The effect of sauna on cardiac and skeletal muscle function in patients with HFpEF (SAUNA-HFpEF): rationale and design

Patients with heart failure with preserved ejection fraction (HFpEF) often experience dyspnea, fatigue, and exercise intolerance, which are closely linked to skeletal muscle dysfunction and structural abnormalities. The only proven intervention to enhance exercise capacity and quality of life in these patients is regular endurance exercise training. However, its long-term effectiveness is often limited due to poor patient adherence and mobility restrictions caused by sarcopenia, cachexia, or frailty. Therefore, novel therapeutic approaches targeting these unmet needs are urgently required. Sauna-HFpEF is an academic-led, mechanistic, prospective, single-arm, single-center pilot study designed to assess the safety, feasibility, and efficacy of intermittent hyperthermia (sauna therapy) in improving exercise capacity and quality of life in patients with heart failure with preserved ejection fraction (HFpEF), as well as to explore the underlying mechanisms. A total of 18 clinically stable outpatients with HFpEF were enrolled and participated in twice-weekly sauna sessions at 60°C over a 10-week period. Assessments were conducted at baseline and after the intervention, including: echocardiography, cardiopulmonary exercise testing, six-minute walk test, body composition analysis to assess skeletal muscle mass and fat tissue, isokinetic skeletal muscle strength measurement of the quadriceps, daily physical activity monitoring using wearable accelerometers for one week, blood biomarkers, including NT-proBNP, renal function, and inflammatory markers (GDF-15, IL-6), and quality-of-life questionnaires (SF-36, HADS, EQ-5D). Furthermore, to explore the underlying mechanisms of a potential sauna-induced effect, patients underwent two ultrasound-guided punch biopsies of the musculus vastus lateralis in the right quadriceps - one before and one after the intervention. The collected samples were analyzed for structural, metabolic, and mitochondrial changes to gain further insights into the physiological adaptations. Sauna-HFpEF is the first study to investigate the safety and efficacy of sauna therapy using a comprehensive bed-to-benchside approach within the same patient population. This study aimed to address the existing knowledge gap while providing a foundation for the design of a future randomized controlled trial.