The effect of systemic hypoxemia and hypovolemia on pulmonary fine structure was studied and compared in 12 Labrador puppies 6 days to 3 wk old. Central venous and arterial pressures were monitored and arterial pH, PCO2 and PO2 recorded serially. In 4 puppies lung biopsies were taken after a 2 h period of breathing 7% oxygen. Four other puppies were made hypovolemic by acute hemorrhage of 50% of the calculated blood volume and lung biopsies taken after 1 hr. Four control puppies were maintained under anesthesia for 2 hr, breathing an atmosphere of 20% oxygen before lung biopsies were taken. Both hypoxemia and hypovolemia resulted in similar pulmonary ultrastructural changes. These changes which occurred more frequently in areas where the air spaces and blood vessels were expanded, were characterized by aggregation of platelets and leukocytes in the vascular space, focal endothelial cell disruption, interstitial edema and type I epithelial cell discontinuities with exudation of plasma into the alveolar air spaces.
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