Heart rate variability during exertional heat stress: effects of heat production and treatment

Abstract

While EHS has a marked effect on autonomic nervous system modulation and whole-body immersion in 2 °C water results in faster cooling, there were no observed differences in restoration of autonomic heart rate modulation as measured by HRV indices with whole-body cold-water immersion compared to passive recovery in thermoneutral conditions.

Effectiveness of cold water immersion for treating exertional heat stress when immediate response is not possible

“…() following 2 °C CWI (35.7 °C). Thus, we confirm the previous recommendations (Proulx et al., ; Gagnon et al., ; Flouris et al., ) that a similar exit temperature should be used even if cooling of the exertional heatstroke victim is delayed by as much as 40 min.…”

“…It is well accepted that immediate treatment with CWI is the gold standard for EHS and exertional heatstroke (Casa et al., , ; Flouris et al., ). In this study, we examined the effectiveness of CWI (core cooling rates during immersion and core temperature afterdrop following immersion) for treating EHS when delays of 5, 20, and 40 min are present.…”

“…In order to avoid excessive afterdrop following CWI, safe cooling limits have been proposed whereby individuals should be removed from the water bath when T re reaches 38.6 °C (Proulx et al., ). This procedure has been used to ensure the removal of 100% of the heat gained by exercise while reducing the risk of hypothermia (Proulx et al., ; Gagnon et al., ; Flouris et al., ). With respect to the latter, in contrast to our hypothesis, we observed a similar nadir [nadir for the short (35.9 °C), moderate (35.6 °C), and prolonged (35.9 °C) delay conditions, respectively] to that reported by Proulx et al.…”

“…Exertional heatstroke is the second leading cause of death in sports besides cardiac conditions (Mueller & Cantu, ). Early recognition of exertional heatstroke and rapid on‐site cooling of the individual with exertional heatstroke to a near‐normal resting core temperature is paramount to their survival and to minimize heat‐related injury (Casa et al., , ; Flouris et al., ). To ensure patient well‐being, it has been suggested that the treatment of exertional heatstroke must achieve a rectal temperature ( T re ) cooling rate exceeding 0.1–0.2 °C/min when cooling begins immediately and no less than 0.15 °C/min if cooling is delayed (Casa et al., ).…”

Autonomic dysfunction associated with Type 1 diabetes: a role for fitness?

“…In healthy young adults, Flouris et al [5] found that marked exercise-induced hyperthermia (i.e., core body temperature C39.5°C) had a significant effect on ANS control as assessed by HRV which was restored only when core body temperature returned to pre-exercise baseline resting levels. Whether or not this pattern of response is exacerbated in individuals with T1DM or occurs at a lower level of heat stress remains to be elucidated.…”