The cardiovascular response to a 20-minute sauna session at 80 degrees Celsius is not trivial. Heart rate rises to 100 to 150 beats per minute, comparable to brisk walking. Cardiac output increases substantially. The left ventricle is required to pump against reduced peripheral resistance as blood vessels dilate. Plasma volume expands with repeated sessions as the kidneys retain sodium in response to haemodynamic signals. These are genuine cardiovascular training stimuli, and they produce genuine cardiovascular adaptations.
The Plasma Volume Effect
Plasma volume expansion is one of the primary cardiovascular adaptations to both aerobic exercise and regular heat stress. Greater plasma volume improves venous return to the heart, increasing stroke volume and reducing the heart rate required to achieve a given cardiac output. It also improves thermoregulation capacity. The plasma volume expansion from 8 weeks of regular sauna use in controlled studies is similar in magnitude to that produced by 8 weeks of moderate aerobic training, though the two adaptations occur through partially different mechanisms.
The Arterial Stiffness Effect
Several controlled studies have demonstrated significant reductions in pulse wave velocity, the primary marker of arterial stiffness, following 8-week programmes of regular heat therapy. The mechanism involves heat-induced nitric oxide production, which acutely relaxes vascular smooth muscle, and the cumulative effect of repeated vascular distension on arterial wall compliance. This reduction in arterial stiffness is directly relevant to blood pressure control and cardiovascular risk.
Sources
- Laukkanen, J.A., et al. (2018). Cardiovascular and other health benefits of sauna bathing: a review of the evidence. Mayo Clinic Proceedings, 93(8), 1111-1121.
- Brunt, V.E., et al. (2016). Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. Journal of Physiology, 594(18), 5329-5342.
- Ketelhut, S., & Ketelhut, R.G. (2019). Blood pressure and heart rate during sauna bath: assessment by long-term 24h-blood pressure monitoring. Complementary Therapies in Medicine, 44, 218-222.