Effects of lung inflation on pulmonary arterial pressure in dogs with pulmonary edema

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Abstract
The effects of lung inflation from positive airway pressure (Paw) on pulmonary arterial pressure (Ppa) and the slope .DELTA.Ppa/.DELTA.Paw were studied in normal dogs and dogs with pulmonary edema. Under base-line zone 2 conditions with the lungs perfused at constant flow (100 ml/kg per min) and vascular pressures measured relative to pleural (atmospheric) pressure, the slope .DELTA.Ppa/.DELTA.Paw was nearly 1 (at Paw .ltoreq. 5 cmH2O). Pulmonary edema from high capillary pressure and oleic acid caused .DELTA.Ppa/.DELTA.Paw and Ppa to decrease at high lung volumes and Ppa to increase at low lung volumes. These changes were not simulated by vasoactive drugs (adenosine and norepinephrine) but were reproduced by instilling dextran into the lungs and, in part, by occluding the right intermediate bronchus. In pulmonary edema the increased Ppa at low lung volumes is caused by the effects of decreases in the caliber of extra-alveolar vessels, by trapped air or liquid raising alveolar pressure, or by both. The decreased .DELTA.Ppa/.DELTA.Paw and Ppa at high volumes is caused by nonuniform distribution of driving pressures and blood flow.

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