Atrial natriuretic peptide and acute changes in central blood volume by hyperthermia in healthy humans

Background: Hyperthermia induces vasodilatation that reduces central blood volume (CBV), central venous pressure (CVP) and mean arterial pressure (MAP). Inhibition of atrial natriuretic peptide (ANP) could be a relevant homeostatic defense mechanism during hyperthermia with a decrease in CBV. The present study evaluated how changes in plasma ANP reflect the changes in CBV during hyperthermia. Methods: Ten healthy subjects provided with a water perfused body suit increased body core temperature 1 °C. In situ labeled autologous red blood cells were used to measure the CBV with a gamma camera. Regions of interest were traced manually on the images of the whole body blood pool scans. Two measures of CBV were used: Heart/whole body ratio and thorax/whole body ratio. CVP and MAP were recorded. Arterial (ANP _art) and venous plasma ANP were determined by radioimmunoassay. Results: The ratio thorax/whole body and heart/whole body decreased 7 % and 11 %, respectively (p<0.001). MAP and CVP decreased during hyperthermia by 6.8 and 5.0 mmHg, respectively (p<0.05; p<0.001). Changes in both thorax/whole body (R=0.80; p<0.01) and heart/whole body ratios (R=0.78; p<0.01) were correlated with changes in ANP _art. However, there was no correlation between venous ANP and changes in CBV, nor between ANP _art and MAP or CVP. Conclusion: Arterial but not venous plasma concentration of ANP, is correlated to changes in CBV, but not to pressures. We suggest that plasma ANP _art may be used as a surrogate marker of acute CBV changes.