Volume flow measurement in hemodialysis shunts using time-domain correlation.

Volume flow was measured in 58 hemodialysis shunts (32 grafts and 26 radial fistulas) using the color velocity imaging-quantification method. This method is based on time-domain correlation for velocity calculation and integration of time-varying velocity profiles generated by M-mode sampling. Measurements were made in the brachial artery to estimate radial fistula flow or directly in the grafts. Intraoperator reproducibility was 14.9% for fistulas and 11.6% for grafts. Flow rate was significantly lower in abnormal shunts associated with a functional disorder or a morphologic complication (808 ml/min +/- 484) than in shunts associated with no abnormalities (1401 ml/min +/- 562). Receiver operating characteristic curves showed that a flow rate of 900 ml/min for fistulas and 1300 ml/min for grafts provided 81% and 79% sensitivity and 79% and 67% specificity, respectively. A functional disorder or a morphologic complication was associated with all fistulas and grafts in which flow rates were lower than 500 ml/min and 800 ml/min, respectively.     

Portal venous volume flow: in vivo measurement by time-domain color-velocity imaging.

The portal venous velocity and flow volume in 39 patients (16 with liver cirrhosis, 11 with chronic hepatitis, 12 without liver disease) were measured using both color velocity imaging quantification (CVI-Q) and conventional Doppler flowmetry. The average portal venous velocity and flow volume values obtained using the two methods were similar. The correlation coefficients for the paired measurements show positive correlations (velocity: 0.73, p < 0.0001; volume: 0.50, p = 0.001). However, the coefficients of variation between the two methods were not good (velocity: 14.9%, volume: 26.4%). In conventional Doppler flowmetry, the mean velocity to maximum velocity ratio (Vmean:Vmax) is assumed to be constant (Vmean:Vmax = 0.57 in this study). However, the Vmean:Vmax ratios calculated from the flow profile in CVI-Q were 0.67 +/- 0.13 in the patients with liver cirrhosis, 0.58 +/- 0.13 in the patients with chronic hepatitis, and 0.53 +/- 0.08 in the patients without liver disease. Therefore, a measurement method that takes the blood flow profile into account, such as CVI-Q, might be useful for the quantitative measurement of the portal venous velocity and volume.     

Serial fetal lung volume measurement using three-dimensional ultrasound.

OBJECTIVE: To establish reference intervals for fetal lung growth. DESIGN: Longitudinal observational study. SUBJECTS: Fifty-eight women with initially uncomplicated singleton pregnancies were recruited from the antenatal population of a teaching hospital. Four women were excluded from the final analysis because of complications arising in their pregnancy. METHODS: Each subject was serially scanned at monthly intervals. At each visit lung volume was measured using an ultrasound-based computerized three-dimensional imaging system. Multilevel models were used to determine conditional and unconditional reference intervals. RESULTS: Reference intervals for fetal lung growth were derived. Fetal lung volume increases in a non-linear way with gestation. CONCLUSIONS: Our computerized system has the capacity to be used in conjunction with any standard two-dimensional ultrasound scanner in order to measure volume. Lung volume measurement may be useful in predicting pulmonary hypoplasia.     

Time domain measurement of blood flow in the human fetal aorta during normal pregnancy.

OBJECTIVE: To evaluate blood-volume flow-rate measurement in the fetal descending thoracic aorta using a non-invasive, non-Doppler, ultrasound technique. METHODS: This was a cross-sectional, observational study. Volume flow measurements were obtained from the descending thoracic aorta in 59 human fetuses between 20 and 40 weeks' gestation. These were uncomplicated pregnancies that resulted in the live births of appropriately grown infants. The measurements were obtained using a time domain processing technique: color velocity imaging quantification (CVI-Q). RESULTS: The blood-volume flow rate increased consistently from the second trimester until term. The mean values ranged between 100 mL/min at 20 weeks' gestation and approximately 350 mL/min at term. The normalized (weight-adjusted) volume flow rates decreased with increasing gestation, from a maximum of 626 mL/min/kg at 23 weeks to a minimum of 45.6 mL/min/kg at 37 weeks. CONCLUSIONS: The regular measurement of blood-volume flow in the descending fetal thoracic aorta is feasible using CVI-Q. Although there is a considerable learning curve, with adequate training there are potential clinical applications for this non-Doppler technique. However, limitations exist with the currently available technology for clinical use in fetal vascular studies.     

Blood flow measurement using the attenuation-compensated volume flowmeter

Measurement of blood volume flow using Doppler ultrasound has traditionally required determination of the Doppler angle, vessel size, and shape of the velocity profile. In transcutaneous measurements of blood flow, this problem has been a serious drawback in clinical usage.Volume flow is formally defined as the area integral of fluid flux normal to an arbitrary sample plane. Based on this definition, a pulsed Doppler volume flowmeter has been developed which measures flow normal to a thin uniformly illuminated sample volume. Calibration of the flowmeter is described, and implications for clinical use are discussed.     

Predicting in-hospital mortality. A comparison of severity measurement approaches.

Hospital mortality statistics derived from administrative data may not adjust adequately for patient risk on admission. Using clinical data collected from the medical record, this study compared the ability of six models to predict in-hospital death, including one model based on administrative data (age, sex, and principal and secondary diagnoses), one on admission MedisGroups score, and one on an approximation of the Acute Physiology Score (APS) from the revised Acute Physiology and Chronic Health Evaluation (APACHE II), as well as three empirically derived models. The database from 24 hospitals included 16,855 cases involving five medical conditions, with an overall in-hospital mortality rate of 15.6%. The administrative data model fit least well (R-squared values ranged from 1.9-5.5% across the five conditions). Admission MedisGroups score and the proxy APS score did better, with R-squared values ranging from 4.9% to 25.9%. Two empirical models based on small subsets of explanatory variables performed best (R-squared values ranged from 18.5-29.9%). The preceding models had the same relative performances after cross-validation using split samples. However, the high R-squared values produced by the full empirical models (using 40 or more explanatory variables) were not preserved when they were cross-validated. Most of the predictive clinical findings were general physiologic measures that were similar across conditions; only a fifth of predictors were condition-specific. Therefore, an efficient approach to risk-adjusting in-hospital mortality figures may involve adding a small subset of condition-specific clinical variables to a core group of acute physiologic variables. The best predictive models employ condition-specific weighting of even the generic clinical findings.     

Blood flow in the fetal descending aorta; intrinsic factors affecting fetal blood flow, i.e. fetal breathing movements and cardiac arrhythmia

An ultrasonic method combining real-time ultrasonography and pulsed Doppler technique was used for the examination of blood flow in the fetal descending aorta. The mean aortic blood flow velocity in the last trimester of normal pregnancies was 29.0 cm/s; the peak maximum velocity 97.3 cm/s and the mean blood flow 238.4 ml/min/kg. The blood flow velocity did not change significantly with gestational age, the aorta diameter showed a linear growth. During labour, the aortic blood flow in undistressed fetuses was not different from the flow recorded during late pregnancy. Fetal breathing movements modulate the flow velocity signals in the descending aorta, the inferior vena cava and the umbilical vein of the fetus; therefore, when quantifying fetal blood flow, only periods without fetal breathing movements should be considered. A group of fetuses with various types of cardiac arrhythmias was examined. Postextrasystolic potentiation was found to be present already during intrauterine life. The present method enables quantitative evaluation of the hemodynamic effects of cardiac arrhythmias.     

Three-dimensional sonographic volume measurement of the fetal cerebellum

Purpose The objective of this longitudinal study was to evaluate the growth of the fetal cerebellum in normal pregnancy by using three-dimensional ultrasound. Methods Three-dimensional sonographic examinations were performed for 13 appropriate-for-gestational-age fetuses. Fetal cerebellar volume was measured every 2 to 3 weeks after 20 weeks of gestational age until delivery. The common multiplanar technique was used to calculate the fetal cerebellar volume. Results A curvilinear relationship was found between gestational age and cerebellar volume (R² = 78.6%, P < 0.0001), and normal ranges of cerebellar volume measurements for estimating the growth of the fetal cerebellum during normal pregnancy were generated. The data gathered in this study were fairly comparable with previous data obtained using three-dimensional ultrasound. However, the normal ranges of cerebellar volume that we determined were relatively wide throughout pregnancy. Conclusions Our findings suggest that a standard curve for fetal cerebellar volume using three-dimensional ultrasound can play a role in the evaluation of normal cerebellar growth in the fetus. However, we do cast doubt on the reliability and reproducibility of cerebellar volume measurement using three-dimensional ultrasound. Further studies involving a larger sample size and another technique (the rotational method with VOCAL) would be needed to confirm these findings.     

Three-dimensional sonographic volume measurement of the fetal stomach

The objective of this study was to measure the fetal gastric volume using three-dimensional (3-D) ultrasound during pregnancy. Three-dimensional sonographic examinations were performed involving 35 pregnant women from 12 to 38 weeks of gestation. The fetal gastric volume was monitored every 5 min for a minimum of 40 min (40-60 min) in each woman. The rotational technique with Virtual Organ Computer-aided AnaLysis (VOCAL) was used to calculate the fetal gastric volume. Maximum and minimum gastric volumes were curvilinearly associated with the gestational age, respectively (R(2) = 0.611, p < 0.0001, and R(2) = 0.407, p < 0.0001, respectively). A curvilinear relationship was noted between the functional capacity (maximum volume - minimum volume) of the fetal stomach and gestational age (R(2) = 0.531, p < 0.0001). The maximum volume change [(maximum volume - minimum volume/maximum volume) × 100] did not change during pregnancy (mean and standard deviation, 64.1% ± 16.1%). However, gastric emptying cycles could not be determined in this study because of the short observation period and small number of subjects. Our findings suggest that the fetal gastric volume calculated by conventional two-dimensional ultrasound in previous investigations is approximately one-third of the maximum volume using 3-D ultrasound in the present study and that 3-D ultrasound is a superior means of evaluating the fetal gastric volume in utero. However, the data and their interpretation in the present study should be viewed with some degree of caution because of the small number of subjects. Further studies involving a larger sample size are needed to confirm these findings.     

Prenatal prognosis of congenital diaphragmatic hernia using magnetic resonance imaging measurement of fetal lung volume.

OBJECTIVES: To investigate the correlation between fetal lung volume (FLV), measured with magnetic resonance imaging (MRI), and postnatal mortality in newborns with prenatally diagnosed isolated congenital diaphragmatic hernia (CDH). METHODS: In a 4-year prospective multicenter study, 77 fetuses with isolated CDH diagnosed between 20 and 33 weeks' gestation underwent fast spin-echo T2-weighted lung MRI. These MRI-FLV measurements were compared with a previously published normative curve obtained in 215 fetuses without thoracoabdominal malformations and with normal ultrasound biometric findings. FLV measurements were correlated with postnatal survival. The mean gestational age at MRI was 31.3 weeks. RESULTS: The measured/expected FLV ratio was significantly lower in the newborns with CDH who died compared with those who survived (23.6 +/- 12.2 vs. 36.1 +/- 13.0, P < 0.001). When the ratio was below 25%, there was a significant decrease in postnatal survival (19% vs. 40.3%, P = 0.008). Survival was significantly lower for neonates when one lung could not be seen by fetal MRI compared with those fetuses with two visible lungs on MRI (17.9% vs. 62.1%, P < 0.001). CONCLUSION: In isolated CDH, FLV measurement by MRI is a good predictor of postnatal mortality due to pulmonary hypoplasia.     

Three-dimensional sonographic measurement of fetal renal volume

Objective The objective of this longitudinal study was to evaluate the growth of the fetal kidney in normal pregnancies using three-dimensional ultrasound. Methods Three-dimensional sonographic examinations were performed on 13 appropriate-for-gestational-age fetuses. Fetal renal volume was measured every 2 to 3 weeks after 20 weeks gestational age until delivery. Results There was a good linear correlation between left and right renal volumes (r = 0.9614, P < 0.0001). Curvilinear relationships were found between gestational age and left and right renal volume (left: R² = 79.1%, P < 0.0001; right: R² = 74.2%, P < 0.0001), and normal ranges of left and right renal volume measurements for estimating the growth of the fetal kidney during normal pregnancy were generated. There was a difference for each predicted value of the fetal renal volume in the third trimester of pregnancy in our study and in two other previous studies. The left and right fetal renal volume to estimated fetal weight ratios were constant during the pregnancies studied. Conclusion Our findings suggest that fetal renal volume measurement plays a role in assessment of the growth of fetal kidneys. However, we are doubtful about the reproducibility of fetal renal volume measurements made by using three-dimensional ultrasound in utero. Further studies involving larger sample sizes are needed to reevaluate the usefulness and reproducibility of fetal renal volume measurements.     

胎儿大脑中动脉和腹主动脉血流监测对预测胎儿宫内缺氧的价值

目的评价彩超监测胎儿大脑中动脉(MCA)和腹主动脉(AO)血流指标对预测胎儿宫内缺氧的价值。方法应用彩色超声多普勒技术监测165例晚期妊娠胎儿MCA和AO的收缩期最大流速(S)与舒张末期血流速度(D)的比值(S/D)及阻力指数(RI),根据新生儿Apger’s评分分为正常组和缺氧组,回顾性分析胎儿MCA和AO的血流测值的意义。结果宫内缺氧时AO的S/D值和RI值明显高于正常,而MCA的S/D值和RI值明显低于正常。结论监测胎儿AO和MCA的血流指标对预测胎儿宫内缺氧有重要价值。     

Predicting fetal growth restriction with renal volume using 3-D ultrasound: efficacy evaluation

Early detection and management of fetal growth restriction (FGR) is very important in prenatal care and daily practice, because FGR fetuses may suffer increased risk of perinatal morbidity and mortality. Renal volume (RV) might be one of the important parameters of fetal growth. Yet, no prenatal assessment of fetal RV in FGR fetuses by 3-D ultrasound (US) has been reported. We undertook a prospective and cross-sectional study using quantitative 3-D US to assess the efficacy of fetal RV in predicting FGR. All fetuses were singletons and were followed-up to delivery to determine whether they had FGR complications. In total, 221 fetuses without FGR and 28 fetuses with FGR were included. Our results showed fetal RV assessed by 3-D US can differentiate fetuses with FGR from fetuses without FGR. The best predicting threshold for FGR is at the tenth percentile of fetal RV. Using the tenth percentile as the cutoff, the efficacy of fetal RV in predicting FGR was sensitivity 96.4%, specificity 95.9%, positive predictive value 75.0%, negative predictive value 99.5% and accuracy 96.0%, respectively. Fetal RV assessed by 3-D US can be applied to detect FGR prenatally. We believe fetal RV assessment using 3-D US is a useful test in detecting fetuses with FGR.     

Prediction of fetal anemia in rhesus disease by measurement of fetal middle cerebral artery peak systolic velocity.

OBJECTIVE: In red blood cell (RBC) isoimmunized pregnancies fetal anemia is associated with a hyperdynamic circulation. The aim of the present study was to examine further the possible value of fetal middle cerebral artery peak systolic velocity (MCA-PSV) in the management of affected pregnancies. METHODS: A reference range of fetal MCA-PSV with gestation was constructed from the study of 813 normal singleton pregnancies at 20-40 weeks' gestation. Fetal MCA-PSV was also measured in 58 fetuses from RBC isoimmunized pregnancies, with maternal hemolytic antibody concentration of >15 IU/mL at 19-38 weeks' gestation and within 10 days of measurement of fetal hemoglobin concentration in blood obtained either by cordocentesis (n = 43) or at delivery (n = 15). In the RBC isoimmunized pregnancies each of the measured MCA-PSV and hemoglobin concentrations was expressed as a delta value (difference in SDs from the normal mean for gestation). Regression analysis was used to determine the significance of the association between delta MCA-PSV and delta fetal hemoglobin concentration. RESULTS: In the normal pregnancies there was a significant increase in fetal MCA-PSV with gestation (mean MCA-PSV = 10(0.0223 x GA + 0.963)). In RBC isoimmunized pregnancies the fetal MCA-PSV was increased and there was a significant association between delta MCA-PSV and delta hemoglobin concentration (delta hemoglobin = (delta MCA-PSV + 0.093)/-0.356; R(2) = 0.638, P < 0.0001). An MCA-PSV of mean + 1.5 SDs detected 96% of severely anemic fetuses, with a hemoglobin deficit of at least 6 SDs, for a false-positive rate of 14%. CONCLUSION: Measurement of fetal MCA-PSV is a useful method of assessing fetal anemia. In the clinical management of isoimmunized pregnancies a cut-off in MCA-PSV of mean + 1.5 SDs can identify nearly all severely anemic fetuses with a low false-positive rate.     

Comparison of different reference values of fetal blood flow velocity in the middle cerebral artery for predicting fetal anemia.

OBJECTIVES: To compare different normal reference ranges of fetal blood flow velocity in the middle cerebral artery for predicting fetal anemia. METHODS: Eight reference ranges of either middle cerebral artery peak or time-averaged mean velocities were compared using the area under the receiver-operating characteristics (ROC) curve for 113 fetal blood samples from 60 women at risk of fetal red blood cell alloimmunization. RESULTS: The areas under the ROC curves of the different ranges were not significantly different but there were marked differences in sensitivity (range, 7.14-91.78%) and specificity (range, 31.25-96.88%) with the currently used cut-offs. Except for Mari's range, the best theoretical cut-offs, defined as those having the best sensitivity with the best specificity, differed from those in current use, especially when using time-averaged mean velocity. CONCLUSIONS: Any of the previously reported reference ranges perform well in the non-invasive prediction of fetal anemia. However, with the exception of Mari's curve, the currently employed cut-offs for predicting fetal anemia should be changed, some of them markedly, in order to provide reliable support for clinical decisions.     

Distance and volume measurement using three-dimensional ultrasonography.

The purpose of this study was to assess the accuracy of distance and volume measurements obtained by three-dimensional ultrasonography. A tissue-mimicking phantom was scanned using a prototype three-dimensional sonographic imaging system to verify distance measurements. Measurements were taken from the reconstructed three-dimensional sonographic data and compared to the real distances. Volume measurements were obtained by scanning 30 balloons of various shapes, sized 23 ml to 2400 ml. Each balloon was scanned twice in two orientations; three different masks were accomplished for each volume. Each volume measurement of 180 three-dimensional sonographic measurements was compared to conventional two-dimensional ultrasonographic volume estimates and to the actual, measured balloon size. Distance measurements had a mean error of 0.02 +/- 3.65% (range, -4.27 to 7.18%). Two-dimensional sonographic volume estimates using traditional scanner based methods had a mean error of 13.7 +/- 10.1%. Three-dimensional sonographic volume measurements had a mean error of 2.2 +/- 2.9% for regular and irregular objects over the entire range of volumes. The masking required 10 to 30 min. The field of view varied from 10 to 24 cm with a mean object depth of 9.8 cm. Three-dimensional ultrasonographic methods can provide accurate volume measurements of regular and irregular objects and offer improved accuracy compared to traditional two-dimensional methods.     

Umbilical venous volume flow and fetal behavioral states in the normally developing fetus.

OBJECTIVE: To determine the relationship between umbilical venous (UV) volume flow and fetal behavioral states 1F (quiet sleep) and 2F (active sleep) in normal pregnancies at 36-40 weeks of gestation. METHODS: Fetal behavioral states were established in 17 normal pregnancies by means of combined assessment of fetal heart rate patterns (FHRP), and fetal eye and body movements. UV vessel area (mm(2)) as obtained by tracing the inner vessel area using Labview and Imaq Vision software and UV time-averaged flow velocity (mm/s Doppler) were multiplied to calculate UV volume flow (mL/min) including flow/kg fetus. The pulsatility index (PI) in the umbilical artery was also determined. In each woman, all parameters were measured between three and five times in each behavioral state. Data are reported as mean +/- 1 SD and analyzed by paired t-test. RESULTS: No statistically significant behavioral-state-related changes were observed for UV time-averaged velocity and UV volume flow, resulting in UV volume flow/kg fetus of 69.1 +/- 14.9 mL/min*kg at 1F and 71.6 +/- 12.1 mL/min*kg at 2F (not significant). A statistically significant increase (P = 0.02) was established for UV cross-sectional area (46.4 +/- 8.6 mm(2) vs. 49.0 +/- 10.1 mm(2)) and for fetal heart rate (FHR) from 134.2 +/- 10.3 bpm in 1F to 144.2 +/- 7 bpm in 2F. Umbilical artery PI was not significantly different between the two behavioral states. CONCLUSIONS: On the basis of high venous vessel wall compliance, the significant increase in UV cross-sectional area during fetal behavioral state 2F may be determined by a rise in mean venous pressure. The significant rise in FHR may reflect increased fetal cardiac output during state 2F while the resistance at the hepato-ductal pathway remains relatively constant with the purpose of meeting raised energy demands during the active sleep state. This is further supported by the observed trend towards an increase in UV volume flow.     

Reproducibility of ultrasonic fetal volume blood flow measurements

The intraobserver reproducibility of ultrasonic volume blood flow measurements in the human fetus was evaluated in this study. A new approach, simultaneous measurement of the vessel diameter and the flow velocity with a pulsed-wave Doppler ultrasound synchronized with a real-time ultrasound phase-locked echo-tracking system, was used to estimate volume blood flow (VBF) in the fetal descending aorta. Measurements were performed in a longitudinal study on 20 normally grown fetuses. Intraobserver reproducibility of repeated estimations of mean blood flow velocities throughout gestation was very good, with high values of intraclass correlation coefficient (IntraCC 0·80–0·91) and low values of coefficient of variation (CV 4–11%). The IntraCC of repeated vessel diameter measurements throughout gestation was low (0·30–0·68), whereas the values of CV were acceptable (< 12%), with the exception of the period between 140 and 167 gestational days (CV > 12%). The lower reproducibility of vessel diameter measurement contributed directly to the relatively low reproducibility of VBF estimations overall (IntraCC 0·25–0·70; CV 17–28%), as these are calculated from a formula using both flow velocity and vessel diameter. Nevertheless, the synchronized approach gives absolute values of vessel diameter, flow velocity and VBF comparable with values reported in the human fetus previously. The new method provides, by taking the vessel wall pulsations into consideration and by measuring diameter and velocity simultaneously, a more complete information on fetal haemodynamics and fetal physiology.     

Lack of influence of fetal hemoglobin levels or erythrocyte indices on the severity of sickle cell anemia.

Persons with sickle cell anemia who have elevated fetal hemoglobin or lowered erythrocyte mean corpuscular volume are reputed to have less severe clinical manifestations and a greater probability of survival. This study examines the relationship between seven clinical indicators of morbidity in sickle cell anemia and seven hematological parameters that were collected from 214 patients. Risks of sickle cell crisis, acute chest syndrome, hospital admissions, cerebrovascular accident, aseptic necrosis, meningitis/septicemia, and death were used as indicators of morbidity. The hematological parameters included percent fetal hemoglobin, absolute fetal hemoglobin, percent hemoglobin A2, hemoglobin concentration, packed cell volume, mean corpuscular volume, and mean corpuscular hemoglobin concentration. Statistical analyses of the data showed no relationship between the hematological parameters and six of the seven clinical indicators of the severity of sickle cell anemia. The only significant finding was an increased risk of stroke in those patients with lower levels of fetal hemoglobin. Therefore, with this exception, there is no predictable relationship between morbidity and mortality in sickle cell anemia and levels of fetal hemoglobin or erythrocyte indices. Thus, the general belief that there is an association between severity of sickle cell anemia and the levels of fetal hemoglobin has not been established.