Stewart, Glenn M.

AbstractHeart failure (HF) patients appear to exhibit impaired thermoregulatory capacity during passive heating, as evidenced by diminished vascular conductance. Although some preliminary studies have described the thermoregulatory response to passive heating inHF, responses during exercise in the heat remain to be described. Therefore, the aim of this study was to compare thermoregulatory responses inHFand controls (CON) during exercise in the heat. TenHF(NYHAclasses I–II) and eightCONwere included. Core temperature (Tc), skin temperature (Tsk), and cutaneous vascular conductance (CVC) were assessed at rest and during 1 h of exercise at 60% of maximal oxygen uptake. Metabolic heat production (Hprod) and the evaporative requirements for heat balance (Ereq) were also calculated. Whole‐body sweat rate was determined from pre–post nude body mass corrected for fluid intake. WhileHprod(HF: 3.9 ± 0.9;CON: 6.4 ± 1.5 W/kg) andEreq(HF: 3.3 ± 0.9;CON: 5.6 ± 1.4 W/kg) were lower (P < 0.01) forHFcompared toCON, both groups demonstrated a similar rise inTc(HF: 0.9 ± 0.4;CON: 1.0 ± 0.3°C). Despite this similar rise inTc,Tsk(HF: 1.6 ± 0.7;CON: 2.7 ± 1.2°C), and the elevation inCVC(HF: 1.4 ± 1.0;CON: 3.0 ± 1.2 au/mmHg) was lower (P < 0.05) inHFcompared toCON. Additionally, whole‐body sweat rate (HF: 0.36 ± 0.15;CON: 0.81 ± 0.39 L/h) was lower (P = 0.02) inHFcompared toCON. Patients withHFappear to be limited in their ability to manage a thermal load and distribute heat content to the body surface (i.e., skin), secondary to impaired circulation to the periphery.