EFFECTS OF POSITIVE AIRWAY PRESSURE ON UPPER AIRWAY DILATOR MUSCLE-ACTIVITY AND VENTILATORY TIMING

To determine upper airway (UA) and ventilatory responses to nasal cont inuous positive airway pressure (CPAP) and expiratory positive airway pressure (EPAP), we quantitated changes in alae nasi (AN), and geniogl ossus (GG); electromyographic (EMG) activity, ventilatory timing, and end-expiratory lung volume (EELV) at various levels of CPAP and EPAP I n six normal subjects during wakefulness and in seven during sleep. Th e same measurements were also made before and after UA anesthesia in s ix normal subjects during wakefulness. During both wakefulness and sle ep, CPAP application significantly increased EELV and decreased AN and GG EMG activities. In contrast, EPAP significantly increased EMG acti vities of both muscles while also Increasing EELV during wakefulness. The EMG responses were less marked during sleep. Anesthesia of the UA abolished the EMG responses to CPAP but not to EPAP. These results sug gest that, in normal subjects, CPAP application causes a reflex reduct ion in UA dilator muscle activity mediated by UA sensory receptors. In contrast, EPAP increased UA dilator muscle activity, with the respons e mediated by conscious influences or reflexes arising outside of the UA.