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PubMed2001

Laser-Doppler-anemometry studies of flow behavior in rigid and elastic varicose vein models.

Flow behavior and velocity were studied in six varicose vein models with simulated arteriovenous anastomoses (AVAs). Experiments were performed to determine whether incoming flow entering from AV-anastomoses or small feeder veins could create either small jet streams or velocity fluctuation, which might then cause veins to bulge and get tortuous. Flow was analyzed in areas of flow change. Studies were performed in rigid Plexiglas and elastic, silicon rubber models that exactly replicated the geometry and compliance of varicose veins. Flow was visualized with dyes for steady flow and with a birefringent solution for pulsatile flow studies. Local velocity was measured with a laser-Doppler-anemometer (LDA). Very low forces and shear stresses were found on the interior wall opposite the entrance of the simulated AV anastomoses. However, these values were ten times that of an idealized flow in a straight tube without added flow from simulated AV anastomoses.

Blood Flow Velocity↗
PubMedDate not supplied

Testicular microvascular blood flow: alteration after Leydig cell eradication and ischemia but not experimental varicocele.

Testicular microvascular blood flow is known to exhibit vasomotion, or pulsatile flow. In the present study we have used laser-Doppler flowmetry to study microvascular blood flow in the rat testis and to examine the response of the microvasculature to pharmacological stimulation and pathophysiological conditions. With a mean microvascular flow rate of 13.3 +/- 1.7 perfusion units (PU), the mean cycle amplitude was 3.4 +/- 0.6 PU, and the cycle frequency was 10.3 +/- 0.8 cycles per minute. Blood flow parameters did not differ between left and right testes, between scrotal testes and testes in a 35 degree C glass testicle receptacle, or among testicular regions. Perifusion of seminiferous tubules and their vasculature with 0.1 microgram/microliter epinephrine significantly reduced microvascular blood flow and eliminated vasomotion. Elimination of Leydig cells and intratesticular testosterone also eliminated vasomotion but did not significantly alter mean blood flow rates. Thirty days after imposition of experimental left varicocele (ELV) there were no significant changes in microvascular blood flow parameters. Testicular torsion of sufficient degree and duration to destroy spermatogenesis did not induce a change in mean microvascular blood flow rate 24 hours after repair of torsion, but testicular vasomotion was eliminated in the majority of animals. We conclude that microvascular flow is altered in some testicular pathologies and not in others. The mechanisms underlying changes in microvascular blood flow are at present unknown.

Animals↗
PubMedDate not supplied

Color and conventional image-directed Doppler ultrasonography: accuracy and sources of error in quantitative blood flow measurements.

Accuracy of two systems--conventional (DRF 400, Diasonics) and color-coded (Angiodynograph, Quantum/Phillips) image-directed Doppler ultrasonography--was investigated using an in vitro model that generated both monophasic and triphasic pulsatile flow patterns. Estimated and actual blood volume flow rates showed good correlations, but the sampling with a hand-held transducer led to wide variations in measurement error for the conventional (-69.2% to 50%) and the color-coded (-79.3% to 265.7%) systems. By performing multiple measurements, one could improve accuracy considering only the maximal values of a series instead of the mean values. Accuracy was impaired by interposed muscular or fatty tissue due to false low time-average velocity measurements caused by a loss of Doppler signal. Comparison of both systems revealed significant differences between pulsatility index values (p less than 0.001), blood flow velocities (p less than 0.001), and blood volume flow rates (p less than 0.05 for program flow, p less than 0.001 for manual and automatic flow program of the color-coded system).

Blood Flow Velocity↗
PubMed2003

An in vitro assessment by means of laser Doppler velocimetry of the medtronic advantage bileaflet mechanical heart valve hinge flow.

OBJECTIVE: The aim of this study was to evaluate the hinge flow field characteristics of the Medtronic Advantage bileaflet valve and compare them with the flow fields of the St Jude Medical standard valve. The present study provides laser Doppler velocimetry results for the Advantage and St Jude Medical valves to make a direct comparison of the flow fields of the 2 valve designs. This study aids in determining the preclinical efficacy of Medtronic's new bileaflet valve hinge design. METHODS: Two-dimensional laser Doppler velocimetry was used to measure the velocities in the hinge regions of size 29 Medtronic Advantage and St Jude Medical standard bileaflet valve designs. Exact dimensional models of the bileaflet valves, including the hinge regions, were cast from transparent plastic materials to conduct these measurements under simulated physiologic conditions. Laser Doppler velocimetry measurements were conducted under physiologic conditions, with the valves placed in the mitral position of a pulsatile flow loop. Measurements were taken at several elevation levels in the hinge region. Multiple measurement locations obtained in each plane provided a grid work by which the flow fields could be detailed. RESULTS: Velocity measurements obtained for each valve design in the hinge recess were used to reconstruct the flow fields. For the Advantage valve, the peak velocities during leakage flow in the hinge at zero depth, one-third depth, and two-thirds depth levels into the hinge recess were 0.9, 1.6, and 1.8 m/s, respectively. Corresponding values for the St Jude Medical valve were 1.3, 1.6, and 2.1 m/s, respectively. From the reconstructed flow fields, the flow patterns seen within the 2 hinge designs exhibited similar features, with more dynamic flow patterns observed in the Advantage hinge during the forward flow phase. CONCLUSIONS: The present study demonstrated that the hinge flow dynamics of the Advantage bileaflet design were similar to those of the St Jude Medical hinge design. The velocities within the hinge were slightly higher for the St Jude Medical valve but not significantly different. There appears to be more dynamic flow through the hinge of the Advantage valve during the forward flow phase.

Blood Flow Velocity↗
PubMed1995

Spontaneous remission of double pulsatile umbilical venous flow in twin-twin transfusion syndrome: a case report.

Double umbilical pulsatile venous flow is a rare event generally associated with fetal right heart failure. We observed, at 21 weeks' gestation, this venous flow pattern in a case of twin-twin transfusion syndrome occurring in the recipient twin affected by severe hydrops. In spite of a spontaneous remission of fetal hydrops at 30 weeks, the fetus died suddenly in utero, 2 weeks later. We hypothesized that this unexpected event was related to reversed acute twin-twin transfusion, and concluded that fetal hydrops remission in twin-twin transfusion syndrome must not be considered as a reassuring prognostic index but as an indication of the need for continuing biophysical monitoring.

Adult↗
PubMed1997

Unsteady fluid dynamics of several mechanical prosthetic heart valves using a two component laser Doppler anemometer system.

Five typical mechanical heart valves (Starr-Edwards, Björk-Shiley convexo-concave (c-c), Björk-Shiley monostrut, Bicer-Val, and St. Jude Medical) were tested in the mitral position under the pulsatile flow condition. The test program included measurements of velocity and turbulent stresses at 5 downstream locations. The study was carried out using a sophisticated cardiac simulator in conjunction with a highly sensitive 2 component laser Doppler anemometer (LDA) system. The continuous monitoring of parametric time histories revealed useful details about the complex flow and helped to establish the locations and times of the peak parameter values. Based upon the nondimensional presentation of data, the following general conclusions can be made. First, all the 5 valve designs created elevated turbulent stresses during the accelerating and peak flow phases, presenting the possibility of thromboembolism and perhaps hemolysis. Second, the difference in valve configuration seemed to affect the flow characteristics; third, the bileaflet design of the St. Jude valve appeared to create a lower turbulence stress level.

Biomechanical Phenomena↗
PubMed2003

Changes in carotid artery flow velocities after stent implantation: a fluid dynamics study with laser Doppler anemometry.

PURPOSE: To study the influence of stent size and location on flow patterns in a physiological carotid model. METHODS: Wallstents were positioned in silicon models of the carotid artery at various locations: 2 stents appropriately sized to the anatomy were placed in (1) the internal carotid artery (ICA) and (2) the ICA extending completely into the common carotid artery so as to cover the external carotid artery (ECA) orifice. Another 2 stents were placed in the ICA extending (1) partially and (2) completely into the bulb to simulate stent displacement and disproportion between stent size and the original vessel geometry. Measurements were performed with laser Doppler anemometry (LDA) using pulsatile flow conditions (Reynolds number=250; flow 0.431 L/min; ICA:ECA flow rate ratio 70:30) in hemodynamically relevant cross sections. The hemodynamic changes were analyzed with 1-dimensional flow profiles. RESULTS: With the stent in the ICA, no changes of the normal flow profile were seen. For stents positioned in the ICA and extending partially or completely into the carotid bulb, the flow behavior was affected by the resistance of the stent to flow in the ECA. Hemodynamically relevant disturbances were seen in the ICA and ECA, especially in the separation zones (regions along the walls just after a bifurcation, bend, or curve). The ICA:ECA flow rate ratios shifted from 70:30 to 71.3:28.7 and from 70:30 to 75.1:24.9, respectively, in the 2 malpositioned stent models. With the stent placed in the ICA extending completely into the CCA, the ICA:ECA flow rate ratio shifted from 70:30 to 72.4:27.6. In this configuration, there were no notable flow changes in the ICA, but a clear diminishing of the separation zones in the ECA separation zones. CONCLUSIONS: Anatomically correct positioning of appropriately sized stents does not lead to relevant flow disturbances in the ICA. In the ECA, depending on the position, size, and interstices of the stent, the physiological flow was considerably disturbed when any part of the stent covered the inflow of the vessel. Disturbances were seen when the stent was positioned into the bulb. For clinical application, stent location and size must be carefully determined so that the stent covers the bifurcation completely or is in the ICA only.

Blood Flow Velocity↗
PubMed1994

Comparative study of the hydrodynamic function of the size 19mm and 21mm St. Jude Medical Hemodynamic Plus Bileaflet Heart valves.

The hydrodynamic function of the St. Jude Medical Hemodynamic Plus Bileaflet Heart valve has been compared to the function of the standard St. Jude valve, the Carbomedics, Duromedics and the Monostrut valves in a pulsatile flow simulator. Size 19mm and 21mm tissue annulus diameter valves have been studied for use in small aortic roots. The size 19mm St. Jude hemodynamic Plus had lower forward flow pressure drops and lower total energy losses than the other valves studied. The size 19mm St. Jude Hemodynamic Plus valve should provide lower forward flow pressure drops and energy losses for the patient with a small aortic root, than the other types of prostheses included in the study.

Aortic Valve↗
PubMed1989

Doppler spectral waveform generation in vitro: an aid to diagnosis of vascular disease.

This paper describes a microcomputer controlled pump which generates pulsatile flows similar to those found in the human peripheral circulation. Continuous wave Doppler ultrasound was used to investigate the flows generated by the pump and the behaviour of diagnostic indices derived from the spectra was examined. Sonograms were recorded from elastic and rigid tubes with various degrees of axisymmetric constriction. Heart rate, stroke volume, severity of vessel constriction, vessel wall elasticity, distal resistance, and systemic peripheral impedance were varied in turn and the resulting Doppler spectra compared. Indices considered were the pulsatility index, spectral broadening index and peck Doppler frequency. In general, the indices lacked the sensitivity to detect low to moderate levels of disease.

Humans↗
PubMed2005

Vascular reactivity and atheromatous plaques in post-menopausal women on tibolone treatment. Open prospective study with Doppler ultrasonography in internal carotid artery.

BACKGROUND: Arteriosclerosis is the main cause of ischaemic ictus. The middle cerebral and anterior cerebral arteries, which irrigate over 70% of the entire cerebral tissue, spring from the internal carotid. Additionally, it is in the extracraneal vessels that embolism, thrombosis and stenosis originate more frequently. AIM: To evaluate the variations in blood flow (pulsatility index: PI) and to assess the evolution of atherogenic lesions (thickening of the vascular intima and the presence of atheromatous plaques) in the internal carotid artery after tibolone therapy. SUBJECTS AND METHODS: A total of 116 healthy menopausal women were included in this open, prospective and comparative study. Of them, 101 subjects completed the 48 weeks follow-up. Subjects were allocated in two groups: group T (n = 55) received 2.5mg/day of tibolone daily and group C (n = 61) was a free-treatment control group. To evaluate both resistance to blood flow and the existence and evolution of atheromatous plaques in the internal carotid, an ultrasonograph with a pulsed Doppler was used. The PI was used as the parameter of vascular tone. To study atherosclerotic lesions in the internal carotid artery, we used morphological criteria. Measurements were done before entering in the study, and at 12, 24, 36 and 48 weeks of treatment. RESULTS: After tibolone treatment the PI in the internal carotid artery was observed markedly diminished. Moreover, tibolone reduces both the thickness and length of atheromatous plaque and the degree of vascular stenosis. CONCLUSION: tibolone administration reduced the carotid atheromatous plaque in thickness and length and improved cerebral perfusion.

Arteriosclerosis↗
PubMed2006

3D dynamical ultrasonic model of pulsating vessel walls.

The aim of this work is to introduce a novel 3-D model of pulsating vessels, through which the dynamic acoustic response of arterial regions can be predicted. Blood flow is numerically simulated by considering the fluid-dynamic displacements of the scatterers (erythrocytes), while a mechanical model calculates the wall displacement due to fluid pressure. The acoustic characteristics of each region are simulated through the FIELD software. Two numerical phantoms of a carotid artery surrounded by elastic tissue have been developed to illustrate the model. One of them includes a plaque involving a 50% stenosis. B-mode and M-mode images are produced and segmented to obtain the wall displacement profile. A cylindrical holed phantom made of cryogel mimicking material has been constructed for the model validation. In pulsatile flow conditions, fluid and wall displacements have been measured by Doppler ultrasound methods and quantitatively compared to simulated M-mode images, showing a fairly good agreement.

Arteries↗
PubMed1994

A new and simple technique to achieve a confluent and flow resistant endothelium on vascular ePTFE-grafts using human serum.

Confluent endothelialisation of vascular grafts in vitro before implantation has been suggested as a way to improve patency. With the aim of creating a confluent endothelium or expanded polytetrafluoroethylene (ePTFE) vascular grafts, using a minimum of allo- or xenogenic material, we have investigated the use of human serum for endothelial cell (EC) growth and adhesion to the grafts. Loss of fibronectin from the serum was measured before and after coating. After serum- or collagen I-precoating, the grafts were seeded with cultured adult human endothelial cells from the great saphenous vein and then kept under rotational culture conditions for 2 days. To evaluate the endothelial resistance to detachment the grafts were mounted in parallel to a heart-lung machine, delivering a pulsatile flow of human blood for 1 hour. Evaluation was performed using scanning electron microscopy (SEM). By simply pressing serum through the graft wall, fibronectin corresponding to 19 micrograms/cm2 graft surface was consumed. It was possible to achieve a confluent endothelium on both serum- and collagen I-precoated grafts (n = 8). After being subjected to blood flow, SEM revealed a complete endothelial lining of the grafts (n = 12) except for two serum-precoated grafts which showed < or = 10% and between 10 and 20% denuded areas, and one collagen-coated graft that showed < or = 10% of denuded area. This method provides a way to achieve a confluent and flow resistant endothelial lining on ePTFE vascular grafts.

Blood↗
PubMed1995

Pulsatile total artificial heart using a reversible rotary pump.

A pump circuit was assembled and examined for use as an implantable artificial heart. The circuit consisted of a gear pump and 4 artificial heart valves. Mitral and pulmonary arterial valves were placed at the inflow port of the pump, and aortic and tricuspid valves were placed at the outflow port. The mitral and the tricuspid valves were connected to each reservoir at 10 mm Hg, and the aortic and the pulmonary arterial valves were connected to the head tanks at 80 and 20 mm Hg, respectively. The pump discharged pulsatile flows into both systemic and pulmonary arteries alternately by switching the direction of rotation periodically. Because the rated discharge was 1.7 L/min for the gear pump used, the measured flow rate was 0.8-0.75 L/min at a heart rate of 60-110 bpm.

Aortic Valve↗
PubMed1993

Quantification of regurgitant flow through bileaflet heart valve prostheses: theoretical and in vitro studies.

A theoretical treatment using turbulent jet theory has yielded a new equation for predicting regurgitant flow through bileaflet heart valve prostheses, the most commonly implanted mechanical valve design. Previously reported techniques assuming an axisymmetric jet are not applicable to the slot-like orifices presented in these valves. The equations were therefore rederived in the context of the prosthetic valve geometry. The purpose of this study was to develop such a method and demonstrate its applicability in principle by using in vitro models. The method was validated under both steady and pulsatile flow conditions. Having derived a method geometrically specific to the orifices presented in bileaflet mechanical heart valves, it should be applicable from patient to patient due to the rigid nature of the valve. These idealized in vitro studies, along with the accompanying theoretical derivation, will guide implementation in the clinical setting.

Echocardiography, Doppler↗
PubMed1990

Middle cerebral artery flow velocity waveforms in fetal hypoxaemia.

In 81 small-for-gestational age fetuses (SGA) colour flow imaging was used to identify the fetal middle cerebral artery for subsequent pulsed Doppler studies. Impedence to flow (pulsatility index; PI) was significantly lower, and mean blood velocity was significantly higher, than the respective reference ranges with gestation. Fetal blood sampling by cordocentesis was performed in all SGA fetuses and a significant quadratic relation was found between fetal hypoxaemia and the degree of reduction in the PI of FVWs from the fetal middle cerebral artery. Thus, maximum reduction in PI is reached when the fetal PO2 is 2-4 SD below the normal mean for gestation. When the oxygen deficit is greater there is a tendency for the PI to rise, and this presumably reflects the development of brain oedema.

Blood Flow Velocity↗
PubMed2004

On flow effects in balanced steady-state free precession imaging: pictorial description, parameter dependence, and clinical implications.

PURPOSE: To present a pictorial description of the origin of flow effects in balanced steady-state free precession (SSFP) imaging that can result in considerable frequency offset-dependent signal changes originating from outflow of spins that can still contribute to the total SSFP signal (out-of-slice contributions), to analyze the parameter dependence and slice broadening associated with outflow effects, and to illustrate clinical implications such as frequency offset-dependent flow artifacts and spatial misencoding. MATERIALS AND METHODS: Computer simulations were used to create a pictorial description of flow effects that illustrates the origin and parameter dependence of the observed signal changes and links their frequency dependency to the phase distribution of spins flowing in and out of the imaging slice. Slice broadening associated with out-of-slice contributions and flow-related signal enhancement was characterized by an effective slice thickness, which depends on flow rate, the T2* decay of signal magnitude from spins that have left the imaging slice, and the ratio of the net out-of-slice magnetization relative to the thickness of the imaging slice. RESULTS: Both simulated SSFP signal intensities and effective slice broadening vary with flip angle and demonstrate a nonlinear dependence on inflow. Simulations with bloodlike T1 and T2 show that the effective slice thickness can be as large as 15 times the prescribed slice thickness. These effects can have significant clinical implications such as large frequency offset-dependent signal enhancement, pulsatile flow artifacts, and spatial misrepresentation of blood signal that has already left the imaging slice. CONCLUSION: Flow-related signal changes in SSFP imaging exhibit highly complex parameter dependence, which predominantly has to be associated with frequency offset-dependent outflow effects and a resulting broadening of the slice thickness.

Artifacts↗
PubMed2000

Echocardiography, color-coded Doppler imaging, and abdominal sonography, a non-invasive method for investigation of heart and aortic morphology and function in female gottingen minipigs: method and reference values for M-mode, B-mode, and flow parameters.

OBJECTIVE: The aim of the study reported here was to set up a method for echocardiography (EC) and abdominal sonography and to obtain EC reference values for left ventricular (LV) morphology and function and sonographic abdominal aortic morphology, function, and flow values in conscious, unsedated Gottingen minipigs. METHODS: Applying a standardized investigation procedure, the following parameters were measured by use of M-mode EC, color-coded Doppler imaging, and B-mode sonography, or were calculated, in 58 female minipigs: LV end-diastolic and end-systolic diameter, interventricular septum thickness, LV caudal wall thickness, LV end-diastolic volume and end-systolic volume, fractional shortening, ejection fraction, and percentage of thickening of interventricular septum and LV caudal wall. In addition, morphology, pulsatility, flow values, and flow patterns in the abdominal aorta were recorded or calculated during abdominal sonography and color-coded Doppler imaging. RESULTS: Variable EC values were obtained due to individual variations of motor activity. Variation could be reduced by accustoming the animals to a standardized investigation procedure. Reference values could be obtained for EC, partially indicating clear correlation with body weight. Color-coded Doppler and Doppler spectra did not indicate flow disturbances in large arterial abdominal vessels. CONCLUSIONS: Results indicate that handling during EC and sonography can cause discomfort in unsedated minipigs that may interfere with recording of valid reference values for functional cardiac parameters in young animals. Accustoming the animals to a standardized investigation procedure reduces stress to a satisfactory level and enables data recording. Thus the minipig is considered suitable for assessment of cardiovascular parameters in experimental or toxicologic studies.

Animals↗
PubMed2006

Preoperative evaluation of the right gastroepiploic artery using abdominal ultrasonography.

Preoperative evaluation of the right gastroepiploic artery was performed by abdominal ultrasonography to determine whether the graft was adequate for coronary artery bypass. The gastroepiploic artery was used when the graft diameter was greater than 2 mm with pulsatile flow. Postoperative angiography revealed the gastroepiploic artery dominant, and the graft diameter measured by angiography was almost the same size as that of abdominal ultrasonography. The right gastroepiploic artery (GEA) has been an important arterial graft in coronary revascularization, and the opportunities to use this artery as the in situ or free graft have been increasing lately. However we sometimes experience cases in which the GEA is not suitable for the graft because the diameter is not large enough to anastomose or the blood flow is poor. The aim of this study was to evaluate the graftability of the GEA using abdominal ultrasonography preoperatively.

Angiography↗