Mean Blood Velocity Research Articles

Middle cerebral artery flow velocity waveforms in fetal hypoxaemia

In 81 small-for-gestational age fetuses (SGA) colour flow imaging was used to identify the fetal middle cerebral artery for subsequent pulsed Doppler studies. Impedence to flow (pulsatility index; PI) was significantly lower, and mean blood velocity was significantly higher, than the respective reference ranges with gestation. Fetal blood sampling by cordocentesis was performed in all SGA fetuses and a significant quadratic relation was found between fetal hypoxaemia and the degree of reduction in the PI of FVWs from the fetal middle cerebral artery. Thus, maximum reduction in PI is reached when the fetal PO2 is 2-4 SD below the normal mean for gestation. When the oxygen deficit is greater there is a tendency for the PI to rise, and this presumably reflects the development of brain oedema.

Vascular effects of intravenous infusion of the angiotensin converting enzyme inhibitor perindoprilat

This study was aimed at evaluating the hemodynamic changes after acute inhibition of the renin-angiotensin system in hypertensive patients. Twenty-one subjects with essential hypertension were randomized into three groups of seven subjects each. In group I, the direct vascular vasodilator dihydralazine was administered at a dose of 4 micrograms/kg per min. Groups II and III received a continuous intravenous infusion of the angiotensin converting enzyme (ACE) inhibitor perindoprilat at a dose of 1 microgram/kg per min and 2.5 micrograms/kg per min, respectively. Brachial artery hemodynamics and aortic distensibility were evaluated non-invasively. Vascular reactivity was evaluated by the cold-pressor test. In all three groups, an identical decrease in blood pressure was observed (P less than 0.001), followed by a slight (but not significant) decrease in the heart rate in both perindoprilat groups, and an important tachycardia in the dihydralazine group (P less than 0.001). Brachial artery diameter was increased in the high-dose perindoprilate group from 0.437 +/- 0.014 to 0.479 +/- 0.013 cm (P less than 0.02), but remained unchanged in the two other groups. No significant changes in brachial artery mean blood velocity and blood flow were observed. In group III, aortic distensibility increased almost twice as much as in the two other groups, but this difference was not statistically significant. The pressor response to the cold-pressor test was not modified in the three groups; the heart rate response was almost completely abolished in groups II and III, but increased in the dihydralazine group (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of Fetal Anemia by Measurement of the Mean Blood Velocity in the Fetal Aorta

Prediction of Fetal Anemia by Measurement of the Mean Blood Velocity in the Fetal Aorta

Doppler examination of the middle cerebral artery in anemic fetuses

In 24 red cell isoimmunized pregnancies the fetal middle cerebral artery mean blood velocity increased with anemia. The blood velocity was not related to fetal blood PO2 and the relation of increased velocity to anemia was not affected by the pulsatility index. These findings suggest that the hyperdynamic circulation is a consequence of decreased blood viscosity.

Effect of beta adrenoceptors and thyroid hormones on velocity and acceleration of peripheral arterial flow in hyperthyroidism

Brachial artery flow patterns were studied in 10 hyperthyroid and 10 normal subjects. Mean blood velocity and flow were evaluated by pulsed Doppler, and peak systolic acceleration was calculated by computer-assisted digitization of the instantaneous velocity curve. Compared to control subjects, hyperthyroid patients had higher velocity and flow (p < 0.01, p < 0.02) and higher peak systolic acceleration (p < 0.01). In hyperthyroid patients, measurements were repeated after (1) mechanical exclusion of the hand from brachial circulation, (2) short-term β-blocker treatment and (3) inducement of the euthyroid state. Exclusion of the hand reduced velocity and flow (p < 0.001) but did not change peak systolic acceleration. Beta blockade induced disparate changes of velocity and flow but reduced peak systolic acceleration (p < 0.05). In the euthyroid state, decreased blood velocity (p < 0.01), flow (p < 0.02) and acceleration (p < 0.02) were observed. A hyperkinetic arterial circulation consisting of an increase in both velocity and acceleration is thus observable in hyperthyroidism. Hand exclusion showed that velocity seems to be influenced by peripheral factors while β blockade suggests that acceleration is dependent of β 1 adrenoceptors. Comparison between euthyroidism and hyperthyroidism indicates that both mean blood velocity and peak systolic acceleration are influenced by thyroid hormones.

Transcranial Doppler ultrasonographic changes after treatment for arteriovenous malformations.

We performed transcranial Doppler ultrasonography on 15 patients with arteriovenous malformations before and after embolization or surgical resection to compare quantitatively the hemodynamic effects of these two treatments. Changes in mean blood velocity and pulsatility index were analyzed in 19 treated feeding arteries. Blood velocity decreased by a mean of 38.1% or 46.5 cm/sec (p less than 0.0001, two-tailed paired t test); decreases were greater for surgically resected arteries (46.2% or 55.9 cm/sec, p less than 0.003) than for embolized arteries (30.8% or 38.0 cm/sec, p less than 0.0003). Pulsatility index increased by a mean of 54.7% or 0.25 (p = 0.0001); increases were greater for surgically resected arteries (65.8% or 0.29, p = 0.0045) than for embolized arteries (44.8% or 0.20, p less than 0.001). The differences in the changes in blood velocity and pulsatility index between treatment groups were not significant. These data demonstrate that embolization results in hemodynamic changes that are qualitatively similar to those occurring after surgical resection of arteriovenous malformations. Transcranial Doppler ultrasonography is a reliable and convenient noninvasive method for monitoring hemodynamic effects of treatments for arteriovenous malformations.

めまい患者の椎骨・総頸動脈血流におよぼす循環改善剤の影響

To investigate the effects of drugs for vascular disturbances, the ultrasonic doppler method was used to measure the vertebral and common carotid arterial hemodynamics in patients with vertigo. We used Brovincamine and Moxisylyte to treat cerebrovascular disturbances, and used sodium carbonate (7%) and papaverine as systemic vasodilators. Patients were administered 100 mg of Brovincamine (5 cases),150 mg of Moxisylyte (5cases) 200 mg of papaverine (5 cases) orally, and 50 ml of sodium bicarbonate (5 cases) intravenously. Sixty minutes after administration of Brovincamine or Moxisylyte, mean blood velocity of the vertebral arteries on only the slower side increased, and the difference of blood velocity between the right and left sides decreased.

Prediction of fetal anemia by measurement of the mean blood velocity in the fetal aorta

In 68 red blood cell isoimmunized pregnancies the mean velocity of blood in the fetal aorta was measured by pulsed Doppler ultrasonography, and the fetal hemoglobin concentration was determined in blood samples obtained by cordocentesis. The values were compared to reference ranges of mean aortic velocity and hemoglobin for gestation, which were determined from 218 218 pregnancies that were not complicated by fetal hemolysis. In the red blood cell isoimmunized pregnancies there was a significant positive correlation between the aortic mean velocity and the hemoglobin deficit for the nonhydropic fetuses and a significant negative correlation between these two parameters for the hydropic fetuses.

Anterior cerebral artery velocity changes in disease of the middle cerebral artery stem.

Transcranial Doppler ultrasonography can map the changes in blood velocity that result from stenosis or occlusion of the middle cerebral artery. To evaluate patterns of collateral blood flow in disease of the middle cerebral artery stem, we used both cerebral angiography and transcranial Doppler ultrasonography to study the systolic blood velocities in both anterior cerebral arteries in 10 consecutive patients with middle cerebral artery stenosis or occlusion. Five patients had no evidence of hemodynamically significant carotid disease and good-quality measurements of systolic velocity in each anterior cerebral artery. Two of the five patients had middle cerebral artery stem stenosis and the other three had occlusion. The ratios of mean blood velocity in the normal compared with the abnormal side for the five patients (mean 1.34 +/- 0.23, range 1.15-1.74) were significantly higher than ratios for 10 controls (mean 1.04 +/- 0.12, range 0.76 +/- 1.19) using an unpaired t test (t = 3.492, 0.0005 less than p less than 0.005). Our results suggest that transcranial Doppler ultrasound measurements of anterior cerebral artery blood velocity may be a useful index of collateral blood flow from the anterior cerebral artery territory into the middle cerebral artery territory. Changes in mean velocity ratio may document the evolution and adequacy of collateral blood flow over the cerebral convexity in middle cerebral artery stem disease. In addition, the changes in anterior cerebral artery blood velocity appear to be an important corroborative finding for middle cerebral artery stem occlusion.

Nongeometric Doppler stroke volume determination

Accurate noninvasive measurement of cardiac output is a long-sought goal with obvious advantages. Numerous methods have yielded varying success. Recent Doppler echocardiographic studies have produced promising results. 1,2 These studies depend on geometric measurements, that is, the cross-sectional flow area of a valve or vessel. Stroke volume is then calculated as the product of the mean blood velocity by Doppler (flow velocity integral or “stroke distance”) and orifice area. Although correlations with hemodynamically measured stroke volume and cardiac output have been satisfactory, many limitations are inherent in the requirement for accurate cross-sectional flow area, including (1) changes in the flow area itself with changing cardiac output; (2) inaccurate true orifice measurement because of inaccurate edge detection by M-mode or 2-dimensional echocardiography due to poor resolution, assumption of a circular crosssection or because the functional area may be less than the measured area (seen as a halo around a color flow jet in cross-section); and (3) nonlaminar flow without a flat flow profile at the site of measurement. A method to eliminate the need for geometric measurements when measuring blood velocity at a point where flow is laminar and velocity profile flat would be advantageous. We developed a method with these characteristics and preliminary results are encouraging. We report the initial investigation of this approach. The basis of the nongeometric method is the relation: stroke volume = ejection time × ejection rate (SV = ET × ER). Thus, if the ejection time and ejection rate are known, stroke volume can be calculated. The left ventricular ejection time can be measured with precision from Doppler flow traces. 4 The ejection rate can be determined indirectly—we recently demonstrated the close relation between mean velocity calculated from the Doppler spectral envelope as blood is ejected and the volume ejection rate determined by thermodilution. 5 The latter was calculated from the relation: ejection rate = stroke volume/ejection time (LVER = SV/LVET). Of note, in the validation investigations the ejection time was determined using both the carotid pulse and the Doppler tracing independently. 5 To ensure laminar flow with a flat velocity profile, the Doppler sample volume was placed in the center of the aortic valve orifice. 6 The relation between Doppler-derived mean ejection flow velocity and thermodilution-derived volume ejection rate yielded the following regression equation 5: y = 494x − 66 ml/s, where y is mean left ventricular volume ejection rate in ml/s and x is Doppler mean flow velocity in m/s. Thus, by measuring mean Doppler velocity at the aortic valve orifice, the regression equation yielded the left ventricular ejection rate. 5

The Effects of Brovincamine on the Common Carotid Hemodynamics in Patients with Cerebral Circulatory Insufficiency

This study was performed to clarify the effects of brovincamine on the common carotid hemodynamics in patients with cerebral circulatory insufficiency.A total of 38 patients including 14 males and 24 females were enrolled in this study. Their ages ranged from 55 to 84 years old and the mean age was 72 years old. They were given orally 60mg of brovincamine daily for 6 months. The common carotid hemodynamics by ultrasonic quantitative flow measurement system were evaluated during brovincamine administration.Mean blood flow and mean blood velocity of the common carotid artery significantly increased in 1, 3, and 6 months after therapy. On the other hand, circulatory resistance of the brain significantly decreased in 1, 3, and 6 months after therapy.These results indicate that brovincamine therapy may have beneficial effects on the common carotid hemodynamics in patients with cerebral circulatory insufficiency.

Mean blood velocities and flow impedance in the fetal descending thoracic aorta and common carotid artery in normal pregnancy

A linear array pulsed Doppler duplex scanner was used to establish reference ranges for mean blood velocities and flow impedance (Pulsatility Index = PI) in the descending thoracic aorta and in the common carotid artery from 70 fetuses in normal pregnancies at 17–42 weeks' gestation. The aortic velocity increased with gestation up to 32 weeks, then remained constant until term, when it decreased. In contrast, the velocity in the common carotid artery increased throughout pregnancy. The PI in the aorta remained constant throughout pregnancy, while in the common carotid artery it fell steeply after 32 weeks. These results suggest that with advancing gestation there is a redistribution of the fetal circulation with decreased impedance to flow to the fetal brain, presumably to compensate for the progressive decrease in fetal blood Po 2.

Opposite effects of hypertension and smoking on large artery wall shear conditions.

Wall shear phenomena were studied in the brachial artery in non-smoking and smoking normotensive and hypertensive subjects of similar age. Pulsed Doppler investigation revealed brachial artery diameter, and mean and systolic blood velocities (at the centerline of the vessel). A Poiseuillean blood velocity distribution was used to determine the wall shear rate and stress from velocity, diameter and viscosity. This was expressed in terms of mean and systolic values. Although hypertension and smoking both increased blood viscosity, hypertension reduced mean and systolic shear rates and stresses in non-smokers but not in smokers, and smoking increased mean and systolic shear rates and stresses in hypertensives but not in normotensives. Thus, the decreasing shear effect of hypertension was blunted by smoking, while the increasing shear effect of smoking was elicited by hypertension, suggesting an interaction of these factors on wall shear conditions.

Aortic Blood Flow Measurement

Aortic blood flow (ABF) was measured with a specially designed ultrasonic probe (diameter 6.8 mm, length 50 cm) introduced into the esophagus. The aortic diameter was measured using an A-scan system. Mean blood velocity was obtained with a continuous-wave Doppler velocimeter. The ABF was calculated from these two parameters. The precision of the measurement was assured by the external orientation of the transducers enclosed in a latex water-inflated balloon. A reproducibility study was conducted by a double-blind method. The differences between different operators were less than 5 % in a series of 11 patients. In over 21 patients, 300 comparative measurements with thermodilution showed a correlation coefficient of 0.97. Using this technique the hemodynamic effects of ornithine-vasopressin and etilefrin were compared in two groups of 6 female patients under general anesthesia, during local injection, for conization of the uterine cervix. After injection, systolic blood pressure rose 31 and 29 % (p <0.01) in the ornithine-vasopressin and etilefrin groups, respectively. Heart rate decreased 16 and 10% respectively. ABF decreased 43% under ornithine-vasopressin (p < 0.001), but increased 12% (NS) in the etilefrin group. The difference between the two groups was significant (p < 0.001). The stroke volume into descending aorta fell 40% in the ornithine-vasopressin groups (p < 0.01), but under etilefrin it increased 13% (NS). There was a significant difference between the two groups (p < 0.001). Hemodynamic changes appear to be less pronounced in the etilefrin group. The preservation of ABF and stroke volume under etilefrin should be an element of a better cardiovascular protection and a better tissular perfusion. Only the use of ABF measurements shows hemodynamic differences between the two groups.

A transmission line modelling approach to the interpretation of uterine Doppler waveforms.

An electrical analogue model of an artery that terminates into a vascular bed is presented. The model consists of an uniform transmission line that represents the artery and a load impedance that represents the vascular bed. The transmission line parameters are based on a well-established first-order approximation of the Navier-Stokes equations for fluid flow in distensible tubes. The model can be used to predict the incident and reflected components of both the arterial pressure and flow waveforms. In addition, it can predict the vessel diameter change and the mean blood velocity waveforms. In this study, the model was applied to the uterine artery so that the characteristics of the utero-placental circulation can be related to Doppler ultrasound recordings. It was found that the presence of the dicrotic notch in the uterine artery time-velocity waveform is the result of wave reflection and that a persistent notch past 20 weeks' gestation may be indicative of an abnormally high placental bed resistance. It is shown that the simulation results are consistent with the known physiological data and the clinically recorded uterine Doppler waveforms.

Cordocentesis in the assessment of the small-for-gestational age fetus.

Fetal blood sampling by cordocentesis in a group of 239 severely small-for-gestational age fetuses revealed a high incidence of chromosomal anomalies (17%). Furthermore, some of the fetuses were hypoxemic and demonstrated abnormalities in carbohydrate, lipid and protein metabolism. There were significant correlations between the degree of fetal hypoxemia and abnormalities in Doppler measurements of impedance to flow in the maternal uterine arteries and in the fetal umbilical artery, and of mean blood velocity measured in the fetal descending thoracic aorta and in the common carotid artery. Maternal hyperoxygenation in some cases improved fetal oxygenation and corrected some of the abnormalities in the Doppler measurements of fetal circulation.

Doppler determination of cardiac output in infants and children: Comparison with simultaneous thermodilution

Ten children, aged six weeks to 13 years, without intracardiac shunts or lesions that could cause turbulent flow in the ascending aorta or aortic regurgitation, underwent cardiac catheterization, including cardiac output measurements by thermodilution. Simultaneously with each of six consecutive thermodilution injections, mean and maximal blood velocities in the ascending aorta were measured by pulsed Doppler echocardiography from the suprasternal notch. Aortic root and aortic orifice diameters were measured with M-mode and cross-sectional echocardiography. One patient had to be excluded from the analysis because of inadequate Doppler recordings. The best agreement with the results of the thermodilution was observed when internal systolic aortic root diameter was combined with mean velocity (r = 0.97, y = 0.90x + 0.28, SEE = 0.31 liters/min). When cardiac output was normalized for body size, there was still a good correlation between the results of these two methods.

Relation of Fetal Hypoxia in Growth Retardation to Mean Blood Velocity in the Fetal Aorta

SOOTHILL, PETER W.; BILARDO, C. M.; NICOLAIDES, KYPROS H.; CAMPBELL, STUART Author Information

Maternal oxygen therapy for intrauterine growth retardation.

Humidified oxygen (55%) was administered continuously through a face mask to 5 patients whose pregnancies (4 singleton and 1 twin) were all complicated by severe intrauterine growth retardation, oligohydramnios, high blood-flow impedance in the fetal aorta and umbilical artery, and low mean blood-velocity in the fetal thoracic aorta. All the fetuses were hypoxic and 2 were acidotic. After maternal hyperoxygenation, the fetal pO2 increased to within or near the normal range, and resulted in a sustained increase in the mean blood-velocity in the fetal thoracic aorta. 5 fetuses survived with minimum neonatal morbidity. The effect of maternal hyperoxygenation on the fetal pO2 in such cases may prove to be a useful method of assessing placental function and guiding management.

Vasoactivity of the major intracranial arteries in newborn infants.

Blood flow to the head and arms was measured by a new volumetric Doppler technique in 30 preterm infants and 10 full term infants. At least 80% of this blood flow is considered to perfuse the brain. At the same time mean blood velocity in the middle and anterior cerebral arteries was measured by Duplex Doppler scanning. While blood flow to the head and arms remained substantially constant in both groups over the first 48 hours of life (60 ml/100 g brain weight/min), blood velocity doubled in both cerebral arteries in the preterm group. The term infants had higher blood velocities in both arteries at all times, but the velocities also increased over 48 hours, although to a lesser extent than in the preterm group. These findings imply that the major intracranial arteries are themselves vasoactive, being dilated at birth and subsequently constricting, possibly as an autoregulatory response to rising arterial blood pressure. While vasodilated, the cerebral arteries will be less efficient at damping pressure transients, placing preterm infants at particular risk of periventricular haemorrhage during the early hours of life. The implications for possible approaches to the prevention of cerebral haemorrhage are discussed.