Hemodynamic foundation of umbilical arterial Doppler waveform analysis

This paper reviews various in vitro and in vivo studies which have been conducted to investigate the influence of central and peripheral circulatory factors on the Doppler indices. These studies indicate that the Doppler indices are affected by both central and peripheral hemodynamics. Of the central factors, the heart rate influences the indices predominantly through the variations during the diastolic phase of the cardiac cycle. This was confirmatory of the clinical findings. Of the other central factors, cardiac contractility may not affect the rising slope of the Doppler waveform. Regarding the peripheral hemodynamics, both in vitro and in vivo studies confirm that the indices reflect the changes in the peripheral resistance; however, opposition to flow in a pulsatile flow can be adequately described only by impedance. Initial in vivo and in vitro studies demonstrate that the indices correlate well with the impedance parameters. However, this is true only when the central circulation remains stable.