The physiologic response to hypoxia may be determined by variables such as exposure pattern and inducible nitric oxide synthase (iNOS) expression. Blood pressure (BP) and heart rate (HR) responses to daily exposure (X 3 days) of intermittent hypoxia (IH) vs. continuous hypoxia (CH) (equivalent total exposure time) were compared. The relation between BP and HR responses and iNOS expression under IH and CH conditions was also examined. On 3 consecutive days, 10 normal males had six 10-min. hypoxic exposures (oxyhemoglobin saturation, SpO2: 80-90%), with each exposure separated by 10 min. of normoxia. Subjects also had 3 consecutive days of CH (60 min/day; SpO2: 80--90%). IH and CH exposure blocks were separated by a ≥7 days. BP, HR, and SpO2 were recorded during the 5 min. prior to and the last 5 min. of each daily IH and CH exposure. Venous blood for iNOS mRNA was obtained before exposure on day l, and 2 hrs. after the last exposure on day 3. HR, systolic and diastolic BP were significantly (p0.05) increased from baseline- to end-exposure on each day, regardless of IH or CH. There was a significant negative correlation (p0.01) between both diastolic and mean BP with iNOS at the end of the day 3 IH session. Hypoxic stress reflected by IH and CH is associated with significant, but comparable changes in BP. Negative correlation between BP and iNOS mRNA in conjunction with IH, but not CH, exposure suggests that the hemodynamic response to IH may be modulated by iNOS.
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