Superior pharyngeal constrictor activation in obstructive sleep apnea

Respiratory-related superior pharyngeal constrictor (SPC) muscle activity was determined in 18 obstructive sleep apnea (OSA) patients during wakefulness and sleep. Hooked-wire electrodes were implanted into the SPC muscle via a nasopharyngoscope. During quiet breathing in wakefulness, phasic expiratory SPC-muscle activity was consistently present in six subjects and intermittently present in 12 subjects, particularly following a swallow. The SPC muscle showed two patterns of activation during spontaneous obstructive apneic episodes in non-rapid-eye-movement (NREM) sleep: (1) activation during airway reopening, with or without waning phasic or tonic activation in the first half of the ensuing apnea (n = 13); and (2) absence of activation during apneas or arousals (n = 5). Activation on airway reopening following spontaneous apneas usually occurred on inspiration. When the apneic episodes were eliminated by application of nasal continuous positive airway pressure (CPAP), SPC-muscle activity was absent in NREM sleep in 16 subjects, but phasic expiratory activity persisted in two subjects. Sudden withdrawal of nasal CPAP in NREM sleep induced airway closure without a change in SPC-muscle activity. Arousal prior to or immediately after reapplication of nasal CPAP was associated with SPC-muscle activation during inspiration or expiration, and airway reopening. The results in OSA subjects indicate that SPC-muscle activation is similar to that of pharyngeal dilator muscles during spontaneous and induced apneas, and is not necessary to induce upper-airway closure during NREM sleep in OSA subjects.