Purpose: Heart failure (HF) patients appear to exhibit altered thermoregulatory responses during exercise in the heat. However, the extent to which these responses are altered due to physiological impairments independently of biophysical factors associated with differences in metabolic heat production (Hprod), evaporative heat balance requirements (Ereq) and/or body size, is presently unclear. Therefore, we examined thermoregulatory responses in 10 HF and 10 age-matched controls (CON) similar in body size during exercise at a fixed rate of Hprod, and therefore Ereq in a 30[degrees]C environment.

Methods: Rectal temperature (Trec), local sweat rate (LSR), and cutaneous vascular conductance (CVC) were measured throughout 60-min of cycle ergometry. Whole-body sweat rate (WBSR) was estimated from pre-post nude body weight corrected for fluid intake.

Results: Despite exercising at the same rate of Hprod (HF: 338+/-43; CON: 323+/-31W, p=0.25), the rise in Trec was greater (p<0.01) in HF (0.81+/-0.16[degrees]C) than CON (0.49+/-0.27[degrees]C). In keeping with a similar Ereq (HF: 285+/-40; CON: 274+/-28W, p=0.35), no differences in WBSR (HF: 0.45+/-0.11; CON: 0.41+/-0.07L/h, p=0.38) or LSR (HF: 0.96+/-0.17; CON: 0.79+/-0.15mg/cm2/min, p=0.50) were observed between groups. However, the rise in CVC was lower in HF than CON (HF: 0.83+/-0.42; CON: 2.10+/-0.79au/mmHg, p<0.01). Additionally, the cumulative body heat storage estimated from partitional calorimetry was similar between groups (HF: 154+/-106; CON: 196+/-174kJ, p=0.44).

Conclusions: Collectively, these findings demonstrate that HF patients exhibit a blunted skin blood flow response, but no differences in sweating. Given that HF had similar body heat storage to controls at the same Hprod, their greater rise in core temperature can be attributed to a less uniform internal distribution of heat between the body core and periphery.