Aims: We examined the thermoregulatory response to heat exposure in patients with chronic heart failure.
Methods and results: Skin blood flow (SkBF) was measured in HF subjects and matched controls. Cutaneous vascular conductance (CVC) was calculated from laser-Doppler SkBF and blood pressure. To assess the nitric oxide contribution to thermoregulatory responses, subcutaneous microdialysis membranes were placed beneath the laser-Doppler probes to infuse N(G)-nitro-l-arginine methyl ester (l-NAME), or Ringer's solution. Core (T(C)) and skin temperatures (five sites, T(Sk)) were continuously recorded. Subjects were studied during normothermia then at 38 degrees C, 50%RH within a climate chamber. T(C) and T(Sk) did not differ between HF and controls during normothermia and heating induced similar increases in both groups. During heating, CVC rose in both groups, but significantly less so in HF (HF 43.9+/-7.8 vs. controls 58.0+/-7.5% CVC(max), P<0.05). l-NAME attenuated SkBF responses in the control (58.0+/-7.5 vs. 34.6+/-5.1% CVC(max), P<0.001) and HF subjects (43.9+/-7.8 vs. 27.0+/-2.2% CVC(max), P<0.005), with a larger effect evident in the controls (P<0.05).
Conclusion: HF patients exhibit impaired thermoregulatory responses to heat exposure. Lower SkBF in HF, which defends blood pressure during heat exposure, also predisposes these subjects to heat intolerance.