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PubMedDate not supplied

[Doppler sonography--effect of fetal position, site of the placenta and measurement site of the fetal aorta].

The influence of fetal position, the site of placenta and the site of measurement in the fetal aorta on doppler-flow parameters was investigated in patients with uncomplicated pregnancies. In 20 cases the S/D-ratio was obtained in three different regions of the descending aorta. Measurements superior the renal vessels showed comparable values (4.1-4.3). No differences were found between signals obtained cranial or caudal of the diaphragma. Measurements at the aortal bifurcation showed significantly increased median values (6.6, p less than 0.05). No differences could be obtained concerning the influence of fetal position or site of placenta on S/D-ratio. All median values of a total of 197 patients were in the range of 4.8. Therefore it may be concluded that the above mentioned parameters do not have significant influence on doppler flow parameters in fetal vessels. However, a proximal site of measurement in the descending aorta fetalis should be reassured.

Aorta↗
PubMed1987

Relative effectiveness of three stimulus variables for locating a moving sound source.

A study is reported in which it is shown that observers can use at least three types of acoustic variables that indicate reliably when a moving sound source is passing: interaural temporal differences, the Doppler effect, and amplitude change. Each of these variables was presented in isolation and each was successful in indicating when a (stimulated) moving sound source passed an observer. These three variables were put into competition (with each indicating that closest passage occurred at a different time) in an effort to determine their relative importance. It was found that amplitude change dominated interaural temporal differences which, in turn, dominated the Doppler effect stimulus variable. The results are discussed in terms of two interpretations. First, it is possible that subjects based their judgements on the potential discriminability of each stimulus variable. However, because the stimuli used involved easily discriminable changes, subjects may instead have based their judgements on the independence of a stimulus variable from different environmental situation conditions. The dominance ordering obtained supports the second interpretation.

Attention↗
PubMed2006

Probing the superfluid velocity with a superconducting tip: the Doppler shift effect.

We address the question of probing the supercurrents in superconducting (SC) samples on a local scale by performing scanning tunneling spectroscopy (STS) experiments with a SC tip. In this configuration, we show that the tunneling conductance is highly sensitive to the Doppler shift term in the SC quasiparticle (QP) spectrum of the sample, thus allowing the local study of the superfluid velocity. Intrinsic screening currents, such as those surrounding the vortex cores in a type II SC in a magnetic field, are directly probed. With Nb tips, the STS mapping of the vortices, in single crystal 2H-NbSe(2), reveals both the vortex cores, on the scale of the SC coherence length xi, and the supercurrents, on the scale of the London penetration length lambda. A subtle interplay between the SC pair potential and the supercurrents at the vortex edge is observed. Our results open interesting prospects for the study of screening currents in any superconductor.

Journal Article↗
PubMed2002

Doppler echocardiographic effects of medetomidine on dynamic left ventricular outflow tract obstruction in cats.

OBJECTIVE: To evaluate the effects of medetomidine on dynamic left ventricular outflow tract (LVOT) obstruction in cats with left ventricular hypertrophy. DESIGN: Clinical trial. ANIMALS: 6 domestic shorthair cats with echocardiographic evidence of dynamic LVOT obstruction. PROCEDURE: Cats were restrained in lateral recumbency, and baseline M-mode and Doppler echocardiographic examinations were performed. An ECG was recorded continuously, and blood pressure was measured indirectly with Doppler instrumentation. Medetomidine (20 microg/kg 19.1 microg/lb]) was then administered i.m., and examinations were repeated 15 minutes later. RESULTS: Significant decreases in heart rate, LVOT velocity, and the LVOT pressure gradient were documented following medetomidine administration. After adjusting for the effects of heart rate by ANCOVA, there were no significant differences in any other systolic or diastolic indices of left ventricular function. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that administration of medetomidine to cats with dynamic LVOT obstruction may result in elimination of outflow tract obstruction; medetomidine may be a suitable sedative and analgesic agent in this subpopulation of cats.

Animals↗
PubMed1992

Transcranial Doppler sonography: effects of halothane, enflurane and isoflurane on blood flow velocity in the middle cerebral artery.

Systolic, diastolic, and mean blood flow velocity in the middle cerebral artery (Vs,mca; Vd,mca; Vm,mca) and pulsatility (Vs-Vd)/Vm of the waveform obtained were recorded in 51 patients before, during and after general anaesthesia. Transcranial Doppler (TCD) sonographic variables were measured in the awake patient and after induction of anaesthesia with thiopentone 5-6 mg kg-1. After tracheal intubation, 17 patients received 0.8% halothane and 66% nitrous oxide in oxygen for 30 min (15 min normoventilation; 15 min hyperventilation). The inspired halothane concentration was then increased to 1.6% for 45 min (15 min normoventilation; 15 min hyperventilation; 15 min normoventilation with nitrous oxide replaced by oxygen). Enflurane (1.7% for 30 min and 3.4% for 45 min) was given to another 17 patients; 17 other patients received isoflurane (1.2% and 2.4%). Mean arterial pressure (MAP), nasopharyngeal temperature, end-tidal carbon dioxide concentration, inspired and end-tidal anaesthetic agent concentrations, haemoglobin concentration, PVC and TCD variables were measured at the end of each 15 min period. After recovery from anaesthesia, TCD variables were measured again. There were no intergroup differences in changes in MAP, nasopharyngeal temperature, haemoglobin concentration and PCV. Halothane, enflurane and isoflurane at low doses and normoventilation had little influence on TCD variables compared with awake values. In large concentrations with nitrous oxide in oxygen and normoventilation, there were differences between the volatile agents. Halothane increased blood flow velocities, but enflurane and isoflurane caused little change. Hyperventilation always decreased blood flow velocities and increased pulsatility.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

[Effect of Doppler ultrasound on perinatal mortality of high risk pregnancies: required patient sample?].

The clinical value of Doppler ultrasound in obstetrics is related to the question whether pregnancy course and outcome will be improved when this method is introduced into obstetrical management. Recently a couple of randomized controlled management studies have been published and the majority of these trials showed significant beneficial effects. Even perinatal mortality may possibly be reduced, but none of these trials was large enough to achieve a significant reduction. Giles and Bisits [12] performed a metaanalysis by combining evidence from 6 of these trials in high risk pregnancies and could demonstrate a 50% reduction in perinatal mortality at a significance of 5%. But they did not report whether the sample size was large enough to detect this difference with the usually required power of at least 80%. Therefore the question remains whether obstetrical management should be changed in view of these results. Additionally, a clinically useful estimate is needed to determine the chance to reproduce the assumed beneficial effect. The present paper describes the statistical method for calculating the appropriate sample size needed in each group of a trial to detect a predefined treatment difference with specified significance and power. This method is applied in detail to the results of the meta-analysis of Giles and Bisits [12] and a minimal sample size of 1458 high risk pregnancies in each group is calculated. As the Doppler and the control groups actually contained 2102 and 2133 high risk patients respectively, these sample sizes proved to be large enough to detect a 50% reduction in perinatal mortality with a power of at least 80%. Furthermore, 59 high risk pregnancies would need to be managed by Doppler in order to prevent 1 case of perinatal death. In other words, it should be possible to prevent 4 perinatal death cases per 1000 total births when the high risk proportion is 25%.

Bias↗
PubMed2002

Tumor vascularity: evaluation in a murine model with contrast-enhanced color Doppler US effect of angiogenesis inhibitors.

PURPOSE: To determine the ability of contrast material-enhanced ultrasonography (US) to depict tumor growth and vascularity in a murine model of prostate carcinoma treated with an angiogenic inhibitor. MATERIALS AND METHODS: Thirty-five genetically engineered mice with spontaneously occurring prostate tumors were monitored on a weekly basis with gray-scale and color Doppler US with a 15-MHz linear transducer. Eighteen mice were treated with an adenoviral vector to deliver a soluble form of the Flk1 receptor (VEGFR-2), a vascular endothelial growth factor receptor designed to block tumor angiogenesis. The remaining 17 animals were injected with saline and used as controls. Tumor volumes were calculated on the basis of serial US measurements. Color Doppler US was performed in every tumor before and after intravenous injection of 0.1 mL per kilogram of body weight of a US contrast agent. US images were evaluated for tumor size, pattern of vascularity, and extent of vascularity (vascularity index). Findings at US were correlated with findings at autopsy in 30 animals. RESULTS: Estimates of tumor volume at US correlated well with tumor measurements at autopsy (r =.89, P <.001). Marked differences in tumor size and slope of increasing tumor volume were evident at US between treated and control mice after treatment (P <.016, analysis of variance). The US contrast agent markedly increased color Doppler US signal intensity with an 800% (from 10% to 12,700%) change in the mean number of color pixels per imaging field, and showed vascularity in areas of tumor not identified on precontrast images in 70% (109 of 156 studies). No correlation was found between the pattern of vascularity or vascularity index before or after contrast material administration and tumor size, treatment status, or histologic assessment of tumor vascularity. CONCLUSION: Contrast-enhanced US improves visualization of tumor vascularity. However, histologic patterns of tumor vascularity do not correlate with Doppler US depiction of blood flow in these vessels.

Angiogenesis Inhibitors↗
PubMed1999

Blood flow in healthy gallbladder walls on color and power Doppler sonography: effect of wall thickness and gallbladder volume.

OBJECTIVE: The purpose of this study was to determine the effect of gallbladder contraction on the conspicuity of flow in the normal gallbladder wall. SUBJECTS AND METHODS: Ten healthy adult volunteers without clinical evidence of gallbladder disease participated in the study. After patients fasted overnight, the gallbladder was scanned using gray-scale, color Doppler, and power Doppler sonography. The subjects were then given a standard meal consisting of 478 ml of a carbohydrate-rich dietary supplement, and the imaging sequence was repeated 20 and 45 min thereafter. Mural flow was graded using a four-step grading scheme. Gallbladder volume, wall thickness, and visibility of mural flow at all three time points were statistically compared. RESULTS: Enhanced mural flow was seen after meal consumption in all but one volunteer. Overall, mural flow was significantly greater 45 min after eating than at baseline or 20 min on color Doppler sonography (p = .004) and power Doppler sonography (p = .008). CONCLUSION: Flow in the gallbladder wall is a normal finding that is seen more easily when the gallbladder is contracted. This fact must be kept in mind when sonography is used with patients in whom acute cholecystitis is suspected, particularly if they do not fast before sonography.

Adult↗
PubMed1983

[Doppler echocardiography in the genesis of precordial murmurs in patients with morphological changes of the thorax of the pectus excavatum type].

A complete Doppler effect echocardiographical study was performed on 15 patients with pectus excavatum type deformations of the chest (first, second, and third degree of hollowing). Fourth-degree patients were excluded, since they proved unable to cooperate fully when lying down. An ATL Mark I 500 B Eco Doppler was used in M mode. A typical tricuspid pattern was observed. This was clearly superimposed on the aortic wall, with its D point closely conjoined to the anterior part of the vessel. This finding was obtained by bringing the sound to the 5th intercostal space, in a vertical instead of a medio-lateral orientation. The Doppler effect was normal at the low atrium, mitral, left ventricular efflux chamber almost at the level of the aortic valve, giving rise to a mixed spectral curve, with an aortic shape in the systole and a tricuspid shape in the diastole. A sample volume at the lung level resulted in a spectral curve turning negatively. There was distinct turbulence at its nadir, even though the examination was performed in complete expiratory apnoea. This lung flow turbulence indicated that the acoustic observation of a systolic murmur in some patients was attributable to partial compression exerted by the sunken sternum on the pulmonary artery or its left branch.

Echocardiography↗
PubMed1983

Development of tolerance during nitrate therapy: dissociation of arterial and venous effects. A doppler echocardiographic study.

Using pulsed Doppler echocardiography as a noninvasive method to assess central venous return, nine healthy volunteers were studied before and after isosorbide dinitrate given four times daily for 8 days. First dose isosorbide dinitrate led to a drop in heart rate and mean arterial pressure, and right ventricular inflow velocities decreased. With sustained treatment effects on systemic venous return remained unaltered, whereas reduction in heart rate and in mean arterial pressure was lost. Regarding this disappearing response as indicating a form of tolerance, venous hemodynamic nitrate effects were unaltered by development of tolerance on the arterial side.

Adult↗
PubMed1999

Measurement of tissue motion.

A number of ultrasonic methods are available for the detection of tissue motion as it occurs physiologically in the body. The detection of echoes from within the body in less than 1 ms after the initial transmission of ultrasound and the Doppler effect have enabled a range of instrumentation to be developed. The subject owes a great deal to advances in transducer design, electronics and computer technology. Over many years fast B-mode imaging and M-mode traces of boundary position versus time have been the main clinical tools. Currently new sophisticated detection and imaging techniques are being produced based on the Doppler effect and on tracking motion in tissue images. The measurement of several velocity components is permitting velocity vectors to be determined more completely, adding to accuracy. Not surprisingly, cardiology is the main field of application but there are other areas of interest, e.g. vascular, musculo-skeletal and foetal function studies.

Artifacts↗
PubMed1986

Time domain formulation of pulse-Doppler ultrasound and blood velocity estimation by cross correlation.

The Doppler effect is usually described as a frequency shift of the backscattered signals from moving targets with respect to the frequency transmitted. Recently, real-time blood flow imaging has become possible thanks to the development of a new velocity estimator based on phase-shift measurements of successive echoes. However, this method suffers from the well-known limitations of pulse-Doppler instruments. A new formulation is presented which describes the pulse-Doppler effect on the successive echoes from a cloud of moving targets as a progressive translation in time due to the displacement of the scatterers between two excitations. This approach allows us to generate efficiently computer-simulated data in order to evaluate accurately the various processing techniques. Furthermore, it leads to a novel class of velocity estimators in the time domain which measure the time shifts which are proportional to the local blood velocity. Among them, the cross correlation of the received rf signals turns out to be well suited. A local cross-correlation function is first calculated from a consecutive pair of range-gated echoes and the time shift is then determined by searching for the time position with the maximum correlation. The time-correlation technique is shown to provide accurate velocity profiles with broadband transducers. Moreover, the classical velocity limitation of pulse-Doppler is overcome because there is no ambiguity in measuring a time shift instead of a phase shift. These major advantages should make quantitative flow mapping possible and more reliable.

Blood Flow Velocity↗
PubMed2004

Experimental study of the Doppler shift generated by a vibrating scatterer.

We report an experimental study of the backscattering of a sound wave of frequency f by a surface vibrating harmonically at frequency F (F << f) and amplitude A in the regime where the Doppler effect overcomes bulk nonlinear effects. When the duration to of the analyzed time series of the scattered wave is small compared to the vibration period, the power spectrum of the backscattered wave is proportional to the probability density function of the scatterer velocity, which presents two peaks shifted from f by roughly 2fAomega/c (omega = 2piF). On the contrary, when t0 >> F(-1), sidebands at frequencies f +/- nF (n integer) appear in the power spectrum, which are due to the phase modulation of the backscattered wave induced by its reflection on a moving boundary. We use the backscattered power spectrum to validate the phase modulation theory of the Doppler effect in the latter case for 2kA << 1 and 2kA approximately > 1 (k = 2pif/c, where c is the wave velocity) and we test the validity of an acoustic nonintrusive estimator of A as a function of power spectrum bandwidth and of A itself.

Journal Article↗
PubMed2003

Spectral and modal formulations for the Doppler-shifted field scattered by an object moving in a stratified medium.

Spectral and normal mode formulations for the three-dimensional field scattered by an object moving in a stratified medium are derived using full-field wave theory. The derivations are based on Green's theorem for the time-domain scalar wave equation and account for Doppler effects induced by target motion as well as source and receiver motion. The formulations are valid when multiple scattering between the object and waveguide boundaries can be neglected, and the scattered field can be expressed as a linear function of the object's plane wave scattering function. The advantage of the spectral formulation is that it incorporates the entire wave number spectrum, including evanescent waves, and therefore can potentially be used at much closer ranges to the target than the modal formulation. The normal mode formulation is more computationally efficient but is limited to longer ranges. For a monochromatic source that excites N incident modes in the waveguide, there will be roughly N2 distinct harmonic components in the scattered field. The Doppler shifts in the scattered field are highly dependent upon the waveguide environment, target shape, and measurement geometry. The Doppler effects are illustrated through a number of canonical examples.

Journal Article↗
PubMed1990

Relation of pulmonary vein to mitral flow velocities by transesophageal Doppler echocardiography. Effect of different loading conditions.

It has previously been demonstrated that predictable changes occur in mitral flow velocities under different loading conditions. The purpose of this study was to relate changes in pulmonary venous and mitral flow velocities during different loading conditions as assessed by transesophageal echocardiography in the operating room. Nineteen patients had measurements of hemodynamics, that is, mitral and pulmonary vein flow velocities during the control situation, a decrease in preload by administration of nitroglycerin, an increase in preload by administration of fluids, and an increase in afterload by infusion of phenylephrine. There was a direct correlation between the changes in the mitral E velocity and the early peak diastolic velocity in the pulmonary vein curves (r = 0.61) as well as a direct correlation between the deceleration time of the mitral and pulmonary venous flow velocities in early diastole (r = 0.84). This indicates that diastolic flow velocity in the pulmonary vein is determined by the same factors that influence the mitral flow velocity curves. A decrease in preload caused a significant reduction in the initial E velocity and prolongation of deceleration time, and an increase in preload caused an increase in E velocity and shortening of deceleration time. An increase in afterload produced a variable effect on the initial E velocity and deceleration time and was dependent on the left ventricular filling pressure. The change in systolic forward flow velocity in the pulmonary vein was directly proportional to the change in cardiac output (r = 0.60). The pulmonary capillary wedge pressure correlated best with the flow velocity reversal in the pulmonary vein at atrial contraction (r = 0.81). Use of pulmonary vein velocities in conjunction with mitral flow velocities can help in understanding left ventricular filling.

Aged↗