Pulsed Doppler Sample Volume Research Articles

Flow volume measured by duplex ultrasound in native arteriovenous fistula for hemodialysis: a case report

Background : Native arteriovenous fistula (AVF) is the vascular access of choice for hemodialysis patients. AVF lasts longer than artificial grafts or central venous catheters. In addition, AVF has fewer complications than other vascular accesses. The use of Doppler ultrasound is used to facilitate fistula construction (vascular mapping) including AVF maturation to see if AVF can be used.
 Doppler ultrasound monitoring for maturation of AV fistulas should be monitored sonographically until the fistula is ready for use, especially when maturation is slow and in patients whose veins cannot easily be assessed by physical examination alone (eg because of obesity). The AVF DUS flow volume measurement may be the only imaging tool that can be used to monitor a fistula even during its maturation. Even so, DUS should always be done before AVF is used for the first time. This examination provides baseline data on vascular access, which can be useful in subsequent tests performed to evaluate functional problems.
 Case report : A man, 52 years old who has done AV Fitula two weeks ago. Currently patients are using a double lumen catheter (CDL) for routine hemodialysis. One day the patient had his CDL removed. Even though the patient feels thrill in the AV fistula, the nephrorologist still doubts whether the AV fistula is ripe and can be used. For this reason, a Duplex Ultrasound is performed to assess the diameter, velocity flow, PSV and TAMV .By positioning the sample volume in the presumed stenosis site, the Doppler velocity test detects a systolic peak velocity.
 Conclusion: Color flow Doppler imaging should be used as a tool to screen for areas of high velocity and to aid in the optimal placement of the pulsed Doppler sample volume. The pulsed Doppler sample volume should be set at the smallest size possible to detect discrete changes in blood flow meanwhile doppler ultrasound should be use in monitoring for maturation of AV fistulas

Measurement errors in serial echocardiographic assessments of aortic valve stenosis severity.

Transthoracic echocardiography (TTE) evaluation of aortic stenosis (AS) is routinely performed using the continuity equation. Inaccurate measurements of the left ventricular (LV) outflow tract (LVOT) diameter are considered the most common source of error in AS grading. We hypothesized that inconsistency in LVOT velocity time integral (VTI) is an under-recognized cause of AS assessment error. We sought to determine which parameters contribute most towards inconsistencies in AS grading by studying the prevalence of different errors in a historic cohort. We identified patients with mild to severe AS with multiple studies from our database from 1994 to 2018 (n = 988 patients, 2859 studies). Errors were defined when: (1) LVOT diameter changed by > 2mm, (2) LVOT VTI changed by > 15% without change in LV function from the initial TTE, (3) aortic valve (AV) maximum velocity (Vmax), mean pressure gradient (ΔP) or AV VTI decreased by > 15% without change in LV function from prior study. The most common error was the LVOT VTI measurement with 22% prevalence. LVOT diameter, AV VTI, AV Vmax and AV ΔP measurement caused errors in < 7% studies. Patients with normal LV function and more severe AS were more likely to have LVOT VTI errors (P < 0.05). LVOT VTI is a frequent, under-recognized source of error in assessing AS. Greater attention should be directed toward the proper positioning of the pulsed Doppler sample volume, particularly in patients with higher grades of AS and normal systolic function, to ensure accurate and reproducible assessment of AS.

Fetal isovolumetric time intervals as a marker of abnormal cardiac function in fetal anemia from homozygous alpha thalassemia-1 disease.

To determine whether fetal isovolumetric time intervals can be an early sonographic marker of fetal anemia in fetuses with homozygous alpha thalassemia-1. Pregnancies at risk for fetal homozygous alpha thalassemia-1 disease at 18-22weeks were recruited before cordocentesis for hemoglobin typing. Isovolumetric contraction time (ICT) and isovolumetric relaxation time (IRT) intervals were measured by placing pulsed wave Doppler sample volume within the left ventricle to obtain the mitral and aortic waveform. Time intervals were compared between the affected group of homozygous alpha thalassemia-1 fetuses and the unaffected group. Among 70 fetuses at risk, 28 cases were diagnosed as affected by homozygous alpha thalassemia-1 disease. Mean ICT and ICT+IRT intervals in the affected group were significantly longer than in the unaffected group (47.9±12.5ms vs 35.0±6.7ms, p<0.001; and 96.2±13.6ms vs 80.9±10.6ms, p<0.001. ICT effectively predicted affected fetuses with 71.4% sensitivity and 78.6% specificity using a cutoff value ≥40ms. Isovolumetric contraction time was significantly prolonged in fetal anemia from homozygous alpha thalassemia-1 during the early stage of hydropic changes. Because of its simple measurement and high efficacy, ICT can be a useful marker for prenatal screening of abnormal cardiac function in fetal anemia. © 2017 John Wiley & Sons, Ltd.

Abstract 8772: Clinical Correlates of Pulmonary Artery Pulse Wave Velocity in Normal Subjects

Background: In contrast to systemic artery, much less is known about age-related change in pulmonary artery stiffness. Pulse wave velocity (PWV) is an index for vascular stiffness. The purpose of this study is to assess pulmonary artery PWV and investigate their relations to age, body mass index (BMI), pulmonary artery systolic pressure, left ventricular (LV) diastolic pressure, and systemic artery PWV in normal subjects. Methods: Echocardiography with tissue Doppler imaging was performed in 92 normal subjects from 6 to 80 years. To measure pulmonary artery PWV, pulsed Doppler flow wave transmission time (T) between main pulmonary artery proximal (pulmonary valve) and distal point (pulmonary artery bifurcation) were measured. The distance (D) from the pulsed Doppler sample volume in the pulmonary valve to the pulmonary artery bifurcation was measured. The pulmonary artery PWV was defined as T/D. Pulmonary artery systolic pressure was calculated by use of the modified Bernoulli equation, with right atrial pressure assumed to be 10 mmHg. The ratio of early transmitral flow velocity (E) to early mitral annular myocardial velocity (Em) was used as an echocardiography-derived estimate of LV diastolic pressure. Results: Average value of pulmonary artery PWV was 179±58 cm/sec (range: 78 to 450cm/sec), in good agreement with literature values measured using invasive means. Pulmonary artery PWV did not correlate with heart rate. There were significant relationships between pulmonary artery PWV and age (r = 0.69, p &lt; 0.01), body mass index (r = 0.46, p &lt; 0.01), and pulmonary artery systolic pressure (r = 0.54, p &lt; 0.01). A weak but significant relationship between systemic arterial PWV and pulmonary artery PWV was observed (r = 0.38, p &lt; 0.01). There was no significant relationship between pulmonary artery PWV and mitral E/Em. Conclusions: We provide the first evidence of age-related increase in pulmonary artery pulse wave velocity, its association with increasing pulmonary artery systolic pressure and systemic vascular stiffening, and its negative impact on body mass index. Pulmonary artery pulse wave velocity may serve as a novel cardiovascular risk factor.

Relationship between cavitation, rapid loss of echogenicity, and drug release from echogenic liposomes.

Echogenic liposomes (ELIPs), encapsulating air and drug, are being developed for use as vesicles for ultrasound-mediated drug release. Both calcein and a thrombolytic drug have been encapsulated in ELIP and released with 6-MHz color Doppler ultrasound in an in vitro flow system. To elucidate the role of stable or inertial cavitation in loss of echogenicity and drug release, ELIPs were insonified with 6-MHz pulsed Doppler ultrasound within the same flow system. A 10-MHz focused passive cavitation detector (PCD) was placed confocally with the pulsed Doppler sample volume. B-mode images and PCD signals were recorded during ELIP infusion (5 ml/min) and exposed to pulsed Doppler over a range of peak rarefactional pressure amplitudes (0–1.4 MPa) at two pulse repetition frequencies (1250 and 2500 Hz). The mean digital intensities were calculated on each image within two regions of interest placed upstream and downstream of the Doppler sample volume. The thresholds for rapid loss of echogenicity were ascertained from six B-mode images acquired over 30 s. These thresholds were compared to stable and inertial cavitation thresholds. The implications of these data on the mechanism of rapid liberation of gas and drug release will be discussed. [Work supported by the NIH R01 HL059586 and NIH R01 HL7400]

Behavior of Pulmonary Venous Flow during Fetal Respiratory Movements

To test the hypothesis that fetal pulmonary venous flow pulsatility index is lower during fetal respiratory movements than in apnea. Case control. SETTINGS/PATIENTS: Twenty-two normal fetuses of mothers without systemic disease were examined in apnea (controls) and in the presence of fetal respiratory movements (cases). Fetuses were examined by prenatal Doppler echocardiography with color flow mapping. The pulsatility index of the pulmonary vein was obtained by placing the pulsed Doppler sample volume over the right upper or left lower pulmonary vein, and calculating the ratio (maximum velocity [systolic or diastolic]-presystolic velocity/mean velocity). Mean gestational age was 28.9 +/- 2.9 weeks. During fetal apnea, mean systolic, diastolic, and presystolic velocities were, respectively, 0.35 +/- 0.08 m/s, 0.26 +/- 0.07 m/s, and 0.09 +/- 0.03 m/s. In the presence of fetal respiratory movements, mean systolic, diastolic, and presystolic velocities were, respectively, 0.33 +/- 0.1 m/s, 0.28 +/- 0.08 m/s, and 0.11 +/- 0.04 m/s. Pulsatility index pulmonary vein in apnea was 1.25 +/- 0.23 (1.69 to 0.82), and during fetal respiratory movements it was 0.97 +/- 0.2 (1.53 to 0.61). We showed a significant reduction in impedance of pulmonary venous flow, represented by pulmonary vein pulsatility index, during fetal respiratory movements, reflecting modifications of the left atrial dynamics and enhancement of left ventricular compliance.

Cabrol Composite Graft for Aortic Root Replacement: Echocardiographic Imaging

A 55-yr-old woman with history of Marfan syndrome presented with an enlarging aortic arch aneurysm. Fifteen years ago, she had undergone repair of an aortic root aneurysm. A preoperative transthoracic echocardiogram (TTE) revealed normal biventricular function, 3+ tricuspid regurgitation, a small nonobstructive mechanical aortic prosthesis, and an aortic root graft. The distal ascending aorta and aortic arch were dilated, measuring 5 cm in diameter. Left heart catheterization showed normal coronary arteries originating from the aortic root graft, with the left adjacent to the right. The patient was scheduled for aortic arch reconstruction and tricuspid valve repair.

OP02.04: Cardiac biometry and function in fetuses with intracardiac echogenic foci

reflecting a good fetal clinical status. In apnea, the pressure of intrathoracic organs on the fetal heart, mainly the non-expanded lungs, limits ventricular distensibility. Impedance to pulmonary venous flow to the left atrium is represented by the pulsatility index. To test the hypothesis that fetal pulmonary venous flow pulsatility index is lower during fetal respiratory movements than in apnea were our purpose. Methods: Twenty-two normal fetuses of mothers without systemic disease were examined in apnea (controls) and in the presence of fetal respiratory movements (cases). Fetuses were examined by prenatal Doppler echocardiography with color flow mapping. The pulsatility index of the pulmonary vein was obtained placing the pulsed Doppler sample volume over the right upper or left lower pulmonary vein, and applying the formula [maximum velocity (systolic or diastolic)pre-systolic velocity]/mean velocity. Results: Mean gestational age was 28.9 ± 2.9 weeks. During fetal apnea, mean systolic, diastolic and pre-systolic velocities were, respectively, 0.35 ± 0.08 m/s, 0.26 ± 0.07 m/s and 0.09 ± 0.03 m/s. In the presence of fetal respiratory movements, mean systolic, diastolic and pre-systolic velocities were, respectively, 0.33 ± 0.1 m/s, 0.28 ± 0.08 m/s and 0.11 ± 0.04 m/s. Pulsatility index pulmonary vein in apnea was 1.25 ± 0.23 (1.69 to 0.82), and during fetal respiratory movements it was 0.97 ± 0.2 (1.53 to 0.61). Conclusions: We showed a significant reduction in impedance of pulmonary venous flow, represented by pulmonary vein pulsatility index, during fetal respiratory movements, reflecting modifications of the left atrial dynamics and enhancement of left ventricular compliance.

OP02.03: Dynamics of pulmonary venous flow during respiratory movements in the fetus

Respiratory movements influence fetal circulation. Their presence indicates an intact, non-depressed nervous system, reflecting a good fetal clinical status. In apnea, the pressure of intrathoracic organs on the fetal heart, mainly the non-expanded lungs, limits ventricular distensibility. Impedance to pulmonary venous flow to the left atrium is represented by the pulsatility index. To test the hypothesis that fetal pulmonary venous flow pulsatility index is lower during fetal respiratory movements than in apnea were our purpose. Twenty-two normal fetuses of mothers without systemic disease were examined in apnea (controls) and in the presence of fetal respiratory movements (cases). Fetuses were examined by prenatal Doppler echocardiography with color flow mapping. The pulsatility index of the pulmonary vein was obtained placing the pulsed Doppler sample volume over the right upper or left lower pulmonary vein, and applying the formula [maximum velocity (systolic or diastolic)-pre-systolic velocity]/mean velocity. Mean gestational age was 28.9 ± 2.9 weeks. During fetal apnea, mean systolic, diastolic and pre-systolic velocities were, respectively, 0.35 ± 0.08 m/s, 0.26 ± 0.07 m/s and 0.09 ± 0.03 m/s. In the presence of fetal respiratory movements, mean systolic, diastolic and pre-systolic velocities were, respectively, 0.33 ± 0.1 m/s, 0.28 ± 0.08 m/s and 0.11 ± 0.04 m/s. Pulsatility index pulmonary vein in apnea was 1.25 ± 0.23 (1.69 to 0.82), and during fetal respiratory movements it was 0.97 ± 0.2 (1.53 to 0.61). We showed a significant reduction in impedance of pulmonary venous flow, represented by pulmonary vein pulsatility index, during fetal respiratory movements, reflecting modifications of the left atrial dynamics and enhancement of left ventricular compliance.

Acoustic Streaming in Ovarian Cysts

The purpose of this study was to investigate the hypothesis that endometriomas do not show acoustic streaming and then to quantify the streaming velocity of the particles within ovarian cysts that do show acoustic streaming. Ovarian cysts greater than 2 cm in diameter, with internal echoes seen on B-mode sonography, were prospectively evaluated for the presence of acoustic streaming. If acoustic streaming was present, a 2-mm pulsed Doppler sample volume was then placed within the distal portion of the cyst, and the streaming velocity was recorded. Follow-up included review of subsequent sonographic examinations, surgical notes, and histopathologic reports, with the latter being considered the final results if available. Acoustic streaming was detected in 10 (38%) of 26 ovarian cysts, but of the 10 endometriomas, none (0%) showed acoustic streaming (P = .002). Acoustic streaming was detected in 86% (n = 6) of cystadenomas. Four of these were serous cystadenomas, which all showed acoustic streaming, with a velocity range of 1.5 to 3.6 cm/s. Two mucinous cystadenomas showed acoustic streaming with velocities of 0.8 and 2.0 cm/s. Endometriomas appear as cysts containing homogeneous, low-level, "ground glass" echoes on gray scale sonography. Other types of ovarian cysts can also have these appearances. Endometriomas do not show acoustic streaming. Cystadenomas may have streaming velocities within a defined range. Acoustic streaming assessment may therefore prove to be an additional useful tool in assessing ovarian cysts and in completely excluding endometrioma as a diagnosis if a cyst shows acoustic streaming.

The Fetal Doppler Mechanical PR Interval: A Validation Study

Objective: To evaluate the accuracy of pulsed Doppler-derived fetal PR interval measurements obtained by physicians participating in a multicenter prospective fetal echocardiographic study. Methods: Echocardiograms on healthy fetuses were performed and evaluated by 15 pediatric cardiologists/perinatologists across the United States who are participating in a larger clinical trial involving fetuses at risk for autoantibody-associated congenital heart block. Prior to enrolling women in the main trial, each physician was provided with a teaching tape to demonstrate how the pulsed Doppler-derived PR interval is measured. The procedure involves placing a gated pulsed Doppler sample volume in the left ventricle at the junction of the anterior leaflet of the mitral valve and the left ventricular outflow tract in an apical 5-chamber view, and simultaneously obtaining left ventricular filling and emptying. Time intervals are measured from the onset of the mitral A wave (atrial systole) to the onset of the aortic pulsed Doppler tracing (ventricular systole). This represents the mechanical PR interval. Each physician measured the pulsed Doppler-derived fetal PR interval on 5 different subjects recruited from the physician’s specific site. To validate each physician’s technique, the tapes were sent to a central facility and the same intervals were remeasured by an experienced central reader (D.M.F.). A physician was determined to have adequate ability to measure the fetal PR interval if all 5 measurements were within ± 30 ms of the central reader’s measurements, where 30 ms corresponds to 25% of the mean observed in normative PR interval data. This difference was deemed to be the minimum clinically important difference in Doppler PR interval. Results: Fourteen of the 15 physicians were considered to have adequate ability to measure the fetal PR interval according to our established criterion. The overall mean difference between the physicians and the central reader’s measurements was –0.26 ± 11.04 ms (p = 0.84). In addition, 95% of the observed differences were included in the interval (–22.23 to 21.81), which is well within our clinically acceptable range of ± 30 ms. Conclusions: The pulsed Doppler assessment of the mechanical PR interval in the fetus can be accurately performed after minimal training. This technique may be a valuable tool for identification of early and potentially reversible conduction abnormalities in fetuses at risk for more advanced and permanent forms of heart block associated with maternal antibodies to SSA/Ro-SSB/La.

Pulmonary vein pulsatility in fetuses of diabetic mothers: prenatal Doppler echocardiographic study.

To verify the hypothesis that the pulmonary vein pulsatility index is higher in fetuses of diabetic mothers than it is in normal fetuses of nondiabetic mothers. Twenty-four fetuses of mothers with either gestational or previous diabetes (cases), and 25 normal fetuses of mothers without systemic disease (control) were examined. Fetuses were examined through prenatal Doppler and color flow mapping. The pulmonary vein pulsatility index was obtained by placing the pulsed Doppler sample volume over the right superior pulmonary vein and applying the formula (systolic velocity - presystolic velocity)/mean velocity. The mean gestational age of the study fetuses was 30.3 2.7 weeks, and gestational age of the controls was 29 3.3 weeks, with no significant difference in gestational age between groups (p=0.14). Fetuses of diabetic mothers had a mean pulmonary vein pulsatility index of 1.6 1, and those of the control group had an index of 0.86 0.27. Fetuses of diabetic mothers had pulmonary vein pulsatility indexes (parameter easily obtained through Doppler echocardiography that may be related to fetal diastolic function) higher than those in fetuses of mothers with normal glycemia.

44-MHz LiNbO/sub 3/ transducers for UBM-guided Doppler ultrasound

In the post genome-sequencing era, physiological phenotyping of genetically engineered mice is critical to further our understanding of the functional consequences of specific genetic defects. We have developed a 40-50 MHz ultrasound biomicroscopy-(UBM) guided, pulsed Doppler system for the sensitive detection of in vivo blood velocity waveforms in the mouse embryonic cardiovascular system. Our approach uses separate transducers for simultaneous imaging and Doppler blood flow measurements. To this end, unfocused, air-backed lithium niobate (LiNbO3) transducers provide sensitive Doppler detection and the flexibility of adjusting the axial position of the pulsed Doppler sample volume over many millimeters depth range of the collimated ultrasound beam. In this paper we describe the fabrication and characterization of the electromechanical and ultrasonic beam properties of 44-MHz LiNbO3 Doppler transducers. We further demonstrate the utility of these Doppler transducers for interrogating blood vessels such as the dorsal aorta over a range of mouse embryonic stages and axial range-gate depths.

Isovolumic relaxation time corrected for heart rate has a constant value from infancy to adolescence

J Am Soc Echocardiogr 2003;16:221-2.

Transthoracic Doppler echocardiographic measurement of flow velocity and flow velocity reserve in the great cardiac vein and in the left anterior descending coronary artery in children with left ventricular volume overload secondary to ventricular septal defect

M of coronary vein flow and flow velocity reserve has been used as a measure of myocardial blood perfusion. Coronary vein blood flow and flow velocity reserve have been assessed by invasive techniques with thermodilution catheters and Doppler catheters. Recent advances in Doppler and color echocardiographic techniques enable measurements of flow velocities in the great cardiac vein (GCV) and left anterior descending (LAD) coronary artery in children. It may be possible to extend the technique to the assessment of GCV flow in patients with congenital heart disease. This study assesses GCV flow velocity and flow velocity reserve in pediatric patients with left ventricular (LV) volume overload due to a left-to-right shunt, and compares flow velocity reserve in the GCV with flow velocity reserve in the LAD artery. • • • Between October 1999 and July 2001, 36 consecutive patients aged 0.3 to 3 years with ventricular septal defect who underwent cardiac catheterization were prospectively enrolled in the study. The control group consisted of 18 age-matched normal children. They were referred to us because of precordial murmur and enlarged cardiothymic silhouette on chest radiographs. No evidence of structural cardiovascular disease was detected in any subject by 2-dimensional and Doppler echocardiography. All patients’ parents received an explanation of the study and gave informed consent. Studies were performed in a quiet resting state. Echocardiographic examination of the patients was performed in the cardiac catheterization laboratory before routine heart catheterization. Premedication consisted of pethidine hydrochloride administered subcutaneously 1 hour before catheterization. Sedation with thiopental sodium (3 mg/kg) was intravenously administered when necessary. Echocardiographic examination was performed in normal control patients in an outpatient clinic. Sedation with 50 mg/kg chloral hydrate was adminisstered when necessary in young children. Transthoracic Doppler echocardiographic examination was performed using an Aloka SSD-ProSound5500 (Aloka Inc, Tokyo, Japan) with a 5.0or 7.5MHz transducer. The bifurcation of the left main coronary artery into the LAD and left circumflex arteries was imaged from the standard short-axis view of the great vessels. The velocity scale was decreased to the minimum range and then gradually increased until color signals were optimized within the vessel lumen. The color gain was also adjusted to minimize color flow scatter, and the Doppler filter was set at 200 to 400 Hz. After demonstration of coronary color flow signals, the pulsed Doppler sample volume was placed within the LAD artery just distal to the bifurcation of the left main coronary artery, and the sample volume decreased to 0.5 to 1.0 mm. Because the GCV is usually running in the interventricular groove along From the Department of Pediatrics, Akita University School of Medicine, Akita, Japan. Dr. Harada’s address is: Department of Pediatrics, Akita University School of Medicine, Akita 010-8543, Japan. E-mail: kharada@doc.med.akita-u.ac.jp. Manuscript received October 31, 2001; revised manuscript received and accepted January 14, 2002. TABLE 1 Clinical Characteristics and Doppler Measurements

Overview: the current role of the vascular diagnostic laboratory.

T HE TESTING METHODS used in the noninvasive vascular diagnostic laboratory have evolved over the last 40 years to bridge the gap between the subjective clinical assessment of vascular disorders and invasive contrast studies of the arteries and veins. Many of the early noninvasive tests utilized continuous wave Doppler ultrasound to detect blood flow. These tests were referred to as indirect methods because they relied on detection of major changes in pressure or flow produced by arterial or venous disease. Therefore, only hemodynamically significant lesions could be identified reliably. The indirect tests included the periorbital Doppler examination for extracranial carotid artery disease, the continuous wave Doppler evaluation for deep vein thrombosis, and segmental arterial blood pressure measurement in the extremities. Some of these tests, such as measurement of ankle systolic blood pressure, still are useful in the clinical setting, but most have given way to the direct approach of duplex scanning. 1 The principal advantage of duplex scanning is that it obtains both anatomic and physiologic information directly from sites of vascular disease. Since duplex scanning emerged in the 1980s as the preferred noninvasive test for extracranial carotid artery disease, advances in ultrasound technology have extended its applications to the vessels of the abdomen and extremities. This combination of B-mode imaging and spectral analysis of pulsed Doppler signals provided the first opportunity to accurately characterize vascular disease without resorting to invasive procedures. The duplex approach is based on the concept that arterial lesions produce localized disturbances in blood flow patterns that can be characterized by analysis of Doppler flow signals. Accordingly, the B-mode image is used to place a pulsed Doppler sample volume within the vessel of interest, and the local flow pattern is assessed by spectral waveform analysis. Although the B-mode image may be valuable for identifying anatomic variants, arterial wall thickening or calcification, and thrombi in the venous system, it has not been possible to determine accurately the degree of arterial narrowing from the B-mode image alone. Therefore, the classification of arterial disease severity mainly is based on interpretation of pulsed Doppler spectral waveforms. Color-flow imaging is an alternative to spectral waveform analysis for displaying Doppler information. Within certain technical limitations, the color-flow image permits visualization of moving blood in the plane of the B-mode image; it can be helpful for identifying vessels, particularly when they are small, deeply located, or anatomically complex. However, it is difficult to assess disease severity based on the color-flow image alone, and spectral waveforms still are necessary for accurate disease classification. While the noninvasive vascular diagnostic laboratory initially was of interest only to vascular

Velocity distributions in the left ventricular outflow tract in patients with valvular aortic stenosis. Effect on the measurement of aortic valve area by using the continuity equation.

The cross-sectional velocity distribution in the left ventricular outflow tract was studied in 40 patients with valvular aortic stenosis. Doppler colour flow mapping and a time-interpolation method were used to construct the cross-sectional velocity and time-velocity integral (TVI) profiles at different levels. By using pulsed Doppler, the subaortic flow velocity was sampled from the anterior, middle and posterior regions along the diameter of the left ventricular outflow tract (at 0.5 to 1.0 cm proximal to the aortic anulus) in the apical long axis view. Thus, for each patient, three aortic valve areas were calculated by using the continuity equation. Each patient was assigned to one of three subgroups according to the left ventricular ejection fraction (EF): subgroup I with EF < or = 25% (n = 10), subgroup II with 25% < EF < or = 50% (n = 17) and subgroup III with EF > 50% (n = 13). Velocity distributions in the three subgroups were compared to each other. (1) The velocity distribution in the left ventricular outflow tract was skewed with the highest velocities and TVIs along the anterior wall and septum. The skewness of the velocity distribution was more pronounced in the apical long axis view than in the four chamber view (P < 0.05). The extent of skewness of the TVI profile was positively correlated to the left ventricular EF both in the long axis view (r = 0.63; P < 0.001) and in the four chamber view (r = 0.57; P < 0.001). (2) Pulsed Doppler sampling from different regions along the diameter produced different TVIs, and therefore yielded significantly different calculated aortic valve areas, especially in subgroup III. Due to the skewness of the velocity distribution in the left ventricular outflow tract, location of the pulsed Doppler sample volume significantly affects the accuracy of aortic valve area calculation by using the continuity equation, especially in patients with relatively high left ventricular EF. In patients with low EF, selection of pulsed Doppler sampling site is less important.

Experimental study of the effects of pulsed Doppler sample volume size and position on the Doppler spectrum

With a pulsed Doppler system, the recorded Doppler spectrum is expected to vary depending upon the sample volume size relative to the diameter of the vessel, the position of the sample volume in the vessel and the velocity profile. In the in vitro experiments described in this paper, the velocity profile was kept constant by using steady parabolic flow in a flow model. As the Doppler sample volume size and position were changed, the maximum variations of quantitative measurements from the Doppler spectrum were determined. The maximum, mean and mode frequencies and spectral broadening index (SBI) were affected by the position of the sample volume but to a lesser degree by its length (1.5–5.0 mm) relative to the 9.5 mm beam path length across the tube. When the centre of the Doppler sample volume was moved within the central 25% of the tube, the maximum variations were as follows: maximum frequency 3–5%, mean frequency 8–9%, mode frequency 8–9% and SBI 16–18%, where the range indicates the effect of increasing the sample volume size. Based on these results obtained under steady flow conditions in vitro, it is concluded that quantification of pulsed Doppler spectra may be feasible if the sample volume is positioned within the central 25% of the vessel.

Effect of frequency dependent processes on pulsed Doppler sample volume

The change in the frequency spectrum of ultrasound pulses as a result of frequency dependent attenuation and scatter is known to alter the spectrum of Doppler signals from blood flow parallel to the beam axis. It is shown here that the change in pulse shape accompanying this pulse spectrum change as a result of these processes, together with the velocity dispersion accompanying frequency dependent attenuation and linked to it by the Kramers-Kronig relations, will change the pulsed Doppler sample volume shape and position.

Does color-flow imaging improve the accuracy of duplex carotid evaluation?

To determine whether color-flow imaging enhances the accuracy of noninvasive carotid evaluation, the results of carotid duplex examinations from two laboratories, one with color-flow and the other with standard duplex imaging were compared. The techniques used by both laboratories were identical. All studies were interpreted by one of the authors, using the same criteria. From October 1988 through December 1989, 307 internal carotid arteries were evaluated with both color-flow imaging and standard angiography; and 206 underwent routine duplex scanning and angiography. Perfect agreement between test and angiographic results was significantly better with color-flow (86.6%) than with conventional duplex scanning (79.6%), p = 0.034 (t test for independent samples). Significantly fewer vessels were over classified by one category with color-flow (8.5%) than with routine duplex scanning (16.5%), p = 0.006. However, no difference was found in the number underclassified by one category (4.5% vs 3.4%), p = 0.5. Although these data support the accuracy of both modalities, there appears to be a trend toward improved results with the newer method. We attribute this to more precise placement of the pulsed Doppler sample volume afforded by the color-flow image.