Atrial Natriuretic Peptide and Acute Changes in Central Blood Volume by Hyperthermia in Healthy Humans

Abstract

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.

Keywords: ANP; blood pool imaging; central blood volume; heating; natriuretic peptides; nuclear medicine.

Fig. (1)

Regions of interest (ROI) of the thorax, heart, and proximal femur as traced manually on scintigrams obtained using in vitro Tc-99m labeled autologous red blood cells.

Fig. (2)

Linear regression between changes in CBV (expressed as change in the ratio of the blood pool in the thoratic region relative to the whole body; “thorax/whole body”) and absolute change in arterial plasma ANP concentration in pg/ml (upper panel: R=0.80; p<0.01) and between CBV (expressed as change in the ratio of the blood pool in the heart region relative to the whole body; “heart/whole body”) and absolute change in arterial plasma ANP concentration in pg/ml (lower panel: R=0.78; p<0.01).