A comparison of Doppler ultrasound waveform indices in the umbilical artery--I. Indices derived from the maximum velocity waveform

Various Doppler waveform indices have been used for assessment of the fetal circulation. Comparisons were made to show what relations exist between the indices, and to identify any differences or difficulties which might arise from using one as opposed to another in clinical practice. Both normal pregnancy and cases of fetal growth failure were studied. Indices were obtained from the maximum velocity envelope of the umbilical artery waveform using a curve fitting technique. The values were very reproducible for all indices. The FHR, which varied over the entire normal range, did not significantly affect the values of any index. The downstream impedance indices calculated included the AB ratio, pulsatility index (PI) and Pourcelot ratio. These all gave very closely correlated results for normals but discrepancies occurred in the at risk group, where values were elevated. This could be attributed to differences in the underlying distributions. The indices suggested for cardiac contractility were not as closely related to each other, and moreover the differences between them showed no clear pattern. None of the indices varied independently of the others. The rising slope, which is by definition related to the PI, was more highly correlated with the downstream indices than the relative flow rate index.     

An investigation of simulated umbilical artery Doppler waveforms. II. A comparison of three Doppler waveform quality indices

Three Doppler waveform quality indices based upon assessment of the noise of the maximum frequency envelope of simulated umbilical artery waveforms were investigated. These indices were: an estimate of the correlation between successive waveforms (QI1), a local linearity measure (QI2) and a ratio of two regions of the Fourier transform amplitude spectrum of the maximum frequency envelope (QI3). Simulated umbilical artery waveforms were acquired from a physiological flow phantom. A test population was used consisting of a large number of waveforms where one of three physical variables had been adjusted to produce waveforms of varying quality. These three physical variables were: beam-vessel angle, beam-vessel axial misalignment and attenuator thickness. For this group of waveforms the accuracy of estimation of the maximum frequency envelope and pulsatility index (PI) were known. All three quality indices gave good separation of high- and low-quality waveforms based upon threshold values of the accuracy of PI and maximum frequency envelope. The dependence of each quality index on fetal breathing, waveform length and waveform pulsatility was investigated. QI2, the local linearity measure, showed most promise in its independence from these variables.     

Doppler ultrasound waveforms in the fetal umbilical artery: quantitative analysis technique

Doppler ultrasound waveforms from the fetal umbilical artery were analyzed by a new quantitative technique. Normal pregnancy and cases of fetal growth failure were considered. Data from the spectrum analyzer were dumped to a microcomputer, the velocity waveforms calculated and a representative waveform obtained by ensemble averaging. This curve was then fitted by a 4-parameter analytic function. We introduce R, the relative flow rate index, which measures the ratio of the average flow rate before the systolic peak to the average rate during the remainder of the cardiac cycle. In cases of fetal growth failure this ratio was significantly greater than in normal pregnancy. Other new quantities defined are the normalized systolic decay time index and the constant flow ratio. The AB ratio was also calculated. Fetal growth failure has been associated with raised placental resistance. We suggest that the fetus can initially compensate for this by increasing cardiac contractility. This can be seen by interpreting the R and AB values together. Our analysis technique enables the waveform to be efficiently described, and provides useful diagnostic information about placental function and fetal wellbeing.     

Color Doppler sonographic assessment of placental circulation in the first trimester of normal pregnancy.

Our aim was to study placental circulation during the first trimester of normal pregnancy. For this purpose, 108 single pregnancies from 4 to 15 gestational weeks were evaluated through conventional Doppler ultrasonography. The flow velocity waveforms from the retrochorionic arteries (spiral-radial arteries) and the umbilical artery were assessed using the peak systolic velocity, resistive index, and pulsatility index). Intervillous flow velocity waveform was evaluated from the maximum velocity. The earliest color signal from the retrochorionic circulation was registered at 4.5 weeks along with gestational sac visualization. The venous Doppler signal from the intervillous space and the Doppler signal from the umbilical artery were recorded with an embryo visible from the end of week 5 onward. The retrochorionic, intervillous, and umbilical peak systolic velocities increase, whereas the resistive and pulsatility indices decrease progressively during early pregnancy with a significant correlation with gestational age. Similarly, intervillous maximum velocity gradually increases throughout the first trimester of pregnancy. Despite some methodologic problems related to Doppler technology and the vessels studied color Doppler sonography appears to be an adequate tool to assess the physiologic changes in the placental circulation during early pregnancy.     

彩色多普勒超声监测生长迟缓胎儿脐动脉血液循环的变化

目的 应用彩色多普勒超声监测生长迟缓（IUGR）胎儿的脐动脉血液循环。方法 测定130例妊娠20－42周妇女（其中正常49例,IUGR81例）脐动脉时间平均血流速度（TAMX）,收缩期最大血流速度与舒张末期血流速度的比值（S／D）,搏动指数（PI）,阻力指数（RI）,收缩期最大血流速度（Vmax)与舒张末期血流速度（Vmin)。结果 正常孕妇随孕龄增长,胎盘功能增强,胎儿血液循环日渐丰富,IUGR者则明显障碍,在20周时脐动脉TAMX显著下降,在30周后S／D,PI及RI显著升高,Vmin显著下降,在35周时Vmax显著下降,出现舒张期血流停止或倒流。结论 彩色多普勒超声可直接测定脐动脉血流循环,能在早期诊断UGR,判断病情及估计预后。     

Normal values of fetal ductus venosus blood flow waveforms during the first stage of labor.

OBJECTIVE: To present normal values of fetal ductus venosus blood flow waveforms during the first stage of labor during and between contractions. MATERIALS AND METHODS: Seventy-eight women between the 37th and 41st weeks of gestation were included in the study. At distinct stages of cervical dilation, blood flow velocity waveforms of the fetal ductus venosus during and between contractions were visualized in fetuses with a normal non-stress test. The pulsatility index for veins, peak velocity index for veins and fetal heart rate were calculated off-line. The means +/- standard deviations (SD) during and between contractions were compared using the Wilcoxon test. RESULTS: Ductus venosus blood flow velocity waveforms were visualized during 331 contractions and 375 episodes of uterine quiescence in 74 of 78 fetuses (95%) during normal labor. The mean +/- standard deviation values of pulsatility and peak velocity indices for veins during contractions were 1.66 +/- 0.85 (median: 1.56, range: 0.29-4.69) and 1.46 +/- 0.65 (median: 1.34, range: 0.26-3.13), respectively. Between contractions the values were 0.48 +/- 0.19 (median: 0.46, range: 0.14-1.00) for the pulsatility index and 0.44 +/- 0.18 (median: 0.42, range: 0.14-1.00) for the peak velocity index for veins. These differences during and between contractions were highly significant (P-value < 0.0001), whereas the fetal heart rate showed no significant differences. CONCLUSION: There are significant differences in fetal ductus venosus blood flow waveforms during and between labor contractions. Further studies should evaluate whether these normal values of the fetal ductus venosus are beneficial for risk evaluation in fetuses with an abnormal non-stress test and/or intrauterine growth restriction.     

Cerebral blood flow velocity: the influence of myocardial contractility on the velocity waveform of brain supplying arteries.

Indices of Doppler-derived velocity waveforms of arteries perfusing the brain are used as relative measures of neonatal brain blood flow. Using a dog model, we investigated the influence of changes in myocardial contractility, induced by dobutamine, on the blood flow velocity waveform of the vertebral artery. The following indices of the velocity waveform were investigated during control states and during 5 or 10 micrograms/kg/min dobutamine infusion: peak systolic flow velocity (PSFV), temporal mean flow velocity (TMFV), end-diastolic flow velocity (EDFV) and acceleration time (ACC-time). PSFV and ACC-time of the vertebral artery showed a strong relationship with myocardial contractile state. These results indicate that PSFV of an artery supplying the brain or indices which combine PSFV with MFV or EDFV should not be used for noninvasive assessment of brain blood flow or cerebral vascular resistance. ACC-time may prove to be very useful in assessing changes in myocardial contractile state.     

Normal and respiratory variations of the hepatic and portal venous duplex Doppler waveforms with simultaneous electrocardiographic correlation.

To understand hepatic vein (HV) and portal vein (PV) duplex waveforms and their normal and respiratory variations, HV and PV duplex sonography with simultaneous electrocardiography was performed on 11 volunteers. Absolute velocities of the waveforms' components and their ratios were determined at mid-inspiration, full inspiration, full expiration, and Valsalva maneuver. The normal HV waveform was variable in shape and component velocities and ratios but essentially consisted sequentially of (1) an antegrade systolic wave resulting from movement of the tricuspid annulus toward the cardiac apex and occurring shortly after QRS; (2) a retrograde v-wave resulting from atrial overfilling and occurring immediately after the T-wave; (3) an antegrade diastolic wave resulting from opening of the tricuspid valve and occurring shortly after the T-wave; and (4) a retrograde a-wave resulting from atrial contraction and occurring immediately after the P-wave. The ratio of the maximum systolic velocity to maximum diastolic velocity varied from 1.0 to 2.8 (mean 1.4). Systolic-to-diastolic ratio decreased during inspiration but was always greater than 0.6 and increased during expiration. The Valsalva maneuver diminished waveform pulsatility. PV waveforms were more triphasic than biphasic but less pulsatile, flow was totally antegrade, and respiratory changes were less remarkable than HV waveforms. All normal HV and most normal PV waveforms showed multiphasicity that corresponded to cyclic cardiac changes. The shapes of these waveforms were variable and were modified by respiratory movements.     

Clinical trial of umbilical artery Doppler waveform quality indices.

The ability of two Doppler waveform quality indices to discriminate between high- and low-quality waveforms was tested using 427 sets of umbilical artery Doppler waveforms from patients. The waveforms had been acquired using a 4-MHz continuous-wave Doppler unit. The quality indices (QI) were based on an assessment of the degree of noise of the maximum frequency envelope of the waveforms, and were first a correlation between successive waveform envelopes (QI1), and, second, a sum of local linearity measures (QI2). The sets of waveforms were graded subjectively according to the clarity of the outline of the waveforms, the degree of interference in the region of the spectrum above the outline, and in terms of the degree of variability caused by fetal breathing. At 90% sensitivity for detection of low-quality waveforms according to a high envelope clarity score, the specificities were 68.2% and 52.7%, respectively, for QI1 and QI2. QI1 was independent from pulsatility index and waveform length, but showed strong dependence on fetal breathing. QI2 showed strong independence from pulsatility and fetal breathing and reasonable independence from waveform length. Both QI1 and QI2 performed poorly when there was a large degree of noise in the region of the spectrum above the envelope; however, this poor performance was often related to the inability of the maximum frequency follower to estimate correctly the maximum frequency envelope in those conditions so that the high waveform quality values reflected the erroneous calculation of pulsatility index in those cases.     

Human fetal pulmonary artery velocimetry: repeatability and normal values with emphasis on middle and distal pulmonary vessels.

OBJECTIVES: To establish the nature and gestational age dependency of flow velocity waveforms from fetal middle and distal arterial pulmonary branches in the second half of normal pregnancy and to determine repeatability and inter-relationship of flow velocity waveform recordings from proximal, middle and distal arterial pulmonary branches. DESIGN: Cross-sectional study. SUBJECTS/METHODS: A total of 111 singleton normal pregnancies between 20 and 40 weeks of gestation were studied using a color-coded Doppler ultrasound system. Pulmonary waveforms were obtained at the level of the fetal cardiac four-chamber view. Repeatability was tested from two recordings at 15 min time-intervals in 25 separate normal pregnancies. RESULTS: Acceptable repeatability of flow velocity waveforms from fetal arterial pulmonary branches was established with coefficients of variation below 15%. The nature of middle arterial pulmonary flow velocity waveforms was similar to that of proximal waveforms and showed a gestational age-related change for diastolic velocity parameters, peak systolic/peak diastolic ratio and pulsatility index. The distal arterial pulmonary branch displayed a monophasic forward flow velocity profile throughout the cardiac cycle. All velocity parameters of the distal branch remained unchanged with advancing gestation, with the exception of the pulsatility index. Significant inter-pulmonary changes were found for all pulmonary arterial waveform parameters. CONCLUSIONS: Alteration in pulmonary vascular resistance may play a role in gestational age-related changes, whereas changes in vessel branching/diameter and in the distance between the heart and more distal arterial pulmonary vessels may cause inter-pulmonary differences.     

Intraobserver and interobserver variability of transabdominal Doppler velocimetry measurements of the fetal ductus venosus between 10 and 14 weeks of gestation.

OBJECTIVE: To assess the intraobserver repeatability and interobserver reproducibility of transabdominal Doppler ultrasound measurements of ductus venosus blood flow in fetuses between 10 and 14 weeks of gestation. DESIGN: A prospective study with the following end-points: coefficient of variation, intraclass correlation coefficients within and between observers, repeatability coefficient and Cohen's kappa coefficient. SUBJECTS AND METHODS: Doppler velocimetry indices (maximum peak systolic velocity during ventricular systole, end-diastolic velocity during atrial contraction, peak systolic velocity/end-diastolic velocity ratio and pulsatility index for veins) were successfully measured three times by the same trained observer in 67 fetuses. Of these, in 24 fetuses, the measurements were then repeated by a second trained observer. In addition, both observers classified qualitatively the blood flow as being normal or abnormal with regard to the presence or absence/reversal of flow during atrial contraction. RESULTS: The intraobserver repeatability of the pulsatility index for veins measurements was considered good with a coefficient of variation of 8.9% and an intraclass correlation coefficient value of 0.62. However, inconsistencies occurred in maximum peak systolic velocity, end-diastolic velocity and systolic/diastolic ratio measurements, which had coefficients of variation of 19%, 28.5%, and 25.4%, respectively. The corresponding intraclass correlation coefficient values were 0.70, 0.69 and 0.60. Interobserver reproducibility of these indices was unsatisfactory, the coefficient of variation varying between 11.5% and 47.2% and the intraclass correlation coefficient between 0.18 and 0.44. Agreement between the repeated observations with regard to interpretation of normal or abnormal blood flow varied from moderate (interobserver) to very good (intraobserver). CONCLUSIONS: There was considerable variability in all Doppler indices except for the intraobserver repeatability of the pulsatility index for veins measurement. This makes the implementation of the semiquantitative Doppler indices in a screening setting difficult. On the contrary, qualitative classification of the flow velocity waveforms seemed to be a reproducible method.     

Doppler velocimetry of normal human fetal venous intrapulmonary branches.

OBJECTIVES: To describe the nature of flow velocity waveforms from fetal middle and distal venous pulmonary branches in the second half of normal pregnancy in relation to gestation, and to test repeatability and interrelationships of flow velocity waveform recordings from proximal, middle and distal venous pulmonary branches. DESIGN: Cross-sectional study. SUBJECTS/METHODS: A total of 111 normal singleton pregnancies between 20 and 40 weeks' gestation were studied using a color-coded Doppler ultrasound system. Pulmonary waveforms were obtained at the level of the fetal cardiac four-chamber view. Repeatability was tested from two recordings at 15-min time intervals in 25 separate normal pregnancies. RESULTS: The nature of middle and distal venous pulmonary flow velocity waveforms was comparable with that of proximal waveforms. Acceptable repeatability of pulmonary venous flow velocity waveforms with coefficients of variation below 15% was established for nearly all velocity parameters and their ratios. A gestational age-dependent change was found for all flow velocity waveform parameters including pulsatility index for veins at both middle and distal venous levels. Significant inter-pulmonary changes were observed for nearly all pulmonary venous waveform parameters. CONCLUSIONS: It is speculated that increase in volume flow and venous pulmonary pressure gradient plays a role in gestational age-dependent changes, whereas changes in vessel diameter and distance between the heart and more distal venous pulmonary vessels are responsible for inter-pulmonary changes.     

中晚孕期正常胎儿静脉导管血流动力学研究

目的 建立中晚孕期正常胎儿静脉导管多普勒血流参数参考范围。方法 应用彩色多普勒超声检查138例16-41孕周正常单胎胎儿。在静脉导管入口处记录静脉导管血流波形，测定血流参数包括：心室收缩期峰值流速（S）、心室舒张期峰值流速（D）、心房收缩期最大流速（A）、平均流速（Vmean）、S／A值、S／D值、（S-A）／S值、（S-A）／D值和（S-A）／Vmean值。结果 正常胎儿静脉导管的血流参数S、D、A、Vmean随着孕龄的增加而增加（均P〈0．01或P〈0．05）；而S／A、（S-A）／S、（S-A）／Vmean和（S-A）／D值随着孕龄增加而减低（均P〈0．01或P〈0．05），S／D与孕龄相关性差（r=0．1，P〉0．05）。结论 正常胎儿静脉导管血流波形呈特殊的三相波形，血流速度随着孕龄增加而增加，而阻力指数随着孕龄增加而减低，S／D值在妊娠中持续不变。     

Doppler waveforms in the renal arteries of normal children

Blood velocity waveforms in peripheral arteries vary such that decreasing vascular resistance results in a relative increase in diastolic velocity at steady state. We measured blood velocity in renal arteries of 20 children (age: 119 months ± 37 months; weight: 38 kg ± 15 kg) to establish normal values, and to explore the relationship between these waveforms and central hemodynamics. Using image-directed pulsed Doppler echocardiography, M-mode measurements and cardiac index were recorded. Renal hila were visualized via the flank for Doppler sampling. Peak systolic velocity (A) and minimal diastolic velocity (B) were determined. The results (mean ± SD) were as follows: Renal artery A/B = 2.9 ± 0.74 (range 1.9 to 5.1). Characteristic waveforms were identical bilaterally and had continuous diastolic foward flow: A/B was independent of central hemodynamics within the resting normal range, varying inversely with age and size.     

Doppler studies in normal kidneys of preterm and term neonates: changes in relation to gestational age and birth weight.

OBJECTIVE: The purpose of this study was to establish normative data for the flow velocity waveform indices of the renal arteries in the neonatal population and to evaluate the differentiation between birth weight and gestational age of neonates. METHODS: Color sonography was performed in 65 neonates on the fifth day of life. Mean flow velocity was assessed, and measurements of the systolic/diastolic velocity ratio, resistive index, and pulsatility index were performed by online calculation. RESULTS: All established values of renal arteries showed no significant differences in the right and left kidneys (P > .05). These values were not correlated with gestational age and birth weight (P > .05). CONCLUSIONS: Peak systolic velocity, systolic/diastolic velocity ratio, and resistive index and pulsatility index values remain stable despite gestational age or birth weight and not different between the right and left kidneys.     

Doppler evaluation of fetal hemodynamics

Human umbilical hemodynamics was investigated in 27 pregnant patients with gestational ages from 29 to 43 weeks using a pulsed Doppler flowmeter. The signals were analyzed by Fast Fourier Transform using a minicomputer. Coherent averaging of the signals, along with the computation of maximum velocity, mean velocity and the first moment of Fourier spectra about the zero frequency axis were performed. Hemodynamic indices were measured utilizing a comprehensive feature characterization technique of the blood flow velocity waveform. It was observed that coherent averaging reduced spectral variance thus relatively simplifying the analyses. The Pulsatility Index based on the first moment of the Fourier spectra indicated a higher umbilical flow change during the fetal cardiac cycle, than that predicted by the peak velocity Pulsatility Index. We also observed a high Pulsatility Index in association with three cases of oligohydramnios indicating the possibility of an elevated placental circulatory impedance. Variation in the peak velocity up to 20% was also noted with fetal breathing movements. Further studies are necessary to determine the clinical relevance of these findings.     

Comparison of color Doppler uterine artery indices in a population at high risk for adverse outcome at 24 weeks' gestation.

OBJECTIVE: To compare uterine artery Doppler velocity and impedance indices in the presence and absence of uterine artery waveform notches, in the prediction of adverse pregnancy outcome in high-risk women. METHODS: One hundred and fifty-seven women identified at Doppler screening as being at 'high risk' underwent a further uterine artery Doppler assessment at 24 weeks' gestation. Pulsatility and resistance indices and minimum, time averaged and time averaged maximum velocities were measured, and the presence of bilateral notches noted. Adverse outcomes were pre-eclampsia, birth weight less than the tenth centile, placental abruption and intrauterine death. The best cut-off for each parameter was assessed by univariate logistic regression, and the comparative performance of the screening parameters was assessed using kappa values. RESULTS: The best performing index in the presence of bilateral notches was mean resistance index, for a cut-off of 0.67, giving a kappa value of 0.65. Mean pulsatility index and lowest pulsatility index performed similarly well, both with kappa values of 0.58. All velocity indices apart from lowest minimum velocity had kappa values of < 0.4. When indices were analyzed, irrespective of notch status, mean resistance and mean pulsatility indices performed similarly, with kappa values of 0.49 and 0.46, respectively; mean minimum velocity had a kappa value of 0.4. CONCLUSIONS: In a high-risk population, uterine artery Doppler mean resistance indices perform better than do velocity indices in the prediction of adverse pregnancy outcome, irrespective of notch status.     

A Doppler waveform index to characterize hepatic vein velocity pattern and evaluate hepatic fibrosis

PURPOSE: To describe a Doppler waveform index representing the hepatic vein flow velocity pattern and to examine its relationship to the degree of hepatic fibrosis. METHODS: Doppler waveforms were obtained in 66 patients scheduled for percutaneous liver needle biopsy and categorized as normal (with a retrograde flow phase) or abnormal (without retrograde flow). Waveforms were also characterized using a hepatic vein waveform index (HVWI): (maximum - minimum velocity)/(maximum velocity). Biopsy specimens were graded for fibrosis. RESULTS: There was a highly significant decrease in HVWI with increasing fibrosis score in the biopsy (p < 0.001, Jonckheere trend test). The biopsy showed cirrhosis in 14 of 29 patients (48%) with absent retrograde flow and 5 of 37 patients (14%) with a normal flow pattern. Using HVWI as the criterion, cirrhosis was present in 13 of 21 (62%) patients with HVWI < 0.75, in 6 of 31 (19%) patients with 0.75 < HVWI < 1.50, and in none of 14 (0%) patients with HVWI > 1.50. CONCLUSIONS: HVWI is inversely correlated to the degree of liver fibrosis and may be more efficient than the presence or absence of retrograde flow in diagnosing and grading hepatic fibrosis.     

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

This study examines four methods, automated and manual, 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/B 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 significant difference was found between the automated and the manual methods of determining PI. When PI was measured manually, there was a better correlation between the A/B ratio, RI, and degree of absence of end diastolic frequencies than when the automated methods were used.     

Recording of blood flow velocity waveforms in the uteroplacental and umbilical circulation: reproducibility study and comparison of pulsed and continuous wave Doppler ultrasonography

Reproducibility of the blood flow velocity waveforms (FVW) recorded from the umbilical artery and the arcuate arteries on the right and left side of the placenta was examined in 8 women with normal pregnancies and anterior placentas. The FVW were recorded using a 2-MHz pulsed Doppler ultrasound system in combination with a real-time linear-array scanner. The FVW were characterized by the pulsatility index (PI) and systolic/diastolic (S/D) ratio. For the PI, the mean coefficients of variation between six operator pairs in the umbilical artery and the left and right arcuate arteries were 8.4%, 26%, and 21.5%, respectively. These findings suggest that, in clinical practice, the umbilical artery FVW is reproducible, but the usefulness of arcuate artery FVW is limited by the wide variation of Doppler signals. Paired recordings of FVW were obtained from the umbilical, arcuate, and uterine arteries using pulsed wave and continuous wave Doppler ultrasonography in a randomized order in another 21 pregnant women with anterior placentas. There was no difference between the two Doppler modes for any of the measured waveform indices.