The effect of intermittent hyperthermia (sauna) on functional capacity and quality of life in patients with heart failure and preserved ejection fraction: SAUNA-HFpEF

Background Heart failure with preserved ejection fraction (HFpEF) represents a major health and economic challenge worldwide. Previous studies have shown reduced exercise capacity and skeletal muscle function in patients with HFpEF. Intermittent hyperthermia (sauna) is comparable to moderate endurance training and could potentially improve exercise capacity and muscle function. This non-pharmacological intervention is of particular importance for frail patients with movement limitations. Objective To evaluate the safety and efficacy of sauna therapy on exercise capacity and quality of life in patients with HFpEF. Additionally, our data should enable finding the best frequency and length of sauna sessions and understanding the work mechanisms. Methods SAUNA-HFpEF is a pilot, prospective, mechanistic trial. Patients diagnosed with HFpEF according to ESC guidelines were included. The intervention was conducted twice weekly for 10 weeks in a bio sauna (60°C). Sauna sessions were done in groups of 5 patients. Blood pressure measurements were performed prior to, immediately after, and 20 minutes post-sauna. The following tests were performed on all patients before and after the 10-week intervention: echocardiography, cardiopulmonary exercise testing (CPET), 6-minute walking test (6MWT), muscle endurance of the right quadriceps, body composition (bioelectric impedance analysis), blood tests, skeletal muscle biopsies from the vastus lateralis muscle, quality of life questionnaires (SF-36, HADS, EQ-5D), and daily activity monitoring using an accelerometer. Results Eighteen clinically stable outpatients were included in the analysis. Sauna therapy was safe, with no side effects reported. Compared to baseline data, the following parameter improved (mean±SD): peak VO2 (18.2±5.7 vs. 20.6±5.7 ml/min/kg, p<0.001; 1558±451 vs. 1726±496 ml/min, p=0.002), anaerobic threshold (10.6±3.5 vs. 12.9±3.6 ml/min/kg, p=0.02), 6MWT (494±95 vs. 533±111 m, p=0.006), and muscle endurance (288±106 vs. 319±112 Nm, p=0.03). NT-proBNP levels showed no significant change (245±315 vs. 199±179 pg/ml, p=0.37). Additionally, depression scores improved significantly (6.6±3.9 vs. 4.9±3.7, p=0.025), as did social functioning scores (44.5±11.6 vs. 48.3±10.1, p=0.04). Data regarding enzymatic mitochondrial function (Complex I, IV, citrate synthase), fatty acid and glucose oxidation (CPT1B, PPARα, CD36, PDK4), and atrophy-related proteins (FBOX-32 and TRIM63) are still pending and will be available to present during the ESC. No safety issues were encountered. Conclusion Sauna therapy is a safe and promising non-pharmacological treatment for patients with HFpEF, demonstrating significant benefits in exercise capacity and quality of life. These findings suggest that incorporating sauna therapy into the management of HFpEF could enhance patient outcomes. Further randomized studies with larger sample sizes and longer follow-up periods are needed to confirm these results.