Fetal blood flow velocity waveforms in relation to changing peripheral vascular resistance.

In an acute experiment in Texel ewes, Doppler flow velocity waveforms from the fetal descending aorta were related to peripheral vascular resistance as calculated from perfusion pressure divided by electromagnetically measured volume flow in the descending aorta. Vascular resistance was increased by stepwise embolization of the peripheral circulation via repeated bolus administration of Sephadex G-25 microspheres. A rise in peripheral vascular resistance was associated with a reduction in peak and end-diastolic flow velocity and an increase in Pulsatility Index. Clinically, if similar changes are observed in growth retarded fetuses, the findings are usually interpreted to represent 'uteroplacental insufficiency'. Present data provide direct evidence that raised peripheral vascular resistance does indeed produce such waveform changes.