Comparison of umbilical artery flow velocity waveform indices as measured by continuous wave Doppler ultrasound.

Abstract

This study examines four methods, automated and man· ual, of calculating the pulsatility index (PI) of fetal umbilical artery flow velocity waveforms (FVW) and compares these values to the resistance index (RI), the A/8 ratio, and the degree of absence of end diastolic frequencies. The FVWs were obtained by the Doptek continuous wave Doppler ultrasound. All of the maximum envelope indices had significant correlations; a highly C ontinuous wave Doppler ultrasound systems are becoming more widely used for the mea· surement of fetal and maternal flow velocity waveforms (FVW) in the prediction of pregnancy complications and in the assessment of fetal well being. t.z There are presently three main angle independent indices used to evaluate the FVW: 1) the A/8 ratio, or the peak systolic to end diastolic ratio; 3 2) the resistance index (RI), or peak systolic minus end diastolic frequencies divided by the peak systolic frequency;• and 3) the pulsatility index (PI), or peak systolic minus the nadir (or negative peak) diastolic frequencies divided by the mean maximum frequency over one cardiac cycle. 5 In the analysis of the umbilical artery FVW from normal preg· nancies, there is a highly significant correlation between these indices. 6 In some pathological pregnancies in significant difference was found between the automated and the manual methods of determining Pl. When PI was measured manually, there was a better correlation between the A/8 ratio, Rl, and degree of absence of end diastolic frequencies than when the automated methods methods were used. KEY woRos: Doppler, ultrasound, flow velocity waveform, pulsability index, blood flow (J Ultrasound Med 7:549, 1988). which the end diastolic frequencies are greatly reduced or even absent, however the A/B ratio and the Rl cannot be used, because the former approaches infinity and the latter approaches unity. 67 For this reason, the PI has become the most commonly used index in the assessment of peripheral impedance to downstream flow in complicated pregnancies.Most continuous wave Doppler machines use an onboard spectrum analyzer to estimate the maximum envelope of the FVW in calculating Pl. The analyzer can determine an intensity-weighted mean for FVW and calculate PI as well. A manual method with a light pen is also available to evaluate FVW envelope. This study examines these methods of determining PI in both normal and in pathologic pregnancies, and compares these values to the A/B , RI, and degree of absence of end diastolic frequencies. METHODSThe Doptek (continuous wave Doppler ultrasound and spectrum analyzer 9000, Doptek Ud, Chichester, UK) offers three methods for calculating maximum FVW en-

Extent of absent end‐diastolic flow in umbilical artery and outcome of pregnancy

“…Unfortunately, the PI values automatically estimated online by the ultrasound system did not completely correspond to the sequences of waveforms used for calculation of the T a /T tot ratio (89 of the 170 (52%) waveforms were the same for both calculations). It has been shown by others that there is poor correlation between manually and automatically estimated PI, owing to the varying definitions of maximum velocity 23 . Manual PI calculation is laborious and time-consuming and is thus not suited for routine use.…”

“…Very few studies have focused on fetuses with AEDF separately from those with REDF. Gilbert et al 23 . examined loss of end‐diastolic flow as a percentage of the cardiac cycle in relation to PI in 20 pregnant women.…”

“…Very few studies have focused on fetuses with AEDF separately from those with REDF. Gilbert et al 23 examined loss of end-diastolic flow as a percentage of the cardiac cycle in relation to PI in 20 pregnant women. Malcus et al 24 developed computerized waveform pattern-recognition software with 10 standard velocity waveforms for the UA (REDF waveforms were not *Arbitrary cut-off value determined from distribution of T a /T tot ratio values and fetal outcome (Figure 3).…”