Cricothyroid muscle in respiration.

Abstract

Although the phonatory activity of cricothyroid muscle is well-known, its respiratory role often remains unrecognized. Recent data suggest this muscle plays a major role in the overall regulation of breathing by its control of expiratory resistance and flow. Cricothyroid contraction in expiration results in vocal elongation increasing glottic size. Such a mechanical effect reduces airway resistance and shortens expiratory duration. By such a mechanism, the rate of respiration may ultimately be modified using the larynx as the principal effector of this control. In this regard, cricothyroid expiratory activity is a pressure-sensitive evoked response influenced by afferent vagal stimuli. Its activity is triggered by a critical threshold of pressure-increase with respect to time, and its duration is directly dependent on the duration of positive subglottic pressure. The threshold of cricothyroid activation is reduced in hypercapnia and elevated in hypocapnic states.