Regional lung function in patients with increased unilateral transradiancy of the lung in the presence of cardiac disease.

Regional lung function has been studied with xenon-133 in two patients with unilateral transradiancy of the lung and coincidental cardiac disease. One patient had severe mitral stenosis with pulmonary venous and pulmonary arterial hypertension, the other had a secundum type of atrial septal defect with a pulmonary blood flow which was increased to 25 litres per minute. In both instances the overall perfusion of the transradiant lung was diminished but the regional distribution of blood flow was the same within both the `normal' and the transradiant lung. In the patient with mitral stenosis there was an abnormal increase in upper zone perfusion resulting in a reversal of the normal pattern of pulmonary blood flow while in the patient with an atrial septal defect the blood flow difference between the upper and lower zones was decreased and thus the normal vertical gradient was less. These studies suggest that the hypoplastic pulmonary arteries in the transradiant lung reacted in the same way to alterations in pressure and flow as the vessels in the other lung.