152 BLOOD FLOW IN THE ASCENDING AND THE DESCENDING AORTA IN TERM NEWBORN INFANTS

Abstract

The combination of 2-dimensional real-time and pulsed Doppler echocardiography provides a noninvasive method of measuring blood flow and has been used to study blood flow at the lower thoracic level of the descending aorta (DA) in the human fetus. Using these techniques, we evaluated the proportion of cardiac output distributed through the DA in 13 term newborn infants (mean±SEM BW 3551±95 g, GA 40.1±0.3 w). Blood flow velocity was measured using a 3.5 MHz, range gated, pulsed Doppler velocity meter with the transducer positioned in the suprasternal notch. Blood flow in the ascending aorta (AA) was measured at the aortic root level and descending flow below the isthmus. The internal diameter of the AA was assessed at the level of the aortic valve using M-mode echocardiography and the diameter of the DA in the posterior atrioventricular groove with the use of the 2-D long axis view. Blood flow in the AA was 789±42 ml/min and in the DA 499±26 ml/min indicating that 63.5% of the left ventricular output is distributed through the DA. The mean blood flow velocity was comparable at both sites, whereas the mean diameter of the DA was 19% smaller than the diameter of the AA. In healthy term newborn infants approx. 2/3 of cardiac output is directed to the DA and 1/3 to brachial and carotid arteries. The changes in aortic blood flow are correlated with the changes in aortic diameter.