The acute effects of passive heating on endothelial function, muscle microvascular oxygen delivery, and expression of serum HSP90α.

Abstract

Passive heating has been a therapeutic tool used to elevate core temperature and induce increases in cardiac output, blood flow, and shear stress. We aimed to determine the effects of a single bout of passive heating on endothelial function and serum heat shock protein 90α (HSP90α) levels in young, healthy subjects. 8 healthy subjects were recruited to participate in one bout of whole-body passive heating via immersion in a 40°C hot tub to maintain a 1°C increase in rectal temperature for 60min. Twenty-four hours after heating, shear-rate corrected endothelium-dependent dilation increased (pre: 0.004±0.002%SRAUC; post: 0.006±0.003%SRAUC; p=0.034) but serum [HSP90α] was not changed (pre: 36.7±10.3ng/mL; post: 40.6±15.9ng/mL; p=0.39). Neither resting muscle O2 utilization (pre: 0.17±0.11mL O2 min-1 (100g)-1; post: 0.14±0.09mL O2 min-1 (100g)-1); p=0.28) nor mean arterial pressure (pre: 74±11mmHg; post: 73±11mmHg; p=0.79) were influenced by the heating intervention. Finally, time to peak after cuff release was significantly delayed for % O2 sat (TTPpre=39±8.9s and TTPpost=43.5±8.2s; p=0.007) and deoxy-[heme] (TTPpre=41.3±18.1s and TTPpost=51.4±16.3s; p=0.018), with no effect on oxy-[heme] (p=0.19) and total-[heme] (p=0.41). One bout of passive heating improved endothelium-dependent dilation 24h later in young, healthy subjects. This data suggests that passive heat treatments may provide a simple intervention for improving vascular health.