Transit-time Ultrasonic Flow Research Articles

Parallel strip waveguide for ultrasonic flow measurement in harsh environments.

Wetted ultrasonic transit time flow meters typically consist of one or more pairs of transducers, containing piezoelectric elements, which alternate between transmitting and detecting an ultrasonic pulse. Typical piezoelectric materials and the adhesives used to attach the piezoelectric element in such devices can be damaged by hostile environments, such as extreme temperature, potentially limiting possible applications of ultrasonic flow measurement techniques. We have investigated a design for a flow meter with an integrated thermal buffer waveguide consisting of five parallel stainless steel strips. These, in addition to thermal protection, may function as a transducer array, with the possibility of steering the emitted field. Because the buffer strips used in the transducer assembly are thin, one might expect Lamb-like guided waves to propagate along it. However, the finite width of the strips has a significant effect on the propagation characteristics of the guided waves. In this work, the effect of the waveguide's small rectangular cross-section has been studied. Additionally, we have examined the effect of thermal gradients on the average sound speed and dispersion characteristics of such strip waveguides. We also suggest modifications to the plate geometry, which can alter both the frequency content and the shape of the transmitted pulse, potentially giving a better signal to use in flow measurement.

Renal haemodynamic response to amino acids infusion in an experimental porcine model of septic shock.

Acute kidney injury (AKI) is common in sepsis. Treatments allowing maintenance of renal blood flow (RBF) could help to prevent AKI associated with renal hypoperfusion. Amino acids (AA) have been associated with an increase of RBF and glomerular filtration rate (GFR) in several species. The aim of this study was to evaluate the effects of an AA infusion on RBF and GFR in a porcine model of septic shock. A total of 17 piglets were randomly assigned into three groups: Sham (Sham, n = 5), sepsis without AA (S-NAA, n = 6), sepsis treated with AA (S-AA, n = 6). Piglets preparation included the placement of ultrasonic transit time flow probes around left renal artery for continuous RBF measurement; ureteral catheters for GFR and urine output evaluation; pulmonary artery catheter for cardiac output (CO) and pulmonary arterial pressure measurements. Mean arterial pressure (MAP) and renal vascular resistance (RVR) were also determined. Septic shock was induced with a live Pseudomonas aeruginosa infusion. Crystalloids, colloids and epinephrine infusion were used to maintain and restore MAP > 60 mmHg and CO > 80% from baseline. Renal haemodynamic did not change significantly in the Sham group, whereas RBF increased slightly in the S-NAA group. Conversely, a significant increase in RVR and a decrease in RBF and GFR were observed in the S-AA group. AA infusion was associated with a higher requirement of epinephrine [340.0 (141.2; 542.5) mg vs. 32.5 (3.8; 65.0) mg in the S-NAA group P = 0.044]. An infusion of amino acids impaired renal haemodynamics in this experimental model of septic shock.

Electronic circuit design for reciprocal operation of transit-time ultrasonic flow meters

The reciprocal operation theory has been used in the circuit design of transit-time ultrasonic flow meters (USMs) to promote their zero flow performances. In this paper, the authors analyzed the transfer functions of the inter-conversion between acoustic and electric signals on each transducer, indicated that the equivalent load consistency for each transducer between the transmitting and the receiving phases would guarantee the transmitting and the receiving transfer functions equal, and thus guarantee the reciprocal operation of the USM system. In order to achieve the “load consistency” condition in practical systems with non-ideal parameters, a method of applying short pulse excitation and fixing the equivalent load in the “free oscillation period” of the transmitting transducer is proposed. Based on this method, several circuit designs are shown in the paper, the impedance preferences are also analyzed. Practical experiments done with these circuits show clear improvement in both promoting the accordance of the signals received in both directions and reducing the zero flow error in the measurement.

Excitation signal's influence on ultrasonic transit time flow meter's performance

Ultrasonic flow meter performance was analyzed. Ultrasound transit time was used for flow rate estimation. Time of flight was measured using cross correlation processing. Simultaneous channels excitation was used. Ultrasonic signals were excited using low voltage (4V pp) signal generator, received signals were amplified 30 dB and simultaneously acquired by 100 Ms/s 10 bit analog-to-digit converters. Subsample delay estimation was used. Flow rate was varied from 10 l/h to 200 l/h. Measurement channel diameter 8 mm was used. It is complicated to obtain the unbiased reference signal for correlation processing. Various combinations of signals travelling in measurement channel were used for cross-correlation processing. Performance of correlation function and time of flight estimator variance were studied. Variable gain amplifier usually is used for signal dynamic range matching to A/D converter input. Gain influence on time of flight was a subject to study. It has been concluded that gain control introduces systematic errors in time of flight estimator. Influence of the temperature of electronics (pulser, receiver, A/D converter, reference clock etc.) and ultrasonic transducers on the delay estimator was studied. It was concluded that the major temperature-related systematic error comes from the pulser. Performance of the meter was studied when narrowband and spread spectrum signals were used for ultrasound excitation across temperature and flow rate range. It has been concluded that spread spectrum signal allows for better zero flow stability over temperature and lower time of flight variation.

Influence of lung injury on cardiac output measurement using transpulmonary ultrasound dilution: a validation study in neonatal lambs

Transpulmonary ultrasound dilution (TPUD) is a promising method for cardiac output (CO) measurement in severely ill neonates. The incidence of lung injury in this population is high, which might influence CO measurement using TPUD because of altered lung perfusion. We evaluated the influence of lung injury on the accuracy and precision of CO measurement using TPUD in an animal model. In nine neonatal lambs, central venous and arterial catheters were inserted and connected to the TPUD monitor. Repeated lavages with warmed isotonic saline were performed to gradually induce lung injury. CO measurements with TPUD (COtpud) were compared with those obtained by an ultrasonic transit-time flow probe around the main pulmonary artery (COufp). An increase in oxygenation index was used as an indicator of induced lung injury during the experiment. Post-mortem lung injury was confirmed by histopathological examination. Fifty-five sessions of three paired CO measurements were analysed. The mean COufp was 1.53 litre min(-1) (range 0.66-2.35 litre min(-1)), and the mean COtpud was 1.65 litre min(-1) (range 0.78-2.91 litre min(-1)). The mean bias (standard deviation) between the two methods was 0.13 (0.15) litre min(-1) with limits of agreement of ±0.29 litre min(-1). The overall percentage error was 19.1%. The accuracy and precision did not change significantly during progressive lung injury. Histopathological severity scores were consistent with heterogeneous lung injury. The capability to track changes in CO using TPUD was moderate to good. The accuracy and precision of CO measurement using TPUD is not influenced in the presence of heterogeneous lung injury in an animal model.

Acoustic propagation in viscous fluid with uniform flow and a novel design methodology for ultrasonic flow meter

Ultrasonic flow meter with non-invasive no-moving-parts construction has good prospective application for space on-orbit fluid gauging. In traditional pulse transit time flow meter, inconsistency of ultrasonic transducers leads to measurement error and plane wave theory, bases of transit time flow meter, is valuable only for low-frequency wave propagation in inviscid fluid and will lose feasibility when fluid viscosity is considered. In this paper, based on the hydrodynamics of viscous fluid, wave propagation with uniform flow profile is mathematically formulated and a novel solution for viscous fluid using potential theory is firstly presented. Then a novel design methodology of continuous ultrasonic flow meter is proposed, where high measurement rangeability and accuracy are guaranteed individually by solving the integral ambiguity using multi-tone wide laning strategy and the fractional phase shift using phase lock loop tracking method. A comparison with transit time ultrasonic flow meter shows the advantage of proposed methodology. In the end, parametric analysis of viscosity on wave propagation and ultrasonic flow meter is compressively investigated.

Cardiac output measurement with transpulmonary ultrasound dilution is feasible in the presence of a left-to-right shunt: a validation study in lambs

Cardiac output (CO) monitoring remains complex in newborns as most of the current technologies fail to accurately measure systemic blood flow in the presence of shunts. We validated CO measurements using transpulmonary ultrasound dilution (TPUD) in a neonatal lamb model with a left-to-right shunt. Regular arterial and central venous catheters were inserted into seven lambs (3.5-8.3 kg). A surgically constructed left-to-right aorto-pulmonary Gore-Tex(®) shunt was intermittently opened and closed, while CO was manipulated by creating haemorrhagic hypotension. CO measurements with TPUD (COtpud) were compared with those obtained by an ultrasonic transit-time flow probe positioned around the main pulmonary artery (COufp). We performed 72 sessions of three paired CO measurements. The mean COufp was 1.00 litre min(-1) (range 0.47-1.75 litre min(-1)) and mean COtpud 1.05 litre min(-1) (range 0.54-1.87 litre min(-1)). With an open shunt, the mean Qp/Qs ratio was 1.8 (range 1.3-2.6). A comparison between COufp and COtpud showed a mean bias (sd) of 0.03 (0.09) and 0.07 (0.10) litre min(-1), respectively, for measurements with a closed and an open shunt. The percentage error was 18% and 20% for measurements with a closed and an open shunt. Polar plot analysis showed good trending ability for both closed and open shunt groups. TPUD is a reliable technology to measure CO in the presence of a left-to-right shunt.

Intermedin (IMD/AM2) dilates the pig coronary vascular bed through release of nitric oxide

Background: This study investigated the effects of intermedin/ adrenomedullin-2 (IMD/AM2), an endogenous agonist for calcitonin-like calcitonin receptors, on coronary and systemic hemodynamics. Methods: Ultrasonic transit time flow probes were placed around the left anterior descending (LAD) artery in the anesthetized, open-chest pig (n=6). A catheter was placed into the proximal LAD. Intracoronary arterial bolus injections of IMD, adrenomedullin (hADM13-52) and calcitonin gene related peptide (CGRP) (1, 3, 10 μg) were performed and the changes in the velocity of coronary blood flows were continuously recorded. Results: Intracoronary artery bolus injections of IMD, hADM13-52 and CGRP increased coronary blood flow in a dose-dependent manner. At the studied doses, IMD was more potent than CGRP and hADM13-52 and did not alter systemic arterial pressure, cardiac output and cardiac index. Intracoronary artery injection of NG-Nitro-Larginine- methyl ester (L-NAME) significantly decreased the coronary vasodilator response (CVR) to IMD. Conclusion: The present data suggest that IMD possesses marked vasodilator activity in the pig coronary vascular bed. The present data further suggest that IMD acts on a receptor in the coronary vascular bed that is coupled to endothelial nitric oxide release. The degree of the CVR to IMD may serve as functional marker for the integrity of endothelial cells in resistance segments of the coronary circulation

Predictive Value of IntraoperativeIn SituRadial Artery Conduit Flow Assessment Prior to Harvesting during Coronary Artery Bypass Surgery

Radial artery (RA) is increasingly preferred as the second best conduit in coronary artery bypass grafting (CABG). Harvesting techniques affect the integrity of the RA with implications for the immediate and late outcome. The aim of this study was to describe a simple intra-operative technique that allows the quality of the RA to be assessed prior to its harvesting during CABG. The study group consisted of 54 patients who underwent CABG. A 2-cm vertical incision was made over the nondominant RA pulse. A limited pedicle of the RA was positioned inside the metal cradle of the flexible flow probe. Baseline transit-time ultrasonic flow and pulsatility index (PI) were measured. Average IN SITU RA flow was 18.6 ml/min (range 4-51 ml/min). Of 14 IN SITU RAs, all but three RAs were found to have adequate flow characteristics and were used as conduits. In the three unsuitable RAs, one had complete obliteration and no flow; one had visible calcifications and very low flow and the third one had a weak pulse, low flow and high PI. Routine assessment of IN SITU RA flow characteristics via a 2-cm incision provides useful information about RA conduit quality prior to its formal harvesting during CABG. Despite considerable skepticism about the use of the radial artery due to its vasospastic potential, this technique may increase utilization rates of the RA as a conduit during CABG, in particular in many young diabetic patients.

Direct measurement of hepatic blood flow during living donor liver transplantation in children

Background The changes in liver blood flow associated with living donor liver transplantation (LDLT) in children have not yet been studied. The aim of the present study was to investigate changes in hepatic hemodynamics before and after pediatric partial liver transplantation. Methods In 7 pediatric recipients with congenital cholestasis and native liver Child-Pugh classes B and C, portal vein flow (PVF) and hepatic arterial flow (HAF) were measured using an ultrasonic transit time flow meter before removal of the native liver and after transplantation and compared with donor left PVF and donor left HAF. Results The mean portal contribution to total hepatic blood flow was markedly decreased in the recipient native liver compared with that in the donor (69% ± 15% vs 32% ± 15%; P = .0003) and after reperfusion changed to almost the same ratio as that in the donor liver (73% ± 18%; P < .0001). Conclusion The extreme imbalance between PVF and HAF that is common in implanted partial liver in adult LDLT recipients was not observed in pediatric LDLT. After transplantation of an appropriately sized liver graft, the portal contribution to total liver blood flow normalized to the value for normal liver.

Expanded Pediatric Cardiovascular Simulator for Research and Training

A mock circulation system has been developed to approximate key anatomic features and simulate the pressures and flows of an infant. Pulsatile flow is generated by 10 cc pulsatile ventricles (Utah infant ventricular assist device). Systemic vasculature is mimicked through the use of 3/8" ID bypass tubing with two flexible reservoirs to provide compliance. Vascular resistance, including pulmonary, aortic, and major branches, is controlled via a series of variable pinch clamps. The coronary branch has a dynamic resistor so that the majority of flow occurs during diastole. The system is instrumented to measure key pressures and flows. Right atrial pressure, left atrial pressure, pulmonary artery pressure, and mean aortic pressure are measured with high-fidelity pressure catheters (Millar Instruments, Houston, TX). Flows are measured by transit time ultrasonic flow probes (Transonic Systems, Ithaca, NY) in the pulmonary artery, aorta, coronary artery, and brachiocephalic artery along with assist device flow. The system can be tuned to create the hemodynamic values of a pediatric patient under normal or heart failure conditions. Once tuned to the desired hemodynamic conditions, the loop may be used to test the performance of various circulatory support systems including the intra-aortic balloon pump, left and right ventricular assist devices, or cardiopulmonary support systems such as extracorporeal membrane oxygenation.

Cardiac Output Measurement in Ventilated Lambs with a Significant Left-to-Right Shunt Using the Modified Carbon Dioxide Fick Method

Background: It remains a great challenge to measure systemic blood flow in critically ill newborns. In a former study we validated the modified carbon dioxide Fick (mCO₂F) method for measurement of cardiac output in a newborn lamb model. In this new study we studied the influence of a left-to-right shunt on the accuracy of the mCO₂F method. Objective: To analyze the influence of a left-to-right shunt on the agreement between cardiac output measurement with the mCO₂F method and ultrasonic transit time pulmonary blood flow in a lamb model. Methods: The study was approved by the Ethical Committee on Animal Research of the Radboud University Nijmegen and performed in 8 random-bred lambs. A Gore-Tex® shunt was placed between the left pulmonary artery and the descending aorta. This aortopulmonary shunt was intermittently opened and closed, while cardiac output was manipulated by creating hemorrhagic hypotension. Cardiac output measurement with the mCO₂F method (Q^mCO2F) was compared with pulmonary blood flow obtained by a transit time ultrasonic flow probe positioned around the common pulmonary artery (Q^APC). Results: Bias, defined as Q^mCO2F – Q^APC, was calculated for each measurement. With an open shunt there was a significant left-to-right shunt (mean Qp/Qs ratio 2.26; range 1.56–3.69). Mean bias (SD) was –12.3 (50.4) ml·kg^–1·min^–1 and –12.3 (42.7) ml·kg^–1·min^–1 for measurements with a closed and open shunt, respectively (no statistical significant difference). Conclusions: Cardiac output measurement with the mCO₂F method is reliable and easily applicable in ventilated newborn lambs, also in the presence of a significant left-to-right shunt.

1805 超音波ドップラー流速分布計測法に適したマイクロバブルの数密度について(OS18-1 超音波を利用した流動場の計測,オーガナイズドセッション)

At hydraulic power stations, it is very important to measure inlet flowrate for the plant management. Pitot tubes were commonly used to measure flow rates in steel penstocks for the performance tests of hydraulic turbines. Due to the difficulties of installations of Pitot tubes, transit time ultrasonic flow meters are being popular instead. However, accuracies of transit time ultrasonic flow meters are sensitive for velocity profiles which depend on Reynolds numbers and pipe surface roughness. Recently, ultrasonic pulse Doppler flow meters are considered to be suitable tool for the measurements of flowrates in steel penstock because it can measure instantaneous velocity profiles directly without draining the water in steel penstock. In this paper, we investigate number densities of the micro bubbles as tracer particles for the flowrate measurements using Ultrasonic Pulse Doppler Method.

Quantification of Left to Right Shunt in Patent Ductus Arteriosus by Color Doppler

Ultrasound is a reliable tool to diagnose patent ductus arteriosus in premature infants but no reliable noninvasive method exists to quantify ductal flow. The aim of this study was to quantify the size of the shunt via persistent ductus arteriosus from pixel counts in color Doppler flow images. A cotton band was placed around the ductus arteriosus of newborn lambs to adjust the magnitude of flow. For flow measurements, ultrasonic transit time flow probes were applied around the ascending aorta and ductus arteriosus. Twenty-four different flow states were attained in four newborn lambs. An Acuson Sequoia scanner equipped with a 7 MHz transducer was used to register Doppler data and images with maximal color distribution during diastole in the pulmonary artery longitudinal sections (PALS). Each image-pixel was matched with the color velocity bar and the pixels were assigned to the corresponding flow velocity. The total area showing color relative to the area of the PALS correlated well with the amount of ductal flow ( r = 0.87, r 2 = 0.75, p < 0.001). When Qp/Qs was >1.4:1, more than 40% of the area in PALS in diastole exhibited color information. Similarly, the color pixel velocities squared correlated with the size of the shunt. Quantification of the percentage of pixels in a color Doppler registration via a computer-based analysis shows a high correlation with the size of ductal shunting. (E-mail: solweig.harling@med.lu.se)

The effect of traction treatment on blood flow in the immature hip--an animal study

9 immature pigs (age: 8-12 weeks) underwent longitudinal traction with 10%, 30%, and 50% body weight followed by overhead traction with 10% and 30% body weight. Microcirculation of the femoral head was monitored by a laser-doppler flow probe and macrocirculation within the lateral circumflex artery by an ultrasonic perivascular transit time flow probe. Changes in blood flow during each traction period were compared to the preceding resting period and expressed in percentages. With any type of longitudinal and overhead traction a trend towards an improvement in micro-and macrocirculation of the hip joint was observed although no significant differences could be detected. Our results encourage the use of traction as a concept in management of developmental dislocation of the hip.

Ultrasonic pulse-Doppler flow meter application for hydraulic power plants

At hydraulic power stations, Pitot tubes have commonly been used to measure flow rates in steel penstocks for performance testing of hydraulic turbines. Due to the difficulties of Pitot tube installation, transit-time ultrasonic flow meters are becoming a popular replacement, but their accuracy is sensitive to velocity profiles that depend on Reynolds numbers and pipe surface roughness. Ultrasonic pulse Doppler flow meters have recently gained favor as suitable tools to measure flow rates in steel penstocks because they can measure instantaneous velocity profiles directly. Field tests were conducted at an actual hydraulic power plant using an ultrasonic pulse Doppler flow meter, and it was found capable of measuring velocity profiles in a large steel penstock with a diameter of over one meter and Reynolds number of more than five million. Furthermore, two ultrasonic transducers were placed on the pipe surface to validate the multi-line measurement of asymmetric flow. Each transducer recorded the velocity profile simultaneously from the pipe centerline to its far wall during plant operation. Velocity profiles were obtained from three-minute measurements to improve the accuracy of flow rate measurements.

Experimental validation of uterine artery volume blood flow measurement by Doppler ultrasonography in pregnant sheep

To test the hypothesis that Doppler-derived (calculated) uterine artery volume blood flow (cQ(UtA)) reflects accurately volume blood flow measured directly (mQ(UtA)) in an experimental setting. Five pregnant sheep were instrumented at 122-130 days of gestation under general anesthesia. After a 4-day recovery period, maternal hemodynamics were varied by administering to the sheep under general anesthesia noradrenaline, beta-blocker, low oxygen gas mixture, epidural bupivacaine and ephedrine, consecutively. The central venous pressure was obtained with the help of a thermodilution catheter. The mean arterial pressure and acid-base status were monitored using a 16-gauge polyurethane catheter inserted into the descending aorta via a femoral artery. A 6-mm transit-time ultrasonic perivascular flow probe was used to measure the mQ(UtA). Doppler ultrasonography of the uterine artery was performed and volume blood flow was obtained simultaneously by the transit-time ultrasonic perivascular flow probe during each phase of the experiment. A total of 31 observations were made. The mQ(UtA) varied between 90 and 800 (mean +/- SD, 419 +/- 206) mL/min during the experiments. The corresponding values for the cQ(UtA) were 110 and 900 (mean +/- SD, 459 +/- 211) mL/min. There was a significant correlation (R = 0.76; P < 0.0001) between mQ(UtA) and cQ(UtA). The mQ(UtA) correlated positively with Doppler-derived uterine artery absolute velocities, i.e. peak systolic (R = 0.50; P = 0.004), end-diastolic (R = 0.53; P = 0.002) and time-averaged maximum (R = 0.69; P < 0.0001) and time-averaged intensity weighted mean (R = 0.75; P < 0.0001) velocities. cQ(UtA) correlates well with volume blood flow measured directly. Doppler-derived uterine artery absolute blood flow velocities reflect uteroplacental volume blood flow in pregnant sheep. Published by John Wiley & Sons, Ltd.

Intermedin (IMD/AM2) dilates the pig coronary vascular bed through release of nitric oxide

The present study was designed to investigate the effects of IMD/AM2 (IMD), an endogenous agonist for calcitonin-like calcitonin receptors (CLCR), on coronary and systemic hemodynamics. Ultrasonic transit time flow probes were placed around the left anterior descending artery in the anesthetized, open-chest pig. Intracoronary arterial bolus injections (IAB) of IMD, hADM13–52 and CGRP increased coronary blood flow in a dose-dependent manner. IMD at the doses studied was more potent than CGRP and hADM13–52 and did not alter systemic arterial pressure, cardiac output and cardiac index. IAB of L-NAME significantly decreased the coronary vasodilatory response (CVR) to IMD. The present data suggest that IMD possesses marked vasodilator activity in the pig coronary vascular bed. The present data further suggest the CVR to IMD in the pig is mediated by release of nitric oxide from endothelial CLCR. The degree of the CVR to IMD may serve as functional marker for the integrity of endothelial cells in resistance segments of the coronary circulation. This study was supported by Gulhane Military School of Medicine (# AR-2006-20).

A randomized comparison of intraoperative indocyanine green angiography and transit-time flow measurement to detect technical errors in coronary bypass grafts

Early coronary bypass graft failures may be preventable if identified intraoperatively. The purpose of this investigation was to compare the diagnostic accuracy of two intraoperative graft assessment techniques, transit-time ultrasound flow measurement and indocyanine green fluorescent-dye graft angiography. Patents undergoing isolated coronary artery bypass grafting with no contraindications for postoperative angiography were enrolled in the study. Patients were randomly assigned to be evaluated with either indocyanine green angiography (Novadaq Spy angiography system; Novadaq Technologies Inc, Concord, Ontario, Canada) and then transit-time ultrasonic flow measurement (Medtronic Medi-Stim Butterfly Flowmeter TTF measurement system; Medtronic Inc, Minneapolis, Minn) or transit-time flow then indocyanine green angiography. Patients underwent x-ray angiography on postoperative day 4. The primary end point of the trial was to determine the sensitivity and specificity of the two techniques versus reference standard x-ray angiography to detect graft occlusion or greater than 50% stenosis in the graft or perianastomotic area. Between February 2004 and March 2005, 106 patients were enrolled and x-ray angiography was performed in 46 patients. In total, 139 grafts were reviewed with all three techniques and 12 grafts (8.2%) were demonstrated to have greater than 50% stenosis or occlusion by the reference standard. The sensitivity and specificity of indocyanine green angiography to detect greater than 50% stenosis or occlusion was 83.3% and 100%, respectively. The sensitivity and specificity of transit-time ultrasonic flow measurement to detect greater than 50% stenosis or occlusion was 25% and 98.4%, respectively. The P value for the overall comparison of sensitivity and specificity between indocyanine green angiography and transit-time flow ultrasonography was .011. The difference between sensitivity for indocyanine green angiography and transit-time flow measurement was 58% with a 95% confidence interval of 30% to 86%, P = .023. Indocyanine green angiography provides better diagnostic accuracy for detecting clinically significant graft errors than does transit-time ultrasound flow measurement.

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