Unequal pressures in the central pulmonary arterial branches in patients with pulmonary stenosis. The influence of blood velocity and anatomy.

Significantly different pressures in the right (RPA) and left (LPA) pulmonary artery were observed at catheterization in patients with pulmonary valvar stenosis and no branch stenosis. The lower pressures in the RPA showed a "valley" during systole and were similar in contour and amplitude to the main pulmonary arterial (MPA) pressure; the LPA pressure, however, had a normal contour, and the peak systolic and mean pressures were higher than those in the MPA and RPA. Angiocardiograms, phonograms, and a simple analysis of fluid mechanics suggest that this pressure pattern is related to (1) the high-velocity jet in the MPA and (2) the anatomy of the central pulmonary arterial branches (bifurcation), the LPA originating more distally than the RPA. The high-velocity jet bypasses the origin of the RPA and breaks up in the distal MPA near the origin of the LPA. The kinetic energy is then reconverted into pressure, causing the higher LPA pressures. In patients with transposition of the great arteries and subvalvar pulmonary stenosis, the anatomy of the main pulmonary arterial bifurcation is different from normal, the RPA originating more distally than the LPA. The high-velocity jet may bypass the origin of the LPA and break up near the more distal origin of RPA, and the pressures in the RPA can be higher than those in the MPA and LPA.