Brief airway occlusion produces prolonged reflex inhibition of inspiratory muscles in obstructive sleep apnea.

STUDY OBJECTIVES

The human inspiratory muscles respond to a brief occlusion of the upper airway during inspiration with a profound short-latency reflex inhibition. This inhibition contrasts with the excitatory stretch reflex of limb muscles and may protect the airway from aspiration. It was postulated that this reflex would be altered in subjects with obstructive sleep apnea (OSA) who have repetitive upper airway occlusion.

DESIGN

Subjects underwent overnight polysomnography, as well as muscle reflex studies. For the reflex studies (performed during wakefulness), occlusions lasting 250 milliseconds were delivered during inspiration. Surface electromyogram was recorded over the scalenes, parasternal intercostals, and chest wall (overlying diaphragm).

SETTING

Research and sleep laboratories.

PARTICIPANTS

Nineteen subjects with untreated OSA (9 moderate and 10 severe) and 9 healthy control subjects.

MEASUREMENTS AND RESULTS

In the subjects with severe OSA, the duration of the inhibition was prolonged by at least 25% compared with control subjects. The peak of the inhibitory response for scalenes occurred significantly later for subjects with severe OSA than for control subjects (by 76 +/- 5 ms vs 60 +/- 3 ms [mean +/- SEM], respectively). Onset latencies of the later excitatory response were delayed for scalenes, parasternal intercostals, and chest wall recordings (eg, scalenes: 105 +/- 9 ms for subjects with severe OSA vs 83 +/- 5 ms for control subjects).

CONCLUSIONS

The latency of peak inhibition and duration of inhibition were positively correlated with the respiratory disturbance index for all muscle groups. These changes may reflect adaptation in central respiratory paths due to repetitive loading during sleep.