Heart Failure Modulates Thermoregulatory Control Independently Of Differences In Physical Characteristics And Metabolic Heat Production

Abstract

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 thus Ereq, in a 30°C environment. METHODS: Rectal temperature (Trec), local sweat rate (LSR), and cutaneous vascular conductance (CVC) were measured during 60-min of cycle ergometry. Whole-body sweat rate (WBSR) was estimated from pre-post nude body weight corrected for fluid intake. Hprod and Ereq, as well as dry heat loss (Hdry) and evaporative heat loss from the skin (Esk) ─ assuming all secreted sweat evaporated, were calculated using partitional calorimetry. RESULTS: Despite exercising at the same rate of Hprod (HF: 338±43; CON: 323±31W, p=0.25), Trec was greater (p<0.01) in HF (0.81±0.16°C) than CON (0.49±0.27°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. Similarly, Hdry was comparable between groups (HF: 22.9±3.2; CON: 20.4±5.0W, p=0.14). Consequently, the cumulative body heat storage was similar between groups (HF: 154±106; CON: 196±174kJ, p=0.44). Furthermore, CVC was lower in HF than CON (HF: 0.83±0.42; CON: 2.10±0.79au/mmHg, p<0.01). CONCLUSIONS: Collectively, these findings demonstrate that HF patients exhibit an impaired skin blood flow response, but no differences in sweating. Given that HF had similar body heat storage to CON 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.