Inspiratory-resistive loading increases the ventilatory response to arousal but does not reduce genioglossus muscle activity on the return to sleep

Cori JM, Nicholas CL, Baptista S, Huynh I, Rochford PD, O'Donoghue FJ, Trinder JA, Jordan AS. Inspiratory-resistive loading increases the ventilatory response to arousal but does not reduce genioglossus muscle activity on the return to sleep. J Appl Physiol 113: 909-916, 2012. First published July 19, 2012; doi: 10.1152/japplphysiol.00608.2012.-Arousals from sleep are thought to predispose to obstructive sleep apnea by causing hyperventilation and hypocapnia, which reduce airway dilator muscle activity on the return to sleep. However, prior studies of auditory arousals have not resulted in reduced genioglossus muscle activity [GG-electromyogram (EMG)], potentially because airway resistance prior to arousal was low, leading to a small ventilatory response to arousal and minimal hypocapnia. Thus we aimed to increase the ventilatory response to arousal by resistive loading prior to auditory arousal and determine whether reduced GG-EMG occurred on the return to sleep. Eighteen healthy young men and women were recruited. Subjects were instrumented with a nasal mask with a pneumotachograph, an epiglottic pressure catheter, and intramuscular GG-EMG electrodes. Mask CO2 levels were monitored. Three-to 15-s arousals from sleep were induced with auditory tones after resting breathing (No-Load) or inspiratory-resistive loading (Load; average 8.4 cmH(2)O.l(-1).s(-1)). Peak minute ventilation following arousal was greater after Load than No-Load (mean +/- SE; 8.0 +/- 0.6 vs. 7.4 +/- 0.6 l/min, respectively). However, the nadir end tidal partial pressure of CO2 did not differ between Load conditions (43.1 +/- 0.6 and 42.8 +/- 0.5 mmHg, respectively), and no period of reduced GG activity occurred following the return to sleep (GG-EMG baseline, minimum after Load and No-Load = 2.9 +/- 1.2%, 3.1 +/- 1.3%, and 3.0 +/- 1.3% max, respectively). These findings indicate that the hyperventilation, which occurs following tone-induced arousal, is appropriate for the prevailing level of respiratory drive, because loading did not induce marked hypocapnia or lower GG muscle activity on the return to sleep. Whether similar findings occur following obstructive events in patients remains to be determined.