Increased Pulmonary Vascular Resistance in the Dependent Zone of the Isolated Dog Lung Caused by Perivascular Edema

Measurements of the distribution of blood flow in an isolated dog lung made with radioactive xenon showed a great increase in vascular resistance in the dependent zone of the lung in the presence of a raised pulmonary venous pressure in some preparations. Evidence that this increased vascular resistance was caused by perivascular edema consisted of the general correlation with interstitial edema, the regional distribution of the effect, the sensitivity to the arteriovenous pressure difference, the effect of certain infusions particularly hypertonic urea, and the demonstration of edema around the small arteries and veins in rapidly frozen sections. The mechanism of the increased resistance is postulated as an interference with the tethering effect of the lung parenchyma which normally holds the vessels open. The possible role of this mechanism in the increased pulmonary vascular resistance of patients with pulmonary venous hypertension is discussed.