Atrial natriuretic peptide during head‐up tilt induced hypovolaemic shock in man

Abstract

To evaluate the importance of right atrial filling pressure versus central blood volume for the plasma concentration of atrial natriuretic peptide in man, head-up tilt to 50 degrees maintained until the appearance of presyncopal symptoms was carried out in six healthy males. Head-up tilt increased thoracic electrical impedance from 35.4 +/- 0.9 (mean and SE) to 39.2 +/- 0.9 ohm, mean arterial pressure from 64.5 +/- 3.6 to 76.6 +/- 3.0 mmHg and heart rate from 51 +/- 3 to 85 +/- 4 beats min-1 (P less than 0.01). After 35 +/- 7 min presyncopal symptoms appeared, together with a decrease in mean arterial pressure to 51 +/- 4 mmHg and in heart rate to 59 +/- 7 beats min-1 (P less than 0.01). Central venous pressure (2.1 +/- 1.0 mmHg) did not change significantly, but atrial natriuretic peptide decreased from 9.4 +/- 1.6 to 4.2 +/- 1.3 pmol l-1 (P less than 0.01) and was inversely related to thoracic impedance (r = -0.65, n = 44, P less than 0.001). The results indicate that changes in the central blood volume rather than in central venous pressure determine the secretion of atrial natriuretic peptide in man.