Short read
Radtke and colleagues at Inselspital and the University of Bern measured the acute response to a fixed sequence, published in the European Journal of Preventive Cardiology in 2016: 2 consecutive Finnish sauna sessions at 80 degrees, followed by head-out immersion in water at 12 degrees. The modality is sauna with cold water immersion afterwards. 37 men took part under medical supervision in three groups: 12 with chronic heart failure, mean age 61.8, 13 with coronary artery disease, mean age 61.2, and 12 controls without heart disease, mean age 60.9.
Cardiac output and heart rate rose in all groups after sauna and cold water, except in the coronary group after the sauna session. Systolic blood pressure fell during the sauna in every group, with its lowest point after 6 minutes, and the cold water raised it again. Compared with the controls, the heart failure group showed similar haemodynamic changes, and neither excessive adrenergic activity nor complex arrhythmias occurred. The sympathovagal ratio from heart rate variability stayed unchanged in heart failure, while in the coronary and control groups it rose after the first sauna session and remained elevated for longer.
The study includes men only, in three small groups of 12 to 13, in one supervised session with medically stable patients. There is no follow-up and no statement on what regular repetition does. The heart rate variability data describe the reaction to this one session.
The finding is a tolerability result for stable patients under supervision, and it does not replace a medical assessment. It also does not support the common claim that contrast bathing trains the autonomic nervous system: what it shows is an acute sympathetic shift, not a lasting adaptation.