1. A surface electrode was used to record electromyographic activity of the posterior crico-arytenoid muscle during breathing in normal subjects and patients with airflow obstruction.
2. Phasic activity of the posterior crico-arytenoid muscle was demonstrated. This was present on inspiration and absent on expiration.
3. Phasic inspiratory activity in normal subjects was present only during periods of voluntary hyperventilation, increasing with tidal volume, whereas in patients with airflow obstruction inspiratory activity was present even during resting breathing and failed to increase further during voluntary hyperventilation.
4. The posterior crico-arytenoid muscle may be considered as an inspiratory muscle acting analogously to other accessory respiratory muscles.