Inspiratory muscle activity as a trigger causing the airways to open in obstructive sleep apnea

This report discusses mechanisms causing the airways to open during obstructive sleep apnea (OSAS). In 4 male patients with OSAS, 92 nonrapid eye movement (NERM) sleep apnea episodes and 37 rapid eye movement (REM) sleep apnea episodes were analyzed breath by breath during a one-night study. We calculated the pressure time index of the diaphragm (the product of inspiratory time/cycle duration (Tl/Ttot) and mean transdiaphragmatic pressure swing), evaluated the sleep stages via EEG, and performed frequency spectrum analysis of the EMG of the diaphragm. It was found that with each occluded inspiratory effort the tension time index of the diaphragm (TTdi) increased progressively to reach or slightly exceed the fatigue threshold, 0.15 to 0.18 (during NREM sleep the TTdi of the last occluded breath was 0.195 +/- 0.045 and during REM sleep the TTdi of the last occluded breath was 0.153 +/- 0.037); that a close time relationship was observed as well between the onset of arousal and the opening of the airways. Our data suggest that the airways may be triggered to open by a protective reflex originating in the larynx or the inspiratory muscles upon reaching a certain degree of contraction.