Non-invasive blood pressure measurements and aortic blood flow velocity in neonates

We studied the systolic blood pressure difference between the upper and the lower extremities in healthy newborn infants and the effect of the isthmic narrowing of the aorta on the possible difference. The blood pressure was measured with an oscillometric blood pressure device from every extremity of 36 healthy infants aged 2-5 days. A Doppler echocardiography was performed for each infant to measure the aortic blood flow velocity in the ascending aorta and in the aortic arch above and below the isthmic narrowing. The mean blood pressure readings (S.D.) were the following: the right arm 76.8 (7.3)/48.1 (6.9), the left arm 77.5 (7.4)/51.6 (7.0), the right thigh 77.7 (7.1)/40.7 (5.8), the left thigh 76.8 (6.4)/39.6 (5.8), the right calf 75.5 (7.1)/46.6 (5.7) and the left calf 77.1 (8.6)/48.7 (6.7). The aortic blood flow was faster below the isthmic narrowing of the aorta (1.15 +/- 0.19 m/s) than in the ascending aorta (0.93 +/- 0.12 m/s) or in the aortic arch above the isthmus (0.99 +/- 0.15 m/s). The calculated pressure gradient between the ascending aorta and aorta below the isthmus was 2.0 +/- 1.8 mmHg and between opposite sides of the isthmus 1.5 +/- 1.2 mmHg. Unlike in childhood and adolescence, the systolic blood pressure in the lower extremities of healthy newborn infants is not higher than in the upper extremities. The physiological narrowing of the aortic arch does not explain this phenomenon. If blood pressure measurements are performed on a neonate to rule out aortic coarctation, the readings obtained must be interpreted in respect to normal values in newborns.