Progressive central hypovolaemia in man--resulting in a vasovagal syncope? Haemodynamic and endocrine variables during venous tourniquets of the thighs

Hypotensive functional haemorrhage induced by venous pooling of blood in the legs has been reported to be characterized by a vasovagal reaction. In the present study these observations were extended by determination of the hormonal profile developed during progressive central hypovolaemia and an emotionally induced vasovagal syncope. In six subjects venous pooling resulted in normotensive central hypovolaemia, in one subject hypotensive central hypovolaemia was induced, and one subject experienced an emotionally induced vasovagal syncope. During normotensive central hypovolaemia heart rate increased from 58 +/- 4 to 76 +/- 4 beats min-1 (P less than 0.05) and cardiac output fell from 6.1 +/- 0.4 to 4.1 +/- 0.2 1 min-1. Pulse pressure and central venous pressure decreased from 64 +/- 4 to 53 +/- 4 mmHg, and from 8 +/- 2 to 3 +/- 2 mmHg, respectively. Adrenaline and noradrenaline increased from 87 +/- 10 to 120 +/- 20 pg/ml and from 196 +/- 33 to 370 +/- 50 pg/ml, respectively. Angiotensin II increased from 13 +/- 4 to 36 +/- 6 pg/ml and aldosterone from 63 +/- 9 to 180 +/- 27 pg/ml. In hypotensive central hypovolaemia the decrease in mean arterial pressure was accompanied by a decrease in heart rate and increments in the plasma concentrations of pancreatic polypeptide, indicating increased vagal activity and beta-endorphin, while plasma noradrenaline was unchanged. In emotionally induced syncope heart rate decreased to cardiac arrest for 13 s, associated with increments in the plasma concentrations of pancreatic polypeptide and beta-endorphin. It is concluded that normotensive functional haemorrhage in man is associated with increased sympathetic activity and that the qualitatively similar observations obtained during an emotionally and a hypovolaemic-induced hypotensive episode indicate that the hypotensive functional haemorrhage is characterized by a vasovagal reaction.