Passive heat therapy for cardiovascular disease: current evidence and future directions

Passive heat therapy is gaining popularity as an intervention to promote cardiovascular, physiological, and, to a lesser degree, thermoregulatory adaptations in patients with cardiovascular disease. Despite this, the efficacy of heat therapy to elicit these adaptations remains unknown. We searched five databases for original research, screening 2913 studies and identifying 18 eligible studies. Heat therapies included Waon therapy, balneotherapy, water perfused trousers, Finnish sauna, and foot immersion. Interventions were administered across various time frames (20-90 min) and performed 3-7 times per week, for durations of 2-8 weeks. The studies collectively involved a diverse population (mean age: 67 (10) years) with cardiovascular diseases. Heat therapy was consistently shown to improve ejection fraction, flow-mediated dilation, brain natriuretic peptide levels, New York Heart Association classification, and 6 min walk distance. However, positive effects on resting heart rate and blood pressure were infrequently observed, and thermoregulatory responses scarcely reported. Heat therapy may increase sweat rate during heat exposure and reduce resting core temperature, but adaptive skin blood flow responses were not observed. Passive heat therapy shows promising utility in patients with cardiovascular disease, while secondary benefits such as markers of thermoregulatory adaptation may also be observed, these require further investigation.