Effects of Sauna Alone Versus Postexercise Sauna Baths on Short-term Heart Rate Variability in Patients With Untreated Hypertension

PURPOSE: We measured the effects of sauna bathing alone or a 30-minute exercise session followed by sauna bathing on short-term heart rate variability (HRV) in subjects with untreated hypertension. METHODS: Ten patients with untreated hypertension (age 59 +/- 10 years) were randomly assigned to (1) a control resting session, (2) two 8-minute sauna-only sessions (S), or (3) a 30-minute aerobic exercise session at 75% of maximal heart rate followed by a sauna session (ES). Spectral analysis of HRV was measured with a Polar S810 heart rate monitor at baseline, during the sauna session, and 15 and 120 minutes after the sauna session (T15 and T120). A Fast Fourier Transformation was used to quantify the power spectral density of the low-frequency (LF) and high-frequency (HF) bands. RESULTS: For S and ES conditions, LF (NU, normalized unit) and LF/HF were significantly higher (P < .05 and P < .01) in the first and second sauna sessions, and HF (NU) was significantly lower (P < .05, first sauna). At baseline and T15 for S and ES versus control, LF (NU) and LF/HF were significantly higher (P < .05), and HF (NU) was significantly lower (P < .05), without any effect of the 30-minute exercise session. CONCLUSIONS: A single sauna session induced a significant alteration of autonomic cardiovascular control in patients with untreated hypertension, with an increased sympathetic and decreased parasympathetic drive. These alterations were normalized within 15 to 120 minutes after sauna bathing. Additional studies are required to document long-term effects of chronic sauna bathing on autonomic control in patients with hypertension.