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Received June 2, 2006
Revised June 21, 2006
Accepted after revision June 22, 2006
1 The University of British Columbia, School of Human Kinetics
2 The University of British Columbia, Faculty of Medicine
3 The University of British Columbia
* To whom correspondence should be addressed. E-mail: bill.sheel{at}ubc.ca.
We determined the effects of 10 daily exposures of intermittent hypoxia (IH; 1 hr day-1; oxyhaemoglobin saturation = 80%) on muscle sympathetic nerve activity (MSNA, peroneal nerve) and the hypoxic ventilatory response (HVR) before, during, and after an acute 20 minute isocapnic hypoxic exposure. We also assessed the potential parallel modulation of the ventilatory and sympathetic systems following IH. Healthy young men (n = 11; 25 ± 1 yr) served as subjects and pre and post IH measures of MSNA were obtained on six subjects. The IH intervention caused HVR to significantly increase (pre IH = 0.30 ± 0.03; post IH = 0.61 ± 0.12 l min-1 SaO2-1). During the 20 minute hypoxic exposure sympathetic activity was significantly greater than baseline and remained above baseline after withdrawal of the hypoxic stimulus, even though oxyhaemoglobin saturation had normalized and ventilation and blood pressure had returned to baseline levels. When compared to the pre IH trial, burst frequency increased (P < 0.01), total MSNA trended towards higher values (P = 0.06), and there was no effect on burst amplitude (P = 0.82) during the post IH trial. Following IH the rise in MSNA burst frequency was strongly related to the change in HVR (r = 0.79, P < 0.05) suggesting that these sympathetic and ventilatory responses may have common central control.
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