Head Exposure to Cold during Whole-Body Cryostimulation: Influence on Thermal Response and Autonomic Modulation

April Head Exposure to Cold during Whole-Body Cryostimulation: Influence on Thermal Response and Autonomic Modulation Julien Louis 0 1 Karine Schaal 0 1 Franois Bieuzen 0 1 Yann Le Meur 0 1 Jean-Robert Filliard 0 1 Marielle Volondat 0 1 Jeanick Brisswalter 0 1 Christophe Hausswirth 0 1 0 1 Research Department, Sport Expertise and Performance (SEP) Laboratory, French National Institute of Sport, Expertise and Performance (INSEP), Paris, France, 2 Sports Performance Laboratory, Sports Medicine Program, University of California Davis, Sacramento, California, United States of America, 3 Medical Department, French National Institute of Sport, Expertise and Performance (INSEP), Paris, France, 4 Laboratory of Human Motricity, Education Sport and Health, University of Nice Sophia Antipolis , Nice , France 1 Academic Editor: Xiaoming He, The Ohio State University , UNITED STATES Recent research on whole-body cryotherapy has hypothesized a major responsibility of head cooling in the physiological changes classically reported after a cryostimulation session. The aim of this experiment was to verify this hypothesis by studying the influence of exposing the head to cold during whole-body cryostimulation sessions, on the thermal response and the autonomic nervous system (ANS). Over five consecutive days, two groups of 10 participants performed one whole-body cryostimulation session daily, in one of two different systems; one exposing the whole-body to cold (whole-body cryostimulation, WBC), and the other exposing the whole-body except the head (partial-body cryostimulation, PBC).10 participants constituted a control group (CON) not receiving any cryostimulation. In order to isolate the head-cooling effect on recorded variables, it was ensured that the WBC and PBC systems induced the same decrease in skin temperature for all body regions (mean decrease over the 5 exposures: -8.6C1.3C and -8.30.7C for WBC and PBC, respectively), which persisted up to 20-min after the sessions (P20). The WBC sessions caused an almost certain decrease in tympanic temperature from Pre to P20 (-0.28 0.11C), while it only decreased at P20 (-0.140.05C) after PBC sessions. Heart rate almost certainly decreased after PBC (-8.6%) and WBC (-12.3%) sessions. Resting vagal-related heart rate variability indices (the root-mean square difference of successive normal RR intervals, RMSSD, and high frequency band, HF) were very likely to almost certainly increased after PBC (RMSSD:+49.1%, HF: +123.3%) and WBC (RMSSD: +38.8%, HF: +70.3%). Plasma norepinephrine concentration was likely increased in similar proportions after PBC and WBC, but only after the first session. Both cryostimulation techniques stimulated the ANS with a predominance of parasympathetic tone activation from the first to the fifth session and in slightly greater proportion with WBC than PBC. The main result of this study indicates that the head exposure to cold during whole-body cryostimulation may not be the main factor responsible for the effects of cryostimulation on the ANS. - Competing Interests: The authors have declared that no competing interests exist Over the last decade, there has been increasing interest in the study of the influence of the autonomic nervous system (ANS) on the modulation of cardiac activity. Specifically, the link between a diminished parasympathetic modulation of heart rate and the occurrence of cardiovascular diseases or altered post-exercise recovery has been studied as well in the medical domain as in the sporting realm [1]. At rest, the equilibrium between the two branches of the ANS confers a cardioprotective background; the sympathetic branch acting as an accelerator of heart rate through humoral and neural pathways, and the parasympathetic branch acting as a brake on heart rate through neural pathways. Strong positive correlations have been reported between the magnitude of cardiodeceleration after exercise and health [2,3]. At the opposite, impairment or postponement of parasympathetic activation after exercise has been shown to be associated with an increased risk of cardiovascular accident such as sudden cardiac death. Some studies suggest that myocardial exposure to high levels of norepinephrine may result in receptor-mediated cytotoxic effects and apoptosis as well as receptor-mediated hypertrophic effects [4,5], dramatically increasing the risk of mortality [1]. The prevention of such effects by increasing vagal activity has become a priority for researchers. Body exposure to cold is well known to alter the modulation of the ANS. Cold stimulation triggers peripheral vasoconstriction, leading to a shift in blood volume toward the core [6,7]. The resulting increase in central pressure in turn activates the baroreflex, responsible for reducing sympathetic nerve activity while shifting autonomic heart rate control toward a parasympathetic dominance. Numerous studies have shown that water immersion is an effective strategy to increase parasympathetic activity, particularly after exercise in athletes [810]. More generally, cooling the body after exercise has become a natural recovery strategy commonly used in numerous sports. Body exposure to cold has been shown to aid recovery by altering blood flow [11] and improving perceptions of recovery [9,12]. Body exposure to cold may also exert important effects on post-exercise recovery at the cardiovascular level [13]. As exercise causes an intensity-dependent parasympathetic withdrawal and sympathetic increase, a prompt recovery of parasympathetic activity is desirable after exercise. For example, Stanley et al. [9] reported that both cold water immersion (CWI, 5-min in 14C water) and contrast water therapy (CWT, alternating 1-min in 14.2C and 2-min in 35.5C water), significantly aided post-exercise parasympathetic reactivation compared to passive recovery in endurance trained athletes. They also reported that this effect was larger with CWI than CWT, suggesting that combining a greater cold stimulus increased the effectiveness of water immersion. Contrary to water immersion protocols, the effects of dry air whole-body cryostimulation (WBC, classically range from -110C to -160C) on post-exercise autonomic recovery is not well documented, even though this recovery method has become increasingly used in the sporting realm [12,14]. However, thanks to a very cold stimulus, WBC could induce larger parasympathetic activation than cold water immersion [15]. Accordingly, significant increases in heart rate variability (HRV) indices of parasympathetic activity (the root-mean square difference of successive normal R-R intervals, RMSSD, and high frequency band, HF) have been reported after a WBC session performed as well after exercise in elite synchronized swimmers [15] as in healthy nonathletic women [16]. More recently, in a study from our team, we also recorded a significant increase in parasympathetic activity within the 20-min following a single WBC session pe (...truncated)