Airway Mechanics and Breathing Function

Beyond producing voice, the larynx is a valve in the airway. By widening and narrowing the glottis across the breathing cycle and by mounting protective reflexes such as cough and laryngospasm, the larynx helps regulate airflow and keeps the lower airway clear and protected.

Definition

Airway mechanics at the larynx refers to the way the glottis and laryngeal muscles regulate airflow and resistance during breathing and mediate protective airway reflexes, alongside the larynx's roles in phonation and swallowing.

Scope

The topic covers the respiratory role of the larynx: how the glottis changes caliber during inspiration and expiration, how this modulates airway resistance, and how laryngeal reflexes protect and clear the airway. It is a reference description of normal airway physiology at the level of the larynx, not a guide to airway management or to treating obstruction.

Core questions

• How does the glottis change during inspiration and expiration?
• How does the larynx influence airway resistance?
• Which muscle opens the airway, and what happens if it fails?
• What protective reflexes does the larynx provide for the airway?

Key concepts

• Glottic abduction during inspiration
• Posterior cricoarytenoid as the sole abductor
• Laryngeal contribution to airway resistance
• Expiratory glottic narrowing (laryngeal braking)
• Cough reflex
• Laryngospasm and the laryngeal closure reflex

Mechanisms

During quiet breathing the glottis widens slightly on inspiration as the posterior cricoarytenoid muscles abduct the vocal folds, lowering the resistance to airflow, and narrows again on expiration; these phasic movements are tied to the respiratory rhythm and can act as a brake that smooths expiratory flow (Brancatisano et al., 1983; Bartlett, 1989). The larynx is therefore a variable resistor in the airway: because the glottis is one of the narrowest points of the upper airway, changes in its caliber have a marked effect on resistance. The posterior cricoarytenoid is the only muscle that opens the glottis, so its activity is essential for an open airway during breathing (Standring, 2020). The larynx also generates protective responses — the cough reflex to expel material and the laryngeal closure reflex (which, when exaggerated, is laryngospasm) to seal the airway against aspiration (Bartlett, 1989).

Clinical relevance

The laryngeal control of airflow and the dependence of airway opening on a single abductor muscle explain why laryngeal pathology or bilateral nerve injury can compromise breathing. This entry describes normal airway physiology for reference and education and is not a basis for managing airway compromise in any individual.

History

Respiratory physiology long treated the upper airway as a passive conduit, but twentieth-century studies showed that the larynx actively modulates airflow across the breathing cycle and contributes substantially to airway resistance, a view consolidated in physiological reviews of laryngeal function (Brancatisano et al., 1983; Bartlett, 1989).

Key figures

• Dudley Bartlett
• Ludwig Engel

Seminal works

• bartlett-1989
• brancatisano-1983

Frequently asked questions

Does the larynx do anything during normal breathing?

Yes. The vocal folds move apart slightly during inspiration and narrow during expiration, so the larynx actively helps regulate airflow and is one of the main sites of upper-airway resistance.

Why is the posterior cricoarytenoid muscle so important?

It is the only muscle that abducts (opens) the vocal folds, so it is essential for keeping the airway open during breathing; if both sides are paralysed the airway can be critically narrowed.