An investigation of the changes in aortic diameter and an evaluation of their effect on Doppler measurement of cardiac output in pregnancy

Abstract

Measurement of cardiac output by means of Doppler ultrasound is based on the velocity of aortic blood flow and therefore requires that aortic diameter should not change between measurements. Work has been published which suggests that, in pregnancy, aortic diameter varies significantly with systemic blood pressure. The implication of this is that aortic diameter must be remeasured for each determination of cardiac output in pregnant patients. This study investigated the changes in aortic diameter with blood pressure in patients having spinal anaesthesia for caesarean section. Aortic diameter did appear to vary with blood pressure but this variation was within the error of the measurement and did not significantly affect the accuracy of the technique.