Passive Heat Therapy Reduces Aortic And Carotid Artery Stiffness And Intima-Media Thickness In Middle-Aged And Older Adults

Aging is accompanied by stiffening of the large elastic arteries and adverse arterial remodeling, which increase risk for cardiovascular diseases (CVD). Passive heat therapy—chronic use of hot baths and saunas—is associated with lower CVD risk. However, it is unknown if a heat therapy intervention affects arterial stiffness and structure in middle-aged and older (MA/O) adults without overt clinical disorders. Purpose To determine if passive heat therapy, via hot water immersion, in healthy MA/O adults: 1) reduces arterial stiffness, as measured by carotid-femoral pulse wave velocity (c-f PWV; i.e., aortic stiffness) and common carotid artery (CCA) and superficial femoral artery (SFA) β-stiffness index; and 2) alters arterial structure, as measured by CCA and SFA intima-media thickness (IMT) and vessel diameter. Methods 23 healthy, minimally active MA/O men and postmenopausal women (57-79 years) were randomized to participate in 30, 60-minute sessions (3-4x/week over 8-10 weeks) of either hot water immersion (40.5°C, N=12, 5M/7F, 68±2 years) or thermoneutral water immersion (36°C, “sham”, N=11, 4M/7F, 66±2 years). Ultrasound- and tonometry-based measures of arterial stiffness and structure were measured at baseline and 24-72 hours after the final water immersion session. Data are mean ± SEM; P-values were determined by 2-way mixed-design ANOVA with Tukey's post-hoc tests. Results In the large elastic arteries (i.e., the arteries that stiffen with aging), heat therapy reduced c-f PWV from 8.7±0.6 to 8.0±0.7 m/s (p=0.03) and CCA β-stiffness index from 10.6±1.6 to 7.8±0.8 (p=0.02); however, heat therapy did not change SFA β-stiffness index (15.0±1.6 vs. 14.6±1.6, p=0.99), a more muscular artery. Heat therapy also improved selective measures of arterial structure. In the CCA, heat therapy decreased IMT from 0.70±0.01 to 0.66±0.02 mm (p<0.01) without affecting diameter (7.4±0.2 vs. 7.2±0.2 mm, p=0.90). Conversely, in the SFA, heat therapy did not alter IMT (0.56±0.02 vs. 0.57±0.02 mm, p>0.99), but tended to increase diameter from 7.6±0.2 to 7.9±0.3 mm (p=0.06), which likely occurred due to repeated increases in vascular shear stress to the lower body during hot water immersion sessions. No changes were observed in any outcome in sham subjects (c-f PWV: 8.5±0.5 vs. 8.4±0.4 m/s, p=0.85; CCA β-stiffness index: 10.0±2.2 vs. 9.9±2.6, p=0.96; CCA IMT: 0.70±0.02 vs. 0.70±0.02 mm, p=0.92; SFA β-stiffness index: 15.2±2.1 vs. 16.0±2.9, p=0.93; CCA diameter: 7.5±0.1 vs. 7.4±0.1 mm, p=0.42; SFA IMT: 0.57±0.03 vs. 0.56 ±0.03 mm, p=0.85; SFA diameter: 7.8±0.4 vs. 7.9±0.3 mm, p=0.98). Conclusion Heat therapy subjects demonstrated clinically relevant reductions in aortic and carotid artery stiffness, and in CCA IMT, all of which are independent predictors of future CVD risk. As such, heat therapy may be a promising lifestyle-based intervention for improving arterial health and thereby reducing CVD risk in MA/O adults.