Effect Of Passive Heat Stress On Arterial Compliance.

Abstract

We previously observed that stroke volume and thus cardiac output during heat stress are under-estimated when measured with the Modelflow method. The Modelflow method uses aortic compliance estimated from subject characteristics such as age and gender to compute stroke volume from arterial blood pressure waveforms. Estimates assume that an applied perturbation does not change the elastic characteristics of aorta. However, cold stress acutely decreases central and peripheral arterial compliance. During heat stress, an underestimated Modelflow stroke volume can theoretically be explained by a more compliant aorta, but the effect of acute heat stress on arterial compliance is unknown. PURPOSE: To test the hypothesis that increased core temperature elevates central and peripheral arterial compliance, as measured with pulse wave velocity (PWV). METHODS: Using Doppler ultrasound, carotid-femoral (central) and carotid-radial (peripheral) arterial PWV were measured on eight subjects (age 37 ± 11 years; mass 68.8 ± 11.1 kg) before and during passive heat-stress induced increases in core temperature of 0.47 ± 0.05, 1.03 ± 0.12, and 1.52 ± 0.07°C (0, 0.5, 1.0, and 1.5°C, respectively). Comparisons of PWV at each core temperature were evaluated with a one-way repeated measures ANOVA. RESULTS: Central PWV did not significantly change as core temperature increased 0, 0.5, 1.0, and 1.5°C (677 ± 161, 617 ± 72, 659 ± 74, and 766 ± 207 cm/ms, respectively; P=0.125). Similarly, peripheral PWV did not change over the same core temperature change (855 ± 192, 772 ± 95, 759 ± 49, and 858 ± 247 cm/ms, respectively, P=0.557). CONCLUSIONS: Contrary to our hypothesis, central and peripheral arterial compliance, measured by PWV, does not change with heat stress. Given that heat stress did not change aortic compliance, it is unlikely that this is the source of the error resulting in Modelflow underestimating cardiac output. Supported by NIH Grants HL61388 & HL84072