EFFECTS OF SUSTAINED AND REPETITIVE ISOCAPNIC HYPOXIA ON VENTILATION AND GENIOGLOSSAL AND DIAPHRAGMATIC EMGS

We compared the effects of sustained isocapnic hypoxia (SIH; 20 min) a nd repetitive isocapnic hypoxia (RIH; 10 2-min episodes) on ventilatio n (ill), genioglossal (EMGgg) and diaphragmatic electromyographic (EMG di) activities, and supraglottic airway resistance in 11 normal supine male subjects (36.6 +/- 2.2 yr) during wakefulness. Seven of the subj ects had control measurements on a separate day. Desaturation was simi lar (arterial O-2 saturation 80-84%) in the SIH and RIH protocols. SIH and RIH caused a biphasic ventilatory response: early augmentation of VI (169.5 +/- 6.9 and 168.9 +/- 4.3% of baseline, respectively; not s ignificant) followed by a significant roll-off(VI after 20 min of cumu lative hypoxia 153 +/- 4.0 and 150.8 +/- 10.2% respectively; not signi ficant). Moving-time-average EMGdi signals (peak inspiratory and phasi c) demonstrated a similar biphasic response in the two protocols. Mean EMGgg responses, however, differed. During SIH, peak inspiratory EMGg g increased early and remained elevated. Phasic and tonic EMGgg signal s showed a similar trend. During RIH, early augmentation of peak inspi ratory and phasic EMGgg signals was followed by a marked roll-off in a ctivity such that by the 10th hypoxic episode neither value increased above baseline. In the 2-min periods between hypoxic episodes, there w as a progressive suppression of peak inspiratory and phasic EMGgg valu es below baseline. Supraglottic airway resistance did not change signi ficantly during either SIH or RIH. VI and phasic EMGs did not change d uring control experiments. We conclude that in awake normal male subje cts SIH and RIH cause similar biphasic responses in ill and EMGdi acti vity. Phasic EMGgg activity responses differ between SIH and RIH: EMGg g remains augmented during SIH, whereas during RIH early augmentation is followed by marked suppression.