Effect of Passive Heat Stress and Hypohydration on Arterial Compliance in Females

Abstract

Passive heat stress increases arterial compliance, yet it is unknown if hydration status modulates this relationship. Further, limited data exist on the relationship between passive heat stress and arterial compliance in females. PURPOSE: To investigate the effect of hydration status on arterial compliance in females while normothermic and hyperthermic (via passive heat stress). METHODS: In a randomized order, eight females (22.6 ± 2.0 y; 60.5 ± 5.1 kg; 166.4 ± 6.1 cm) were passively heated on two separate occasions until core temperature (TC) increased 1.0°C while beginning euhydrated (EU) or hypohydrated (HY; via 24-h fluid restriction). Pre-trial hydration status was confirmed via percent body mass change from baseline (%BMC; EU: 0.29 ± 0.74, HY: -1.26 ± 0.55%) and serum osmolality (Sosm; EU: 283 ± 2, HY: 288 ± 4 mOsm/kg; all p < 0.01). During the EU trial, subjects were provided water (%BMC; -0.70 ± 0.72%, Sosm; 285 ± 4 mOsm/kg). Subjects became further dehydrated in the HY trial (%BMC; -2.56 ± 0.54%, Sosm; 294 ± 4 mOsm/kg; p < 0.05). At baseline (BL) and a 1.0 °C TC increase (1.0 °C), arterial compliance was assessed centrally and peripherally using ultrasound to measure pulse wave velocity (cPWV and pPWV, respectively) at the carotid, radial, and femoral arteries. RESULTS: Hypohydration did not affect baseline cPWV (EU: 451.1 ± 40.2 vs. HY: 424.5 ± 55.1 cm/s, respectively; p = 0.289) or pPWV (EU: 613.5 ± 45.9 vs. HY: 589.2 ± 53.4 cm/s, p = 0.316). The change in pPWV observed with heat stress was dependent on hydration status (p = 0.042), such that when EU, pPWV decreased (BL: 613.5 ± 45.9; 1.0 °C: 569.8 ± 74.2 cm/s, p = 0.018) but there was no change when HY (BL: 589.2 ± 53.4; 1.0 °C: 590.8 ± 56.7 cm/s, p = 0.913). cPWV increased during heat stress independent of hydration status (BL: 437.8 ± 48.6; 1.0 °C: 496.0 ± 70.4 cm/s, p = 0.001). CONCLUSIONS: Mild dehydration does not affect arterial compliance in normothermic conditions, but passive heat stress decreases central compliance (i.e., increases cPWV) independent of hydration status. Peripheral arterial compliance increases with heat stress (i.e., decrease in pPWV) but only when starting and maintaining a euhydrated state, not when hypohydrated. These data have implications for the acute effects of heat stress on arterial compliance in females.