From the University of Ottawa Heart Institute Prevention and Rehabilitation Centre, Ottawa, Ontario, Canada.
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History of the SaunaSauna, the only Finnish word adopted for use in the English language, describes a particular style of steam bath. The 2000-year-old sauna bathing tradition is more popular in Finland than anywhere else in the world. There are 1.4 million saunas in regular weekly use in Finland and almost every family has one. Originally, the sauna was a place to bathe, as it was the only available clean place with abundant water.1 The use of the Finnish sauna has spread throughout the world and Finns who emigrated to North America decades ago brought with them this unique bathing custom. Private saunas are not very common in North America, but public saunas are gaining popularity.According to Finnish tradition, sauna baths stimulate circulation and respiration, reduce muscular tension as well as cleanse and rejuvenate the skin and body through perspiration.2,3 In the traditional Finnish sauna, the body is exposed to temperatures in the range of 70° to 100°C (158°-212° F) and at a low relative humidity (10-15%). Humidity is created in the sauna by throwing water on the "kiuas" (heater), which often is covered in rocks that retain the heat. The cold water falling on these rocks produces "löyly" (vapor or steam). In Finland the kiuas is referred to as the heart and the löyly is said to be the soul of the sauna.2 The löyly raises the humidity to 20 to 30% and as it condenses on the skin and in the airways it intensifies the sauna heat even though the temperature may have dropped slightly. Some bathers prefer not using löyly, which results in a "dry" sauna whose humidity is around 5%, permitting perspiration to dry quickly, thereby having a cooling effect. The Finnish Sauna Society recommends the temperature at the level of the bather's head to be 80° to 100°C (176°-212° F) with humidity somewhere between 40 to 60 g of water/kg dry air. (To view images of the traditional Finnish sauna, see the Finnish Sauna Society web site at: www.sauna.fi/pages/today.htm.) Countries such as Germany and Turkey have different preferences for bathing conditions: the German sauna environment is less humid and Turkish saunas have higher humidity and less heat. The bathing time is generally in the range of 5 to 15 minutes and varies depending on individual adaptation to the high temperatures. The body temperature rises during a sauna bath to 38° to 39° C (100°-102° F) according to the temperature, humidity, and time spent bathing.4There is a high incidence of coronary heart disease in Finland, and sauna bathing has received considerable attention as a potential risk factor. In Finland, almost 90% of individuals older than 80 years of age,3 and as many as 85 to 100% of post-myocardial infarction (MI) patients still take sauna regularly.5 For some time it was believed that a hot and humid environment, which usually is tolerated by healthy individuals, imposed a burden on the cardiovascular system and may pose serious problems to those with cardiovascular disease (CVD).6,7 Much of the negative publicity surrounding sauna use in cardiovascular response to thermal stress was regarding saunas where temperatures and humidity were not that of typical Finnish sauna bathing.8 Several investigators have studied the physiologic effect of sauna bathing on the heart. This review will summarize what has been found and how this relates to patients with compromised cardiovascular systems.Physiological Changes in the Sauna EnvironmentThere are various physiological changes that accompany the heat and humidity of the sauna environment.