Repeated measurement of hypoxic ventilatory response as an intermittent hypoxic stimulus.

Measurement of hypoxic ventilatory response (HVR) involves an exposure to hypoxia which, if repeated over several days might act as an intermittent hypoxic stimulus. The purpose of this study was to measure HVR repeatedly over 5 days to determine whether it was affected by repeated measurement. Nine healthy male subjects completed an isocapnic HVR test, on one occasion, followed 5 days later by one measurement each day for 5 days. Each test lasted approximately 5-8 min with inspired oxygen concentration declining to as a low as 5-6%. No systematic trend was observed in HVR over the 5-day period (p>0.05). There were no significant differences in HVR between any of the test days. Regression failed to show any trend in HVR over the five sequential days. The calculated mean coefficient of variation for HVR for each subject was 27%. There is no evidence that the short exposure to hypoxia as part of HVR measurement is a co-intervention when measured repeatedly over 5 days in physiological studies.