Early activation of the coagulation system during lower body negative pressure

P>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 center dot 6 +/- 0 center dot 7 Omega, mean +/- SD; P < 0 center dot 001), signifying a reduced CBV. Heart rate was unchanged during LBNP, while mean arterial pressure decreased (84 +/- 5 to 80 +/- 6 mmHg; P < 0 center dot 001) along with stroke volume (114 +/- 22 to 96 +/- 19 ml min-1; P < 0 center dot 001) and cardiac output (6 center dot 4 +/- 2 center dot 0 to 5 center dot 5 +/- 1 center dot 7 l min-1; P < 0 center dot 01). Plasma thrombin-antithrombin III complexes increased (TAT, 5 +/- 6 to 19 +/- 20 mu g l-1; P < 0 center dot 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 center dot 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.