Pulmonary blood- and extravascular water volumes during prolonged post-hemorrhagic systemic hypotension.

Abstract

AbstractIn cats prolonged hemorrhagic hypotension had been shown to increase the pulmonary arterial pressure and vascular resistance. Pulmonary extravascular water volume and pulmonary blood volume have been evaluated early and late in such a period of post‐hemorrhagic hypotension. 51Cr‐labelled erythrocytes and 125I‐labelled albumin were injected intravascularly to animals with an opened chest and on positive pressure ventilation. One upper lung lobe was then suddenly clamped, removed and frozen. The lung lobe tissue and a simultaneously taken blood sample from a large vessel were measured for total w‐eight, dry weight and tracer content. The lobe's blood volume and extravascular water volume were then calculated per unit extravascular lung dry weight. A second lung lobe was removed and treated similarly at a later stage. 1 /2 h after the blood loss there was a marked reduction in lung blood volume and at the same time some increase in pulmonary extravascular water volume indicating constriction of postcapillary capacitance vessels. After 3 h of hypotension pulmonary extravascular water volume was found to be the same as before the hemorrhage although the pulmonary arterial pressure increased. This indicated that the increase in vascular resistance must predominantly be due to vasoconstriction at precapillary sites. The reduction in the lungs' blood volume remained at these late stages indicating that capacitance vessels were still constricted. When hyperinflations of the lungs were omitted in the experimental period, there was a tendency towards water accumulation in the lungs.