DESCENDING AORTIC BLOOD-FLOW VELOCITY AS A NONINVASIVE MEASURE OF CARDIAC-OUTPUT IN CHILDREN

In previous work, we postulated that mean aortic flow velocity (MAFV) might be a direct measure of cardiac index. To investigate the assumpt ions inherent in this relation, we measured body surface area, aortic cross-sectional area (two-dimensional ultrasonography) and MAFV (Doppl er ultrasonography) in 70 normal children. For a direct check of the r elation, we simultaneously measured cardiac index (Fick technique) and MAFV (Doppler ultrasonography) in 25 children after cardiac surgery. In the normal group, we found that body surface area was directly prop ortional to aortic cross-sectional area (R 0.94), and MAFV at rest was the same in the ascending and descending aorta (t test, p < 0.05). In the intensive care patients, MAFV in the descending aorta was directl y proportional to cardiac index over a wide clinical range [MAFV (cm/s ) = CI (L/min/m2) . 7.7 - 1.2]. The assumptions made when deriving the relation between MAFV and cardiac index appear to be valid whether me asured in the ascending or descending aorta. However, the scatter of r esults limits its clinical value. Mean aortic flow velocity is probabl y of greater use as a trend indicator and has the potential for contin uous display using an esophageal Doppler probe when measured in the de scending aorta.