Pulmonary pressure-flow relation after trauma and hemorrhagic shock

The significance of pulmonary pressure-flow relation and its correlation to alveolar dead space and histological lesions of the lung were evaluated in ten mongrel dogs, which were subjected to standardized bone trauma and hemorrhagic hypotension at 40 mm Hg for 3h. These results were compared with those of 5 control dogs without trauma and shock. Two different pressure-flow curves were obtained by consecutive measurements of cardiac output and mean pulmonary artery pressure during stepwise arterial hemorrhage and reinfusion. In each experiment, the difference between the two curves at CO of 100 ml/kg min was obtained and represents an increase in pulmonary artery pressure (delta MPP). This increase in pulmonary artery pressure is flow-independent and, therefore, can be used as a quantitative indicator of pulmonary vasoconstriction or vascular obstruction. Severity of shock (uptake) as well as grade of early histological lesions of the lung (microthrombi, edema, hemorrhage) and increased alveolar dead space after reinfusion were associated with a more pronounced shift of the pulmonary pressure-flow curve. In severe experimental shock, therefore, a consistent pattern of pulmonary hemodynamics, lung histology, and respiratory function was demonstrated by the pulmonary pressure-flow relation. This approach permits estimation of the effects of therapeutic interventions and may be suitable for assessing postshock pulmonary impairment.