Altered thermoregulatory responses in heart failure patients exercising in the heat

Abstract Heart 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 in HF , responses during exercise in the heat remain to be described. Therefore, the aim of this study was to compare thermoregulatory responses in HF and controls ( CON ) during exercise in the heat. Ten HF ( NYHA classes I–II) and eight CON were included. Core temperature ( T c ), skin temperature ( T sk ), and cutaneous vascular conductance ( CVC ) were assessed at rest and during 1 h of exercise at 60% of maximal oxygen uptake. Metabolic heat production ( H prod ) and the evaporative requirements for heat balance ( E req ) were also calculated. Whole‐body sweat rate was determined from pre–post nude body mass corrected for fluid intake. While H prod ( HF : 3.9 ± 0.9; CON : 6.4 ± 1.5 W/kg) and E req ( HF : 3.3 ± 0.9; CON : 5.6 ± 1.4 W/kg) were lower ( P < 0.01) for HF compared to CON , both groups demonstrated a similar rise in T c ( HF : 0.9 ± 0.4; CON : 1.0 ± 0.3°C). Despite this similar rise in T c , T sk ( HF : 1.6 ± 0.7; CON : 2.7 ± 1.2°C), and the elevation in CVC ( HF : 1.4 ± 1.0; CON : 3.0 ± 1.2 au/mmHg) was lower ( P < 0.05) in HF compared to CON . Additionally, whole‐body sweat rate ( HF : 0.36 ± 0.15; CON : 0.81 ± 0.39 L/h) was lower ( P = 0.02) in HF compared to CON . Patients with HF appear 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.