Immersion in thermoneutral water: effects on arterial compliance

Since thermoneutral head-out water immersion induces an increase in central blood volume and cardiac output along with a decrease in peripheral vascular resistance, we examined here whether thermoneutral immersion leads rapidly to an increase in arterial compliance.

Changes in hemodynamic status and arterial compliance induced by thermoneutral head-out water immersion to the midchest were studied in 26 healthy volunteers (15 women, 11 men) using a non-invasive pulse wave measurement system. Several hemodynamic parameters including stroke volume (SV) and large and small artery compliance were studied in a quiet room with a stable environmental temperature (25 degrees C) and during thermoneutral (34.5 degrees C) head-out water immersion.

In a preliminary study, an agreement between SV estimated by radial pulse contour analysis and that obtained by Doppler echocardiography was observed in ambient air. An increase in SV led to an increase in cardiac output (12%) 10 min after the start of immersion. Heart rate and arterial pressure remained unchanged. Systemic vascular resistance was significantly decreased and total arterial compliance estimated by the SV to aortic pulse pressure ratio was significantly increased. Radial pulse contour analysis confirmed these results with an increase in both large and small artery compliance.

In conclusion, radial pulse contour analysis provides an interesting method for assessing hemodynamic changes under environmental constraints. Our results were consistent with a prompt increase in arterial compliance during acute water immersion.