C. T. Dollery

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.

Regional Uptake of Radioactive Oxygen, Carbon Monoxide and Carbon Dioxide in the Lungs of Patients with Mitral Stenosis

Using radioactive oxygen (O15), carbon monoxide and carbon dioxide with external counting over the chest, it is possible to measure perfusion and diffusion per unit of lung volume. Patients with mitral stenosis, particularly those with high pulmonary artery pressures, may show a higher blood flow through the upper zone of the lung than the lower. This distribution of blood flow is the reverse of that found in normal subjects. The observed changes in blood flow are consistent with the radiological and pathological changes in the pulmonary vascular tree in mitral stenosis.

REGIONAL PULMONARY BLOOD FLOW IN PATIENTS WITH CIRCULATORY SHUNTS

Carbon dioxide labelled with oxygen-15 can be used to compare the blood flow in different regions of the lung. Results obtained with this technique in normal subjects at rest with the chest upright show that there is a much higher perfusion per unit of alveolar volume in the lower zone than in the upper zone. On moderate exercise the flow increases in both zones but the lower zone blood flow remains relatively greater than the upper zone (West and Dollery, 1960). Patients with mitral stenosis differ from the normal in that the moderately severe cases show almost equal perfusion in upper and lower zones and the severe cases have a higher perfusion in the upper than the lower zone (Dollery and West, 1960). This inversion of the normal distribution of blood flow has been observed also in patients with left ventricular failure and pulmonary cedema (Dollery and West, in preparation). The distribution of blood flow in normal subjects probably depends upon the effect of gravity on the low perfusion pressures in the pulmonary circulation. Heart disease may reduce the normal difference in the upper and lower zone clearance rates. To investigate this problem further we have studied a group of patients with congenital shunts between the left and right sides of the heart. These patients have a great variety ofpulmonary pressures and flows. This study was made with a specially selected group of such patients in whom complete hemodynamic investigations had been performed. The results demonstrate differences between the flow patterns in various disorders of the pulmonary circulation and throw some light on the factors that influence the partition of blood flow between different regions of the lung.

A Comparison of the Pulmonary Blood Flow between Left and Right Lungs in Normal Subjects and Patients with Congenital Heart Disease

Carbon dioxide labeled with oxygen-15 has been used to study the regional blood flow in the lungs of patients with pulmonary stenosis. The upper and lower zone flows were normal in patients with isolated pulmonary stenosis, but both were low in patients with the tetralogy of Fallot. A comparison of the two upper zones showed a significantly higher blood flow through the left upper zone in patients with both isolated pulmonary stenosis and the tetralogy of Fallot. A significantly higher flow was also found through the left upper zone than the right of normal subjects. By contrast, patients with atrial septal defect had a higher flow through the right upper zone than the left. Neither difference was as large as in the patients with right ventricular outflow tract obstruction. Patients with ventricular septal defect and those with patent ductus arteriosus had almost identical flow through the two upper zones.