Angiographic evidence of pulmonary vasomotion in the dog.

Pulmonary artery vasomotion is considered to be a factor affecting blood flow through the lungs despite the fact that direct confirmation of pulmonary vascular motion has been difficult to obtain. Indirect evidence has been presented by physiologists using mathematical techniques, involving pressure differences and flow rates. A more direct approach to the study of pulmonary vasomotion would be by pulmonary angiography. This, however, has its limitations because of the dilution of the contrast material introduced into a peripheral vein or the main pulmonary artery. Such htmodilution restricts the clarity of the x-ray shadows produced by the small muscular arteries. Modification in the method of pulmonary angiography obviates most of these problems. This modification consists of a rapid deposition of the opacifying material into a segment of the pulmonary artery via a catheter. Care is taken not to disturb pressure-flow relations by wedging. The contrast material is then viewed by a selective x-ray. The entire sequence is programmed by electronic circuits and is initiated by the R wave of the electrocardiogram. Arteries can thus be seen at a constant, predetermined millisecond within the cardiac cycle. Using this technique of angiography, an investigation was made of the vasomotor responses of the distal portions of the pulmonary circulation in the dog. Angiographic records of induced vascular motion were obtained following the individual injection of vaso-active substances, epinephrine, metaraminol, and 5-hydroxytryptamine, and after hypoxia.