We considered that a moderate reduction of the central blood volume (CBV) may activate the coagulation system.
Lower body negative pressure (
LBNP) is a non-invasive means of reducing CBV and, thereby, simulates haemorrhage. We tested the hypothesis that coagulation markers would increase following moderate
hypovolemia by exposing 10 healthy male volunteers to 10 min of 30 mmHg
LBNP. Thoracic electrical impedance increased during
LBNP (by 2.6 +/- 0.7 Omega, mean +/- SD; P < 0.001), signifying a reduced CBV. Heart rate was unchanged during
LBNP, while mean arterial pressure decreased (84 +/- 5 to 80 +/- 6 mmHg; P < 0.001) along with stroke volume (114 +/- 22 to 96 +/- 19 ml min(-1); P < 0.001) and cardiac output (6.4 +/- 2.0 to 5.5 +/- 1.7 l min(-1); P < 0.01). Plasma
thrombin-
antithrombin III complexes increased (TAT, 5 +/- 6 to 19 +/- 20 microg l(-1); P < 0.05), indicating that
LBNP activated the
thrombin generating part of the coagulation system, while plasma
D-dimer was unchanged, signifying that the increased
thrombin generation did not cause further intravascular clot formation. The plasma
pancreatic polypeptide level decreased (13 +/- 11 to 6 +/- 8 pmol l(-1); P < 0.05), reflecting reduced vagal activity. In conclusion,
thrombin generation was activated by a modest decrease in CBV by
LBNP in healthy humans independent of the vagal activity.