Pressure Revisited: Effects of Intrinsic Laryngeal Muscle Activation

Abstract

Objectives/hypothesis: 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 .

Study design: In vivo animal study.

Methods: 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.

Results: 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.

Conclusions: 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.

Level of evidence: NA, basic science Laryngoscope, 132:1427-1432, 2022.

Keywords: Phonation threshold pressure; in vivo phonation; phonation onset; vocal efficiency.

Fig. 1.

Effect of graded RLN stimulation (activating all adductors) on A, phonation threshold pressure (P_th, pascals), flow (Q, mL/s), and B, glottal distance (% glottal opening compared to baseline). As RLN stimulation increased, P_th increased as Q and glottal distance decreased. RLN = recurrent laryngeal nerve.

Fig. 2.

Effect of graded LCA activation on A, phonation threshold pressure (P_th, pascals), flow (Q, mL/s), and B, glottal distance (% glottal opening). P_th remained largely unchanged as Q and glottal distance decreased with increasing stimulation. LCA = lateral cricoarytenoid.

Fig. 3.

Phonation threshold pressure (P_th, pascals) as a function of graded TA activation across seven graded levels while LCA activation is held constant at four levels (0%, 20%, 60%, and 100% maximal activation). At constant LCA levels, graded TA activation increases P_th. At TA levels 3–7, increasing LCA/IA activation increases P_th. IA = interarytenoid; LCA = lateral cricoarytenoid; TA = thyroarytenoid.

Fig. 4.

Phonation threshold pressure (P_th, pascals) as SLN is stimulated across seven graded levels while RLN is held constant at 40%, 60%, and 80% maximal activation. At low levels of laryngeal adductor activation (40%), a trend for increasing P_th was observed with increasing CT activation. At high levels of adductor activation (80%), graded CT activation decreased P_th. CT = cricothyroid; RLN = recurrent laryngeal nerve; SLN = superior laryngeal nerve.