Tolerance to a hemorrhagic challenge during heat stress is improved with inspiratory resistance breathing

Abstract

The mechanism(s) by which heat stress alters blood pressure control and tolerance to a simulated hemorrhagic challenge is multifaceted; however, heat‐induced reductions in central blood volume play a key role. Inspiratory resistance breathing improves blood pressure control and tolerance during simulated hemorrhage in normothermic individuals. It is unknown if similar improvements occur with this maneuver in heat stress conditions. This study tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated hemorrhage in individuals with elevated internal temperatures. On 2 separate days, 8 subjects performed a simulated hemorrhage challenge (lower body negative pressure, LBNP) to pre‐syncope following an increase in internal temperature of 1.5 °C. During one trial subjects breathed through an inspiratory impedance device set at 0 cmH20 of resistance (Sham) while on the other day the device was set at −7 cmH20 of resistance (Experimental). Tolerance was quantified as cumulative stress index (CSI). Subjects were more tolerant to the LBNP challenge during the Experimental protocol as indexed by a larger CSI (Sham: 520±306 mmHg × min; Experimental: 682±324 mmHg × min, P<0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated hemorrhagic challenge during heat stress.Support NIH‐HL61388 & HL84072