Haemodynamic changes in man during immersion in water at different temperatures

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Abstract
1. Stroke volume and cardiac output were measured using the Doppler ultrasound technique in 16 normal subjects immersed to the neck in water at 33.degree. C, 35.degree. C, 37.degree. C and 39.degree. C. A standard aortic diameter was assumed and results were expressed as percentage changes from pre-immersion resting values. 2. Cardiac output rose progressively at higher temperatures, increasing by 30% at 33.degree. C and by 121% at 39.degree. C. At thermoneutral temperatures (33.degree. C and 35.degree. C) this was achieved by an increase in stroke volume of 50% despite a significant decrease in heart rate. There was a further rise in stroke volume and pulse rate at higher temperatures and a mean tachycardia of 109 .+-. 4 beats/min was noted at 39.degree. C. Calculated peripheral resistance reduced progressively with increasing temperature of immersion. 3. This non-invasive and simple technique may provide a non-exercise-related cardiovascular stress test to study cardiovascular responses in a variety of pathophysiological states.