Thrombocytes and pulmonary vascular resistance during hemorrhagic hypotension.

Abstract

AbstractProlonged hemorrhagic hypotension can induce an increase in pulmonary vascular resistance (PVR). In anesthetized cats with open chests and with positive pressure ventilation aortic blood flow, pulmonary arterial‐, left atrial‐ and femoral arterial pressures were recorded. Eight animals were bled until the mean arterial pressure was 50 nun Hg and this level was main tained for 3 hrs by further bleeding and/or small retransfusions. The animals were then retransfused. Another group of 5 animals were made thrombocytopenic by shunting their blood through a column of glassbeads. These animals were then bled in the same way and kept hypotensive for the same period of time.During hypotension PVR in the first group increased gradually and by 370 per cent (mean value). In the thrombocytopenic group PVR increased only by 125 per cent (mean value) (P<0.01). The number of thrombocytes in arterial blood in the former group of animals decreased gradually by 37 per cent during the hypotensive period. Only in 2 of the 8 animals in this group did examination with light microscopy reveal scattered thrombocyte aggregates in small pulmonary vessels.The thrombocytes thus seem to be involved in the development of increased PVR during hemorrhagic hypotension. The fact that intravascular thrombocyte aggregates were not general ly found may indicate that the thrombocytes act by other mechanisms than by simple vascular obstruction alone.