Changes In Flow Velocity Waveforms Research Articles

An In Vivo Data-Based Computational Study on Sitting-Induced Hemodynamic Changes in the External Iliac Artery.

Although sedentary behavior (characterized by prolonged sitting without otherwise being active in daily life) is widely regarded as a risk factor for peripheral artery disease (PAD), underlying biomechanical mechanisms remain insufficiently understood. In this study, geometrical models of ten external iliac arteries were reconstructed based on angiographic data acquired from five healthy young subjects resting in supine and sitting (mimicked by side lying with bent legs) positions, respectively, which were further combined with measured blood flow velocity waveforms in the common iliac arteries (with each body posture being maintained for 30 min) to build computational models for simulating intra-arterial hemodynamics. Morphological analyses showed that the external iliac arteries suffered from evident bending deformation upon the switch of body posture from supine to sitting. Measured blood flow velocity waveforms in the sitting position exhibited a marked decrease in mean flow velocity while increase in retrograde flow ratio compared with those in the supine position. Hemodynamic computations further revealed that sitting significantly altered blood flow patterns in the external iliac arteries, leading to a marked enlargement of atheroprone wall regions exposed to low and oscillatory wall shear stress (WSS), and enhanced multidirectional disturbance of WSS that may further impair endothelial function. In summary, our study demonstrates that prolonged sitting induces atheropromoting hemodynamic changes in the external iliac artery due to the combined effects of vascular bending deformation and changes in flow velocity waveform, which may provide important insights for understanding the involvement of biomechanical factors in sedentary behavior-related PAD.

Hemodynamic Correlates of Late Systolic Flow Velocity Augmentation in the Carotid Artery

Background. The contour of the common carotid artery (CCA) blood flow velocity waveform changes with age; CCA flow velocity increases during late systole, and this may contribute to cerebrovascular disease. Late systolic flow velocity augmentation can be quantified using the flow augmentation index (FAIx). We examined hemodynamic correlates of FAIx to gain insight into determinants of CCA flow patterns. Methods. CCA Doppler ultrasound and wave intensity analysis (WIA) were used to assess regional hemodynamics in 18 young healthy men (age 22 ± 1 years). Forward waves (W 1) and backward waves (negative area, NA) were measured and used to calculate the reflection index (NA/W 1 = RIx). Additional parameters included W 2 which is a forward travelling expansion/decompression wave of myocardial origin that produces suction, CCA single-point pulse wave velocity (PWV) as a measure of arterial stiffness, and CCA pressure augmentation index (AIx). Results. Primary correlates of FAIx included W 2 (r = − 0.52, P < 0.05), logRIx (r = 0.56, P < 0.05), and AIx (r = 0.60, P < 0.05). FAIx was not associated with CCA stiffness (P > 0.05). Conclusions. FAIx is a complex ventricular-vascular coupling parameter that is associated with both increased expansion wave magnitude (increased suction from the left ventricle) and increased pressure from wave reflections.

Stress phase angle depicts differences in coronary artery hemodynamics due to changes in flow and geometry after percutaneous coronary intervention

The effects of changes in flow velocity waveform and arterial geometry before and after percutaneous coronary intervention (PCI) in the right coronary artery (RCA) were investigated using computational fluid dynamics. An RCA from a patient with a stenosis was reconstructed based on multislice computerized tomography images. A nonstenosed model, simulating the same RCA after PCI, was also constructed. The blood flows in the RCA models were simulated using pulsatile flow waveforms acquired with an intravascular ultrasound-Doppler probe in the RCA of a patient undergoing PCI. It was found that differences in the waveforms before and after PCI did not affect the time-averaged wall shear stress and oscillatory shear index, but the phase angle between pressure and wall shear stress on the endothelium, stress phase angle (SPA), differed markedly. The median SPA was -63.9 degrees (range, -204 degrees to -10.0 degrees ) for the pre-PCI state, whereas it was 10.4 degrees (range, -71.1 degrees to 25.4 degrees ) in the post-PCI state, i.e., more asynchronous in the pre-PCI state. SPA has been reported to influence the secretion of vasoactive molecules (e.g., nitric oxide, PGI(2), and endothelin-1), and asynchronous SPA ( approximately -180 degrees ) is proposed to be proatherogenic. Our results suggest that differences in the pulsatile flow waveform may have an important influence on atherogenesis, although associated with only minor changes in the time-averaged wall shear stress and oscillatory shear index. SPA may be a useful indicator in predicting sites prone to atherosclerosis.

Restrained cerebral hyperperfusion in response to superimposed acute hypoxemia in growth-restricted human fetuses with established brain-sparing blood flow

Objective To investigate the cerebral circulatory response to superimposed acute hypoxemia in growth-restricted fetuses with established brain-sparing flow (BSF) during basal conditions. Material and methods 76 term fetuses suspected of growth restriction were exposed to Doppler velocimetry in the umbilical artery (UA) and middle cerebral artery (MCA), and in 38–39 cases also in Galen's vein (GV), straight sinus (SS), and transverse sinus (TS), before and during an oxytocin challenge test (OCT), and simultaneous to electronic fetal heart rate monitoring. Nonparametric statistical analyses compared presence/absence of established BSF (MCA-to-UA pulsatility index [PI] ratio < 1.08) with a two-tailed P < 0.05 considered significant. Results The OCT (positive/negative) was not different in the BSF group (BSFG, N = 16) and the normal flow group (NFG, N = 60) ( P = 0.2). During uterine contractions, the MCA PI decreased in the NFG, but not in the BSFG. De novo GV pulsations and increase of GV maximum flow velocity occurred during contractions in the NFG, but not in the BSFG. Significant SS flow velocity waveform changes were found in neither group and TS flow changes in the BSFG only. Conclusions Fetuses without established brain-sparing flow during basal conditions responded with both arterial and venous brain-sparing flow during acute hypoxemia, whereas in fetuses with established brain-sparing flow the cerebral circulatory responses were absent or equivocal. Fetuses with established brain-sparing flow may have a limited capacity of further cerebral hyperperfusion during superimposed acute hypoxic stress.

Usefulness of a New Grading System Based on Coronary Flow Velocity Pattern in Predicting Outcome in Patients With Acute Myocardial Infarction Having Percutaneous Coronary Intervention

In acute myocardial infarction, the coronary blood flow velocity waveform changes with the damage in the infarcted myocardium. We developed a grading system using the shorter diastolic deceleration time (DDT), appearance of systolic flow reversal (SFR), and disappearance of systolic anterograde flow. We studied 72 patients with a first anterior acute myocardial infarction. Doppler guidewire monitoring and myocardial contrast echocardiography were performed 10 and 15 minutes after percutaneous coronary intervention, and left ventriculography was performed at discharge (24 +/- 2 days) to measure regional wall motion (SD/chord). Patients were classified into 4 groups according to the coronary blood flow velocity pattern: group I (n = 39), DDT >or=600 ms; group II (n = 10), DDT <600 ms; group III (n = 17), DDT <600 ms with SFR; and group IV (n = 14), DDT <600 ms with SFR and without systolic anterograde flow. The no-reflow phenomenon was observed in no patients in group I, in 3 in group II, in 11 in group III, and all 14 patients in group IV. Regional wall motion was highest in group I and decreased with increasing group number (groups I, II, III, and IV, -1.45 +/- 0.80, -2.36 +/- 0.60, -2.90 +/- 0.50, and -3.20 +/- 0.52 SD/chord, respectively). With the progression of damage in the infarcted myocardium, the DDT shortened first, followed by the appearance of SFR, and then the disappearance of systolic anterograde flow. In conclusion, analysis of the coronary blood flow velocity pattern allows assessment of the severity of microvascular dysfunction and prediction of left ventricular functional outcomes.

Changes in fetoplacental vessel flow velocity waveforms following maternal administration of betamethasone.

To determine the timing of the onset of the umbilical artery flow velocity waveform changes following maternal administration of betamethasone in pregnancies complicated by umbilical artery absent end-diastolic flow, and to explore whether these changes are associated with flow velocity waveform changes in other fetoplacental vessels. This was a prospective study of 12 women with pregnancies complicated by umbilical artery absent end-diastolic flow. Flow velocity waveforms were recorded from the umbilical artery, fetal middle cerebral artery, renal artery, aorta and ductus venosus, before and after maternal betamethasone administration, using real-time pulsed wave Doppler. In all 12 pregnancies, the administration of maternal betamethasone was followed by the return of end-diastolic flow within 24 h. End-diastolic flow was first observed at 4 h and was present in all women studied at 8 h. In addition, there was a statistically significant decrease in the pulsatility index in the fetal aorta at 8 h and the middle cerebral artery at 24 h. No change was observed in the ductus venosus or the renal artery flow velocity waveforms. The findings suggest that, in pregnancies complicated by absent end-diastolic flow in the umbilical artery, maternally administered betamethasone induces a return in umbilical artery end-diastolic flow as early as 4 h, along with widespread vasodilatation throughout the fetoplacental vasculature.

Effects of oophorectomy and hormone replacement therapy on the pulsatility indices of hepatic and renal arteries.

To investigate the flow velocity waveform changes of the hepatic and renal arteries in women with surgical menopause who received hormone replacement therapy versus those who did not. Eighty women who had undergone surgical menopause were divided into 2 groups. The first group (n = 38) consisted of patients who did not receive estrogen treatments after surgery; patients in the second group (n = 42) did receive treatments. The hepatic and renal arteries of patients in both groups were examined by duplex Doppler ultrasonography before the commencement of hormone replacement therapy and after 2 years of treatment, and the pulsatility indices were calculated. No significant differences were detected in the renal and hepatic artery pulsatility indices of patients in the estrogen treatment group (group 2) before and after total abdominal hysterectomy and bilateral salpingo-oophorectomy (P > .05). No significant differences in preoperative and postoperative hepatic arterial pulsatility indices were detected among patients in group 1 (P > .05). Renal artery pulsatility indices measured before and after total abdominal hysterectomy and bilateral salpingooophorectomy did show a statistically significant difference in group 1 (P < .001). In addition, a statistically significant difference was detected before and after surgery in both groups when pulsatility indices were measured at the second-year control dose. Hepatic arterial pulsatility indices are not affected in postmenopausal women, but renal artery pulsatility indices rise to some extent in women not receiving hormone replacement therapy.

WS12‐07Fetal venous and arterial circulation in hypoxic IUGR. From adaptation to decompensation

ObjectiveTo evaluate the changes in flow velocity waveforms in the mid‐cerebral artery and in the transverse cerebral sinus in growth restricted fetuses and to correlate these changes between them and with (1) flow velocity waveforms in the ductus venosus and (2) changes in computerized analysis of fetal cardiotocogram.DesignFetuses between 22 and 37 weeks' gestation with an estimated fetal weight below the 5th centile were included in this prospective longitudinal study. Doppler measurements in the umbilical artery, descending aorta, middle cerebral artery, transverse cerebral sinus and ductus venosus were recorded. Fetal heart rate was analyzed by a computer system according to the Dawes‐Redman criteria.ResultsBlood flow within the midcerebral artery and that in the cerebral transverse sinus follow a mirror image distribution. Arterial redistribution is already present when alteration in the venous cerebral circulation develops.We measured a significant correlation between pulsatility index in the transverse cerebral sinus and in the ductus venosus over the study period and at delivery. There was a negative correlation between these indices and short and long‐term variability of the fetal heart rate. There was a parallel increase in pulsatility in the ductus venosus and the transverse cerebral sinus. These changes were inversely correlated with fetal heart rate variability and preceded fetal distress.ConclusionCerebral venous blood flow in IUGR fetuses may be a useful additional investigation to (1) understand better the mechanism of cerebral redistribution in hypoxemic IUGR and (2) to discriminate between fetal adaptation and fetal decompensation in chronic hypoxemia.

Longitudinal changes in the ductus venosus, cerebral transverse sinus and cardiotocogram in fetal growth restriction.

To evaluate the changes in flow velocity waveforms in the transverse cerebral sinus in growth-restricted fetuses and to correlate these changes with (1) flow velocity waveforms in the ductus venosus and (2) changes in computerized analysis of the fetal cardiotocogram. Fetuses between 22 and 37 weeks' gestation with an estimated fetal weight below the fifth centile were included in this prospective longitudinal study. Doppler measurements of the umbilical artery, descending aorta, middle cerebral artery, transverse cerebral sinus and ductus venosus were recorded. Fetal heart rate was analyzed by a computer system according to the Dawes-Redman criteria. We measured a significant correlation between pulsatility index in the cerebral transverse sinus and in the ductus venosus over the study period and at delivery. There was a negative correlation between these indices and short- and long-term variability of the fetal heart rate. There was a parallel increase in pulsatility in the ductus venosus and the transverse cerebral sinus. These changes were inversely correlated with fetal heart rate variability and preceded fetal distress. Cerebral venous blood flow in IUGR fetuses may be a useful additional investigation to discriminate between fetal adaptation and fetal decompensation in chronic hypoxemia.

Absence of flow velocity waveform changes in uterine arteries after bilateral internal iliac artery ligation

A case is reported of bilateral internal iliac artery ligation during cesarean delivery for intractable hemorrhage. Uterine artery Doppler flow velocity waveforms were documented before and after the procedure. After the ligation the uterine arteries could still be visualized in the appropriate anatomic location, and no changes in Doppler flow velocity waveforms were documented.

Monitoring umbilical cord puncture and intravascular transfusions with Doppler ultrasound

Complications of percutaneous umbilical blood samplings and intravascular transfusions can be detected rapidly, easily and efficiently by Doppler ultrasound and therefore the operator can react as early as possible. In addition to real-time sonography Doppler ultrasound allows for assessment of haemodynamical changes due to intravascular transfusions both on the venous and arterial side of umbilical perfusion. Because of immediate recognition of bradycardia and other fetal cardiac frequency alterations as well as increase of resistance to blood flow on the arterial side the operator can react promptly. On the venous side correct application of transfused volume is monitored continuously by changes of flow velocity waveforms during injection and allows to assess dislocation of the needle.

Fetal and neonatal cerebral circulation: a pulsed Doppler study.

We studied the relation between the fetal cerebral circulation and changes in the cerebral circulation directly after birth. With a combined real time ultrasound/pulsed Doppler technique flow velocity waveforms from the fetal umbilical- and carotid-circulation were monitored. Pulsatility Index (PI) was computed and the ratio between Umbilical PI and Carotid PI was calculated. Flow velocity waveforms of the cerebral circulation before birth were related to anterior cerebral artery flow velocity waveforms recorded immediately after birth. The study shows that changes in flow velocity waveforms associated with the intra uterine brain-sparing effect are related to poor obstetrical outcome. Furthermore is shown that the brain-sparing effect in the fetal period is associated with higher PI values in the cerebrovascular circulation in the neonatal period. It is suggested that changes in these PI values, representing changes in cerebrovascular resistance, might be indicative of cerebral ischemia in the neonate.

Changes in flow velocity waveforms in umbilical and uterine artery following haemodialysis. Case report.

Changes in flow velocity waveforms in umbilical and uterine artery following haemodialysis. Case report.

Characteristics of the Umbilical Artery Velocity Waveform as Function of Measurement Site

In 30 uncomplicated singleton pregnancies, varying in duration between 24 and 40 weeks, the variability of the flow velocity waveform (FVW) along the course of the umbilical artery was investigated. Blood flow velocities were recorded at 4 locations in the vessel: within the fetal abdomen, 0-5 cm from the origin of the umbilical cord, in the free-floating part, and 0-5 cm from its insertion in the placenta. From the Doppler signals recorded, the pulsatility index (PI) and a parameter for the frequency distribution index (FDI) were calculated. PI values differed among the locations, but no unequivocal tendency could be demonstrated. Statistical analysis, including multiple regression analysis for maternal and menstrual age and fetal heart rate, showed no significant difference in PI and FDI values for any of the 4 locations. It can be concluded that in uncomplicated pregnancies, possible changes in FVW (quantified by PI) along the course of the umbilical artery have no clinical relevance. Therefore, standardization for the sampling site when measuring PI in this vessel seems to be unnecessary.