Menstrual Cycle Effect on the Control of Skin Blood Flow during Exercise at High Core Temperatures

摘要

Skin blood flow (SkBF) is linearly related to core temperature (Tc) during exercise. A break point occurs in the relationship during exercise such that the increase in SkBF per unit increase in Tc is attenuated in men at a Tc of approximately 38 degrees celsius. Five women were studied during exercise (35 min) at 80% VO2 peak during the mid-follicular phase and mid-luteal phase of the menstrual cycle to determine if the onset of this vasoconstrictor activity is affected by the elevated luteal Tc. Tc was measured every 30 s by a thermocouple placed in the esophagus. SkBF was measured twice per min by venous occlusion plethysmography. Tc and SkBF were calculated for the point. The onset of vasoconstrictor activity occurred at about 37.53 (+ or - 0.1) degrees celsius and in the mid-follicular phase and at 38.20(+ or 0.2) degree celsius in the mid-luteal phase. Both Tc and SkBF were significantly increased at the onset of vasoconstrictor activity in the luteal phase (p < or = 0.05). Heart rate averaged 150 (+ or - 11) and 161 (+ or - 9) beats min at the break point during the follicular and luteal phases, respectively. These data indicate that onset of vasoconstrictor activity occurred at an increased Tc and SkBF during the luteal than in the follicular phase and therefor is not dependent on a critical exercise SkBF or Tc but may be explained by another regulatory mechanism, perhaps arterial pressure regulation.