Finnish sauna bathing and vascular health of adults with coronary artery disease: a randomized controlled trial.

Regular Finnish sauna use is associated with a reduced risk of cardiovascular mortality. However, physiological mechanisms underlying this association remain unknown. This study determined if an 8-wk Finnish sauna intervention improves peripheral endothelial function, microvascular function, central arterial stiffness, and blood pressure in adults with coronary artery disease (CAD). Forty-one adults (62 ± 6 yr, 33 men/8 women) with stable CAD were randomized to 8 wk of Finnish sauna use (n = 21, 4 sessions/wk, 20-30 min/session, 79°C, 13% relative humidity) or a control intervention (n = 20, lifestyle maintenance). Brachial artery flow-mediated dilation (FMD), carotid-femoral pulse wave velocity (cf-PWV), total (area under the curve) and peak postocclusion forearm reactive hyperemia, and blood pressure (automated auscultation) were measured before and after the intervention. After the sauna intervention, resting core temperature was lower (-0.27°C [-0.54, -0.01], P = 0.046) and sweat rate during sauna exposure was greater (0.3 L/h [0.1, 0.5], P = 0.003). The change in brachial artery FMD did not differ between interventions (control: 0.07% [-0.99, +1.14] vs. sauna: 0.15% [-0.89, +1.19], interaction P = 0.909). The change in total (P = 0.031) and peak (P = 0.024) reactive hyperemia differed between interventions due to a nonsignificant decrease in response to the sauna intervention and an increase in response to control. The change in cf-PWV (P = 0.816), systolic (P = 0.951), and diastolic (P = 0.292) blood pressure did not differ between interventions. These results demonstrate that four sessions of Finnish sauna bathing per week for 8 wk does not improve markers of vascular health in adults with stable CAD.NEW & NOTEWORTHY This study determined if unsupervised Finnish sauna bathing for 8 wk improves markers of vascular health in adults with coronary artery disease. Finnish sauna bathing reduced resting core temperature and improved sweating capacity, indicative of heat acclimation. Despite evidence of heat acclimation, Finnish sauna bathing did not improve markers of endothelial function, microvascular function, arterial stiffness, or blood pressure.

Acute effect of passive heat exposure on markers of cardiometabolic function in adults with type 2 diabetes mellitus.

Heat therapy is a promising strategy to improve cardiometabolic health. This study evaluated the acute physiological responses to hot water immersion in adults with type 2 diabetes mellitus (T2DM). On separate days in randomized order, 13 adults with T2DM [8 males/5 females, 62 ± 12 yr, body mass index (BMI): 30.1 ± 4.6 kg/m2] were immersed in thermoneutral (34°C, 90 min) or hot (41°C, core temperature ≥38.5°C for 60 min) water. Insulin sensitivity was quantified via the minimal oral model during an oral glucose tolerance test (OGTT) performed 60 min after immersion. Brachial artery flow-mediated dilation (FMD) and reactive hyperemia were evaluated before and 40 min after immersion. Blood samples were drawn to quantify protein concentrations and mRNA levels of HSP70 and HSP90, and circulating concentrations of cytokines. Relative to thermoneutral water immersion, hot water immersion increased core temperature (+1.66°C [+1.47, +1.87], P < 0.01), heart rate (+34 beats/min [+24, +44], P < 0.01), antegrade shear rate (+96 s-1 [+57, +134], P < 0.01), and IL-6 (+1.38 pg/mL [+0.31, +2.45], P = 0.01). Hot water immersion did not exert an acute change in insulin sensitivity (-0.3 dL/kg/min/µU/mL [-0.9, +0.2], P = 0.18), FMD (-1.0% [-3.6, +1.6], P = 0.56), peak (+0.36 mL/min/mmHg [-0.71, +1.43], P = 0.64), and total (+0.11 mL/min/mmHg × min [-0.46, +0.68], P = 0.87) reactive hyperemia. There was also no change in eHSP70 (P = 0.64), iHSP70 (P = 0.06), eHSP90 (P = 0.80), iHSP90 (P = 0.51), IL1-RA (P = 0.11), GLP-1 (P = 0.59), and NF-κB (P = 0.56) after hot water immersion. The physiological responses elicited by hot water immersion do not acutely improve markers of cardiometabolic function in adults with T2DM.NEW & NOTEWORTHY Heat therapy has been shown to improve markers of cardiometabolic health in preclinical and clinical studies. However, the effects of heat therapy in individuals with type 2 diabetes mellitus (T2DM) remain understudied. We examined the acute effect of hot water immersion on glucose tolerance, flow-mediated dilation, reactive hyperemia, inflammatory markers, and heat shock proteins in adults with T2DM. Hot water immersion did not acutely improve the markers studied.

Thermoregulation During Pregnancy: a Controlled Trial Investigating the Risk of Maternal Hyperthermia During Exercise in the Heat.

OBJECTIVES: Despite the well-established benefits of exercise, pregnant women are discouraged from physical activity in hot/humid conditions to avoid hyperthermia (core temperature (Tcore) ≥ 39.0 °C). Recent epidemiological evidence also demonstrates greater risk of negative birth outcomes following heat exposure during pregnancy, possibly due to thermoregulatory impairments. We aimed to determine (1) the risk of pregnant women exceeding a Tcore of 39.0 °C during moderate-intensity exercise in the heat; and (2) if any thermoregulatory impairments are evident in pregnant (P) versus non-pregnant (NP) women. METHODS: Thirty participants (15 pregnant in their second trimester or third trimester) completed two separate exercise-heat exposures in a climate chamber (32 °C, 45%RH). On separate occasions, each participant cycled on a semi-recumbent cycle ergometer for 45 min at a workload representative of a moderate-intensity (1) non-weight-bearing (NON-WB), or (2) weight-bearing (WB) activity. Thermoregulatory responses were monitored throughout. RESULTS: The highest rectal temperature observed in a pregnant individual was 37.93 °C. Mean end-exercise rectal temperature did not differ between groups (P:37.53 ± 0.22 °C, NP:37.52 ± 0.34 °C, P = 0.954) in the WB trial, but was lower in the P group (P:37.48 ± 0.25 °C, vs NP:37.73 ± 0.38 °C, P = 0.041) in the NON-WB trial. Whole-body sweat loss was unaltered by pregnancy during WB (P:266 ± 62 g, NP:264 ± 77 g; P = 0.953) and NON-WB P:265 ± 51 g, NP:300 ± 75 g; P = 0.145) exercise. Pregnant participants reported higher ratings of thermal sensation (felt hotter) than their non-pregnant counterparts in the WB trial (P = 0.002) but not in the NON-WB trial, (P = 0.079). CONCLUSION: Pregnant women can perform 45 min of moderate-intensity exercise at 32 °C, 45%RH with very low apparent risk of excessive maternal hyperthermia. No thermoregulatory impairments with pregnancy were observed.