Jayasinghe, Rohan

Heart failure (HF) patients are susceptible to heat strain during exercise, secondary to blunted skin blood flow (SkBF) responses, which may be explained by impaired nitric oxide (NO)-dependent vasodilation. Folic acid improves vascular endothelial function and SkBF through NO-dependent mechanisms in healthy older individuals and patients with cardiovascular disease. We examined the effect of folic acid supplementation (5 mg/day for 6 wk) on vascular function [brachial artery flow-mediated dilation (FMD)] and SkBF responses [cutaneous vascular conductance (CVC)] during 60 min of exercise at a fixed metabolic heat production (300 ẆHprod) in a 30°C environment in 10 patients with HF (New York Heart Association Class I–II) and 10 healthy controls (CON). Serum folic acid concentration increased in HF [preintervention (pre): 1.4 ± 0.2; postintervention (post): 8.9 ± 6.7 ng/ml, P = 0.01] and CON (pre: 1.3 ± 0.6; post: 5.2 ± 4.9 ng/ml, P = 0.03). FMD improved by 2.1 ± 1.3% in HF ( P < 0.01), but no change was observed in CON postintervention ( P = 0.20). During exercise, the external workload performed on the cycle ergometer to attain the fixed level of heat production for exercise was similar between groups (HF: 60 ± 13; CON: 65 ± 20 external workload, P = 0.52). Increases in CVC during exercise were similar in HF (pre: 0.89 ± 0.43; post: 0.83 ± 0.45 au/mmHg, P = 0.80) and CON (pre: 2.01 ± 0.79; post: 2.03 ± 0.72 au/mmHg, P = 0.73), although the values were consistently lower in HF for both pre- and postintervention measurement intervals ( P < 0.05). These findings demonstrate that folic acid improves vascular endothelial function in patients with HF but does not enhance SkBF during exercise at a fixed metabolic heat production in a warm environment.

AbstractHeart failure (HF) patients appear to exhibit impaired thermoregulatory capacity during passive heating, as evidenced by diminished vascular conductance. Although some preliminary studies have described the thermoregulatory response to passive heating inHF, responses during exercise in the heat remain to be described. Therefore, the aim of this study was to compare thermoregulatory responses inHFand controls (CON) during exercise in the heat. TenHF(NYHAclasses I–II) and eightCONwere included. Core temperature (Tc), skin temperature (Tsk), and cutaneous vascular conductance (CVC) were assessed at rest and during 1 h of exercise at 60% of maximal oxygen uptake. Metabolic heat production (Hprod) and the evaporative requirements for heat balance (Ereq) were also calculated. Whole‐body sweat rate was determined from pre–post nude body mass corrected for fluid intake. WhileHprod(HF: 3.9 ± 0.9;CON: 6.4 ± 1.5 W/kg) andEreq(HF: 3.3 ± 0.9;CON: 5.6 ± 1.4 W/kg) were lower (P < 0.01) forHFcompared toCON, both groups demonstrated a similar rise inTc(HF: 0.9 ± 0.4;CON: 1.0 ± 0.3°C). Despite this similar rise inTc,Tsk(HF: 1.6 ± 0.7;CON: 2.7 ± 1.2°C), and the elevation inCVC(HF: 1.4 ± 1.0;CON: 3.0 ± 1.2 au/mmHg) was lower (P < 0.05) inHFcompared toCON. Additionally, whole‐body sweat rate (HF: 0.36 ± 0.15;CON: 0.81 ± 0.39 L/h) was lower (P = 0.02) inHFcompared toCON. Patients withHFappear to be limited in their ability to manage a thermal load and distribute heat content to the body surface (i.e., skin), secondary to impaired circulation to the periphery.