THE SMALL PULMONARY ARTERIES STUDIED BY A NEW INJECTION METHOD

Abstract

In the study of the pulmonary vascular bed by injection methods, assessment hitherto has been visual. A method incorporating a radioactive substance with the radio-opaque medium has enabled measurements of the small arterial bed (2 mm to 30 [mu] vessels) to be made. The measurement is expressed in terms of volume of small arteries per unit volume of lung and the mean and the range for normal lungs has been identified. Lungs with a reduced vascular bed have been grouped according to the causes, such as mitral valve disease, aortic valve disease, pulmonary hypertension, left ventricular failure, and emphysema. The method has shown much reduction of the small arterial bed of the lung in cases of aortic valve disease and of systemic hypertension and cardiac infarction with left ventricular hypertrophy. This reduction takes place at a very early stage of left ventricular failure or possibly even before this occurs. There is already some experimental support for this view. An analysis of 10 cases of emphysema is presented and the results indicate that the reduction in the small arterial bed is much more than the macroscopic appearance of the emphysema would suggest. Smaller vessels have disappeared while many of those remaining have thickened walls with narrowing of the lumen. This method measures the total reducing effect of these changes. The findings in the differing groups of cardiac and respiratory disease are in accord with the view that elevation of capillary pressure or damage to the capillary bed acts as an immediate stimulus to restriction of the associated small arterial bed to protect the capillaries. Such reduction may be identified by measurement before it has produced changes that can be confidently observed by the microscope.