Hemodynamic and thermoregulatory responses to lower body water immersion

Introduction: Lower body water immersion (LBWI) is experienced in the marine industry, but the physiological responses to LBWI are unclear. The purpose of the current experiment was to test the effects of water temperature and immersion duration on rectal temperature, heart rate, stroke volume, blood pressure, metabolic rate, and thermal sensation in healthy subjects. Methods: Nine young men underwent two 60-min trials of seated LBWI to the iliac crest in a counterbalanced fashion. On one occasion, the water was 35°C (LBWI-Neutral) and on the other it was 13°C (LBWI-Cold); the upper body remained thermoneutral and dry throughout. Results: As expected, exposure to cold water reduced mean skin temperature and individuals reported cold thermal sensation. Mean arterial pressure was significantly higher at 60 min of LBWI-Cold (86 ± 7 mmHg) compared to LBWI-Neutral (76 ± 5 mmHg) while heart rate tended to be lower. The change in rectal temperature from baseline to 30 min of LBWI-Cold (Δ = -0.01 ± 0.21°C) was significantly smaller than the change in T re from 30 to 60 min of LBWI-Cold (Δ = -0.46 ± 0.16°C). Despite this accelerated drop in core temperature during minutes 30-60, metabolic rate did not increase significantly. Conclusion: LBWI-Cold reduces core temperature and increases arterial blood pressure via an increase in total peripheral resistance. This experimental model may help scientists better understand the body during cold stress. Further, people who are occupationally exposed to cold water (when the torso, hands, and arms remain thermoneutral) may be at increased risk for hypothermia.