Evaluation of blood flow velocity in the ascending aorta and main pulmonary artery of normal subjects by Doppler echocardiography

Blood flow velocity measurements were made in the ascending aorta and proximal main pulmonary artery of 20 adult normal subjects (12 men and eight women, age range 21 to 46 years) with the use of a commercial prototype ultrasound instrument combining a spectrum analyzer-based, pulsed Doppler velocimeter with a two-dimensional sector scanner. The sector scanner was used to produce two-dimensional images of the main pulmonary artery so that the Doppler sample volume could be placed parallel to the flow stream. A 2.25 MHz right-angle M-mode ultrasound transducer was positioned in the suprasternal notch and was used to measure blood flow velocity in the ascending aorta. There were significant differences (p < 0.001) between the ascending aorta and main pulmonary artery (PA) in the following blood flow parameters: peak flow velocity (aorta = 92 cm/sec, PA = 63 cm/sec), average acceleration (aorta = 940 cm/sec², PA = 396 cm/sec²), acceleration time (aorta = 98 msec, PA = 159 msec), deceleration time (aorta - 197 msec, PA = 172 msec), average deceleration (aorta = 473 cm/sec², PA = 356 cm/sec²), and ejection time (aorta = 294 msec, PA = 331 msec). These data indicate that despite a four to five times higher arterial resistance in the systemic circuit compared to the pulmonary circuit, blood is accelerated two to three times more rapidly in the ascending aorta than in the main pulmonary artery. Also, the peak flow velocity is higher in the aorta and is achieved earlier in systole than in the pulmonary artery. In addition to providing insight into the normal physiology of flow in the great arteries, these Doppler measurements in normal subjects should provide a quantitative data base for evaluating flow velocity patterns in patients with known or suspected cardiac disorders under a variety of physiologic conditions.