Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans.
Level 2 - randomized trial
Controlled clinical trial with a sham comparison arm.
PubMed 27270841 · doi:10.1113/JP272453
What was done
Twenty young, sedentary participants were assigned to an 8-week intervention (4-5 sessions per week) consisting of either passive heat therapy (n = 10; immersion in a 40.5°C bath sufficient to maintain rectal temperature ≥ 38.5°C for 60 min per session) or thermoneutral water immersion (n = 10; sham). Outcomes included flow-mediated dilatation, dynamic arterial compliance, aortic pulse wave velocity, intima media thickness, blood pressure, and endothelium-independent dilatation.
What was found
Heat therapy increased flow-mediated dilatation from 5.6 ± 0.3% to 10.9 ± 1.0% (P < 0.01) and superficial femoral dynamic arterial compliance from 0.06 ± 0.01 to 0.09 ± 0.01 mm2 mmHg-1 (P = 0.03). Heat therapy also reduced aortic pulse wave velocity from 7.1 ± 0.3 to 6.1 ± 0.3 m s-1 (P = 0.03), carotid intima media thickness from 0.43 ± 0.01 to 0.37 ± 0.01 mm (P < 0.001), and mean arterial blood pressure from 83 ± 1 to 78 ± 2 mmHg (P = 0.02), with reported reductions in diastolic blood pressure. No changes were observed in the sham group, nor were changes observed in carotid arterial compliance, superficial femoral intima media thickness, or endothelium-independent dilatation.
Why it matters
Repeated hot water immersion induces vascular remodeling and improvements in endothelial function comparable to exercise training in sedentary adults. This indicates passive heat therapy could serve as an alternative cardiovascular intervention for individuals with limited exercise capacity.
Limits
The sample size was very small (n = 20 total, 10 per arm). The abstract does not specify whether assignment was randomized. The cohort consisted exclusively of young, healthy sedentary adults, limiting generalizability to older or diseased populations, and long-term clinical outcomes were not evaluated.
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