Physiologic pressure differences between main and branch pulmonary arteries in infants.

SUMMARY Systolic pressure differences of 6 to 45 mm Hg were found between the main and branch pulmonary arteries in 37 of 242 infants undergoing diagnostic cardiac catheter-ization. Eleven of these 37 infants were restudied, and all had lost the pressure difference regardless of the underlying cardiac defect. A similar pressure difference was noted in lambs studied at thoracotomy with direct measurement of main and branch pulmonary arterial pressures. Increasing pulmonary blood flow caused a rise in pressure differences and also evoked a difference in some older lambs when none was originally present. Cineangiography in infants with a pressure difference showed no discrete narrowing or poststenotic dilatation of the pulmoinary arteries. The main pulmonary artery was a large domed structure from which relatively small right and left branches arose at sharp angles from the inferior and posterior surfaces. The size, disparity, and angulation probably caused turbulence with, at times, a loss of pressure. Systolic flow murmurs may be common. In assessment of pulmonary vascular resistance, it is therefore important to recognize that a portion of the total pressure drop across the lungs after birth reflects maturational changes of the larger pulmonary arteries as well as of the muscular arterioles. Physiologic peripheral pulmonic stenosis Pulmonary anatomy of the infant C HANGES in pulmonary vascular resistance at birth and in the newborn period have been studied in human infants and in the 410 Pulmonary vascular resistaince young of many experimental animals.1-8 An abrupt drop in resistance, attributed to expansion of the alveoli, the opening of the pulmonary capillary network, rise of oxygen tension, and bradykinin release,9 occurs at birth with the onset of respiration. A second, more gradual decrease follows in weeks or months as postnatal regression of muscular hypertrophy of arteries and arterioles occurs. This evolution of pulmonary resistance has been previously investigated by measurement of right ventricular or main pulmonary arterial pressures. In infants during cardiac catheteri-zation, we often found a pressure difference between main and branch pulmonary arteries so that calculated pulmonary vascular resistance was lower if the pressure for the branch