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Although arterial blood flow is physiologically non-periodic under resting conditions, periodic flow assumption has been widely adopted in most hemodynamic studies. So far, it remains unclear how the non-periodicity of blood flow would influence local hemodynamic parameters, especially wall shear stress (WSS) that associates closely with endothelial function and vascular disease. In this study, numerical simulations of blood flows in sixteen normal carotid artery bifurcations were performed under measured non-periodic and averaged periodic flow conditions, respectively, with the obtained results being compared in terms of five typical WSS metrics (i.e., mean WSS (MWSS), time-averaged WSS (TAWSS), oscillatory shear index (OSI), transverse WSS (transWSS), and average temporal gradient of WSS (WSSTG)) in the atheroprone low-WSS regions. It was found that simplifying the physiologically non-periodic flow condition into a periodic one did not significantly alter the major features of WSS distribution, but resulted in underestimations of some WSS metrics. Specifically, the degree of underestimation was largest (27.2% ± 8.3%) for WSSTG, smallest (0.5% ± 0.4%) for MWSS, while moderate (5.1% ± 3.2% ~ 9.2% ± 4.1%) for other WSS metrics. Statistical analyses revealed that the cycle-to-cycle variability of flow velocity waveform (var-V) and the planarity of internal carotid artery correlated strongly with the periodic flow assumption-induced underestimations of WSS metrics. These findings suggest that taking the non-periodic characteristic of blood flow into consideration could be important for studying hemodynamics in arteries with a large var-V or specific morphological characteristics, especially when WSSTG is the main hemodynamic parameter of concern.

OBJECTIVE The pathophysiology of right ventricular outflow tract obstruction (RVOTO) in twin-to-twin transfusion syndrome (TTTS) recipients is incompletely understood. We aimed to investigate the development and spectrum of RVOTO in TTTS recipients. METHODS A prospective longitudinal cohort study was conducted between 2015 and 2017. Echocardiographic assessment was performed in recipients from TTTS diagnosis until the neonatal period. RESULTS Prenatal RVOTO, defined as abnormal flow velocity waveforms across the pulmonary valve (PV), was diagnosed in 12.9% (16/124) of recipients at TTTS diagnosis. Postnatal RVOTO was found in 6.7% (7/105) of surviving recipients. All recipients with severe postnatal RVOTO showed prenatal RVOTO at TTTS diagnosis. In 5.6% (6/108) of cases, prenatal RVOTO appeared only after laser therapy, and in 1.9% (2/108), this progressed to mild postnatal pulmonary stenosis. Elevated peak systolic PV velocities were more frequently associated with postnatal RVOTO compared with prenatal finding of functional pulmonary atresia. Postnatal RVOTO was associated with early manifestation of TTTS but was equally found in all Quintero stages. CONCLUSION In the spectrum of postnatal RVOTO, severe cases show prenatal RVOTO at TTTS diagnosis. However, RVOTO can develop after laser or even in the neonatal period and in all Quintero stages. A potential risk factor for postnatal RVOTO is early TTTS manifestation.

To compare the uterine artery pulsatility index (UtAPI-AP) before labor and immediate postpartum (UtAPI-PP) in hypertensive disorders of pregnancy (HTNP) and normotensives near term.Pregnancies ≥36 weeks admitted for labor induction in our institution from October 2015 to October 2017 were included. We excluded active labor, multiple gestations, fetal demise, and those with inadequate uterine artery sampling. Our primary outcome was to compare the UtAPI-AP and UtAPI-PP between subjects with HTNP (gestational hypertension, preeclampsia with and without severe features) and normotensive participants. Our secondary outcomes were to compare the UtAPI-AP and UtAPI-PP by subgroups (severe HNTP, non-severe HTNP, and controls) and the UtAPI-PP in participants while on MgSOWe included 108 women (HTNP = 71; controls = 37). The UtAPI-AP was higher in the HTNP group (.85 ± .3 vs. .71 ± .2; P .001); however, the UtAPI-PP was not different between groups (1.11 ± .3 vs. 1.16 ± .4; P = .46). The UtAPI-AP was higher in the severe HTNP group than controls (P = .004), but there was no significant difference in the UtAPI-PP between subgroups. Our results remained unchanged after adjusting for confounders. The UtAPI while on MgSOThe increased UtAPI in patients with HTNP resolves soon after delivery. MgSO

Purpose: To assess the subendometrial and uterine artery blood flow and pattern of the waveform of the uterine artery in cases of recurrent pregnancy loss compared with normal controls.Subjects and...

Objectives To investigate time-interval variables of ductus venosus (DV) flow velocity waveforms (FVWs) in twin-to-twin transfusion syndrome (TTTS), comparing the results with reference ranges from normal singleton fetuses. The impact of laser surgery and the effect of prognostic factors were also evaluated. Methods In 107 TTTS cases, DV-FVWs of both recipients and donors were recorded 1 day before and 2 days after laser therapy. Time intervals for systolic (S) and early diastolic (D) peaks were analyzed retrospectively with regard to acceleration time (acc-S and acc-D for S and D, respectively) and deceleration time (dec-S and dec-D for S and D, respectively). For each variable, Z-scores were calculated with respect to previously reported normal reference ranges. Results Z-scores for all variables showed statistically significant differences from those observed previously in normal fetuses, with the exception of dec-S of donors. The most striking differences were observed in longer dec-S of recipients (P

Objective The aim of this study was to verify the hypothesis that a difference in thymic size exists between small for gestational age (SGA) fetuses, likely constitutional, and intrauterine growth restricted (IUGR) fetuses because of placental causes. Methods We studied 27 SGA and 36 control fetuses. SGA was defined as fetal abdominal circumference (AC) and birthweight

Doppler velocimetry has recently become an informative procedure for the real-time and noninvasive evaluation in fetal hemodynamics. The analysis of flow velocity waveforms in various kinds of vessels has been made for not only clarifying fetal physiology and pathophysiology of various disorders but also for determining the most appropriate intervention from the viewpoint of the integrated management protocol. The unique change in both the arterial and venous flow in normal and compromised fetuses has been demonstrated. Clinical applications of the Doppler technique in monitoring the fetus are reviewed.

The relationship between the placental location and the resistance index (RI) of the ascending branch of bilateral uterine arteries was examined with continuous Doppler ultrasonography, in 48 healthy pregnant women in the 37th to 40th week of gestation. When the placental location was central, there was little difference in the RI between the right and left uterine artery (fundus; 0.61 +/- 0.04 versus 0.58 +/- 0.03, NS, body; 0.48 +/- 0.04 versus 0.47 +/- 0.03, NS, and lower segment; 0.28 +/- 0.03 versus 0.30 +/- 0.04, NS). The RI became smaller when the level of placental attachment was lower toward the cervix. In cases where the placental location has shifted to the right or left of the uterine body, the RI on the placental side was smaller than that of the contralateral uterine artery (0.39 +/- 0.04 versus 0.62 +/- 0.03, p less than 0.01). The physiological and clinical significance of these results are discussed in the following report.

Transvaginal colour Doppler Sonography was used to assess circulation in pelvic vessels in a group of 611 non-pregnant and 88 pregnant patients. A 5 MHz transvaginal probe was used to visualize the pelvic anatomy and blood flow. Further analysis was made by pulsed Doppler where flow velocity waveforms were recorded and analysed by calculation of resistance index (RI). In the normal flow pattern, the diastolic flow component was absent or small and the value of RI was greater than 0.50. In the abnormal flow pattern, the large diastolic flow component was evident and the value of RI was less than 0.50. The transvaginal colour Doppler assessment of tumour vascularity can be used for better non-invasive characterisation of adnexal tumour and may be potentially useful as a screening test for ovarian malignancy. Because of its high sensitivity, specificity and accuracy, transvaginal colour Doppler Sonography is the imaging of choice, in diagnostic procedure of early pregnancy failure and ectopic pregnancy. The guidance of a pulsed Doppler beam by colour flow mapping helps to locate areas of the most abundant flow and makes examination more reproducible, faster and easier.

Summary: Doppler studies of the arcuate and umbilical arteries were performed longitudinally commencing at 24 weeks or less, in 29 pregnant women with chronic hypertension. The hypothesis was that pregnant women with chronic hypertension who develop superimposed gestational proteinuric hypertension and/or deliver small for gestational age babies are those who have abnormal arcuate and/or umbilical flow velocity waveforms. Abnormal arcuate waveforms occurred in 7 women and abnormal umbilical waveforms in 12. Nine babies were small for gestational age, and 6 of them had abnormal arcuate waveforms. Abnormal arcuate waveforms were significantly associated with the delivery of a small for gestational age baby (p = .001) and identified those babies where early delivery was necessary for fetal reasons. All small for gestational age babies had abnormal umbilical waveforms. Superadded gestational proteinuria (or preeclampsia) occurred in 8 pregnancies, however only 3 had abnormal arcuate waveforms. An abnormal arcuate waveform did not predict the later development of gestational proteinuria. An abnormal umbilical waveform however, was associated with the subsequent development of gestational proteinuria. We consider that these findings need to be confirmed in a larger study.

Objectives To analyze the interobserver reliability of measurement of the middle cerebral artery (MCA) pulsatility index (PI) at two different sampling sites. Methods This study included 100 consecutive singleton pregnancies between 24 and 40 weeks with normal fetal growth. The PI was calculated by two independent operators at proximal and distal sampling sites of the near-field MCA. Reliability analyses were performed between observers at each sampling site by means of the intraclass correlation coefficient (ICC) for agreement. Differences between observers were explored and agreement limits calculated by means of the Bland–Altman test. Results Satisfactory flow velocity waveforms were obtained successfully in each fetus at both sampling sites. Peak systolic, end-diastolic and time-averaged maximum velocities were significantly higher at the proximal compared with the distal sampling site. Conversely, PI was significantly higher at the distal compared with the proximal site. ICCs for PI were 0.3 and 0.33 at the proximal and the distal sampling sites, respectively. The 95% interval of the PI differences between observers were + 0.91 and − 1.14 at the proximal and + 1.03 and − 1.08 at the distal sampling sites. In about 30% of the cases the PI difference between observers was greater than 0.5 at both sampling sites. Conclusions Moderate interobserver reliability in the measurement of end-diastolic and time-averaged maximum MCA flow velocities results in limited agreement of the PI calculation at both proximal and distal sampling sites. These results may preclude its clinical applicability. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.

Objectives: It has been previously shown that glucocorticoids alter umbilical artery flow velocity waveforms in singleton pregnancies complicated by umbilical artery absent end diastolic flow. Whether similar effects are evident in multiple pregnancies where one fetus has umbilical artery absent end diastolic flow is not known. Methods: Women with a twin or triplet pregnancy complicated by umbilical artery absent end diastolic flow in one fetus were admitted to hospital for intensive fetal surveillance including daily umbilical artery flow velocity waveform studies, as per hospital protocol. All women received prophylactic betamethasone (11.4 mg × 2, 24 h apart) in anticipation of preterm delivery. Results: Between October 1996 and February 2002, 24 women with a multiple pregnancy complicated by umbilical artery absent end diastolic flow were cared for. Of these, six had a pregnancy with feto-fetal transfusion and excluded from further analysis. Of the remaining 18 women, eight had monochorionic diamniotic twins, eight had dichorionic twins, and two had trichorionic, triamniotic triplets. The median (range) gestation at diagnosis of umbilical artery absent end diastolic flow was 210.5 days (173–241). In nine (50%) of the 18 pregnancies the administration of betamethasone was associated with return of umbilical artery end diastolic flow for a median of 5 days. There was no association between this effect and chorionicity. The median (range) interval from diagnosis of umbilical artery absent end diastolic flow to delivery was 11 days (1–46). Conclusions: As previously reported in singleton pregnancies, the maternal administration of betamethasone in multiple pregnancies with umbilical artery absent end diastolic flow is associated with a transient return of end diastolic flow.

OBJECTIVE: Reverse end-diastolic flow is the most pathological type of the umbilical artery flow velocity waveform. We aimed to investigate whether additional prognostic information can be obtained from umbilical artery waveforms in cases with reverse end-diastolic flow. SUBJECTS AND METHODS: Umbilical artery Doppler velocity waveforms from 44 fetuses with reverse end-diastolic flow were analyzed and the following parameters measured: the highest amplitude and the area below the maximum velocity curve of forward and reverse flow (A, B and C, D, respectively) and the duration of forward and reverse flow (Tc and Td, respectively). Ratios A/B, C/D and Tc/Td were calculated. The cut-off values for A/B, C/D and Tc/Td with the best predictive values for perinatal death were established with the help of receiver operating characteristics curves. The three curves were compared with each other. RESULTS: Of the three ratios, A/B and C/D had the best capacity to predict perinatal death. Both ratios had acceptable sensitivities, specificities and positive predictive values. In this regard, A/B and C/D were comparable. The cut-off values for A/B and C/D were 4.3 and 4.52, respectively. Survivors had I significantly higher A/B and C/D ratios than non-survivors (P = 0.0001 and 0.0003, respectively). Significantly more fetuses with A/B or C/D below the established cut-off values had pulsations in the venous system (P < 0.05). In fetuses with a gestational age < =210 gestational days the survival rate was significantly higher in those with A/B or C/D above the cut-off values (P = 0.03 and 0.003, respectively). CONCLUSIONS: The A/B or C/D ratio can be used for quantification of the reverse end-diastolic flow waveforms in the umbilical artery and may offer additional information to the evaluation of fetal condition. (Less)

Doppler velocimetry has recently become a useful procedure for real-time and non-invasive evaluation of fetal hemodynamics. Analysis of flow velocity waveforms in various types of vessels enables not only clarification of the fetal physiology and pathophysiology of various disorders, but also determination of the most appropriate intervention, from the viewpoint of an integrated management protocol. The unique change in both the arterial and venous flow in normal and compromised fetuses has been demonstrated. Herein, we review the dinical applications of the Doppler technique in monitoring the fetus.

The objective was to evaluate the relation of uterine artery Doppler flow pulsatility index (PI) with total uterine volume reduction following bilateral embolisation of uterine fibroids by injection of polyvinyl alcohol particles. Doppler flow velocity was examined before and within 8 days after embolisation (n = 13). Uterine size was assessed by magnetic resonance imaging (MRI) before, and at 3 and 6 months after, the procedure. Mean PI values (mean of right and left side) obtained before embolisation were negatively related to uterine size (r = −0.68, p = 0.010) but not to uterine volume reduction after the procedure. Mean PI values after the procedure were related to the percentage decrease in uterine volume both at 3 (r = 0.74, p = 0.004) and 6 months (p = 0.73, p = 0.005). Doppler ultrasound measures of the uterine arteries may be used to evaluate reduction of uterine size following fibroid embolisation.

The effect of acute exercise on pregnant women in the last trimester of pregnancy and the changes in fetal umbilical artery flow velocity waveforms were studied. One hundred and forty-three healthy pregnant women underwent an acute exercise test. The exercise was performed on an upright bicycle ergometer for 5 minutes, followed by 30 minutes of recovery. The baseline control values of umbilical artery velocity waveforms were compared with those after exercise. The mean exercise intensity achieved was 67.4% (55-90%) of submaximal exercise. Maternal heart rate rose significantly from a mean of 89 (68-120) beats per minute at rest to a mean of 144 (116-200) beats per minute after exercise (P

Color Doppler ultrasound was used transrectally in 6 mares to locate both the left and right Aa. uterinae and to obtain flow velocity waveforms at defined times (Days 0, 5, 10, 15 and 20) during 4 estrous cycles. Blood flow reflected by the resistance index (RI) was determined for both arteries on 120 occasions. As there was no significant difference and a high correlation in the RI values between the left and right arteries (paired Student's t-test, correlation coefficient r > 0.94 ; P 0.05) could be measured. The results suggest that transrectal Color Doppler sonography is a noninvasive method for examining differences in impedance to uterine blood flow between different mares and cycle periods.

OBJECTIVES To assess ductus arteriosus velocity waveforms in the appropriate and small-for-gestational-age (SGA) fetuses. STUDY DESIGN Ductus arteriosus flow velocity waveforms were obtained in 14 normal fetuses in a longitudinal study and in 139 normal fetuses in a cross-sectional study with pulsed and continuous Doppler ultrasonography. Ductus velocity waveforms were also determined in 25 SGA fetuses whose gestational age ranged between 20 and 34 weeks (mean +/- SD: 30 +/- 4.1 weeks). RESULTS Mathematical modeling demonstrated that the peak systolic velocity, lowest diastolic velocity, and mean velocity of the ductus arteriosus increased with advancing gestation in both the longitudinal and cross-sectional study, but considerable individual variability was seen in the longitudinal study. The pulsatility index did not change significantly. The ductal parameters were in the normal range in all the SGA fetuses. CONCLUSIONS The blood velocity of the ductus arteriosus increase with advancing gestation. Our results suggest that Doppler ultrasonographic study of the fetal ductus arteriosus, unlike Doppler study of the umbilical artery or middle cerebral artery, is not useful as an indicator of adverse fetal outcome.

We studied the usefulness of simultaneous evaluation of the Doppler-derived transmitral flow velocity waveform and left ventricular isovolumic relaxation time (IRT) in patients with coronary artery disease (CAD). Subjects consisted of 26 healthy volunteers, 54 patients with prior myocardial infarction (MI), and 27 patients with CAD but without prior MI. IRT was measured as the time from the beginning of the aortic valve closure sound to the onset of transmitral flow. Peak filling velocity during early diastole (E-wave velocity), peak filling velocity during atrial contraction (A-wave velocity), and IRT were compared among the three groups. No significant difference in A-wave velocity was found among these groups. Whereas E-wave velocity was significantly lower and IRT was significantly longer in patients with CAD but without prior MI than in healthy subjects, no significant differences in E-wave velocity or IRT were observed between patients with prior MI and healthy subjects. We then divided the patients with prior MI into two subgroups, one consisting of 45 patients with mean pulmonary capillary wedge pressure (mPCWP)16 mm Hg and the other consisting of 9 patients with mPCWPor = 16 mm Hg. There was no significant difference in A-wave velocity between the two subgroups and healthy subjects. E-wave velocity was significantly lower in patients with MI and lower mPCWP than in healthy subjects, however, no significant difference in E-wave velocity was found between the patients with MI and higher mPCWP and the healthy subjects. On the other hand, IRT was significantly longer in those with lower mPCWP and significantly shorter in those with higher mPCWP than in healthy subjects. In conclusion, normal transmitral flow velocity waveform with short IRT suggests a 'pseudonormal' pattern due to elevated mPCWP in patients with CAD.

EDITORIAL COMMENT: We accepted this paper for publication because it presents data on the use of colour Doppler imaging in a screening test in healthy nulliparas to assess whether abnormal pregnancy outcome can be identified. Unexpectedly there were 4 perinatal deaths in this series and table 4 indicates that in the only case in which the perinatal death was potentially avoidable the 24-week uterine Doppler studies were normal. There is mounting evidence that Doppler imaging of uteroplacental circulation is useful in the management of identified high-risk pregnancies but the value of the method as a screening test remains unproven. If larger studies confirm the reliability of this investigation to detect patients who are destined to develop preeclampsia then a possible application of this is identification of women who warrant prophylactic aspirin therapy since recent results show that aspirin therapy is not indicated routinely in nulliparas Summary: The accuracy of raised Resistance Index (RI) and early diastolic notching (EDN) of mid-trimester uterine artery flow velocity waveforms in predicting abnormal pregnancy outcome was assessed in a prospective longitudinal study using colour Doppler imaging at 14, 18, and 24 weeks. In 106 healthy nulliparas with a singleton pregnancy studied; 70 had a normal pregnancy outcome, 34 had an abnormal pregnancy outcome, and 2 were lost to follow-up. EDN was more sensitive than raised RI at predicting subsequent abnormal pregnancy outcome but raised RI was more specific at 14 and 18 weeks. Sensitivities were highest for the pregnancies with the more severely abnormal outcomes. Uterine artery Doppler studies in the mid-trimester can predict abnormal pregnancy outcome. The presence of an early diastolic notch is an important feature when defining an abnormal or high resisitance uteroplacental circulation.

To establish the reproducibility of flow velocity waveforms in the human ductus venosus and to assess the influence of fetal behavioural states on these waveforms in normal term fetuses.Reproducibility of Doppler waveform recording and analysis was studied in 10 normal pregnancies. The relation between ductus venosus flow velocities and behavioural states was investigated in 19 other term fetuses. Time-averaged, peak systolic, peak diastolic velocity, peak systolic/diastolic ratio and period time were calculated in both cross sectional studies.Outpatient clinic, department of obstetrics (prenatal diagnosis section), Academic Hospital, Rotterdam--Dijkzigt.Twenty-nine women with normal singleton pregnancies at 36 to 39 weeks of gestation, resulting in uncomplicated births of healthy infants.Within-patient coefficients of variation, ductus venosus waveform recordings were approximately 8 to 10% except for the peak systolic/diastolic ratio (4.3%). A decrease of approximately 30% was established for peak systolic, peak diastolic velocity and time-averaged velocity during behavioural state 1F (quiet sleep) as compared with state 2F (active sleep).Flow velocity waveform recording in the ductus venosus demonstrates acceptable reproducibility. Fetal behavioural state-dependent changes were observed, suggesting a redistribution of umbilical venous blood through the ductus venosus shunt during the quiet sleep state.

Le present article est consacre a deux cas de decollement placentaire a la 29 e et a la 30 e semaine de la grossesse, surveille par Doppler pulse. Le Doppler pulse transvaginal a etabli une onde de vitesse circulatoire anormale de l'artere uterine dans les deux cas. Un foetus presentant une onde de vitesse circulatoire de l'artere ombilicale et de l'artere cerebrale moyenne n'etait pas acidosique mais seulement legerement hydroxique, tandis que l'autre foetus presentant une vitesse circulatoire normale pour l'artere ombilicale mais anormale pour l'artere cerebrale moyenne etait gravement acidosique et hypoxique a la naissance. Il semble que la surveillance au Doppler de la diffusion du sang presente une grande valeur pour le diagnostic rapide de l'asphyxie foetale et que l'onde de vitesse circulatoire utero-placentaire donne une information fiable a partir de laquelle il est possible de diagnostiquer avec surete un decollement placentaire

The aim of this study was to assess the intra- and interobserver variability of second-trimester uteroplacental continuous-wave flow velocity waveforms. The left and right uterine and arcuate resistance indices were measured in women having their routine booking scan at 16–24 weeks' gestation. Four experiments assessed the intra-observer between-frame variability, the intraobserver beat-to-beat variability, the intraobserver temporal variability, and the interobserver variability, using the limits-of-agreement method. The intraobserver between-frame variability was greater than the beat-to-beat variability at three of the four sites. The temporal variability was not significantly different between sites. There were wide interobserver limits of agreement with respect to the reference ranges, although they were greater at arcuate sites than uterine sites. These observations suggest that the reproducibility of the resistance index in continuous wave Doppler uteroplacental flow velocity waveforms is poor, particularly from arcuate sites. The uterine site is preferable and descriptive analysis may be better. Copyright © 1993 International Society of Ultrasound in Obstetrics and Gynecology

Transition of fetal behavioural state IF to 2F coincides with cardiovascular changes measured by Doppler velocimetry e.g. a decrease in pulsatility index (PI) in the internal carotid arteries and in the descending aorta, indicating redistribution of blood flow. Recently, we reported a considerable reduction in fetal urine production rate of 47% during fetal behavioural state 2F as compared to 1F. It was suggested that this reduction is caused by an increase in renal vascular resistance during 2F. Using Doppler ultrasound, flow velocity waveforms (FVW) of fetal renal arteries were recorded during behavioural states 1F and 2F. Fetal behavioural states 1F and 2F were assessed by recording fetal heart rate pattern, eye movements and body movements. The PI of the renal artery FVWs were calculated as an index of renal vascular resistance to blood flow. Fifteen healthy pregnant women between 36 and 40 weeks gestational age were studied and the relationship between fetal renal vascular resistance to blood flow and behavioural states was determined. We found that PI values in the renal arteries did not change relative to behavioural state 1F and 2F. These findings suggest that renal vascular resistance to blood flow is not appreciably different in 1F and 2F. This is in contrast with urine production rate which is almost reduced by half during 2F in the near term fetus.

In 25 pairs of twins delivered by cesarean section, the flow velocity waveform in the umbilical artery was measured and the resistance index calculated. Umbilical artery and vein blood gases were measured at delivery. Results were tabulated by taking the difference in resistance indices between each fetus and plotting these values against the pO2-differences. The data revealed that index differences of more than 10 were of little value in detecting a pO2-difference of > 1 kPa, despite a sensitivity of 100%. The predictive value was only 41%, and specificity 44%. It was obvious, however, that a pO2-difference > 1 kPa occurred only when the resistance index was 76% or more in one fetus and below 76% in the other. The sensitivity of this index parameter was 100%, predictive value 64%, and specificity 78%. In conclusion, the pO2-level in a fetus seems to be unaffected by the impedance in umbilical circulation as long as the resistance index is below 76%. Above this value, there is a significant risk for fetal hypoxaemia.

Aim: To clarify the effects on uterine arterial flow velocity waveforms of uterine contractions following oxytocin infusion and during spontaneous labor. Methods: Uterine arterial flow velocity waveforms were obtained by pulsed Doppler methods from 22 women during an oxytocin challenge test (OCT), 26 women during oxytocin-induced labor, and 40 women during spontaneous labor. Mean resistance index (RI) for bilateral arteries was used for analyses. After the onset of labor, flow velocity waveforms were assessed according to cervical dilatation. During OCT, Doppler flow velocimetry was performed when three uterine contractions occurred per 10-min period. Results: RI values did not differ significantly between induced and spontaneous labor during relaxations at any level of cervical dilatation. However, during contractions, RI was significantly higher for induced labor than for spontaneous labor. Absence or reversal of flow was more frequent in the OCT group than in the induced labor group (P

Transvaginal pulsed color Doppler ultrasound was used to examine 72 patients with a pelvic mass preoperatively. Tumor morphology was assessed, prominent areas of vascularization within the tumor were observed and the pulsatility index and the resistance index of tumor and uterine arteries were measured. Flow velocity waveforms with low pulsatility are considered to reflect neovascularization. The ultrasound diagnoses were compared with histopathological or cytological diagnoses. There were 61 benign, eight malignant and three borderline cases. In 75% of the malignant and 23% of the benign tumors, an intratumoral flow with a low pulsatility was detectable. The mean pulsatility index of tumor blood vessels was 1.2 in benign, 0.7 in malignant and 0.6 in borderline neoplasms. The corresponding mean resistance index values were 0.6, 0.5 and 0.5. The differences were not significant and the overlap between the malignant and benign lesions was large. The pulsatility index and resistance index of uterine arteries were significantly decreased in malignant tumors. The results show that, using a cut-off resistance index value of 0.6, the sensitivity and specificity of color Doppler in the detection of malignant and potentially malignant tumors were 82% and 72%, respectively. However, a practical cut-off level for either pulsatility or resistance indices, that could assist in differentiating between malignant or benign lesions, does not seem to exist. Copyright © 1992 International Society of Ultrasound in Obstetrics and Gynecology

The flow velocity waveform profile in the umbilical artery was measured in 50 pairs of twins during the last week before birth. A significant association was found between high resistance indicies and occurrence of late fetal heart rate decelerations; the higher the resistance, the more frequent the decelerations. Further, the connection between high resistance in the circulation of the umbilical artery and low birth weight was confirmed. Flow velocity measurements in the umbilical artery seem to be a valuable tool in identifying twin fetuses suffering from placental insufficiency.

textabstractMaximum flow velocity waveforms at atrioventricular and outflow tract level were studied cross‐sectionally in 19 human fetuses with conducted and/or blocked supraventricular extrasystoles ranging from 25 to 38 weeks of gestation. At outflow tract level, peak systolic velocity and acceleration time for extrasystolic and post‐extrasystolic beats were compared with those for the immediately preceding normal beat. Regression lines were calculated for peak systolic velocities with filling time. At atrioventricular level, peak‐E wave and peak‐A wave velocities and E/A ratio for the extrasystolic and post‐extrasystolic beats were compared with those for the normal beat. At all levels, time‐averaged velocities were compared with reference charts standardized for gestational age. Peak systolic velocity and acceleration time during the post‐extrasystolic beat were higher than during the normal beat; the Frank‐Starling mechanism, post‐extrasystolic potentiation as well as reduced ventricular afterload may all play a role in this. At all measuring levels, time‐averaged velocity during the extrasystolic beat was strikingly lower than the reference velocities. It is postulated that the increased blood volume and contraction force during the post‐extrasystolic beat cause the valve area to become larger, resulting in a relative decrease in velocities measured by Doppler ultrasound. Copyright

Using a 4-MHz continuous-wave Doppler device, standard rates were established for resistance index (RI) and pulsatility index (PI) of uterine and arcuate arteries of 612 patients with uneventful pregnancies and deliveries. From 18 to 41 weeks of gestation, neither RI nor PI of uterine or arcuate arteries proved to vary with gestational age, maternal heart rate, or maternal age. By contrast, a significant effect of placental location on the measurement results was found in both uterine and arcuate arteries. The differences between measurements on the placental or opposite site are more distinct in arcuate than in uterine arteries. Taking the 90th percentile as a localization gauge, cutoff levels of 0.52 (RI) and 0.98 (PI) were found in uterine arteries. In arcuate arteries, cutoff levels of 0.45 (RI) and 0.82 (PI) were found on the placental site or with a placenta without lateralization. On the nonplacental site of a lateralized placenta, the cutoff levels were 0.51 (RI) and 0.92 (PI).