Background: Moderately cold head-out water immersion stimulates both baro- and cold-receptors, and triggers complex and contradictory effects on the cardiovascular system and its autonomic nervous control. Objectives: To assess the effects of water immersion and cold on cardiovascular status and related autonomic nervous activity. Methods: Hemodynamic variables and indexes of autonomic nervous activity (analysis of heart rate and blood pressure variability) were evaluated in 12 healthy subjects during 3 exposures of 20 min each in the upright position, i.e., in air (AIR, 24-25°C), and during head-out water immersion at 35-36°C (WIn) and 26-27°C (WIc). Results: Plasma noradrenaline, systolic and diastolic blood pressure, and total peripheral resistances were reduced during WIn compared to AIR (263.9 ± 39.4 vs. 492.5 ± 35.7 pg·ml-1, 116.5 ± 3.7 and 65.4 ± 1.7 mmHg vs. 140.8 ± 4.7 and 89.8 ± 2.8 mmHg, 14.1 ± 1.0 vs. 16.3 ± 0.9 mmHg·L-1·min, respectively) while they were increased during WIc (530.8 ± 84.7 pg·ml-1, 148.0± 7.0 mmHg, 80.8 ± 3.0 mmHg, and 25.8 ± 1.9 mmHg·L-1·min, respectively). The blood pressure variability was reduced to the same extent during WIc and WIn compared to AIR. Heart rate decreased during WIn (67.8 ± 2.7 vs. 81.2 ± 2.7 bpm during AIR), in parallel with an increased cardiac parasympathetic activity. This pattern was strengthened during WIc (55.3 ± 2.2 bpm). Conclusions: Thermoneutral WI lowered sympathetic activity and arterial tone, while moderate whole-body skin cooling triggered vascular sympathetic activation. Conversely, both WI and cold triggered cardiac parasympathetic activation, highlighting a complex autonomic control of the cardiovascular system.
ASJC Scopus subject areas
- Public Health, Environmental and Occupational Health