Axial development of velocity fields in the porcine main pulmonary artery system

Abstract

The aim of this study was to provide detailed data on velocity profile development in the normal porcine main pulmonary artery and its main branches. Under spontaneous hemodynamic conditions in twelve open-chest 90kg pigs, perivascular pulsed Doppler ultrasound was used for blood velocity measurements in the entire cross-sectional area in three axial locations in the main pulmonary artery and along one diameter in the main branches. Computerized threedimensional visualizations of the spatial and temporal development of velocity profiles were made throughout the heart cycle. The results were similar one and two diameters downstream of the pulmonary valve. In the early systolic acceleration phase, the velocity profile became skewed, with the highest velocities (132.7 ± 19.4cm · sec−1) towards the inferior to right superior vessel wall, and rotated counterclockwise 45°–90° during the late acceleration to early deceleration phase in 9 out of 11 pigs. Maximum retrograde velocities (31.4 ± 14.9cm · sec−1) were observed at the inferior to the right superior vessel wall in the late systolic deceleration phase and in early diastole. During diastole, low retrograde to insignificant antegrade velocities were observed. Immediately upstream of the pulmonary bifurcation, the velocity profile disclosed two peaks at locations corresponding to the two main branches. A confined area with retrograde velocities was seen at the right vessel wall in late systole. Low-scale antegrade velocities were observed throughout diastole in the entire cross-sectional area. In the left main branch, the velocity profiles were found to be somewhat skewed towards the left vessel wall, corresponding to the smaller curvature of the left main branch, while the velocity profile in the right main branch was skewed against the superior vessel wall throughout systole. This study thus disclosed that the blood velocity profiles in the main pulmonary artery system were skewed and that mean velocity varied 26%–50% between measuring points, exhibiting an as yet unexplained rotational phenomenon. The skewed velocity profile in the porcine pulmonary trunk indicates that single-point blood velocity measurements can only serve as a basis for cardiac output estimations when used with considerable caution.