ROLE OF AIRWAY RECEPTORS IN THE REFLEX RESPONSES OF HUMAN INSPIRATORYMUSCLES TO AIRWAY OCCLUSION

1. This study was designed to investigate the role of airway receptors in the responses of a range of inspiratory muscles to airway occlusio n. The occlusion had a rapid onset (< 10 ms), lasted 250 ms and produc ed only a slight impediment to inspiration. 2. Based on analysis of si ngle trials and averaged rectified electromyographic responses (EMG) i n six subjects, there was a major inhibition (IR) with an onset at 34 +/- 2 ms and a trough at 65 +/- 2 ms, and an excitation (ER) with a pe ak at 105 +/- 2 ms. These two responses are reflex given that voluntar y reaction times to a tap on the chest wall occurred at latencies long er than the peak of ER. 3. The responses to airway occlusion did not a ppear in limb muscles which contracted phasically with inspiration. 4. Anaesthesia of the surface receptors of the upper airway did not atte nuate the responses to occlusion. Because this procedure does not elim inate the inputs from muscle and deep laryngeal pressure receptors, tw o subjects were tested when intubated with a cuffed endotracheal tube so that the occlusion was delivered only to structures below the level of the trachea. Responses to airway occlusion were preserved when all upper airway receptors were 'bypassed'. 5. Responses to airway occlus ion also remained after prolonged inhalation of nebulized lidocaine (l ignocaine) sufficient to block the cough reflex. 6. The receptors medi ating the responses to airway occlusion are therefore likely to reside in inspiratory muscles acting on the chest wall. If so, the short-lat ency inhibition contrasts with the excitatory stretch reflex responses observed in limb muscles.