Haemodynamic changes in man during immersion in water at different temperatures

Area of Science:

• Cardiovascular Physiology
• Thermoregulation
• Non-invasive Monitoring

Background:

• Understanding cardiovascular responses to thermal stress is crucial for assessing physiological resilience.
• Previous methods for cardiovascular stress testing often involve exercise, limiting applicability in certain populations.

Purpose of the Study:

• To investigate the effects of varying water immersion temperatures on stroke volume and cardiac output.
• To evaluate the potential of Doppler ultrasound during water immersion as a non-exercise cardiovascular stress test.

Main Methods:

• Doppler ultrasound was used to measure stroke volume and cardiac output in 16 healthy subjects.
• Subjects were immersed to the neck in water at temperatures ranging from 33°C to 39°C.
• Measurements were compared to pre-immersion resting values, assuming a standard aortic diameter.

Main Results:

• Cardiac output increased progressively with temperature, rising by 30% at 33°C and 121% at 39°C.
• Stroke volume increased by 50% at thermoneutral temperatures (33-35°C) with a decreased heart rate.
• Higher temperatures led to further increases in stroke volume and heart rate (tachycardia), with a simultaneous decrease in peripheral resistance.

Conclusions:

• Water immersion effectively induces significant cardiovascular changes, including increased cardiac output and stroke volume.
• The Doppler ultrasound technique during water immersion is a feasible, non-invasive method for cardiovascular stress testing.
• This approach may be valuable for studying cardiovascular responses in diverse pathophysiological states without requiring exercise.