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Evidence of disrupted human heat balance in heart failure patients exercising in the heat
Author(s) -
Balmain Bryce,
Jay Ollie,
Sabapathy Surendran,
Royston Danielle,
Stewart Glenn,
Jayasinghe Rohan,
Eqbal Yusuf,
Morris Norman
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1290.4
Subject(s) - thermoregulation , chemistry , medicine , sweat , heart failure , vo2 max , heart rate , zoology , cardiology , endocrinology , blood pressure , biology
Heart failure (HF) patients appear to exhibit altered thermoregulatory responses during exercise; however, this has not been examined during exercise in the heat. Accordingly, this study compared thermoregulatory responses and human heat balance parameters of HF and healthy controls (CON) during exercise in a warm environment. Methods Eight HF (NYHA class I–II), and six CON matched for age (HF: 63±7 yr; CON: 64±7 yr; p=0.72) and body surface area (HF: 2.04±0.11 m 2 ; CON: 1.96±0.13 m 2 ; p=0.26) performed a 60‐min cycling test at 60% of their individual peak oxygen uptake in a 30°C environment. Oxygen uptake (VO 2 ), core temperature (T c ), mean skin temperature (T sk ), and forearm cutaneous vascular conductance (CVC) (derived from the ratio of laser Doppler flux to mean arterial pressure) were monitored at rest and during exercise. Whole body sweat rate (WBSR) was determined from pre‐post nude body weight corrected for fluid intake. Metabolic heat production (H prod ) and evaporative heat balance requirements (E req ), as well as dry heat loss (H dry ) and evaporative heat potential (E sk ) – assuming all secreted sweat evaporated, were subsequently calculated. Results During the cycling tests, absolute H prod (HF: 367±96 W; CON: 511±116 W) and H prod per unit mass (HF: 4.1±0.9 W/kg; CON: 6.5±1.3 W/kg) were lower (p<0.05) for HF, and consequently E req (HF: 298±92 W, 3.4±0.9 W/kg; CON: 438±109 W, 5.6±1.3 W/kg) was also lower (p<0.05) for HF compared to CON. Despite a difference in metabolic heat load, H dry was similar (p>0.05) between the two groups (HF: 69±18 W, 0.9±0.4 W/kg; CON: 72±20 W, 0.9±0.2 W/kg). In parallel, increases in T c (HF: 0.94±0.41°C; CON: 0.97±0.29°C) and T sk (HF: 2.48±0.88°C; CON: 3.11±1.02°C) were similar (p>0.05) for both groups. But, increases in CVC were lower (p<0.01) in HF (132±14 %CVC rest ) compared to CON (553±215 %CVC rest ). WBSR tended to be lower (p=0.09) in HF (0.38±0.15 L/hr) compared to CON (0.67±0.31 L/hr). Furthermore, E sk (HF: 2.9±1.0 W/kg; CON: 5.9±2.7 W/kg) was lower for HF; however, the relative difference in E sk to H prod (HF: 70±23%; CON: 86±25%) was similar (p>0.05) between the two groups. Conclusion Despite exercising with a lower H prod per unit mass, HF patients had a similar rise in T c in parallel to a smaller increase in CVC compared to CON. As such, it appears that HF patients are limited in their ability to manage a thermal load and distribute internal heat content among various tissues in the body, secondary to poorer circulation to the periphery. These results suggest that from a thermoregulatory perspective, HF patients primarily exhibit blunted changes in skin blood flow during exercise in the heat. Importantly, it must be noted that both participant groups (HF vs CON) performed exercise at different rates of H prod . Therefore, to perform an unbiased comparison of thermoregulatory responses between groups, we propose that the same H prod per unit mass must be administered and taken into consideration.