Submitted on October 2, 2007
Accepted on February 15, 2008
EFFECTS OF HYPOXIA ON GENIOGLOSSUS AND SCALENE REFLEX RESPONSES TO BRIEF PULSES OF NEGATIVE UPPER AIRWAY PRESSURE DURING WAKEFULNESS AND SLEEP IN HEALTHY MALES
Danny J. Eckert1*, R. Doug McEvoy2, Kate E. George3, Kieron J. Thomson3, and Peter G. Catcheside1
1 Repatriation General Hospital, Adelaide Institute for Sleep Health, South Australia, Australia; School of Molecular and Biomedical Science, Discipline of Physiology, University of Adelaide, South Australia, Australia
2 Repatriation General Hospital, Adelaide Institute for Sleep Health, South Australia, Australia; School of Molecular and Biomedical Science, Discipline of Physiology, University of Adelaide, South Australia, Australia; Department of Medicine, Flinders University, South Australia, Australia
3 Repatriation General Hospital, Adelaide Institute for Sleep Health, South Australia, Australia
* To whom correspondence should be addressed. E-mail: deckert{at}rics.bwh.harvard.edu.
Hypoxia can depress ventilation, respiratory load sensation and the cough reflex, and potentially other protective respiratory reflexes such as respiratory muscle responses to increased respiratory load. In sleep-disordered breathing, increased respiratory load and hypoxia frequently coexist. This study aimed to examine the effects of hypoxia on the reflex responses of 1) the genioglossus (the largest upper airway dilator muscle) and 2) the scalene muscle (an obligatory inspiratory muscle), to negative-pressure pulse stimuli during wakefulness and sleep. We hypothesized that hypoxia would impair these reflex responses. 14 healthy males aged 19-42 years were studied on two separate occasions, ~1 week apart. Bipolar fine-wire electrodes were inserted per orally into the genioglossus muscle and surface electrodes were placed overlying the left scalene muscle to record EMG activity. In random order, participants were exposed to mild overnight hypoxia (SaO2 ~85%) or medical air. Respiratory muscle reflex responses were elicited via negative-pressure pulse stimuli (~-10 cmH2O at the mask, 250 ms duration) delivered in early inspiration during wakefulness and sleep. Negative-pressure pulse stimuli resulted in a short-latency activation followed by a suppression of the genioglossus EMG that did not alter with hypoxia. Conversely, the predominant response of the scalene EMG to negative-pressure pulse stimuli was suppression followed by activation with more pronounced suppression during hypoxia compared to normoxia (mean±SEM suppression duration 64±6 vs. 38±6 ms, p=0.006). These results indicate differential sensitivity to the depressive effects of hypoxia in the reflex responsiveness to sudden respiratory loads to breathing between these two respiratory muscles.
