Cardiovascular regulation during water immersion.

Area of Science:

• Cardiovascular Physiology
• Environmental Physiology
• Exercise Physiology

Background:

• Head-out water immersion at thermoneutral temperatures elevates cardiac output, causing peripheral tissue hyperperfusion.
• Understanding cardiovascular responses to colder water immersion is crucial for assessing physiological adaptations.

Purpose of the Study:

• To investigate cardiovascular responses to cold water immersion (30°C) compared to thermoneutral immersion (34.5°C) at rest and during exercise.
• To explore the physiological significance of hyperperfusion induced by water immersion.

Main Methods:

• Cardiovascular functions were assessed using impedance cardiography in 10 men.
• Measurements were taken at rest and during leg cycle ergometer exercise (95 W·m⁻²) in air, 34.5°C water, and 30°C water.

Main Results:

• Water immersion (both temperatures) increased cardiac output by ~50% at rest, primarily via stroke volume increase.
• Cold water immersion (30°C) resulted in a greater stroke volume increase than thermoneutral immersion, attributed to higher cardiac preload (left ventricular end-diastolic volume).
• Despite reduced total peripheral resistance, arterial pressures were maintained or increased during immersion, and cardiac output remained higher during exercise in water compared to air.

Conclusions:

• Cold water immersion enhances cardiac preload and stroke volume beyond thermoneutral immersion due to peripheral vasoconstriction.
• Cardiovascular adjustments during dynamic exercise are not fundamentally altered by the increased cardiac preload from water immersion.
• Elevated cardiac output during water immersion is essential for maintaining adequate arterial pressure despite reduced vascular resistance.