Chronic heart failure does not attenuate the total activity of sympathetic outflow to skin during whole-body heating

Abstract

Background: Previous studies show that the rise in skin blood flow and cutaneous vascular conductance during heat stress is substantially attenuated in chronic heart failure (CHF) patients. The mechanisms responsible for this finding are not clear. In particular, little is known regarding the responses of skin sympathetic nerve activity (SSNA) that control the skin blood flow during heat stress in CHF patients. We examined the effects of a modest heat stress to test the hypothesis that SSNA responses could be attenuated in CHF.

Methods and results: We assessed SSNA (microneurography) from the peroneal nerve and skin blood flow (forearm laser Doppler) in 9 patients with stable class II-III CHF and in matched healthy subjects during passive whole-body heating with a water-perfused suit. Whole-body heating induced similar increases in internal temperature (≈0.6 °C) in both groups. Whole-body heat stress evoked similar SSNA activation in CHF patients (Δ891±110 U/min) and the control subjects (Δ787±84 U/min; P=0.66), whereas the elevation in forearm cutaneous vascular conductance in patients with CHF was significantly lower than that in healthy control subjects (Δ131±29% vs. Δ623±131%; P=0.001).

Conclusions: The present data show that SSNA activation during a modest whole-body heat stress is not attenuated in CHF. Thus, the attenuated skin vasodilator response in CHF patients is not attributable to a reduction in total activity of sympathetic outflow to skin.

Figure 1

Representative tracings of mean skin temperature (Tsk), internal temperature (Tcore), skin sympathetic nerve activity (SSNA), skin blood flow (SkBF) and sweat rate (SR) during whole body heating in a control subject (upper panel) and a CHF patient (lower panel). SkBF unit: Flux unit. SR unit: mg/cm²/min. Warm: Tsk >37 °C while the increase in Tcore <0.2 °C. WBH: whole body heat stress, the increase in Tcore was greater than 0.5 °C when Tsk was clamped at ~38 °C. Notice the clear SSNA activation in both control subject (upper panels) and CHF patient (lower panels) during WBH.

Figure 2

Mean SSNA, cutaneous vascular conductance (CVC) and SR responses to whole body heating. During the initial period of heating, Tsk increased, but the Tcore did not rise. In the later period of whole body heating, Tsk was clamped at ~38 °C, while the Tcore increased. Mean body temperature (Tbody) was calculated as follows: 0.9×Tcore + 0.1×Tsk.

Figure 3

SSNA, CVC and SR responses to Warm and WBH. CVC is expressed as percent of normothermic baseline (Base). Warm and WBH: see definition in Figure 1. *: significantly different from Baseline (P<0.05). †: significantly different from Control subjects (P<0.05). For CVC (left upper panel), P=0.002 for subject groups; P<0.001 for heating, P<0.001 for the interaction. For SR (left lower panel), P=0.931 for subject groups; P<0.001 for heating, P=0.003 for the interaction. For SSNA burst rate change (right upper panel), P=0.04 for subject groups; P<0.001 for heating, P=0.049 for the interaction. For SSNA total activity change (right lower panel), P=0.342 for subject groups, P<0.001 for heating, P=0.238 for the interaction.