Accuracy of volumetric flow rate measurements: an in vitro study using modern ultrasound scanners

Review of the role of imaging in the diagnosis of priapism

Imaging has a specific role in the diagnosis and management of priapism. The primary imaging modality is ultrasound with colour Doppler (CDUS) which can accurately assess the hemodynamics of the cavernosal arteries. This is particularly useful in equivocal cases and can help differentiate ischemic from non-ischemic priapism as well as confirm the presence and location of arterio-venous fistulae post penile trauma. Furthermore, CDUS is invaluable in the post treatment follow up of non-ischemic priapism. Contrast enhanced magnetic resonance imaging (MRI) can demonstrate the extent of cavernosal necrosis in ischemic priapism and in conjunction with computer tomography (CT) has an important role in excluding underlying malignancy. MRI and CT angiography are used to evaluate pudendal arterial anatomy, which can be extremely variable and aids in the management of non-ischemic priapism. In selected cases of non-ischemic priapism, catheter angiography and transcatheter embolization of arteriovenous fistulae is an effective treatment. This review will examine the specific roles of different imaging modalities in the subtypes of priapism as well as highlight some of the pitfalls encountered in imaging.

Therapeutic outcomes and analysis of Doppler findings in 25 patients with non-ischemic priapism

Non-ischemic priapism (NiP) is painless partial tumescence caused by genital trauma and the formation of intracorporal arterio-venous fistula. This is a retrospective study of 25 men with NiP and reports the long-term erectile function and colour doppler ultrasound (CDUS) findings after treatment for NiP. Unstimulated CDUS was performed at diagnosis, 1 week and at last follow-up after treatment. CDUS traces were analysed: peak systolic velocity (PSV), end diastolic velocity (EDV), resistive index (RI) and mean velocity (MV) were calculated. Erectile function was assessed using the IIEF-EF questionnaire. At the last follow-up (median 24 months), 16 men had normal erectile function (64%): median IIEF-EF score 29 (IQR 28.5-30; σ2 2.78) and nine had erectile dysfunction (36%): median IIEF-EF score 17 (IQR 14-22; σ2 33.6). MV and EDV were statistically higher in those patients with erectile dysfunction at last follow-up compared to patients with normal erectile function: median MV 5.3 cm/s (IQR 2.4-10.5 cm/s; σ2 34) vs 2.95 cm/s (IQR 1.03-3.95; σ2 3.4) p < 0.002 and median EDV 4.0 cm/s (IQR 1.5-8.0; σ2 14.7) vs 0 cm/s (IQR 0-1.75; σ2 2.21) p < 0.004. Erectile dysfunction was observed in 36% of men treated for NiP and was associated with abnormal low resistance resting CDUS waveforms. Further investigation for persistent arteriovenous fistulation should be considered in these patients.

Fetal cardiovascular blood flow MRI: techniques and applications

Fetal cardiac MRI is challenging due to fetal and maternal movements as well as the need for a reliable cardiac gating signal and high spatiotemporal resolution. Ongoing research and recent technical developments to address these challenges show the potential of MRI as an adjunct to ultrasound for the assessment of the fetal heart and great vessels. MRI measurements of blood flow have enabled the assessment of normal fetal circulation as well as conditions with disrupted circulations, such as congenital heart disease, along with associated organ underdevelopment and hemodynamic instability. This review provides details of the techniques used in fetal cardiovascular blood flow MRI, including single slice and volumetric imaging sequences, post-processing and analysis, along with a summary of applications in human studies and animal models.

Use of 3D anatomical models in mock circulatory loops for cardiac medical device testing

INTRODUCTION

Mock circulatory loops (MCLs) are mechanical representations of the cardiovascular system largely used to test the hemodynamic performance of cardiovascular medical devices (MD). Thanks to 3 dimensional (3D) printing technologies, MCLs can nowadays also incorporate anatomical models so to offer enhanced testing capabilities. The aim of this review is to provide an overview on MCLs and to discuss the recent developments of 3D anatomical models for cardiovascular MD testing.

METHODS

The review first analyses the different techniques to develop 3D anatomical models, in both rigid and compliant materials. In the second section, the state of the art of MCLs with 3D models is discussed, along with the testing of different MDs: implantable blood pumps, heart valves, and imaging techniques. For each class of MD, the MCL is analyzed in terms of: the cardiovascular model embedded, the 3D model implemented (the anatomy represented, the material used, and the activation method), and the testing applications.

DISCUSSIONS AND CONCLUSIONS

MCLs serve the purpose of testing cardiovascular MDs in different (patho-)physiological scenarios. The addition of 3D anatomical models enables more realistic connections of the MD with the implantation site and enhances the testing capabilities of the MCL. Current attempts focus on the development of personalized MCLs to test MDs in patient-specific hemodynamic and anatomical scenarios. The main limitation of MCLs is the impossibility to assess the impact of a MD in the long-term and at a biological level, for which animal experiments are still needed.

Z-Score Reference Ranges for Umbilical Vein Diameter and Blood Flow Volume in Normal Fetuses

OBJECTIVES

To establish Z-scores for the diameter and blood flow volume of the umbilical vein (UV) in normal fetuses.

METHODS

This was a prospective study involving 907 normal fetuses. We measured the diameter (Duv) of two different segments of the UV (FUV: the free loop of the UV; FIUV: the fetal intra-abdominal UV). Next, we calculated the blood flow volume (Quv). Z-scores were created for both Duv and Quv using gestational age, femur length, and biparietal diameter as independent variables.

RESULTS

We successfully acquired 858 (94.6%) normal fetal measurements. Between 20 and 39 weeks, the Duv of the FUV and FIUV increased from 0.38 to 0.80 cm and from 0.33 to 0.70 cm, respectively. The Quv of the FUV and FIUV increased from 32.66 to 381.88 ml/min and from 31.50 to 360.15 ml/min, respectively. Linear or quadratic regression models were best fitted between the parameters of UV and the independent variables. Z-scores were successfully determined for both the Duv and Quv.

CONCLUSIONS

The calculation of Z-scores for the Duv and Quv is simple by applying standard statistical methods. These Z-scores may be useful to evaluate placental circulation and provide a rationale for monitoring and evaluating the prognosis of fetuses.

An in vitro Assessment of the Haemodynamic Features Occurring Within the True and False Lumens Separated by a Dissection Flap for a Patient-Specific Type B Aortic Dissection

One of the highest mortality rates of cardiovascular diseases is aortic dissections with challenging treatment options. Currently, less study has been conducted in developing in vitro patient-specific Type B aortic dissection models, which mimic physiological flow conditions along the true and false lumens separated by a dissection flap with multiple entry and exit tears. A patient-specific Stanford Type B aortic dissection scan was replicated by an in-house manufactured automatic injection moulding system and a novel modelling technique for creating the ascending aorta, aortic arch, and descending aorta incorporating arterial branching, the true/false lumens, and dissection flap with entry and exit intimal tears. The physiological flowrates and pressure values were monitored, which identified jet stream fluid flows entering and exiting the dissection tears. Pressure in the aorta’s true lumen region was controlled at 125/85 mmHg for systolic and diastolic values. Pressure values were obtained in eight sections along the false lumen using a pressure transducer. The true lumen systolic pressure varied from 122 to 128 mmHg along the length. Flow patterns were monitored by ultrasound along 12 sections. Detailed images obtained from the ultrasound transducer probe showed varied flow patterns with one or multiple jet steam vortices along the aorta model. The dissection flap movement was assessed at four sections of the patient-specific aorta model. The displacement values of the flap varied from 0.5 to 3 mm along the model. This model provides a unique insight into aortic dissection flow patterns and pressure distributions. This dissection phantom model can be used to assess various treatment options based on the surgical, endovascular, or hybrid techniques.

Endovascular Embolization in Problematic Hemodialysis Arteriovenous Fistulas: A Nonsurgical Technique

Introduction:

In the past, surgical techniques were considered gold standard practice for obliterating the accessory veins, reducing the flow across the high flowing arteriovenous fistulas (AVFs), or for closing the problematic hemodialysis AVFs. However, recently endovascular embolization has emerged as a safe and cost-effective alternative to these surgical techniques. In this study, technical and clinical success, and safety of endovascular embolization have been evaluated for accessory vein obliteration, flow reduction, and fistula closure in problematic AVFs using various embolizing agents.

Methods:

This is a retrospective study of patients with problematic hemodialysis AVFs, who underwent endovascular embolization for accessory vein obliteration, flow reduction, and AVF closure at our center from February 2017 to January 2019 with various embolic agents like vascular plugs (VP), thrombin, coils, and glue. Follow-up was done at 1 week, 3 months, 6 months, and annually thereafter.

Results:

In this study 30 patients with problematic hemodialysis AVFs [Left brachiocephalic fistula (BCF) (n = 22), right BCF (n = 4), and left radiocephalic fistula (RCF) (n = 4)], underwent endovascular embolization for accessory vein obliteration (n = 6), flow reduction (n = 3), and AVF closure (n = 21). Of the 6 patients undergoing embolization for obliteration of accessory collateral, 4 patients had nonmaturing AVFs and 2 patients had symptoms of venous hypertension (VH). Post embolization, all 4 AVFs matured over a month and symptoms of VH completely resolved within a week. Three patients who underwent embolization for flow reduction had patent AVF (on doppler) post procedure and they achieved adequate flow during dialysis with complete resolution of symptoms of VH. Out of 21 patients, who underwent endovascular closure, complete AVF thrombosis was seen in 18 patients only with the use of VP, while 4 patients required additional procedure to achieve complete thrombosis of AVF.

Conclusion:

Endovascular embolization in problematic hemodialysis AVF is a safe and cost-effective alternative to open surgical methods and vascular plug could be embolic agent of choice for AVF closure.

Common Carotid Artery Volume Flow: A Comparison Study between Ultrasound Vector Flow Imaging and Phase Contrast Magnetic Resonance Imaging

Volume flow estimation in the common carotid artery (CCA) can assess the absolute hemodynamic effect of a carotid stenosis. The aim of this study was to compare a commercial vector flow imaging (VFI) setup against the reference method magnetic resonance phase contrast angiography (MRA) for volume flow estimation in the CCA. Ten healthy volunteers were scanned with VFI and MRA over the CCA. VFI had an improved precision of 19.2% compared to MRA of 31.9% (p = 0.061). VFI estimated significantly lower volume flow than MRA (mean difference: 63.2 mL/min, p = 0.017), whilst the correlation between VFI and MRA was strong (R² = 0.81, p < 0.0001). A Bland–Altman plot indicated a systematic bias. After bias correction, the percentage error was reduced from 41.0% to 25.2%. This study indicated that a VFI setup for volume flow estimation is precise and strongly correlated to MRA volume flow estimation, and after correcting for the systematic bias, VFI and MRA become interchangeable.

Blood flow distribution after end-to-side anastomosis with wide arteriotomy in extremity free flap surgery

PURPOSE

Although many studies have investigated the optimal anastomotic procedure for the end-to-side (ETS) procedure with a free flap, no study has focused on the size of the arteriotomy. Some surgeons have recently described the effectiveness of ETS with wide arteriotomy, but the postoperative haemodynamics remains unclear for free flaps created using this technique. The aim of this study was to use ultrasonography to evaluate the postoperative blood flow distribution after ETS with a wide arteriotomy in extremity free flap surgery.

METHODS

We evaluated 20 free flaps in 18 consecutive patients who received an ultrasonographic examination after free flap surgery using the ETS technique with wide arteriotomy for arterial anastomosis. All flaps were examined after surgery and blood flow was calculated for the flap and recipient vessels.

RESULTS

All 20 flaps survived, but one flap developed asymptomatic arterial thrombosis and 19 flaps were analysed. For the ETS technique with wide arteriotomy, peripheral circulation was well preserved in all flaps. Comparison of flap types showed that blood flow was significantly higher in myocutaneous flaps than in fasciocutaneous flaps, but there was no significant difference according to the size of the arteriotomy.

CONCLUSIONS

Given the range of arteriotomy performed using the ETS with a wide arteriotomy technique, the blood flow volume in the flap depended on the type of flap but not on the size of the arteriotomy. A steal phenomenon related to the creation of a wide window in the receipt artery was not found in the analysed retrospective cohort.

Complementing sparse vascular imaging data by physiological adaptation rules

Mathematical modeling of pressure and flow waveforms in blood vessels using pulse wave propagation (PWP) models has tremendous potential to support clinical decision making. For a personalized model outcome, measurements of all modeled vessel radii and wall thicknesses are required. In clinical practice, however, data sets are often incomplete. To overcome this problem, we hypothesized that the adaptive capacity of vessels in response to mechanical load could be utilized to fill in the gaps of incomplete patient-specific data sets. We implemented homeostatic feedback loops in a validated PWP model to allow adaptation of vessel geometry to maintain physiological values of wall stress and wall shear stress. To evaluate our approach, we gathered vascular MRI and ultrasound data sets of wall thicknesses and radii of central and arm arterial segments of 10 healthy subjects. Reference models (i.e., termed RefModel, n = 10) were simulated using complete data, whereas adapted models (AdaptModel, n = 10) used data of one carotid artery segment only, and the remaining geometries in this model were estimated using adaptation. We evaluated agreement between RefModel and AdaptModel geometries, as well as that between pressure and flow waveforms of both models. Limits of agreement (bias ± 2 SD of difference) between AdaptModel and RefModel radii and wall thicknesses were 0.2 ± 2.6 mm and -140 ± 557 µm, respectively. Pressure and flow waveform characteristics of the AdaptModel better resembled those of the RefModels as compared with the model in which the vessels were not adapted. Our adaptation-based PWP model enables personalization of vascular geometries even when not all required data are available.NEW & NOTEWORTHY To benefit personalized pulse wave propagation (PWP) modeling, we propose a novel method that, instead of relying on extensive data sets on vascular geometries, incorporates physiological adaptation rules. The developed vascular adaptation model adequately predicted arterial radius and wall thickness compared with ultrasound and MRI estimates, obtained in humans. Our approach could be used as a tool to facilitate personalized modeling, notably in case of missing data, as routinely found in clinical settings.

Analysis of access flow using duplex ultrasonography and the ultrasound dilutional method

BACKGROUND

This study aimed to evaluate the correlation between duplex ultrasonography (DUS) and ultrasound dilution (UD) measurement's results and determine the factors affecting the correlation of the measured values among other clinical factors in patients.

METHODS

This cross-sectional study was conducted from April 2020 to May 2020 and included 60 patients who visited our dialysis centre. The flow of the fistula was measured in the proximal brachial artery using DUS. While dialysis was performed on the same day, the access flow was measured using the UD method. The correlation and agreement between the access flows acquired by each measurement method were analysed. Similarly, the correlation was analysed by classifying the groups based on the predisposing factor, and statistically significant factors were observed through comparison.

RESULTS

Both measurements showed a moderate positive correlation (r = 0.60, p < 0.01). The bias (mean of UD-DUS) between the two measurements was about 230 mL/min. When the measurement site of DUS was near the inflow artery and in the same anatomical section, a strong correlation with the measurement value of UD was observed (brachial based fistula: r = 0.85, radial based fistula: r = 0.87). Similarly, for patients without diabetes and those who regularly underwent access surveillance for the dialysis route, strong correlations were observed between the two measurements (r = 0.79 and r = 0.88).

CONCLUSIONS

Several factors can influence the correlation between UD and DUS. The findings showed a high correlation for DUS measurement sites within the same anatomical section as the inflow artery, patients without diabetes, and patients undergoing periodic surveillance.

Fetal whole heart blood flow imaging using 4D cine MRI

Prenatal detection of congenital heart disease facilitates the opportunity for potentially life-saving care immediately after the baby is born. Echocardiography is routinely used for screening of morphological malformations, but functional measurements of blood flow are scarcely used in fetal echocardiography due to technical assumptions and issues of reliability. Magnetic resonance imaging (MRI) is readily used for quantification of abnormal blood flow in adult hearts, however, existing in utero approaches are compromised by spontaneous fetal motion. Here, we present and validate a novel method of MRI velocity-encoding combined with a motion-robust reconstruction framework for four-dimensional visualization and quantification of blood flow in the human fetal heart and major vessels. We demonstrate simultaneous 4D visualization of the anatomy and circulation, which we use to quantify flow rates through various major vessels. The framework introduced here could enable new clinical opportunities for assessment of the fetal cardiovascular system in both health and disease.

Partial Volume Effect and Correction for 3-D Color Flow Acquisition of Volumetric Blood Flow

Blood volume flow (VF) estimation is becoming an integral part of quantitative medical imaging. Three-dimensional color flow can be used to measure volumetric flow, but partial volume correction (PVC) is essential due to finite beamwidths and lumen diameters. Color flow power was previously assumed to be directly proportional to the perfused fractional color flow beam area (voxel). We investigate the relationship between color flow power and fractionally perfused voxels. We simulate 3-D color flow imaging using Field II based on a 3.75-MHz mechanically swept linear array. A 16-mm-diameter tube with laminar flow was embedded into soft tissue. We investigated two study scenarios where soft tissue backscatter is 1) 40 dB higher and 2) 40 dB lower, relative to blood. Velocity and power were computed from color flow packets ( n = 16 ) using autocorrelation. Study 1 employed a convolution-based wall filter. Study 2 did not employ a wall filter. VF was computed from the resulting color flow data, as published previously. Partial volume voxels in Study 1 show lesser power than those in Study 2, likely due to wall filter effects. An "S"-shaped relationship was found between color flow power and fractionally perfused voxel area in Study 2, which could be due to an asymmetric lateral-elevational point spread function. Flow computation is biased low by 7.3% and 7.9% in Study 1 and Study 2, respectively. Uncorrected simulation estimates are biased high by 41.5% and 12.5% in Study 1 and Study 2, respectively. Our findings show that PVC improves 3-D VF estimation and that wall filter processing alters the proportionality between color flow power and fractionally perfused voxel area.

The Contributions of Arterial Cross-Sectional Area and Time-Averaged Flow Velocity to Arterial Blood Flow

Background:

Ultrasound has been used for noninvasive assessments of endothelial function in both clinical and athletic settings and to identify changes in muscle blood flow in response to exercise, nutritional supplementation, and occlusion. The purposes of the present study were to examine the reliability and relative contributions of arterial cross-sectional area and time-averaged flow velocity to predict muscle blood flow as a result of fatiguing exercise in men and women.

Methods:

Eighteen healthy men and 18 healthy women performed 50 consecutive eccentric repetitions of the elbow flexors at 60% of their pretest eccentric peak torque at a velocity of 180° s⁻¹. Test-retest reliability and stepwise linear regression analyses were performed to determine the ability of arterial cross-sectional area and time-averaged flow velocity to predict brachial artery muscle blood flow for the men, women, and combined sample.

Results:

There was no systematic test versus retest mean differences (P > 0.05) for any of the ultrasound determined variables. The two-variable regression models significantly improved the ability to predict muscle blood flow and were associated with smaller standard error of the estimates (3.7%–10.1% vs. 16.8%–37.0% of the mean baseline muscle blood flow values) compared to the one-variable models.

Conclusions:

The findings of the present study supported the use of ultrasound for reliable assessments of arterial diameter, arterial cross-sectional area, time-averaged flow velocity, and muscle blood flow from the brachial artery in men and women. Furthermore, time-averaged flow velocity was a more powerful predictor of muscle blood flow than arterial cross-sectional area.

Comparison of hemodialysis arteriovenous fistula blood flow rates measured by Doppler ultrasound and phase-contrast magnetic resonance imaging

OBJECTIVE

The objective of this study was to compare blood flow rates measured by Doppler ultrasound (DUS) and phase-contrast magnetic resonance imaging (MRI) in patients having a hemodialysis arteriovenous fistula (AVF) and to identify scenarios in which there was significant discordance between these two approaches.

METHODS

Blood flow rates in the proximal artery (PA) and draining vein (DV) of newly created upper extremity AVFs were measured and compared using DUS and phase-contrast MRI at 1 day, 6 weeks, and 6 months postoperatively.

RESULTS

Blood flow rates in the PA measured by DUS (1155 ± 907 mL/min, mean ± standard deviation) and by MRI (1170 ± 657 mL/min) were not statistically different (P = .812) based on 78 data pairs from 49 patients. DV DUS flow (1277 ± 995 mL/min) and MRI flow (1130 ± 655 mL/min) were also not statistically different (P = .071) based on 64 data pairs. In both PA and DV, the two methods substantially agreed with each other (Cohen κ: PA, 0.66; DV, 0.67) when flow rates were put into four clinically relevant categories (<300, 300-599, 600-1499, and ≥1500 mL/min). The Bland-Altman analyses of DUS and MRI flow identified six and four outliers for PA and DV, respectively. Seven outliers had higher DUS than MRI flow, with all DUS scan sites having a large lumen or significant local curvature; the other three had lower DUS flow, partly due to an underestimation of lumen diameter by DUS.

CONCLUSIONS

DUS and MRI flow rates are generally comparable in both PA and DV. When DUS is used for flow measurements, careful attention to accurate lumen diameter measurements is needed and scan sites with marked curvature should be avoided. Our result may improve the accuracy of DUS-measured AVF blood flow rate.

Recent technological advancements in cardiac ultrasound imaging

About 92.1 million Americans suffer from at least one type of cardiovascular disease. Worldwide, cardiovascular diseases are the number one cause of death (about 31% of all global deaths). Recent technological advancements in cardiac ultrasound imaging are expected to aid in the clinical diagnosis of many cardiovascular diseases. This article provides an overview of such recent technological advancements, specifically focusing on tissue Doppler imaging, strain imaging, contrast echocardiography, 3D echocardiography, point-of-care echocardiography, 3D volumetric flow assessments, and elastography. With these advancements ultrasound imaging is rapidly changing the domain of cardiac imaging. The advantages offered by ultrasound imaging include real-time imaging, imaging at patient bed-side, cost-effectiveness and ionizing-radiation-free imaging. Along with these advantages, the steps taken towards standardization of ultrasound based quantitative markers, reviewed here, will play a major role in addressing the healthcare burden associated with cardiovascular diseases.

Pilot study evaluating the efficacy of exergaming for the prevention of deep venous thrombosis

OBJECTIVE

Current prophylactic protocols fail to prevent deep venous thrombosis (DVT) in a significant minority of patients, and it remains one of the leading causes of preventable death. We therefore quantified the efficacy of novel game-based exercises (exergaming) to augment femoral venous parameters relative to ankle movement and muscle flexion.

METHODS

Healthy volunteers were recruited to perform a series of ankle and foot exercises using a wireless foot sensor (LEGSys; BioSensics LLC, Watertown, Mass) to navigate a computer cursor sequentially on a screen to the center of 200 circular targets. A single ultrasound technician (W.A.M.) measured each patient's mean flow volume, peak flow velocity, mean flow velocity, and cross-sectional area of the right femoral vein at baseline and obtained immediate postexercise (PEX), 5-minute PEX, and 15-minute PEX measurements. Electromyography (EMG) was performed at baseline and during the exercise. Baseline demographics and medical and surgical comorbidities were also recorded. The primary end point was the difference between baseline and immediate PEX mean flow volume estimates. We secondarily explored the association of baseline characteristics and EMG measurements with femoral vein parameters.

RESULTS

Fifteen healthy subjects (53% male; 28.1 ± 4.6 years) completed the exergaming task within a mean of 4 minutes, 2 ± 21 seconds. Immediately after exercise, the femoral vein mean flow volume, mean velocity, and peak systolic velocity increased by 49%, 53%, and 48%, respectively (P < .02 for each). Mean flow volume and velocity remained significantly elevated 5 minutes after exercise (P < .04 for each). Plantar flexion and dorsiflexion velocities and EMG frequency and intensity were not significantly correlated with PEX mean flow volume estimates (P > .05). Subgroup analysis revealed that women (P < .01) and Hispanics (P < .01) exhibited significantly slower PEX responses. Subjects with the largest improvements in mean flow volume had lower peak plantar flexion velocities (P < .01).

CONCLUSIONS

Exergaming increases mean flow volume, mean flow velocity, and peak systolic velocity within the femoral vein by approximately 50% above baseline. Exergaming represents a novel and potentially attractive method of DVT prevention by augmenting femoral vein mean volume flow and capitalizing on biofeedback. Less forceful but more uniform contractions were found to be most effective at augmenting venous blood flow. Exergaming will require further validation in larger study bases, among patients at higher risk of DVT.

Vector velocity volume flow estimation: Sources of error and corrections applied for arteriovenous fistulas

A method for vector velocity volume flow estimation is presented, along with an investigation of its sources of error and correction of actual volume flow measurements. Volume flow errors are quantified theoretically by numerical modeling, through flow phantom measurements, and studied in vivo. This paper investigates errors from estimating volumetric flow using a commercial ultrasound scanner and the common assumptions made in the literature. The theoretical model shows, e.g. that volume flow is underestimated by 15%, when the scan plane is off-axis with the vessel center by 28% of the vessel radius. The error sources were also studied in vivo under realistic clinical conditions, and the theoretical results were applied for correcting the volume flow errors. Twenty dialysis patients with arteriovenous fistulas were scanned to obtain vector flow maps of fistulas. When fitting an ellipsis to cross-sectional scans of the fistulas, the major axis was on average 10.2mm, which is 8.6% larger than the minor axis. The ultrasound beam was on average 1.5mm from the vessel center, corresponding to 28% of the semi-major axis in an average fistula. Estimating volume flow with an elliptical, rather than circular, vessel area and correcting the ultrasound beam for being off-axis, gave a significant (p=0.008) reduction in error from 31.2% to 24.3%. The error is relative to the Ultrasound Dilution Technique, which is considered the gold standard for volume flow estimation for dialysis patients. The study shows the importance of correcting for volume flow errors, which are often made in clinical practice.

First-week postoperative flow measurements are highly predictive of primary patency of radiocephalic arteriovenous fistulas

PURPOSE

This study was conducted to determine whether volume flow rate at the first postoperative visit could predict early failure of radiocephalic arteriovenous fistulas (RCAVFs).

METHODS

We retrospectively studied the records of 264 patients who received a RCAVF between 2007 and 2013 at our centers. Data collected included patient demographics, medical history, arterial and venous mapping, and volume flow rate intraoperatively after fistula creation but before closing the surgical incision. An intraoperative flow rate &gt;100 mL/minute was targeted. We measured volume flow at the first postoperative visit 1 week after surgery and thereafter as needed.

RESULTS

Intraoperative flow was not a significant predictor of primary patency (p = 0.44) but flow at the first postoperative visit was a statistically significant predictor of fistula primary patency (p = 0.002). No fistula with a blood flow &lt;200 mL/minute at the 1-week postoperative visit reached maturity without receiving a maturation procedure. The hazard ratio for the first follow-up flow (mL/min) was 0.9973 (95% CI 0.9956, 0 .9989), indicating that for every 100 mL increase in blood flow the primary patency increases by 10%.

CONCLUSIONS

Flow rate at the 1-week postoperative visit was the most important predictor of RCAVF patency. Thus, it should be possible to identify patients who would benefit from early intervention or closer follow-up as soon as the first postoperative visit. This should help reduce the use of bridging hemodialysis catheters and minimize the risks of catheter dependency.

Arteriovenous Fistula Development in the First 6 Weeks after Creation

PURPOSE

To assess the anatomic development of native arteriovenous fistula (AVF) during the first 6 weeks after creation by using ultrasonographic (US) measurements in a multicenter hemodialysis fistula maturation study.

MATERIALS AND METHODS

Each institutional review board approved the prospective study protocol, and written informed consent was obtained. Six hundred and two participants (180 women and 422 men, 459 with upper-arm AVF and 143 with forearm AVF) from seven clinical centers underwent preoperative artery and vein US mapping. AVF draining vein diameter and blood flow rate were assessed postoperatively after 1 day, 2 weeks, and 6 weeks. Relationships among US measurements were summarized after using multiple imputation for missing measurements.

RESULTS

In 55% of forearm AVFs (68 of 124) and 83% of upper-arm AVFs (341 of 411) in surviving patients without thrombosis or AVF intervention prior to 6 weeks, at least 50% of their 6-week blood flow rate measurement was achieved at 1 day. Among surviving patients without thrombosis or AVF intervention prior to week 2, 70% with upper-arm AVFs (302 of 433) and 77% with forearm AVFs (99 of 128) maintained at least 85% of their week 2 flow rate at week 6. Mean AVF diameters of at least 0.40 cm were seen in 85% (389 of 459), 91% (419 of 459), and 87% (401 of 459) of upper-arm AVFs and in 40% (58 of 143), 73% (104 of 143), and 77% (110 of 143) of forearm AVFs at 1 day, 2 weeks, and 6 weeks, respectively. One-day and 2-week AVF flow rates and diameters were used to predict 6-week levels, with 2-week prediction of 6-week measures more accurate than those of 1 day (flow rates, R(2) = 0.47 and 0.61, respectively; diameters, R(2) = 0.49 and 0.82, respectively).

CONCLUSION

AVF blood flow rate at 1 day is usually more than 50% of the 6-week blood flow rate. Two-week measurements are more predictive of 6-week diameter and blood flow than those of 1 day. US measurements at 2 weeks may be of value in the early identification of fistulas that are unlikely to develop optimally.

Variation in duplex peak systolic velocity measurement in a multi-site vascular service

Objective:

Duplex US (DUS) is increasingly utilised as a first-line investigation for the assessment of carotid disease. For clinical decision-making, DUS assessment must be accurate and reproducible to ensure reliability. We aimed to investigate the variability in peak systolic velocity (PSV) measurement in a multi-site vascular network.

Methods:

DUS measurements of PSV were taken from continuous and pulsatile flow, generated by a high fidelity phantom, by 12 experienced vascular scientists across four hospitals. Participants were blinded to the actual PSV value (50 cm/s).

Results:

We observed an average error of 13.2% (± 8.3) and 11.6% (± 7.5) in PSV measurements taken from pulsatile and continuous waveforms, respectively. Measurements of PSV using the pulsatile waveform demonstrated statistically significant variation across all hospitals; ((hospital/mean) A 43.9 cm/s, B 61.7 cm/s, C 57.4 cm/s, D 47.7 cm/s, p=0.001). Further analysis demonstrated statistically significant variation in 4 instrumentation-related factors when measuring from a pulsatile waveform (Doppler angle, angle of insonation, velocity range, scale range).

Conclusion:

We observed a significant level of error and variation in PSV measurements across four sites within our vascular network. Variation in instrumentation-related factors may be accountable for this. In light of the centralisation of vascular services, it is increasingly important to unify and implement scanning protocols in order to reduce error and inter-site variability.

Quantifying Blood Flow in the DIEP Flap: An Ultrasonographic Study

Supplemental Digital Content is available in the text.

Background:

The maximum weight of tissue that a single perforator can perfuse remains an important question in reconstructive microsurgery. An empirically based equation, known as the flap viability index (FVI), has been established to determine what weight of tissue will survive on one or more perforators. The equation is FVI = Sum d(n)^4/W, where d is the internal diameter of each perforator and W is the final weight of the flap. It has been shown that if FVI exceeds 10, total flap survival is likely, but if under 10, partial flap necrosis is probable. The aim of this study was to measure absolute flow rates in deep inferior epigastric perforator (DIEP) flap pedicles and assess correlation with the determinants of the FVI, perforator diameter and flap weight.

Methods:

Color Doppler ultrasound was used to quantify arterial flow in 10 consecutive DIEP flap pedicles 24 hours after anastomosis.

Results:

In single-perforator DIEP flaps, flow rate was highly correlated with perforator diameter (r = 0.82, P = 0.01). Mean arterial flow rate was significantly reduced in DIEP flaps with 2 or more perforators (6 vs 38 cm³/min; P < 0.05).

Conclusions:

This study confirms that perforator size is a critical factor in optimizing blood flow in perforator-based free tissue transfer. Further research is required to understand the flow dynamics of perforator flaps based on multiple perforators. However, surgeons should be cognizant that a single large perforator may have substantially higher flow rates than multiple small perforators. Routine FVI calculation is recommended to ensure complete flap survival.

Accuracy of Early Postoperative Clinical and Ultrasound Examination of Arteriovenous Fistulae to Predict Dialysis Use

Aim

The aim of this article is to assess the accuracy of early clinical and ultrasound (US) examination in terms of predicting arteriovenous fistula (AVF) dialysis use.

Methods

Physical and US examination of patent AVF was performed 4 weeks after fistula creation. AVF dialysis use was defined as subsequent use of an AVF for at least six consecutive dialysis sessions with two needles and a blood flow of more than 200 mL/min.

Results

Of 119 AVF patent at 4 weeks, 26 (22%) failed. Clinical examination was 96% sensitive for predicting successful dialysis, but only 21% specific for failure. Vein diameter above 5 mm and an arterial end-diastolic velocity above 110 cm/s were the best US predictors for dialysis use. Vein diameter was slightly better than arterial velocity in terms of predicting maturity (sensitivity: 83% vs 67%, specificity: 68% vs 65%). All assessments predicted AVF maturity (positive predictive value: clinical = 81%, US diameter = 90%, US velocity = 87%) much better than AVF failure (negative predictive value: clinical = 63%, US diameter = 53%, US velocity = 37%).

Conclusion

One month after surgery, a new AVF with a thrill or a vein diameter >5 mm is likely to be used for dialysis. An AVF not meeting these criteria has an increased risk of failure and further investigations may be required.

Internal jugular and vertebral vein volume flow in patients with clinically isolated syndrome or mild multiple sclerosis and healthy controls: results from a prospective sonographer-blinded study

OBJECTIVES & METHODS

We evaluated internal jugular vein and vertebral vein volume flow using ultrasound, in patients with clinically isolated syndrome or mild multiple sclerosis and controls, to determine whether volume flow was different between the two groups.

RESULTS

In patients and controls, internal jugular vein volume flow increased from superior to inferior segments, consistent with recruitment from collateral veins. Internal jugular vein and vertebral vein volume flow were greater on the right in supine and sitting positions. Internal jugular vein volume flow was higher in the supine posture. Vertebral vein volume flow was higher in the sitting posture. Regression analyses of cube root transformed volume flow data, adjusted for supine/sitting, right/left and internal jugular vein/vertebral vein, revealed no significant difference in volume flow in patients compared to controls.

CONCLUSIONS

Our findings further refute the concept of venous obstruction as a causal factor in the pathogenesis of multiple sclerosis. Control volume flow data may provide useful normative reference values.

Duplex ultrasound volumetric flow analysis before and after hemodialysis in patients with brachio-cephalic fistulae

PURPOSE

The United Kingdom Renal Association recommends duplex ultrasound to monitor arteriovenous fistula (AVF) flow rates during surveillance. Significant flow rate changes should prompt further investigation or treatment to avoid a failing fistula. Hemodialysis is known to alter the hemorrheologic and physiologic factors with a potential impact on measured flow rates. The aim of this study was to determine the difference in flow rate measured with duplex ultrasound before and after a single hemodialysis session in patients with brachial-cephalic fistulae.

METHODS

Patients with brachial-cephalic AVFs in our dialysis populations who were undergoing regular hemodialysis without recent intervention (less than six weeks) were invited to participate. Flow measurements were made pre-and post-hemodialysis using a Zonare ultrasound machine. The vascular scientist was always blinded to the pre-hemodialysis flow.

RESULTS

A total of 157 patients were identified with brachial-cephalic fistulae. Following exclusions, 119 patients were eligible. However, a further 58 were excluded because they declined or did not attend leaving 61 patients in the study. Paired t test showed a statistically significant reduction in flow rate of 105 mL/min (P=0.026) post-hemodialysis which equates to a -6.9% change in flow (95% C.I. -12.7 to -0.8%). Bland-Altman analysis showed limits of flow rate agreement between -599 mL/min and +810 mL/min (+/-1.96 s.d.).

CONCLUSIONS

Whilst we have shown a statistically significant change in flow rate post-hemodialysis, this is small and should be taken in the context of previously accepted interobserver variability. Therefore, the practical and financial considerations of implementing an AVF surveillance programme are likely to outweigh the minimal benefit of consistency that would be enabled by strict protocol of pre-hemodialysis flow measurements.

Upper body exercise increases lower extremity venous blood flow in deep venous thrombosis

OBJECTIVE

Sequential compression devices or ambulation prevent deep venous thrombosis (DVT) by enhancing venous blood flow in the lower extremity. However, compression therapy or ambulation may not be possible in patients with lower extremity surgery or trauma. We therefore determined whether upper body exercise increases venous blood flow in the lower extremities as a potential means for preventing DVT.

METHODS

We determined blood volume flow and velocity responses in the common femoral veins to low-intensity (5 W, 75 rpm) upper body cycle ergometry in healthy individuals. Six protocols of single and intermittent bouts of exercise were tested. Upon determination of the most efficacious protocol in these participants, we verified the effects of upper body exercise in patients with acute DVT. Measurements were made before, during, and after exercise using duplex ultrasound imaging.

RESULTS

The study enrolled 15 healthy volunteers (10 men, 5 women; aged 20-40 years) with no history of DVT and 10 patients (aged 31-86 years) with acute DVT. In healthy participants, a single 30-second bout of upper body exercise increased volume flow up to 39% for up to 10 minutes after exercise (P < .05). A single 3-minute bout increased flow to a lesser extent (23% increase; P = .05) for nearly 5 minutes, but a single 1-minute bout did not increase flow. An intermittent protocol of three 30-second bouts of exercise resulted in an increase of 34% to 57% in venous flow (P < .05) for an average increase of 179 ± 53 mL/min. Intermittent 1-minute bouts of exercise tended to increase flow 10% to 40% (P = .06-.08) for an average increase of 149 ± 64 mL/min. Intermittent 3-minute bouts of exercise increased flow 21% to 45% (P < .05) for an average increase of 120 ± 42 mL/min. In patients with acute DVT, the intermittent 30-second upper body exercise protocol increased venous blood flow by 45% to 83% (P < .05) for an average increase of 250 ± 63 mL/min, an effect lasting >13 minutes.

CONCLUSIONS

We report the novel finding that upper body exercise increases lower extremity venous blood flow in healthy volunteers and in acute DVT patients. Three intermittent 30-second bouts of low-intensity upper body exercise elicited the highest response for the least amount of effort and may represent an alternative or adjunct for prophylaxis of DVT in patients with restricted ambulation.

Duplex ultrasound evaluation of hemodialysis access: a detailed protocol

A detailed protocol for the performance and interpretation of duplex ultrasound evaluation of hemodialysis access is described.