Waveform Indices Research Articles

Optimization of Geoscience Laser Altimeter System waveform metrics to support vegetation measurements

The Geoscience Laser Altimeter System (GLAS) has collected over 250 million measurements of vegetation height over forests globally. Accurate vegetation heights can be determined using waveform metrics that include vertical extent and extent of the waveform's trailing and leading edges. All three indices are highly dependent upon the signal strength, background noise and signal-to-noise ratio of the waveform, as the background noise contribution to the waveforms has to be removed before their calculation. Over the last six years, GLAS has collected data during thirteen observation periods using illumination from three different lasers. The power levels of these lasers have changed over time, resulting in variable signal power and noise characteristics. Atmospheric conditions vary continuously, also influencing signal power and noise. To minimize these effects, we optimized a noise coefficient which could be constant or vary according to observation period or noise metric. This parameter is used with the mean and standard deviation of the background noise to determine a noise level threshold that is removed from each waveform. An optimization analysis was used with a global dataset of waveforms that are near-coincident with waveforms from other observation periods; the goal of the optimization was to minimize the difference in vertical extent between spatially overlapping GLAS observations. Optimizations based on absolute difference in height led to situations in which the total extent was minimized as well; further optimizations reduced a normalized difference in height extent. The simplest optimizations were based on a constant value to be applied to all observations; noise coefficients of 2.7, 3.2, 3.4 and 4.0 were determined for datasets consisting of global forests, global vegetation, forest in the legal Amazon basin and boreal forests respectively. Optimizations based on the power level or the signal-to-noise ratio of waveforms best minimized differences in waveform extent, decreasing the percent root mean squared height difference by 25–54% over the constant value approach. Further development of methods to ensure temporal consistency of waveform indices will be necessary to support long-term satellite lidar missions and will result in more accurate and precise estimates of canopy height.

Utero-placental Doppler ultrasound for improving pregnancy outcome

Impaired placentation can cause some of the most important obstetrical complications such as pre-eclampsia and intrauterine growth restriction and has been linked to increased fetal morbidity and mortality. The failure to undergo physiological trophoblastic vascular changes is reflected by the high impedance to the blood flow at the level of the uterine arteries. Doppler ultrasound study of utero-placental blood vessels, using waveform indices or notching, may help to identify the 'at-risk' women in the first and second trimester of pregnancy, such that interventions might be used to reduce maternal and fetal morbidity and/or mortality. To assess the effects on pregnancy outcome, and obstetric practice, of routine utero-placental Doppler ultrasound in first and second trimester of pregnancy in pregnant women at high and low risk of hypertensive complications. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (June 2010) and the reference lists of identified studies. Randomised and quasi-randomised controlled trials of Doppler ultrasound for the investigation of utero-placental vessel waveforms in first and second trimester compared with no Doppler ultrasound. We have excluded studies where uterine vessels have been assessed together with fetal and umbilical vessels. Two authors independently assessed the studies for inclusion, assessed risk of bias and carried out data extraction. We checked data entry. We found two studies involving 4993 participants. The methodological quality of the trials was good. Both studies included women at low risk for hypertensive disorders, with Doppler ultrasound of the uterine arteries performed in the second trimester of pregnancy. In both studies, pathological finding of uterine arteries was followed by low-dose aspirin administration.We identified no difference in short-term maternal and fetal clinical outcomes.We identified no randomised studies assessing the utero-placental vessels in the first trimester or in women at high risk for hypertensive disorders. Present evidence failed to show any benefit to either the baby or the mother when utero-placental Doppler ultrasound was used in the second trimester of pregnancy in women at low risk for hypertensive disorders. Nevertheless, this evidence cannot be considered conclusive with only two studies included. There were no randomised studies in the first trimester, or in women at high risk. More research is needed to investigate whether the use of utero-placental Doppler ultrasound may improve pregnancy outcome.

Establishment of reference ranges for ductus venosus waveform indices in the Japanese population

To establish reference ranges for ductus venosus waveform indices in the Japanese population. In this retrospective cross-sectional study, 791 singleton fetuses of healthy Japanese couples were examined from January 2004 to January 2008. Reference ranges for ductus venosus waveform indices were constructed from cross-sectional data obtained at between 18 and 41weeks of gestation. With a success rate of 84%, a total of 667 measurements in 791 women were eligible for analysis. The median pulsatility index (PI) of fetal ductus venosus decreased from 0.54 at 18weeks of gestation to 0.30 at 41weeks of gestation. The median end-diastolic velocity/peak systolic velocity (a/S) of the ductus venosus increased from 0.56 at 18weeks of gestation to 0.76 at 41weeks of gestation. In this study, we established reference ranges for the PI and a/S of the ductus venosus in the Japanese population, which differed slightly from other published reference data. The results will be useful for further studies to determine the validity of the clinical importance of the ductus venosus for at-risk fetuses.

Word and pseudoword superiority effects reflected in the ERP waveform

A variant of the Reicher-Wheeler task was used to determine when in the event-related potential (ERP) waveform indices of word and pseudoword superiority effects might be present, and whether ERP measures of superiority effects correlated with standardized behavioral measures of orthographic fluency and single word reading. ERPs were recorded to briefly presented, masked letter strings that included real words (DARK/PARK), pseudowords (DARL/PARL), nonwords (RDKA/RPKA), and letter-in-xs (DXXX, PXXX) stimuli. Participants decided which of two letters occurred at a given position in the string (here, forced-choice alternatives D and P). Behaviorally, both word (more accurate choices for letters in words than in baseline nonwords or letter-in-xs) and pseudoword (more accurate choices for letters in pseudowords than in baseline conditions) superiority effects were observed. Electrophysiologically, effects of orthographic regularity and familiarity were apparent as early as the P150 time window (100-160 ms), an effect of lexicality was observed as early as the N200 time window (160-200 ms), and peak amplitude of the N300 and N400 also differentiated word and pseudoword as compared to baseline stimuli. Further, the size of the P150 and N400 ERP word superiority effects was related to standardized behavioral measures of fluency and reading. Results suggest that orthographic fluency is reflected in both lower-level, sublexical, perceptual processing and higher-level, lexical processing in fluently reading adults.

Waveform of Ophthalmic Artery Doppler Flow Predicts the Severity of Systemic Atherosclerosis

Doppler imaging of ophthalmic artery (OA), the first major branch of the internal carotid artery, provides anatomical advantages due to the vertical angle to the body surface and absence of ultrasonic obstacles. It was hypothesized that the Doppler waveform indices of OA correlate with severity of systemic atherosclerosis. The study subjects were 180 patients who underwent cardiac catheterization and OA Doppler imaging (90 patients with coronary artery disease (CAD) and 90 control patients). The ratio of stroke volume to pulse pressure, an index of arterial compliance, was closely associated with the ratio of systolic to diastolic mean velocity (Sm/Dm) in OA. The level of Sm/Dm increased in proportion with the increase in number of stenosed coronary arteries (0-vessel disease 2.1+/-0.3, 1-vessel disease 2.3+/-0.3, multi-vessel disease 2.6+/-0.5, P<0.0001). The Sm/Dm level in OA correlated positively with age, pulse pressure, pulse wave velocity, resistive index and pulsatility index in OA. The best Sm/Dm cut-off to predict CAD was 2.3, and patients with Sm/Dm >2.3 had 8.0-fold risk for CAD. The waveform indices of OA are clinically useful for evaluating the severity of CAD and may help explain the missing link between OA circulation and systemic arterial compliance.

The Use of End-Tidal Capnography to Monitor Non-Intubated Patients Presenting with Acute Exacerbation of Asthma in the Emergency Department

Study Objective To determine if the slope of Phase II and Phase III, and the alpha angle of the expiratory capnographic waveform, as measured via computer-recognizable algorithms, can reflect changes in bronchospasm in acute asthmatic non-intubated patients presenting to the emergency department (ED). Methods In this prospective study carried out in a university hospital ED, 30 patients with acute asthma were monitored with clinical severity scoring and peak flow measurements, and then had a nasal cannula attached for sidestream sampling of expired carbon dioxide. The capnographic waveform was recorded onto a personal computer card for analysis. The patients were treated according to departmental protocols. After treatment, when they had improved enough for discharge, a second set of results was obtained for capnographic waveform recording. The pre-treatment and post-treatment results were then compared with paired-samples t-test analysis. Results On the capnographic waveform pre- and post-treatment, there was a significant difference in the slope of Phase III ( p < 0.001) and alpha angle ( p < 0.001), but not in the Phase II slope ( p = 0.35). There was significant change in peak flow meter reading, but it was poorly correlated with all the capnographic indices. Conclusion The study provides some preliminary data showing that capnographic waveform indices can indicate improvement in airway diameter in acute asthmatics in the ED. Capnographic waveform analysis presents several advantages in that it is effort-independent, and provides continuous monitoring of normal tidal respiration. With further refined studies, it may serve as a new method of monitoring non-intubated asthmatics in the ED.

Correlations between capnographic waveforms and peak flow meter measurement in emergency department management of asthma

BackgroundThe usual method for initial assessment of an acute asthma attack in the emergency room includes the use of peak flow measurement and clinical parameters. Both methods have their own disadvantages such as poor cooperation/effort from patients (peak flow meter) and lack of objective assessment (clinical parameters). We were looking into other methods for the initial asthma assessment, namely the use of capnography. The normal capnogram has an almost square wave pattern comprising phase 1, slope phase 2, plateau phase 3, phase 4 and angle α (between slopes 2 and 3). The changes in asthma include decrease in slope of phase 2, increase in slope 3 and opening of angle α.AimsOur objective was to compare and assess the correlation between the changes in capnographic indices and peak flow measurement in non-intubated acute asthmatic patients attending the emergency room.MethodsWe carried out a prospective study in a university hospital emergency department (ED). One hundred and twenty eight patients with acute asthma were monitored with peak flow measurements and then had a nasal cannula attached for microstream sampling of expired carbon dioxide. The capnographic waveform was recorded onto a PC card for indices analysis. The patients were treated according to departmental protocols. After treatment, when they were adjudged well for discharge, a second set of results was obtained for peak flow measurements and capnographic waveform recording. The pre-treatment and post-treatment results were then compared with paired samples t-test analysis. Simple and canonical correlations were performed to determine correlations between the assessment methods. A p value of below 0.05 was taken to be significant.ResultsPeak flow measurements showed significant improvements post-treatment (p < 0.001). On the capnographic waveform, there was a significant difference in the slope of phase 3 (p < 0.001) and alpha angle (p < 0.001), but not in phase 2 slope (p = 0.35). Correlation studies done between the assessment methods and indices readings did not show strong correlations either between the measurements or the magnitude of change pre-treatment and post-treatment.ConclusionPeak flow measurements and capnographic waveform indices can indicate improvements in airway diameter in acute asthmatics in the ED. Even though the two assessment methods did not correlate statistically, capnographic waveform analysis presents several advantages in that it is effort independent and provides continuous monitoring of normal tidal respiration. They can be proposed for the monitoring of asthmatics in the ED.

Reproducibility of applanation tonometry acquired pulse waveform indices in heart failure and in atrial fibrillation

Reproducibility of applanation tonometry acquired pulse waveform indices in heart failure and in atrial fibrillation

Pulse Wave Analysis Is a Reproducible Technique for Measuring Central Blood Pressure During Hemodynamic Perturbations Induced by Exercise

Central blood pressure (BP) and markers of wave reflection (augmentation index; AIx) measured by radial tonometry have prognostic value independent from brachial BP. The measurement of the central waveform is increasingly used during altered hemodynamics, including exercise, but reliability of the test has not been reported under changed loading conditions. This study aimed to test the technique's reproducibility during major hemodynamic perturbations induced by exercise. Radial waveforms were recorded (SphygmoCor) in 28 healthy subjects (aged 53 +/- 11 years) at rest, during submaximal exercise (cycling at 50, 60, and 70% of maximal age-predicted heart rate (HR)) and immediately after maximal treadmill exercise on two occasions separated by 9 +/- 5 days. Data were compared between testing days. Waveforms were calibrated with brachial BP measured using a mercury sphygmomanometer. Pulse pressure amplification (PPAmp) was defined as the ratio of brachial to central pulse pressure. There was very good reproducibility between visits at all exercise intensities for all waveform measures, including AIx, central pulse pressure, and PPAmp (intraclass correlations at 50% exercise were 0.93, 0.89, and 0.89, respectively; P < 0.001). The mean difference between tests at this intensity was 0 +/- 4% for AIx, 4 +/- 6 mm Hg for central pulse pressure, and -0.02 +/- 0.09 for PPAmp. There were no significant differences between visits for HR, PPAmp, or AIx at rest or with exercise (P > 0.05 for all). Radial tonometry is a reproducible technique for measurement of central waveform indices during perturbations induced by exercise. It should, therefore, be suitable for use in intervention studies in which hemodynamics are altered.

Echo-Doppler ultrasonographic assessment of resistance and velocity of blood flow in the ductus venosus throughout gestation in fetal lambs

It has been postulated that during fetal hypoxia, the blood flow shunted through the ductus venosus increases and may account for upto 70% of the total umbilical flow. The objectives of the present study were to use ultrasonography to determine the velocities and waveform indices of blood flow in the ductus venosus in the fetal lamb. The ductus venosus of 15 lamb fetuses was evaluated weekly from Days 45 to 143 of gestation (Day 0=day of AI). The Doppler indices measured were: S/D, the systole/diastole ratio; RI, the resistance index; and PI, the pulsatility index. The velocity waveforms studied were: SV, the peak velocity during ventricular systole; D, the peak velocity during ventricular diastole; aV, the lowest forward velocity during atrial contraction; and TAMV, the time-averaged maximum velocity. Doppler indices from Days 52 to 143 were highly correlated: S/D versus PI (r=0.96, P<0.0001), and versus RI (r=0.93, P<0.0001); and PI versus RI (r=0.97, P<0.0001). Velocity indices were also positively correlated: velocity SV versus D (r=0.87, P<0.0001), versus aV (r=0.79, P<0.05), and versus TAMV (r=0.98, P<0.0001); D versus aV (r=0.88, P<0.05), and versus TAMV (r=0.87, P<0.05); and aV versus TAMV (r=0.82, P<0.05). Doppler indices were negatively correlated with SV (r=-0.22, P<0.03); D (r=-0.37, P<0.0001); TAMV (r=-0.32, P<0.05) and with aV (r=-0.67, P<0.05). The mean value of each Doppler index decreased 40% from Days 52 to 73 (e.g., PI from 0.82+/-0.08 to 0.51+/-0.10; P<0.05), with no significant changes thereafter. Mean (+/-S.E.M.) values of velocity indices SV, D, aV, and TAMV rose twofold from Days 60 to 115 of gestation (e.g., SV from 54.4+/-8.8cm/s to 104.9+/-19.7 and aV from 24.8+/-6.9 to 54.9+/-5.9; P<0.05). In conclusion, Doppler ultrasonography facilitated assessment of the blood flow pattern in the ductus venosus in lamb fetuses between Days 52 and 143.

Doppler assessment of uterine artery blood flow for the prediction of pregnancy after assisted reproduction treatment

Doppler assessment of uterine artery blood flow for the prediction of pregnancy after assisted reproduction treatment

18: A Comparison of Capnographic Waveform Indices and Peak Flow Meter in the Monitoring of Asthmatic Patients in Emergency Departments

“Time capnography” is the continuous plot of levels of expired carbon dioxide over time producing a capnographic waveform. It is the analysis of such waveforms that forms the basis of this study. The normal capnogram has an almost square-wave pattern which consists of: 1) a latency phase (Phase I), corresponding to the expiration of the anatomical dead space; 2) slope phase (Phase II) corresponding to expiration of mixed air; and 3) plateau phase (Phase III), reflecting the elimination of alveolar air.

New Transcranial Doppler (TCD) Waveform Shape Parameters: A Repeatability/Reproducibility Study

Introduction and Objective Doppler ultrasound is used in nearly every medical discipline for the evaluation of blood flow. The cerebral circulation is of particular interest, but is difficult to interpret because of the complex hemodynamics of the brain's blood flow. However, advances in the field of transcranial Doppler (TCD) could have important clinical and cost-saving benefits. We describe the testing of a novel method for acquiring and analyzing TCD flow velocity waveforms, in conjunction with other physiologic data. We also evaluate the repeatability and reproducibility of the technique. Methods We used custom-designed waveform analysis software to calculate 16 new waveform shape parameters and indices. We present the repeatability and reproducibility results for the new waveform shape parameters, as well as traditional TCD measurements, during repeated vasomotor reactivity studies on five healthy subjects. A ranked score ( mean value of test 1 and 2/coefficient of repeatability) is used to evaluate each parameter. The scores are presented by category: Traditional TCD Measurements, Velocity Minima, Velocity Maxima, Acceleration/Deceleration, Miscellaneous measures (e.g. blood pressure, heart rate), Time Measurements, and Shape Indices. Higher scores indicate better reproducibility. Results The mean scores of all parameters for each testing segment were Baseline 4.60, Hypercapnia 4.34, and Hypocapnia 4.00; showing that Baseline measurements are more easily reproduced than measurements during an intervention, particularly Hypocapnia. Individual parameters with the best reproducibility over all three testing segments are: RI (Resistance Index) 19.02; Mean Resistance ( mean blood pressure/mean velocity) 10.64; Umin (end-diastolic velocity) 9.84; Umaxdias (velocity rise immediately after aortic valve closure) 9.83; and DuDtmax (systolic acceleration) 8.54. We discuss why some parameters are more reliable than others in TCD studies and how the cyclical variations in the cerebral circulation can affect reproducibility. Conclusions This new methodology allows for discrete measurements of Doppler waveforms and would have the ability to track subtle changes during physiological or pharmacological interventions. These advances may aid the interpretation of complex cerebral hemodynamics, and increase the utility of this non-invasive, low-cost technique.

The relationship between fetal inferior vena cava diameter pulse and flow velocity waveforms in normal and compromised pregnancies

Background The circulation is characteristically assessed by pressure and flow. Objective: To evaluate the hemodynamic significance of fetal inferior vena cava (IVC) flow velocity waveform (FVW) indices in relation to the diameter pulse waveform (DPW). Study design Doppler ultrasound and a phase locked loop echo tracking system were used to measure the FVW and the DPW in the fetal IVC, respectively. Subjects We studied 98 normal fetuses (20 to 40 weeks) and 65 compromised fetuses with increased umbilical placental resistance. Results The DPW consisted of four waves (A, X, V, and Y waves). Three components (systolic flow; S, diastolic flow; D, reverse flow; R during atrial contraction) were identified in the FVW. The FVW indices were examined in relation to the X descent {(A − X) / A%} of the DPW. The compromised group was divided into three subgroups by the X descent. In 15 fetuses the waveform was normal. In 32 there was a high pulsatile pattern with deep descent form the A crest to X trough. In 18 the X descent was shallow and the pulsatility appeared reduced. The high and low pulsatile patterns were associated with an increase in the S/D ratio and the R/S ratio, respectively. Conclusion In fetal compromise the high pulsatility DPW may result from increased end-diastolic pressure in response to the increase in ventricular afterload caused by the placental vessel obliteration. The S/D ratio of the FVW may reflect the increasing cardiac afterload. The low pulsatility DPW may indicate depressed myocardial function and output. In the FVW, the R/S ratio may be associated with this.

Doppler waveform indices of the Middle Cerebral Artery of normal fetuses in the first half of pregnancy in the Thai population

To establish the reference ranges of middle cerebral artery (MCA) Doppler indices including pulsatility index (PI), resistance index (RI) and peak systolic velocity (PSV) of the Thai fetuses at gestational age of 11-20 weeks. A descriptive cross-sectional study was conducted at Department of Obstetrics and Gynecology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. Normal singleton pregnancies between 11 and 20 weeks of gestation were recruited into the study for measurements of MCA Doppler indices between November 2005 and August 2006. The trans-abdominal ultrasound, Aloka Model Prosound 5000 (Tokyo) was used. The MCA Doppler data were analyzed for median, 5th, and 95th percentile for each gestational week. The best-fit mathematical model was derived. A total of 300 measurements, with average of 30 +/- 7.35 per gestational week (mean +/- SD) and range 23-45 per gestational week, were obtained from 149 patients. Regression analysis yielded the best-fitted equation of quadratic function as follows: PI = 8.421 - 0.705(GA) + 0.018(GA(2)) (r (2) = 0.452), RI = 1.54 - 0.073(GA) + 0.002(GA(2)) (r (2) = 0.309), PSV = -63.456 + 9.425(GA) - 0.262(GA(2)) (r (2) = 0.504). A nomogram for MCA Doppler indices, including PI, RI and PSV ratio for each gestational age during 11-20 weeks was constructed. This may be a useful aid in the early detection of abnormalities in fetal cerebral blood flow, especially in fetal anemia secondary to hemoglobin Bart's disease.

Ductus venosus Doppler measurement during labor

To assess ductus venosus (DV) indices during the first stage of labor and the effect of ruptured membranes, meconium stained liquor and epidural analgesia (EDA). Prospective cross-sectional study. Eighty-one women with low-risk singleton term pregnancies participated, 51 had normal labor (Group 1), and 30 experienced ruptured membranes and/or stained liquor (Group 2). Of the latter group 14 received EDA. The effect of various interventions and application of EDA on the ductus venosus index (DVI) and pulsatility index for veins (DV PIV) were tested. The feasibility rate was 94%. A significant increase of DV indices (DVI, DV PIV) was found in group 2 (P<0.001 and P<0.0005, respectively). The A-velocity was also significantly lower in group 2 (P<0.02). A markedly significant increase of DV indices (P<0.0001) among participants receiving EDA was observed in group 2. The mean+/-SD indices were: 0.53+/-0.10 for the DVI and 0.68+/-0.14 for the DV PIV in those women. There was a significant positive correlation of DV indices with the duration of amniorrhea in group 2 (PIV: r=0.66; P<0.002; DVI: r=0.68; P<0.001). Long-term amniorrhea seems to affect the fetal venous circulation reflected in increased DV waveform indices.

Longitudinal reference ranges for ductus venosus flow velocities and waveform indices

Serial Doppler measurements of the ductus venosus are used increasingly for monitoring fetuses at risk of hemodynamic compromise, but existing reference ranges are based on cross-sectional studies and thus are less suitable for comparison with serial measurements. We aimed to establish longitudinal reference ranges for ductus venosus flow velocities and waveform indices and to provide the necessary terms for calculating conditional reference ranges for serial measurements. This was a longitudinal study of 160 low-risk pregnancies. Pulsed Doppler ultrasound was used to record ductus venosus blood flow velocities at 4-week intervals from 20-22 weeks of gestation onwards. With a success rate of 93%, 547 measurements (four or five in each fetus) were used to establish reference ranges. The time-averaged maximum velocity was 50 cm/s at 21 weeks of gestation, increased to 60 cm/s at 32 weeks, and remained so until term. Similarly, the peak systolic velocity increased from 59 cm/s at 21 weeks to 71 cm/s at 31 weeks and remained so until term. The end-diastolic velocity showed a continuous increase from 31 cm/s at 21 weeks to 43 cm/s at 40 weeks. The pulsatility index for veins decreased from 0.57 at 21 weeks to 0.44 at 40 weeks. When conditioned by a previous measurement, the reference ranges for the next observation became narrower and commonly shifted compared with those of the entire population. The new longitudinal reference ranges presented here reflect the development of the ductus venosus flow velocities and velocity indices and are thus appropriate for serial measurements, particularly if conditional terms are included.

2363: Reference ranges of flow velocity and calculated waveform indices in ductus venosus after 20 weeks of pregnancy in Korean women

2363: Reference ranges of flow velocity and calculated waveform indices in ductus venosus after 20 weeks of pregnancy in Korean women

Betamethasone effects on ovine uterine and umbilical placental perfusion at the dose used to enhance fetal lung maturation

The purpose of this study was to examine glucocorticoid effects on umbilical placental perfusion. Pregnant sheep instrumented with uterine and umbilical ultrasound transit-time flow probes received 2 doses of 12 mg betamethasone (n = 6) or saline (n = 5) intramuscularly 24 hours apart. Maternal blood pressure and uterine flow did not change during glucocorticoid exposure. Fetal blood pressure increased, and umbilical resistance showed a transient increase after each injection (P < .05), followed by an increase of umbilical flow (P < .05) that was closely correlated to an increase in fetal heart rate (r = 0.85, P < .001), which determines cardiac output of the developing heart. Umbilical waveform indices were decreased over the entire treatment period, indicating a decrease of resistance in the fetoplacental microcirculation (P < .05). Fetoplacental perfusion during glucocorticoid exposure is not limiting for nutrition exchange. Clinical interpretation of Doppler waveform indices needs to be interpreted with caution because they do not reflect dynamics of umbilical placental perfusion.

Inferior vena cava diameter pulse waveforms in the human fetus: relationship with flow velocity waveform

Our purpose was to evaluate the hemodynamic significance of fetal inferior vena cava (IVC) flow velocity waveform indices during fetal development in relation to the diameter pulse waveform. Doppler ultrasound and a phase locked loop echo tracking system were used to measure flow velocity waveform and diameter pulse waveform, respectively. Twenty-seven normal singleton pregnancies were examined from 20 weeks until term at 4-week intervals. The diameter pulse waveform consisted of four waves (A, X, V, and Y waves). The A value (end-diastolic diameter) was associated with the end-diastolic pressure, which causes reverse flow during right atrial contraction. In normal fetuses, a weight-related lower end-diastolic diameter suggested that the end-diastolic pressure was decreased. Except for a positive correlation between the percent reverse flow during atrial contraction and the A value per unit fetal weight, no correlations were found between diameter waveform indices and blood flow velocity waveform indices. The peak velocity index of the velocity waveform significantly correlated with the umbilical artery flow velocity waveform systolic/diastolic ratio. The fetal IVC velocity waveform indices did not yield unequivocal information as to changes in central venous pressure, for which purpose the diameter pulse waveform analysis would seem to be the only available method.