The effects of sustained and repetitive isocapnic hypoxia on ventilation and genioglossal and diaphragmatic emgs. Douglas, McEvoy R, Popovic Rainer M, Saunders Nicholas A, White David P. Veterans Administration Medical Center, National Jewish Center and University of Colorado Health Sciences Center, Denver, Colorado, USA and Repatriation General Hospital and School of Medicine, Flinders University of South Australia, Adelaide, Australia
APStracts 3:0157A, 1996.
We compared the effects of sustained isocapnic hypoxia (SIH, 20 mins) and repetitive isocapnic hypoxia (RIH, ten 2-min episodes) on ventilation (VI), genioglossal and diaphragmatic electromyogram (EMGgg and EMGdi) activities and supraglottic airways resistance (Rua) in 11 normal, supine male subjects (36.6 + 2.2 yrs) during wakefulness. Seven of the subjects had control measurements on a separate day. Desaturation was similar (SaO2 80-84%) in 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, NS) followed by a significant roll-off (VI after 20 mins of cumulative hypoxia 153 + 4.0 and 150.8 + 10.2 % respectively, NS). Moving time average EMGdi signals (peak inspiratory and phasic) demonstrated a similar biphasic response in the two protocols. Mean EMGgg responses, however, differed. During SIH, peak inspiratory EMGgg increased early and remained elevated. Phasic and tonic EMGgg signals showed a similar trend. During RIH, early augmentation of peak inspiratory and phasic EMGgg was followed by a marked roll-off in activity such that by the 10th hypoxic episode neither value increased above baseline. In the 2 minute periods between hypoxic episodes there was a progressive suppression of peak inspiratory and phasic EMGgg below baseline. Rua did not change significantly during either SIH or RIH. Ventilation and phasic EMGs did not change during control experiments. We conclude that in awake normal male subjects SIH and RIH cause similar biphasic responses in ventilation and diaphragmatic EMG activity. Phasic EMGgg activity responses differ between SIH and RIH: EMGgg remains augmented during SIH, whereas during RIH early augmentation is followed by marked suppression. 

Received 30 May 1995; accepted in final form 11 March 1996.
APS Manuscript Number A563-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96