Quantitative transcutaneous measurements of blood flow in carotid artery by means of pulse and continuous wave Doppler methods.

The authors present results of quantitative measurements of blood in vivo in the carotid artery of man. The Doppler pulse technique was used after being previously verified for steady state flows in tubes and for pulsating flows in a canine aorta where the electromagnetic method was also used for comparison.An ultrasonic probe with two transducers was adapted for determination of the angle of the ultrasonic beam in relation to the vessel allowing the measurement of the vessel diameter which was also determined by means of the ultrasonographic B-mode technique.By means of the Doppler pulse method profiles of the blood velocity in the carotid artery were determined as a function of time.The continous wave Doppler technique together with the zero-crossing system and spectral analysis were also used for making measurements.The flow velocity and the shape of the flow curve with time obtained with the above techniques showed good agreement. The measured flow rate in the carotid artery amounted to Q_M = 1.61/min (maximum instantaneous value) and Q₀ - 0.531/min (mean time value).     

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

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

Changes in fetal hemodynamics with terbutaline treatment and premature labor

The aim of this study was to examine the fetal hemodynamic effects of terbutaline treatment and premature labor. Image-directed pulsed and continuous wave Doppler ultrasound studies, using 3.3-MHz and 5-MHz transducers (GE PASII and ATL echocardiographic machines), were used to assess fetal cardiac blood velocities in three groups of pregnancies matched for menstrual age (MA). Group 1: 13 normal pregnancies, mean MA 31 weeks. Group 2: 7 women in premature labor prior to tocolytic therapy, mean MA 32 weeks. Group 3: 8 women treated with terbutaline, average dose 18.8 mg daily, for previous premature labor, mean MA 31 weeks. Heart rate averaged 150 bpm, 135 bpm, and 127 bpm in the terbutaline, premature labor, and normal groups, respectively, and each were significantly different from each other. Products of time velocity interval and heart rate at the aortic valves were 1603 cm +/- 140 cm, 1413 cm +/- 190 cm and 1238 cm +/- 200 cm, and at the mitral valves 1102 cm +/- 170 cm, 812 cm +/- 110 cm, and 878 cm +/- 150 cm in the terbutaline, premature labor, and the normal groups, respectively. Aortic and mitral blood velocity products of time velocity integrals and heart rates were significantly higher (p = 0.01) in the terbutaline group relative to the normal group. In addition, the terbutaline group was significantly higher than the labor group at the mitral valve (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Spatial and temporal resolution of aortic Doppler blood velocity signals in normal human subjects

We have used digital, microcomputer-based methods for the numerical analysis of pulsed, range-gated, ultrasonic Doppler blood velocity signals recorded with an axially aimed transducer from the ascending aorta of normal subjects. We investigated the spatial, temporal and amplitude resolution of our methods for recording and analysis, comparing aortic signals with test signals from a sine wave function generator. The spatial resolution of our system was found to be adequate in spite of the use of a relatively large sample volume. The temporal resolution was significantly influenced by the rate of change of velocity which affected the results of discrete fast Fourier transform analysis. The rate of increase in aortic blood velocity at the start of ejection was linear, following an initial jump in velocity. The amplitude resolution was affected by fluctuations in the amplitude of the Doppler signals. We conclude that our methods do not exaggerate the bluntness of the aortic velocity profile or the linearity of the increase in blood velocity at the start of left ventricular ejection.     

Three-dimensional cross-sectional velocity distribution in the ascending aorta in cardiac patients

Summary. Knowledge of the distribution of velocities across the ascending aorta is important for measurements of cardiac output; for understanding the function of normal and diseased valves and for the evaluation of prosthetic valves. The aim of this study was to investigate, in detail, the spatial distribution of axial velocities in the human ascending aorta, covering a nearly complete cross-section of the lumen in a time continuous modus. During open-heart surgery, blood velocities in the ascending aorta were mapped in 10 patients. All patients had aortic valves with no significant clinical evidence of disease. Pulsed Doppler ultrasound technique was used to measure blood velocity using an intraluminal probe with a 1 mm, 10 MHz crystal connected to a position-sensitive device. The distribution of blood velocity in the aorta 6–8 cm above the valve was characterized by a skewed and irregular peak systolic flow, with maximum velocity posteriorly. There was a positive correlation (n=0.854, P < 0.002) between the maximum skewness slope and the stroke volume. Significant retrograde flow was recorded in all patients in the left posterior part of aorta in late systole and early diastole. The rotation of the point of maximal velocity was anticlockwise in six patients, clockwise in three and alternating in one. The present study shows that there is a considerable individual variation in the velocity distribution in the ascending aorta, with no plane symmetric features, and that large sampling volumes are required for reliable estimates of mean velocity.     

Validation of a sensitivity performance index test protocol and evaluation of colour Doppler sensitivity for a range of ultrasound scanners

The ability to detect flow is the most crucial aspect of an ultrasound (US) system because, if flow cannot be detected, no other aspect of performance matters. The objectives of this study were to validate a Doppler "sensitivity performance index," a figure of merit, and to determine if it could be used to differentiate colour Doppler sensitivity performance in scanners of varying complexity. The sensitivity performance index was developed to give a combined measure of related aspects of sensitivity, such as the lowest detectable velocity, the vessel size and the penetration depth. The colour Doppler sensitivity was evaluated objectively as the lowest detectable velocity signal from the deepest achievable point within the Doppler sensitivity phantom free from extraneous noise in a small diameter vessel (3.2 mm inner diameter). The effect of vessel size and mean velocity on the sensitivity performance index were investigated and it was found that the index was not proportional to vessel size, but this may be accounted for by considering the effect of the acoustic properties of the vessel material, the clutter filter and beam shape. The results obtained using flow phantoms with vessel sizes different from those used in this study are, therefore, not directly comparable to the results found in this study; however, a similar trend should be found in the results for the effect of control settings and a similar range of US scanners. It was found that the Doppler sensitivity performance index was a robust challenging test because none of the US scanners evaluated was capable of achieving the highest sensitivity performance index score, which would be limited by the lowest pump velocity and the deepest point of the vessel within the flow phantom. Therefore, this suggests that this method of determining Doppler sensitivity performance is valuable in the absence of other suitable methods, despite the fact that the relationship between the sensitivity performance index and vessel size is not proportional. Furthermore, use of the Doppler sensitivity performance index for the evaluation of a range of scanners demonstrated that curvilinear transducers have higher sensitivity performance indices than higher-frequency linear transducers, due to the higher achievable penetration depth. The effect of instrument settings was assessed for two transducers, the 4C3 curvilinear general-purpose transducer (Aspen) and the PVM375AT curvilinear general-purpose transducer (Nemio). The colour Doppler sensitivity performance was found to be significantly dependent on the clutter filter setting and the output power setting for both transducers tested. Users need to be aware of the effect of these settings on the colour Doppler sensitivity performance of their US scanner when interpreting the clinical significance of the colour Doppler information.     

Derivation of haemodynamic information from ultrasonic recordings of aortic diameter changes

An ultrasound phase-locked echo-tracking system was used for noninvasive measurements of diameter changes in the upper abdominal aorta of the anaesthetised cat. Comparisons were made between the noninvasively recorded diameter changes and central haemodynamic variables measured with inserted catheters and transducers. It was found that noninvasive observations of aortic diameter changes give reliable information on the direction and relative magnitude of the blood pressure change both in systole and in diastole. Indications of the direction of change of stroke volume, cardiac output, and aortic flow acceleration (a measure of cardiac inotropy) could also be gained. The information, taken together, comprises a pattern of response reflecting cardiovascular adjustments likely to have occurred. It is suggested that the technique is suitable for interpretation of (patho-) physiological changes in the foetus, as well as for determinations of great vessel compliance in man, i.e., in atherosclerosis research.     

Non-invasive evaluation of the long-term results of coarctectomy in childhood

Summary. Nineteen young men operated upon for coarctation of the aorta in childhood were studied with pulse tracings from the femoral and carotid arteries and echocardiographic examination of the heart with estimation of the degree of hypertrophy and valve anomalies. The results were compared with intra-arterial blood-pressure measurements and angiographically measured width of the aortic anastomosis. Patients with markedly distorted pulse curves had the narrowest anastomoses although no uniform pattern could be detected. Although one of the selection criteria was ‘no other known cardiovascular malformation’, only three of the patients had completely normal aortic and mitral valves. Nine of the patients had left ventricular hypertrophy but the degree of hypertrophy could not be correlated to the degree of arterial hypertension. The importance of long-term follow-up of these patients, who in spite of surgery have a remaining cardiovascular excess mortality, is emphasized. Pulse tracings and echocardiography seem to be of value for this purpose.     

脱细胞支架复合兔骨髓间充质干细胞构建组织工程血管

背景:目前临床使用的小口径(<6 mm)人工血管因生物相容性差、远期通畅率低,效果并不理想.因此,学术界一直致力于寻找具有正常血管生物学功能的血管代用品,组织工程血管的构建与功能研究已成为目前热门研究课题.目的:将兔骨髓间充质干细胞与脱细-胞血管支架动态复合培养体外构建组织工程血管,通过体内移植实验,探讨该组织工程血管的组织相容性及通畅率.设计、时间及地点:随机对照实验,细胞学、组织病理学观察,于2006-01/2008-06在南京大学医学院附属鼓楼医院实验室完成.材料:通过去污剂-酶消化法制备兔腹主动脉脱细胞支架;采用密度梯度离心法结合贴壁分离培养法,分离扩增兔骨髓间充质干细胞,将扩增后的干细胞静态种植于脱细胞支架后置于生物反应器中动态培养构建组织工程血管.方法:60只兔随机均分为3组,剪取一段腹主动脉长约1.0 cm,再将移植血管以8/0聚丙烯线间断外翻吻合到腹主动脉上.组织工程血管组:受体为对应抽取骨髓干细胞的实验兔,以组织工程血管为移植血管;脱细胞血管支架组:以脱细胞处理的同种异体腹主动脉为移植血管;同种异体血管组:以同种异体新鲜腹主动脉作为移植血管.主要观察指标:对培养的骨髓间充质干细胞进行免疫组化鉴定;血管移植后3个月行数字减影血管造影、病理切片、扫描电镜等观察移植效果.结果:兔骨髓间充质干细胞在体外培养8 d后形成漩涡状排列,免疫组化结果符合间充质干细胞表型特征:将间充质干细胞与脱细胞支架置于生物反应器培养12 d后,种子细胞在血管腔内黏附生长;血管移植3个月后,组织工程血管组、脱细胞血管支架组通畅率分别为90%,80%,均优于同种异体血管组(25%).移植3个月后苏木精一伊红染色及扫描电镜结果显示,组织工程血管组形成清晰的内、中、外膜3层结构,形态接近正常动脉,内皮细胞覆盖完整;脱细胞血管支架组血管内表面内皮细胞覆盖不完整,伴有附擘血栓形成,内膜轻度增生,伴炎性细胞浸润:同种异体血管组内膜极度增厚、坏死,管腔明显狭窄,伴不同程度的血栓机化.结论:将兔骨髓间充质干细胞复合脱细胞血管支架上,可获得一种具有良好生物相容性和通畅率的生物人工血管.     

Development of a Flexible Implantable Sensor for Postoperative Monitoring of Blood Flow

We have developed a blood flow measurement system using Doppler ultrasound flow sensors fabricated of thin and flexible piezoelectric‐polymer films. These flow sensors can be wrapped around a blood vessel and accurately measure flow. The innovation that makes this flow sensor possible is the diffraction‐grating transducer. A conventional transducer produces a sound beam perpendicular to its face; therefore, when placed on the wall of a blood vessel, the Doppler shift in the backscattered ultrasound from blood theoretically would be 0. The diffraction‐grating transducer produces a beam at a known angle to its face; therefore, backscattered ultrasound from the vessel will contain a Doppler signal. Flow sensors were fabricated by spin coating a poly(vinylidene fluoride–trifluoroethylene) copolymer film onto a flexible substrate with patterned gold electrodes. Custom‐designed battery‐operated continuous wave Doppler electronics along with a laptop computer completed the system. A prototype flow sensor was evaluated experimentally by measuring blood flow in a flow phantom and the infrarenal aorta of an adult New Zealand White rabbit. The flow phantom experiment demonstrated that the error in average velocity and volume blood flow was less than 6% for 30 measurements taken over a 2.5‐hour period. The peak blood velocity through the rabbit infrarenal aorta measured by the flow sensor was 118 cm/s, within 1.7% of the measurement obtained using a duplex ultrasound system. The flow sensor and electronics operated continuously during the course of the 5‐hour experiment after the incision on the animal was closed.     

Non-invasive Assessment by B-Mode Ultrasound of Arterial Pulse Wave Intensity and Its Reduction During Ventricular Dysfunction

Arterial pulse waves contain clinically useful information about cardiac performance, arterial stiffness and vessel tone. Here we describe a novel method for non-invasively assessing wave properties, based on measuring changes in blood flow velocity and arterial wall diameter during the cardiac cycle. Velocity and diameter were determined by tracking speckles in successive B-mode images acquired with an ultrafast scanner and plane-wave transmission. Blood speckle was separated from tissue by singular value decomposition and processed to correct biases in ultrasound imaging velocimetry. Results obtained in the rabbit aorta were compared with a conventional analysis based on blood velocity and pressure, employing measurements obtained with a clinical intra-arterial catheter system. This system had a poorer frequency response and greater lags but the pattern of net forward-traveling and backward-traveling waves was consistent between the two methods. Errors in wave speed were also similar in magnitude, and comparable reductions in wave intensity and delays in wave arrival were detected during ventricular dysfunction. The non-invasive method was applied to the carotid artery of a healthy human participant and gave a wave speed and patterns of wave intensity consistent with earlier measurements. The new system may have clinical utility in screening for heart failure.     

Reproducibility of ultrasonic fetal volume blood flow measurements

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

Effects of atherosclerotic lesions on ultrasonic beam and cw doppler signals

Doppler ultrasound has been shown to be a useful clinical tool in the noninvasive detection of vascular stenoses, occlusion, or plaques. The presence of atherosclerotic lesions in blood vessel walls can distort the Doppler ultrasonic signal, producing inverted or biphasic tracings. This observation, in fact, has been used frequently as a criterion for the diagnosis of plaque formation and calcification of these lesions. To define the source of this distortion, we have examined the effects of various types of atherosclerotic lesions on the transmitted ultrasonic beam generated by a continuous wave (CW) Doppler ultrasonic probe. These results are compared to the Doppler flow tracings obtained by a CW ultrasonic Doppler flowmeter from blood vessels with overlaying lesions in a mock flow system. It is concluded that severe distortion in the form of beam refraction or diffraction can be produced by calcified lesions, resulting in biphasic or inverted flow signals.     

Comparison of standard CPR versus diffuse and stacked hand position interposed abdominal compression-CPR in a swine model

Interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) is an innovative basic life support technique requiring no mechanical adjuncts. Optimizing its performance remains a challenge. Hand-position technique over the abdomen during interposed abdominal compression (IAC) may be important. The purpose of this study was to determine if there is a difference in efficacy depending on the type of abdominal hand-position used. Two different hand positions were studied: open hands, placed side by side, resulting in diffuse abdominal compression and stacked hands, with one on top of the other, producing a more focal compression of the abdomen. Thirty swine were cannulated with micromanometer-tipped pressure transducers in the ascending aorta (Ao) and right atrium (RA), and Millar Doppler-tipped catheters in the descending aorta and inferior vena cava (IVC) to determine flow patterns during cardiopulmonary resuscitation (CPR), During CPR there were no differences in aortic systolic or right atrial systolic pressures. Both forms of IAC-CPR produced greater aortic diastolic and right atrial diastolic pressures then standard CPR (STD-CPR) (P<0.05). Coronary perfusion pressures (CPP), however, were not different. Blood flow directions and velocity patterns showed that STD-CPR chest compressions produce caudally directed blood flow in both the descending aorta and the IVC, and that such flows reverse (becoming cranially directed) during the relaxation phase of chest compression. IAC-CPR produced similar blood flow patterns in the aorta and IVC, as seen with STD-CPR. There were no differences in blood flow patterns between the different forms of IAC-CPR. No CPR-produced trauma difference was found. Abdominal hand position (diffuse or stacked) did not affect blood flow in either the aorta or IVC or resuscitation success in this experimental model. There was a trend towards better outcomes with stacked hands IAC-CPR with 90 versus 70% survival with STD-CPR.     

Abnormal renal and splanchnic arterial Doppler pattern in premature babies with symptomatic patent ductus arteriosus

The flow velocity pattern in the descending aorta, renal arteries, and celiac and superior mesenteric arteries was studied with pulsed Doppler in eight premature babies with symptomatic ductus arteriosus before and after ductal closure, as compared to nine premature babies without ductus arteriosus. There was a decrease or reversal of flow in diastole in the above arteries in babies with ductus and diastolic flow reappeared after ductal closure. This diastolic steal phenomenon has not been previously demonstrated in the abdominal arteries. It may contribute to proneness to ischemic damage of abdominal organs in premature babies.     

Review of intracoronary Doppler catheters

During the last 20 years several types of Doppler catheters have been developed and applied to the measurement of coronary blood flow velocity in man. Validation studies in the laboratory and in animals have shown that these catheters can accurately measure velocity from a small sample volume beside or ahead of the catheter tip. The Doppler transducers have been miniaturized enough (<1 mm dia) to be mounted on subselective coronary catheters or balloon angioplasty catheters without compromising any of the normal catheter functions. Good quality, high fidelity velocity signals have been recorded from many sites within the coronary circulation of patients during coronary arteriography and balloon angioplasty. Coronary flow reserve measured with Doppler catheters is a physiologic index of the severity of a stenosis which, when carefully measured, can be used for assessing lesions, planning treatment, and evaluating the success of interventions.     

Quantitative blood flow in the fetal descending aorta and in the umbilical vein in normal pregnancies. Longitudinal and cross-sectional studies

Quantitative blood flow in the fetal descending thoracic aorta and in the umbilical vein was measured both in a longitudinal study where each of 13 fetuses was examined three times and in a cross-sectional study where 45 fetuses were examined once only in the last trimester of normal pregnancy. The waveform of the velocity curves from fetal descending aorta was examined and the Pulsatility Index, the A/B ratio and the least diastolic velocity were calculated. The longitudinal study showed that all these parameters and the fraction of the flow in the fetal descending aorta, which was distributed to the placental circulation, were constant during the last trimester. The problems of longitudinal inference from cross-sectional studies are discussed. For all 58 fetuses the flow in the descending thoracic aorta was 234 ml/min/kg and in the umbilical vein 127 ml/min/kg. The Pulsatility Index was 1.83, the A/B ratio 4.75, the least diastolic velocity 9.9 cm/s. The fraction of blood flow in the descending aorta distributed to the placental circulation was 55%.     

Baseline correction of phase contrast images improves quantification of blood flow in the great vessels.

PURPOSE: Phase-contrast Cardiovascular Magnetic Resonance Imaging (CMR) generally requires the analysis of stationary tissue adjacent to a blood vessel to serve as a baseline reference for zero velocity. However, for the heart and great vessels, there is often no stationary tissue immediately adjacent to the vessel. Consequently, uncorrected velocity offsets may introduce substantial errors in flow quantification. The purpose of this study was to assess the magnitude of these flow errors and to validate a clinically applicable method for their correction. MATERIALS AND METHODS: In 10 normal volunteers, phase-contrast CMR was used to quantify blood flow in the main pulmonary artery (Qp) and the aorta (Qs). Following image acquisition, phase contrast CMR was performed on a stationary phantom using identical acquisition parameters so as to provide a baseline reference for zero velocity. Aortic and pulmonary blood flow was then corrected using the offset values from the phantom. RESULTS: The mean difference between pulmonary and aortic flow was 26 +/- 21 mL before correction and 7.1 +/- 6.6 mL after correction (p = 0.002). The measured Qp/Qs was 1.25 +/- 0.20 before correction and 1.05 +/- 0.07 after correction (p = 0.001). CONCLUSION: Phase-contrast CMR can have substantial errors in great vessel flow quantification if there is no correction for velocity offset errors. The proposed method of correction is clinically applicable and provides a more accurate measurement of blood flow.     

Intra-vascular blood velocity and volumetric flow rate calculated from dynamic 4D CT angiography using a time of flight technique

We examine a time of flight (TOF) approach for the analysis of contrast enhanced 4D volumetric CT angiography scans to derive and display blood velocity in arteries. Software was written to divide blood vessels into a series of cross sections and to track contrast bolus TOF along the central vessel axis, which was defined by a user, from 4D CT source data. Time density curves at each vessel cross section were fit with quadratic, Gaussian, and gamma variate functions to determine bolus time to peak (TTP). A straight line was used to plot TTP versus vessel path length for all three functions and the slope used to calculate intraluminal velocity. Software was validated in a simulated square channel and non-pulsatile flow phantom prior to the calculation of blood velocity in the major cerebral arteries of 8 normal patients. The TOF algorithm correctly calculates intra-luminal fluid velocity in eight flow conditions of the CT flow phantom where quadratic functions were used. Across all conditions, in phantoms and in vivo, the success of calculations depended strongly on having a sufficiently long path length to make measurements and avoiding venous contamination. Total blood flow into the brain was approximately 17 % of a normal 5 L cardiac output. The technique was explored in vivo in a patient with subclavian steal syndrome, in the pulmonary arteries and in the iliac artery from clinical 4D CT source data.  Intravascular blood velocity and flow may be calculated from 4D CT angiography using a TOF approach.     

Traces: making sense of urodynamics testing--Part 2: uroflowmetry

Uroflowmetry is an electronic recording of urinary flow. It is typically measured by one of two types of transducers. One type measures the weight of urine as it falls into a beaker or container placed on the transducer, and the other uses a spinning disc to measure urinary flow. Uroflowmetry is a non-invasive, comparatively inexpensive study often used to identify voiding abnormalities. Experienced clinicians can use uroflow tracings to differentiate a continuous (normal) flow pattern from abnormal patterns. While uroflowmetry has been found to reliably distinguish normal from abnormal flow patterns, uroflowmetry does not reliably distinguish the underlying cause of voiding abnormalities. Differential diagnosis of poor detrusor contraction strength from bladder outlet obstruction relies on a voiding pressure flow study that combines uroflowmetry with the various pressure studies used to generate a cystometrogram and pelvic floor muscle electromyography.