In general, sauna bathing (Finnish bath) has dry air and high temperature with 80℃ to 100℃ and has a relative humidity of 10% to 20%. Sauna bathing is a popular recreational activity that is generally considered to be safe. Although most people are safe and feel relax, sudden hyperthermic death can occur. Most of victims were middle-aged men, 84% were under the influence of alcohol, and 27% had cardiovascular diseases. Therefore, systemic hyperthermia is often prohibited for heart failure (HF) patients because it increases heart rate by 60% to 70%, change in blood pressure or hormone status, and, thereby potentially serious arrhythmia or cardiac arrest. However, it has potential benefits in regard to reduction of afterload from vasodilation and salt loss, and it is well tolerated by patients with chronic stable HF patients. In some reports, sauna bathing appears to improve left ventricular ejection fraction and decrease brain natriuretic peptide (BNP) level in chronic systolic HF (Table 1).

Waon therapy, which means soothing warmth in Japanese and is not a typical (Finnish) sauna but an experimental infrared-ray dry sauna, is a form of thermal treatment in a dry sauna maintained at a temperature of 60℃ and has been studied exclusively by Tei et al.1) in Japan. Waon therapy warms entire body in a uniformly heated chamber for 15 min and maintains the soothing effect at outside the sauna for a further 30 min. Waon therapy also has proven beneficial effects on peripheral arterial disease.2) By now, Waon therapy is safe and has some beneficial effects and well tolerated by patients with HF. The common mechanisms of action of Waon therapy are improvement of endothelial function by upregulating the endothelial nitric oxide (NO) synthase protein and salt loss, which reduces cardiac preload and afterload from vasodilation. However, sauna bathing may be risky in patients receiving beta-blocker and nitrate, and contraindicated in severe aortic stenosis, unstable angina, recent myocardial infarction, or decompensated HF. Furthermore, sauna bathing should be cautious in patients who are prone to develop orthostatic hypotension. The question arises whether proscription on sauna bathing is overly restrictive.

In this issue of the Journal, the study by Sohn et al.3) evaluated the safety and efficacy of Waon therapy in HF patients on the top of conventional medical therapy. Before this study, Waon therapy has never been introduced in Korea. Although it is a preliminary experience, they concluded that Waon therapy was safe and well tolerated and had some beneficial effects for patients with HF. However, one of the major limitations of the study is its small sample size. Original plan was to evaluate 10 patients, but difficulties in recruitment and follow-up led to the ultimate analysis of only 5 patients. All subjects were safe and well tolerated Waon therapy and there were no serious adverse events. However, it is still unclear whether it is safe on the top of medical therapy. In this paper, the authors included the patients whose medication did not change within previous 3 months but their medications were not presented. In regard to efficacy, we do not know the clinical benefits in 5 patients who did not continue Waon therapy more than 2 weeks. In addition, one patient did not have improvement in clinical symptoms even after complete session of Waon therapy. Therefore, only 4 out of 10 patients have benefits in clinical symptom and echocardiographic variables. Furthermore, there was no control group with bath in room temperature in this paper and this was not a cross-over design. And thereby, it is too impetuous to conclude its clinical benefit based on the results of the current study. Because this study only included patients with chronic stable HF, we should not extrapolate clinical benefits of Waon therapy to all HF patients.

In conclusion, although Waon therapy has been proven its efficacy in chronic stable HF in small, retrospective studies or one prospective study with relatively small sample size, we do not have large prospective randomized trials. Further large clinical research into the safety and clinical benefits of Waon therapy on the top of conventional medical therapy appears warranted.