FLOW WAVE-FORM INDEXES AND RESISTANCE TO BLOOD-FLOW IN CHRONICALLY INSTRUMENTED FETAL SHEEP

Objective: The study is designed to develop and compare flow waveform indices as indicators of flow resistance. The null hypothesis is that there are no differences between indices. Methods: Five fetal sheep were instrumented to measure fetal arterial (FAP) and venous (IVCP) pressures, as well as mean blood flow (MBF) (ml min-1kg-1) and pulsatile aortic blood flow rate (inductive flow transducer). Peripheral resistance [(FAP-IVCP)/MBF] was increased by angiotensin (0.3-1.5 mug min-1 kg-1). The systolic (S), diastolic (D), and mean flow rates (Qmean) of flow pulses were determined. Spectrum analysis yielded the amplitudes Hx of the first 10 harmonics. The indices S/D, D/S, (S-D)/S, S/Qmean, D/Qmean, (S-D)/Qmean, and (H3 + H4)/Qmean (harmonic component index, HCI) were correlated with resistance. Results: HCI correlated significantly better with resistance (average r2 = 0.68) than did the other indices. Conclusion: The harmonic component index can be useful as an indicator of the fetal circulatory situation in Doppler ultrasound velocimetry.