The Effect of Acute Normobaric Hypoxia On Heart Rate And Mean Arterial Pressure at Rest, During annd Post Exercise

Abstract

BACKGROUND: Hypoxia is a potent stressor that induces various physiological changes. Although modifications in autonomic regulation and vascular tone are responses to hypoxia, changes in heart rate and blood pressure may vary depending on individual characteristics, severity of hypoxia and exercise intensity and duration. PURPOSE: The purpose of the current study was to determine the effect of acute normobaric hypoxia on heart rate and mean arterial pressure at rest, during and post-exercise in middle-aged males. METHODS: Eight apparently healthy (35.9 ± 5.7 ml·kg-1·min-1), middle-aged (40.5 ± 2 yr) males volunteered to participate in the present investigation. Participants reported to the exercise physiology laboratory on three separate occasions. On the first visit, subjects underwent a graded exercise test (Excalibur 1300W cycle ergometer) to determine maximal oxygen consumption. The next two visits were separated by a one week washout period. Participants underwent normoxia with exercise (NE) and hypoxia with exercise (HE) in a hypoxia (20.9% vs. 12.5% O2) chamber (Colorado Altitude Training, Louisville, CO) including 2hr baseline, 1h low intensity cycling (50% of hypoxic VO2max) and 2h recovery. Heart rate (HR) measures were obtained every 10 min, and mean arterial pressure (MAP) measures were obtained every 30min throughout the experimental trials. RESULTS: A repeated measures ANOVA revealed a trial (NE and HE) by time interaction for heart rate (p<0.01), and a pair-sample t-test demonstrated that the difference in post exercise HR between HE and NE is greater than pre exercise (p<0.05). MAP demonstrated a trial by time interaction (p<0.05); MAP decreased greater in hypoxia than normoxia post exercise. CONCLUSION: These data suggest that normobaric hypoxia causes a differential hemodynamic response from normoxia in apparently healthy middle aged males at rest and post-exercise.