Key result
Repeated cold water immersion strongly blunts cold shock responses including heart rate and minute ventilation.
Why the study?
Cold water immersion evokes a life-threatening cold shock response that habituates with repeated exposure, but the magnitude and variability of this habituation have not been systematically quantified.
Does repeated cold water immersion induce habituation of the cold shock response?
Meta-Analysis
Does repeated cold water immersion induce habituation of the cold shock response?
Repeated cold water immersion induces habituation of the cold shock response, which may potentially reduce drowning risk.
May support repeated cold water immersion protocols to lower drowning risk; reinforces Level 1 evidence for cold shock habituation.
Cold water immersion (CWI) evokes the life-threatening reflex cold shock response (CSR), inducing hyperventilation, increasing cardiac arrhythmias, and increasing drowning risk by impairing safety behaviour. Repeated CWI induces CSR habituation (i.e., diminishing response with same stimulus magnitude) after ∼4 immersions, with variation between studies. We quantified the magnitude and coefficient of variation (CoV) in the CSR in a systematic review and meta-analysis with search terms entered to Medline, SportDiscus, PsychINFO, Pubmed, and Cochrane Central Register. Random effects meta-analyses, including effect sizes (Cohen's d) from 17 eligible groups (k), were conducted for heart rate (HR, n = 145, k = 17), respiratory frequency (fR, n = 73, k = 12), minute ventilation (Ve, n = 106, k = 10) and tidal volume (Vt, n = 46, k=6). All CSR variables habituated (p < 0.001) with large or moderate pooled effect sizes: ΔHR -14 (10) bt. min−1 (d: −1.19); ΔfR −8 (7) br. min−1 (d: −0.78); ΔVe, −21.3 (9.8) L. min−1 (d: −1.64); ΔVt −0.4 (0.3) L −1. Variation was greatest in Ve (control vs comparator immersion: 32.5&24.7%) compared to Vt (11.8&12.1%). Repeated CWI induces CSR habituation potentially reducing drowning risk. We consider the neurophysiological and behavioural consequences.
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Barwood et al. (2023) conducted a meta-analysis in Cold shock response. Repeated cold water immersion (CWI) vs. Initial/control immersion was evaluated on Heart rate (HR) habituation (d: -1.19, p=<0.001). Repeated cold water immersion induced significant habituation of all cold shock response variables, including heart rate (d: -1.19) and minute ventilation (d: -1.64) (p<0.001).
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