Whole-Body Cold Stimulation Improves Cardiac Autonomic Control Independently of the Employed Temperature

Background/Objectives: The autonomic nervous system (ANS) is considered one of the mechanisms mediating the benefits of whole-body cold stimulation (WBC). Nevertheless, different treatment protocols, different methodologies employed to assess the ANS, and, in particular, difficulties in interpreting the numerous variables obtained represent important barriers to understanding the effects of WBC on the ANS. The present study aimed to explore the effects of WBC on cardiac autonomic control (CAR) as assessed using a single composite percentile-ranked proxy of autonomic balance (ANSI), considering two different WBC temperatures and the same WBC protocol. Methods: Heart rate variability (HRV) was employed to assess the ANS in 23 subjects with obesity who underwent 10 WBC sessions, studied before and after 2 min WBC at −55 °C (15 subjects) or 2 min WBC at −110 °C (8 subjects) both at the first session (T1) and the last one (T10). To overcome some important barriers in data interpretation and age/sex bias, we considered the Autonomic Nervous System Index (ANSI), a single composite percentile-ranked proxy of autonomic control. Results: We observed an improvement in CAR independently of the employed temperature. Both treatments, without distinction, caused a significant increase in the ANSI post-WBC treatment both at T1 and T10 and a significant betterment of the total power of the RR interval variability from pre- to post-treatment at T1 and overall from T1 to T10. Conclusions: WBC was capable of inducing an immediate change in the ANS control (pre- vs. post-treatment both at T1 and T10) and a long-term modulation in cardiac autonomic control (T1-pre vs. T10-pre).