Influence Of Cold Shock Magnitude On Core Temperature Cooling Rates

Immersion in cold (CWI) water may include the cold shock response (CSR), loss of extremity function, and significant body heat loss. Initial stages of CWI increase risk of drowning due to water aspiration and swimming failure. Persons who survive these stages must then contend with hypothermia if CWI is prolonged. Large variability in core temperature (Tc) cooling rates during CWI are reported in the literature, but it is unknown if any CSR elements impact such cooling rates. Given that the central nervous system receives input from similar pathways which regulate CSR and thermoregulation, it is plausible that elements of CSR may be related to core temperature cooling, but this relationship has not been assessed. PURPOSE: Assess the relationship between CSR elements and Tc cooling rates during outdoor CWI. METHODS: Eighty-one (n = 81) military personnel (age: 26 ± 5; ht: 176 ± 8 cm; wt: 80 ± 11 kg) completed a military CWI training exercise which included a 10-min, head-out, CWI (1.5 °C) in cold air (-4 °C). For 10 min before (PRE), 10 min during (IMM), and 10 min after CWI (POST), participants’ Tc, heart rate (HR), mean skin temperature (Tsk), thermal sensation (TS), and shivering sensation (SS) were measured. Pearson correlations were evaluated between Tc cooling (calculated as Tc at the last min of POST subtracted from Tc at the last min of PRE) and HR (peak HR measured during IMM), Tsk (lowest measured during IMM), and TS and SS (lowest TS and highest SS obtained during IMM); significance was set at p < .05. RESULTS: Weak correlations were found between Tc cooling (mean ± SD: 0.1 ± 0.2 °C/min) and HR (136 ± 18 bpm, p = .794; r = .03), Tsk (12.7 ± 3.7 °C, p = .20; r = -.143), TS (-3.4 ± 0.8, p = .375; r = .10), and SS (2.5 ± 0.6, p = 0.478; r = .08). In alignment with previous findings, Tsk was correlated with TS (-3.4 ± 0.8, p < .01; r = .38) and SS (2.5 ± 0.6, p < .01; r = .31). SS was also correlated with TS (p < .001; r = -.45). CONCLUSION: Findings suggest that many elements of CSR (i.e., elevated HR, decreased Tsk, decreased TS, and elevated SS) poorly predict overall cooling rates during field CWI. As such, CSR magnitude may not be suitable for predicting heat loss magnitude during CWI.