Human physiological responses to immersion into water of different temperatures.
Level 3 - non-randomized controlled study
Controlled repeated-measures physiological trial without stated randomization
PubMed 10751106 · doi:10.1007/s004210050065
What was done
A cohort of young men underwent 1-hour head-out water immersion across three water temperatures: thermoneutral (32°C), mild cold (20°C), and cold (14°C), compared to baseline control conditions in ambient air. Investigators measured rectal temperature, metabolic rate, heart rate, blood pressure, diuresis, and plasma concentrations of catecholamines, cortisol, aldosterone, and renin activity.
What was found
Immersion at 32°C did not change core temperature or metabolic rate, but lowered heart rate by 15%, systolic blood pressure by 11%, diastolic blood pressure by 12%, plasma renin activity by 46%, cortisol by 34%, and aldosterone by 17%, while increasing diuresis by 107%. Immersion at 20°C lowered rectal temperature and increased metabolic rate by 93%, with similar reductions in heart rate, blood pressure, and plasma renin activity as at 32°C, and increased diuresis by 89%. Cold immersion at 14°C lowered rectal temperature and increased metabolic rate by 350%, heart rate by 5%, systolic blood pressure by 7%, diastolic blood pressure by 8%, plasma noradrenaline by 530%, dopamine by 250%, aldosterone by 23%, and diuresis by 163%. Plasma adrenaline was unchanged, and cortisol tended to decrease.
Why it matters
This study differentiates hydrostatic pressure effects from cold-induced thermal stress, demonstrating that immersion alone drives humoral suppression and diuresis, whereas cold stress overrides cardiovascular suppression via marked sympathetic nervous system activation.
Limits
The abstract does not state the sample size, sequence randomization, or intervals between immersion sessions. Testing was conducted exclusively in young men, limiting generalizability to women, older adults, or clinical populations.
Cited by
- partial Cold exposure induces a sustained release of dopamine and adrenaline that lasts for multiple hours.