Parameters and standardization in obstetric Doppler

Obstetric Doppler is still largely empirically based, although possible clinical applications are already under examination. This article examines some of the basic instrumentation and hemodynamic issues — which physiological parameters would we ideally like to assess, and what can we do in practice with current Doppler instrumentation? It is shown that the rate of blood flow and the flow resistance are two of the most basic hemodynamic parameters. It is possible to estimate the flow rate with (specialized) Doppler equipment, but there is no method available at present to measure the flow resistance. Analysis of the blood velocity waveform provides some information concerning flow resistance, as long as it can be assumed that other factors that might affect the waveform have not deviated significantly from the norm. Practical considerations in choosing the instrumentation and designing the examination protocol are discussed, and issues of quality control are emphasized.