Doppler Sample Volume Research Articles

Transesophageal Echocardiography Following Left Atrial Appendage Electrical Isolation: Diagnostic Pitfalls and Clinical Implications.

Following left atrial appendage (LAA) electrical isolation, the decision on whether to continue oral anticoagulation after successful atrial fibrillation ablation is based on the study of its mechanical function on transesophageal echocardiography (TEE). In this cohort, LAA contraction is absent and the incorrect interpretation of emptying flow velocities can lead to unwanted clinical sequelae. One hundred and sixty consecutive TEE exams performed to evaluate the LAA mechanical function following its electrical isolation were reviewed by an experienced operator blinded to the original diagnosis of LAA dysfunction. The rate of diagnostic discrepancy in the assessment LAA dysfunction and its clinical implications were evaluated. Diagnostic discrepancy with misclassification of the LAA mechanical function occurred 36% (58/160) of TEE exams. In most cases (57/58), such discrepancy was observed in the setting of an incorrect original diagnosis of a normal LAA mechanical function despite absent/reduced or inconsistent LAA contraction. This main source of this wrong diagnosis was the wrong interpretation of passive LAA flows (34/57; 60%), followed by failure to identify dissociated firing (15/57; 26%). In rare cases (8/57; 14%), velocities of surrounding structures were interpreted as LAA flow due to misplacement of the pulsed-wave Doppler sample volume. Following LAA isolation, the proportion of patients who experienced a cerebrovascular event while off oral anticoagulation due to the misclassification of their LAA mechanical function was 70% (7/10 [95% CI, 40%-89%]). Underdiagnosis of LAA mechanical dysfunction is common in TEEs performed following LAA electrical isolation, and it is associated with an increased risk of cerebrovascular events owing to oral anticoagulation discontinuation despite absent/reduced LAA contraction. Careful review of the TEE exam by an operator with specific expertise in LAA imaging and familiar with the functional implications of LAA isolation is necessary before interrupting oral anticoagulation in this cohort.

Pulsed Wave Doppler Measurements of Maximum Velocity: Dependence on Sample Volume Size.

Pulsed wave (PW) Doppler ultrasound is routinely used in the clinic to assess blood flow. Our annual Doppler quality assurance tests revealed unexpectedly large errors in measurement of maximum velocity, exceeding our tolerance (error >20%), when using certain scanners with small Doppler sample volume dimensions. The aim of this study was to assess the dependence of maximum velocity estimates on PW Doppler sample volume size. A flow phantom with known steady flow was used to acquire maximum velocity estimates (maximum velocities of 24, 39 and 85 cm/s and sample volume range of 0.3-20 mm) with a variety of transducers and scanners in clinical use (51 probes from 4 manufacturers). Selected acoustic outputs were characterized using free-field hydrophone measurements. All maximum velocity estimates were within our tolerance for sample volume sizes ≥1.5 mm, although maximum velocity estimates typically increased with decreasing sample volume size. Errors exceeding our tolerance were commonly found for one manufacturer when using smaller sample volumes, resulting in up to 75% overestimation. Although intrinsic spectral broadening based on transit time considerations may help explain our findings, the sample volume dependence raises potential clinical concerns that users should be aware of and which manufacturers should consider addressing.

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

Development of a Duplex Ultrasound Protocol for Baseline and Follow-Up Imaging of a Branched Aortic Endoprosthesis

Branched endoprostheses for endovascular repair of pararenal and thoracoabdominal aortic aneurysms are undergoing evaluation in prospective clinical trials. Duplex ultrasound has been a cornerstone of surveillance for vascular reconstructions. This paper describes the development and deployment of a standardized duplex imaging protocol to evaluate individuals who have undergone endovascular repair of their thoracoabdominal aortic aneurysm. Ultrasound imaging is performed after an 8 to 12 hour fast to minimize the presence of bowel gas and allow for optimal imaging of abdominal vascular structures. Doppler measurements of peak systolic and end diastolic velocity are made at specific arterial segments in the aorta and the celiac, superior mesenteric, and renal arteries. Resistive indices are also recorded in the segmental and arcuate arteries of both kidneys. Pulsed-wave Doppler is used to record spectral Doppler data and color Doppler is used to image all arterial segments and ensure proper placement of the Doppler sample volume and ensure correct angle of interrogation. Implementation of a standardized duplex ultrasound imaging protocol can be used to image and follow individuals who have received the Thoracoabdominal Branch Endoprosthesis (TAMBE) device and branched endovascular aneurysm repair (BEVAR). Ultrasound may provide complementary findings and may add information to the computed tomography angiography imaging for following these individuals.

Image-Free Ultrasound Blood-Flow Monitoring Circuit System with Automatic Range-Gate Positioning Scheme: A Pilot Study

This work proposes a proof-of-concept ultrasound blood-flow-monitoring circuit system using a single-element transducer. The circuit system consists of a single-element ultrasonic transducer, an analog interface circuit, and a field-programmable gate array (FPGA). Since the system uses a single-element transducer, an ultrasound image cannot be reconstructed unless scanning with mechanical movement is used. An ultrasound blood-flow monitor basically needs to acquire a Doppler sample volume by positioning a range gate at a vessel region on a scanline. Most recent single-transducer-based ultrasound pulsed-wave Doppler devices rely on a manual adjustment of the range gate to acquire Doppler sample volumes. However, the manual adjustment of the range gate depends on the user’s experience, and it can be time consuming if a transducer is not properly positioned. Thus, automatic range-gate-positioning is more desirable for image-free pulsed-wave Doppler devices. This work proposes a circuit system which includes a new automatic range-gate-positioning scheme. It blindly tracks the position of a blood vessel on a scanline by using the accumulation of Doppler amplitude deviations and a hysteresis slicing function. The proposed range-gate-positioning scheme has been implemented in an FPGA for real-time operation and is based on addition-only computations, except for filter parts to reduce the complexity of computation in the hardware. The proposed blood-flow-monitoring circuit system has been implemented with discrete commercial chips for proof-of-concept purposes. It uses a center frequency of 2 MHz and a system-clock frequency of 20 MHz. The FPGA only utilizes 5.6% of slice look-up-tables (LUTs) for implementation of the range-gate-positioning scheme. For measurements, the circuit system was utilized to interrogate a customized flow phantom model, which included two vessel-mimicking channels. The circuit system successfully acquired Doppler sample volumes by positioning a range gate on a fluid channel. In addition, the estimated Doppler shift frequency shows a good agreement with the theoretical value.

A modified Dabestani-Mahan formula estimates a normal pulmonary artery systolic pressure: a single-center retrospective study

Abstract Background Pulmonary artery systolic pressure (PASP) is increasingly used as an important datapoint in clinical decision-making and prognostication even in specialties outside of cardiology. Estimation of PASP by Doppler quantification using tricuspid regurgitation (TR) peak velocity is commonly used and correlates well with invasive measurement by right heart catheterization. Further study of transthoracic echocardiogram (TTE) techniques to estimate PASP is needed to provide this datapoint in the absence of sufficient Doppler data for the TR peak velocity method. One technique using right ventricular outflow tract acceleration time (AT) to estimate mean pulmonary artery pressure (MPAP) has been proposed by Dabestani Et al. by the equation MPAP=90-(0.62x AT). Assuming a linear relationship between MPAP and PASP, as suggested by Chemla Et al. by MPAP=(0.61xPASP)+2, a modified formula PASP=145-AT could possibly estimate a normal PASP ≤25 mmHg. Purpose To examine if a modified Dabestani-Mahan formula PASP=145-AT can estimate a normal PASP ≤25 mmHg as calculated by the TR peak velocity method. Methods We queried the electronic medical record at our institution for a sample of 300 patients who had a TTE performed between 2017 and 2020. Each TTE was reviewed and PASP was estimated for each using the TR peak velocity method. A right atrial pressure of 3 mmHg, 8 mmHg, or 15 mmHg was used in the estimation based on inferior vena cava diameter and collapsibility in keeping with the 2015 American Society of Echocardiography guidelines. A short axis view of pulmonary flow using the pulse-waved Doppler sample volume over the transpulmonary valve jet was then reviewed. The time from onset of ejection to peak flow velocity was measured manually as AT in milliseconds using Change Healthcare Cardiology Web Software Package 14.1.1. The measured AT was averaged over three cardiac cycles. Patients with a heart rate between 60 and 100 beats per minute at time of TTE and with sufficient Doppler data to estimate PASP by TR peak velocity and to measure AT were included in a logistic regression analysis. Results 154 patients were included in the statistical analysis. Patients who had a right ventricular outflow tract acceleration time greater than 120 milliseconds, giving a PASP ≤25 mmHg by the modified formula PASP=145-AT, had a 36 times greater odds of having a PASP ≤25 mmHg by the TR peak velocity method (OR=36.0, 95% CI=10.36–125.12, p<0.001). Conclusion(s) Based on a single-center sample, a right ventricular outflow tract acceleration time greater than 120 milliseconds could be used to estimate a normal pulmonary artery systolic pressure less than or equal to 25 mmHg in the absence of sufficient Doppler data for the commonly used TR peak velocity method. Funding Acknowledgement Type of funding sources: None.

AIUM Practice Parameter for the Performance of Duplex Sonography of Native Renal Vessels

AIUM Practice Parameter for the Performance of Duplex Sonography of Native Renal Vessels

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.

Impact of left ventricular outflow tract flow acceleration on aortic valve area calculation in patients with aortic stenosis

Objective: Due to its circular shape, the area of the proximal left ventricular tract (PLVOT) adjacent to aortic valve can be derived from a single linear diameter. This is also the location of flow acceleration (FA) during systole, and pulse wave Doppler (PWD) sample volume in the PLVOT can lead to overestimation of velocity (V1) and the aortic valve area (AVA). Therefore, it is recommended to derive V1 from a region of laminar flow in the elliptical shaped distal LVOT (away from the annulus). Besides being inconsistent with the assumptions of continuity equation (CE), spatial difference in the location of flow and area measurement can result in inaccurate AVA calculation. We evaluated the impact of FA in the PLVOT on the accuracy of AVA by continuity equation (CE) in patients with aortic stenosis (AS).Methods: CE-based AVA calculations were performed in patients with AS once with PWD-derived velocity time integral (VTI) in the distal LVOT (VTILVOT) and then in the PLVOT to obtain a FA velocity profile (FA-VTILVOT) for each patient. A paired sample t-test (P < 0.05) was conducted to compare the impact of FA-VTILVOT and VTILVOT on the calculation of AVA.Result: There were 46 patients in the study. There was a 30.3% increase in the peak FA-VTILVOT as compared to the peak VTILVOT and AVA obtained by FA-VTILVOT was 29.1% higher than obtained by VTILVOT. p]Conclusion: Accuracy of AVA can be significantly impacted by FA in the PLVOT. LVOT area should be measured with 3D imaging in the distal LVOT.

Doppler US and CT Diagnosis of Nutcracker Syndrome.

Nutcracker syndrome (NCS) is a syndrome caused by compression of the left renal vein (LRV), between the abdominal aorta and the superior mesenteric artery, resulting in hypertension of the LRV and hematuria. Doppler ultrasonography (US) has been commonly used for the diagnosis of NCS. However, several technical issues, such as Doppler angle and sample volume, need to be considered to obtain satisfactory results. In addition, morphologic changes of the LRV and a jetting phenomenon across the aortomesenteric portion of the LRV on contrast-enhanced computed tomography (CECT) are diagnostic clues of NCS. With proper Doppler US and CECT, NCS can be diagnosed noninvasively.

Evaluation of Examiner Performance Using a Duplex Ultrasound Simulator. Flow Velocity Measurements in Dialysis Access Fistula Models

We developed a duplex ultrasound simulator for training and assessment of scanning skills. We used the simulator to test examiner performance in the measurement of flow velocities in dialysis access fistulas. Test cases were created from 3-D ultrasound scans of two dialysis access fistulas by reconstructing 3-D blood vessel models and simulating blood flow velocity fields within the lumens. The simulator displays a 2-D B-mode or color Doppler image corresponding to transducer position on a mannequin; a spectral waveform is generated according to Doppler sample volume location and system settings. Examiner performance was assessed by comparing the measured peak systolic velocity (PSV) with the true PSV provided by the computational flow model. The PSV measured by four expert examiners deviated from the true value by 7.8 ± 6.1%. The results indicate the ability of the simulator to objectively assess an examiner's measurement accuracy in complex vascular targets.

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.

Assessment of modified myocardial performance index in foetuses with growth restriction.

To evaluate the modified myocardial performance index (Mod-MPI) in foetuses with growth restriction and compare this index with appropriate for gestational age foetuses. A prospective cross-sectional case-control study was conducted involving 76 singleton foetuses between 24 and 34 weeks of gestation divided into three groups (24 appropriate growth foetuses, 30 foetuses with estimated weight between the 3rd and 10th percentiles and 22 foetuses with estimated weight < 3rd percentile, according to the Hadlock table). The Mod-MPI was obtained in the plane of the four chamber view, and the spectral Doppler sample volume was placed in the lateral wall of the aorta, close to the mitral valve. Doppler of umbilical artery was normal in all cases. Analysis of variance (ANOVA) was used to compare the groups and the intra-class correlation coefficient (ICC) was used to assess intra- and inter-observer reproducibility. The mean Mod-MPI in the groups of appropriate for gestational age, estimated weight between the 3rd and 10th percentiles, and estimated weight < 3rd percentile was 0.32 +/- 0.05, 0.35 +/- 0.05 and 0.36 +/- 0.06, respectively; there was no statistical difference between the groups (p = 0.072). There was good intra- and inter-observer reproducibility (ICC = 0.726 and 0.760, respectively). Mod-MPI was not significantly different between foetuses appropriate for gestational age and those with growth restriction. Mod-MPI proved to be a feasible and reproducible technique.

Development of a Duplex Ultrasound Simulator and Preliminary Validation of Velocity Measurements in Carotid Artery Models.

Duplex ultrasound scanning with B-mode imaging and both color Doppler and Doppler spectral waveforms is relied upon for diagnosis of vascular pathology and selection of patients for further evaluation and treatment. In most duplex ultrasound applications, classification of disease severity is based primarily on alterations in blood flow velocities, particularly the peak systolic velocity (PSV) obtained from Doppler spectral waveforms. We developed a duplex ultrasound simulator for training and assessment of scanning skills. Duplex ultrasound cases were prepared from 2-dimensional (2D) images of normal and stenotic carotid arteries by reconstructing the common carotid, internal carotid, and external carotid arteries in 3 dimensions and computationally simulating blood flow velocity fields within the lumen. The simulator displays a 2D B-mode image corresponding to transducer position on a mannequin, overlaid by color coding of velocity data. A spectral waveform is generated according to examiner-defined settings (depth and size of the Doppler sample volume, beam steering, Doppler beam angle, and pulse repetition frequency or scale). The accuracy of the simulator was assessed by comparing the PSV measured from the spectral waveforms with the true PSV which was derived from the computational flow model based on the size and location of the sample volume within the artery. Three expert examiners made a total of 36 carotid artery PSV measurements based on the simulated cases. The PSV measured by the examiners deviated from true PSV by 8% ± 5% (N = 36). The deviation in PSV did not differ significantly between artery segments, normal and stenotic arteries, or examiners. To our knowledge, this is the first simulation of duplex ultrasound that can create and display real-time color Doppler images and Doppler spectral waveforms. The results demonstrate that an examiner can measure PSV from the spectral waveforms using the settings on the simulator with a mean absolute error in the velocity measurement of less than 10%. With the addition of cases with a range of pathologies, this duplex ultrasound simulator will be a useful tool for training health-care providers in vascular ultrasound applications and for assessing their skills in an objective and quantitative manner.

Improving the accuracy of effective orifice area assessment after transcatheter aortic valve replacement: validation of left ventricular outflow tract diameter and pulsed-wave Doppler location and impact of three-dimensional measurements.

Echocardiographic calculation of effective orifice area (EOA) after transcatheter aortic valve replacement is integral to the assessment of transcatheter heart valve (THV) function. The aim of this study was to determine the most accurate method for calculating the EOA of the Edwards SAPIEN and SAPIEN XT THVs. One hundred intraprocedural transesophageal echocardiograms were analyzed. To calculate the post-transcatheter aortic valve replacement left ventricular outflow tract (LVOT) stroke volume (SV), four diameters were measured using two-dimensional echocardiography: (1) baseline LVOT diameter (LVOTd_PRE), (2) postimplantation LVOT diameter, (3) native aortic annular diameter, and (4) THV in-stent diameter. Four corresponding areas were planimetered by three-dimensional echocardiography. Two LVOT velocity-time integrals (VTI) were measured with the pulsed-wave Doppler sample volume at (1) the proximal (apical) edge of the valve stent or (2) within the valve stent at the level of the THV cusps. LVOT velocity-time integral with the sample volume at the proximal edge of the valve stent was used with the LVOT and aortic annular measurements above, whereas in-stent VTI was paired with the in-stent THV diameter to yield eight different SVs. Right ventricular outflow tract (RVOT) SV was calculated using RVOT diameter and RVOT VTI and was used as the primary comparator. Transaortic VTI was obtained by continuous-wave Doppler, and EOA calculations using each SV measurement were compared with (1) EOA calculated using RVOTSV and (2) planimetered aortic valve area using three-dimensional echocardiography (AVAplanimetry3D). Post-transcatheter aortic valve replacement EOA calculated using LVOTd_PRE was not significantly different from EOA calculated using RVOTSV (1.88±0.33 vs 1.86±0.39cm(2), P=.36) or from AVAplanimetry3D (1.85±0.28, P=.38, n=34). All other two-dimensional EOA calculations were statistically larger than EOA calculated using RVOTSV. All three-dimensional echocardiography-based EOA calculations were statistically different from AVAplanimetry3D. The most accurate EOA after implantation of a balloon-expandable THV is calculated using preimplantation LVOT diameter and VTI.

PM410 Poor tissue Doppler sample volume placement leads to errors in estimates of left ventricular filling pressures

PM410 Poor tissue Doppler sample volume placement leads to errors in estimates of left ventricular filling pressures

Decreasing Tropomyosin Phosphorylation Rescues Tropomyosin-induced Familial Hypertrophic Cardiomyopathy

Studies indicate that tropomyosin (Tm) phosphorylation status varies in different mouse models of cardiac disease. Investigation of basal and acute cardiac function utilizing a mouse model expressing an α-Tm protein that cannot be phosphorylated (S283A) shows a compensated hypertrophic phenotype with significant increases in SERCA2a expression and phosphorylation of phospholamban Ser-16 (Schulz, E. M., Correll, R. N., Sheikh, H. N., Lofrano-Alves, M. S., Engel, P. L., Newman, G., Schultz Jel, J., Molkentin, J. D., Wolska, B. M., Solaro, R. J., and Wieczorek, D. F. (2012) J. Biol. Chem. 287, 44478-44489). With these results, we hypothesized that decreasing α-Tm phosphorylation may be beneficial in the context of a chronic, intrinsic stressor. To test this hypothesis, we utilized the familial hypertrophic cardiomyopathy (FHC) α-Tm E180G model (Prabhakar, R., Boivin, G. P., Grupp, I. L., Hoit, B., Arteaga, G., Solaro, R. J., and Wieczorek, D. F. (2001) J. Mol. Cell. Cardiol. 33, 1815-1828). These FHC hearts are characterized by increased heart:body weight ratios, fibrosis, increased myofilament Ca(2+) sensitivity, and contractile defects. The FHC mice die by 6-8 months of age. We generated mice expressing both the E180G and S283A mutations and found that the hypertrophic phenotype was rescued in the α-Tm E180G/S283A double mutant transgenic animals; these mice exhibited no signs of cardiac hypertrophy and displayed improved cardiac function. These double mutant transgenic hearts showed increased phosphorylation of phospholamban Ser-16 and Thr-17 compared with the α-Tm E180G mice. This is the first study to demonstrate that decreasing phosphorylation of tropomyosin can rescue a hypertrophic cardiomyopathic phenotype.

High-frame-rate retrospective imaging of mouse-embryo cardiac function using annular array and Doppler-derived gating

A high-frequency (HF) imaging system based on a custom 5-element, 40 MHz annular array has been used to study the cardiovascular development of mouse embryos. High-frame-rate imaging of the heart dynamics was achieved using a retrospective reconstruction method based on Doppler-derived electrocardiogram (ECG) waveforms and respiratory gating was used to suppress motion artifacts. The ECG signals were obtained by measuring blood-flow velocities in major arteries of in-vivo mouse embryos using a custom HF Doppler apparatus made from two 20 MHz, single-element, PZT transducers with a Doppler sample volume of 15 mm. Co-registered M-mode data were acquired from the annular array excited with a 5-channel pulser/receiver. A synthetic-focusing (SF) algorithm was used to improve spatial resolution ( 10 mm) and signal-to-noise ratio (>45 dB). This technique was used on embryos aged from 11.5 to 14.5 days and provided high-resolution, morphologically correct B-mode cine-loops of the heart chamber dynamics at frame rates of 1 kHz. The ultra-fine temporal resolution (1 ms) allowed for precise quantification of the mean cardiac cycle length and detailed visualization of fast events such as opening and closing of the mitral valve. The speckle characteristics of the high-resolution images could be used to assess blood flow and to quantify myocardial strain at each developmental stage of the embryonic heart.

Effect of Velocity Profile Skewing on Blood Velocity and Volume Flow Waveforms Derived From Maximum Doppler Spectral Velocity

Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (Vmax) can lie outside the Doppler sample volume (SV). The link between Vmax and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected Vmax waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in Vmax waveforms when using a small, centered SV, although peak Vmax was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from Vmax was typically within ±15%, although substantial skewing and use of a small SV caused 10%–25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. Vmax pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into Vmax-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the Vmax and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies.

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.