Acute effect of Finnish sauna bathing on brachial artery flow‐mediated dilation and reactive hyperemia in healthy middle‐aged and older adults

Abstract

Regular Finnish sauna bathing is associated with a reduced risk of all‐cause and cardiovascular mortality in middle‐aged and older adults. Potential acute physiological adaptations induced by sauna bathing that underlie this relationship remain to be fully elucidated. The purpose of this study was to determine if typical Finnish sauna sessions acutely improve brachial artery flow‐mediated dilation ( FMD ) and reactive hyperemia ( RH ) in healthy middle‐aged and older adults. Using a randomized crossover design, FMD and RH were evaluated in 21 healthy adults (66 ± 6 years, 10 men/11 women) before and after each of the following conditions: (1) 1 × 10 min of Finnish sauna bathing (80.2 ± 3.2°C, 23 ± 2% humidity); (2) 2 × 10 min of sauna bathing separated by 10 min of rest outside the sauna; (3) a time control period (10 min of seated rest outside the sauna). FMD was taken as the peak change from baseline in brachial artery diameter following 5 min of forearm ischemia, whereas RH was quantified as both peak and area‐under‐the‐curve forearm vascular conductance postischemia. FMD was statistically similar pre to post 1 × 10 min (4.69 ± 2.46 to 5.41 ± 2.64%, P = 0.20) and 2 × 10 min of sauna bathing (4.16 ± 1.79 to 4.55 ± 2.14%, P = 0.58). Peak and area‐under‐the‐curve forearm vascular conductance were also similar following both sauna interventions. These results suggest that typical Finnish sauna bathing sessions do not acutely improve brachial artery FMD and RH in healthy middle‐aged and older adults.

Distinct contributions of skin and core temperatures to flow-mediated dilation of the brachial artery following passive heating

“…Our findings of increased FMD with forearm heating are consistent with existing literature in young adults (7,8); however, the improved FMD with whole body heating is a novel observation. The difference between the current study and others likely relates to differences in measured limbs (e. g., arm vs. leg) (11,30) and recovery time (e.g., immediate in the current study vs. 30-60 min in others) (9,11,30,31). Previous studies have also demonstrated that increased shear stress is important for vascular adaptation with acute (8) and chronic forearm heating ( 14) as well as repeated and episodic increases in core temperature (15).…”

“…The implications of these observations indicate that interventions increasing skin temperature rapidly (e.g., sauna) but with low tolerance times may also be of benefit to vascular function compared to the traditional prolonged core temperature >38.5 C. However, evaluation of the time required to elicit responses are scarce. For example, as little as 10-30 min of forearm heating has been reported to increase FMD in young healthy participants (7,8), whereas 10-20 min of sauna bathing did not change FMD in older healthy people (9). Conversely, 45-60 min of lower leg heating improved femoral artery FMD in older but not young adults (11) and may be of benefit in individuals with limited exercise capacity (e.g., individuals with spinal cord injury) (10).…”

“…The precise mechanisms mediating improved cardiovascular function are unclear in part due to the difficulty of isolating the effects of temperature from the associated hemodynamic responses. Acutely, regional limb heating improves endothelial function of the brachial artery (7,8) and whole body heating additionally reduces blood pressure and aortic stiffness (6,9). However, lower limb/body heating is often accompanied by increased core temperature (10)(11)(12) confounding interpretation of underlying mechanisms.…”

Cardiovascular Adjustments After Acute Heat Exposure

“…Dry saunas, also known as traditional Finnish saunas, typically operate at 80°C-100°C with a low relative humidity. Most studies utilizing dry saunas expose participants to heating cycles lasting 8-15 min separated by short periods of thermoneutral recovery or cold-water showering (24)(25)(26), whereas others have utilized a 30-min continuous exposure (27). Far infrared saunas generate an infrared wavelength of 6-12 μm that can easily penetrate human skin up to 2 inches, essentially inducing a deep heating effect.…”

“…Arm (10,17) and leg (10,11,17) blood flow remain elevated upward of ~30 min after acute heat exposure (Δ body core temperature of ≥0.6°C) and contribute to the increase in systemic vascular conductance. This hyperemic response seems to resolve thereafter in young healthy adults (17) but persists for upward of ~40 min in middle-aged and older adults (25). Vasodilation within the cutaneous circulation is thought to be the primary mediator of the sustained hyperemic response after heat exposure.…”