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J Appl Physiol (January 18, 2007). doi:10.1152/japplphysiol.01338.2006
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Submitted on November 23, 2006
Accepted on January 17, 2007

Cardiorespiratory and cerebrovascular responses to acute poikilocapnic hypoxia following intermittent and continuous exposure to hypoxia in humans

Philip N Ainslie1*, Alice Barach1, Kevin J Cummings2, Carissa Murrell1, Mike Hamlin3, and John Hellemans

1 Physiology, University of Otago, New Zealand
2 Zoology, University of Latrobe, Melbourne, Australia
3 Physiology, University of Canterbury, New Zealand

* To whom correspondence should be addressed. E-mail: philip.ainslie{at}stonebow.otago.ac.nz.

We tested the hypothesis that intermittent hypoxia (IH) and/or continuous hypoxia (CH) would enhance the ventilatory response to acute hypoxia (HVR), thereby altering blood pressure (BP) and cerebral perfusion. Seven healthy volunteers were randomly selected to complete 10-12 days of IH (5-min hypoxia to 5-min normoxia repeated for 90 min) before ascending to mild CH (1560m) for 12 days. Seven other volunteers did not receive any IH before ascending to CH for the same 12 days. Prior to the IH and CH, following 12 days CH and 12-13 days post CH exposure, all subjects underwent a 20-min acute exposure to poikilocapnic hypoxia (FIO2, 0.12) in which ventilation, end-tidal gases, SaO2, BP and middle cerebral artery blood flow velocity (MCAv) were measured continuously. Following the IH and CH exposures, the peak HVR was elevated and was related to the increase in BP (r=0.66 to r=0.88; P<0.05, respectively) and to a reciprocal decrease in MCAv (r=0.73 to r=0.80; vs. pre exposures P<0.05) during the hypoxic test. Following both IH and CH exposures, HVR, BP and MCAv sensitivity to hypoxia were elevated when compared with pre-exposure, with no between-group differences following the IH and/or CH conditions, or persistent effects following 12-day of sea-level exposure. Our findings indicate that IH and/or mild CH can equally enhance the HVR which, by either direct or indirect mechanisms, facilitates alterations in BP and MCAv.




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