Biomedical subjects

E M Pedersen

Publications and source records attributed to E M Pedersen.

At least 73 records · Page 4Linked to original sources

PubMed1996

Comparison of magnetic resonance imaging and Laser Doppler Anemometry velocity measurements downstream of replacement heart valves: implications for in vivo assessment of prosthetic valve function.

BACKGROUND AND AIM OF THE STUDY: The non-invasive, in-vivo assessment of prosthetic valve function is compromised by the lack of accurate measurements of the transvalvular flow fields or hemodynamics by current techniques. Short echo time magnetic resonance imaging (MRI) may provide a method for the non-invasive, in vivo assessment of prosthetic valve function by accurately measuring changes in the transvalvular flow fields associated with normal and dysfunctional prosthetic valves. The objectives of these in vitro experiments were to investigate the potential for using MRI as a tool to measure the complex flow fields distal to replacement heart valves, and to assess the accuracy of MRI velocity measurements by comparison with Laser Doppler Anemometry (LDA), a gold standard. METHODS: The velocity fields downstream of tilting disc, bileaflet, ball and cage, and pericardial tissue valves were measured using both three-component LDA and MRI phase velocity encoding under a steady flow rate of 22.8 l/min, simulating peak systolic flow. The valves were tested under normal and stenotic conditions to assess the MRI capabilities under a wide range of local flow conditions, velocities and turbulence levels. A new short echo time MRI technique (FAcE), which allowed velocity measurements in stenotic jets with high turbulence, was tested. RESULTS: Good overall agreement was obtained between the MRI velocity measurements and the LDA data. The MRI velocity measurements adequately reproduced the spatial structure of the flow fields. In most cases peak velocities were accurately measured to within 15%. CONCLUSIONS: The results indicate that the FAcE MRI method has the potential to be used as a diagnostic tool to assess prosthetic valve function.

Aortic Valve↗

PubMed1996

Magnetic resonance imaging of blood velocity distribution around St. Jude medical aortic valves in patients.

BACKGROUND AND AIMS OF THE STUDY: Complications after replacement of diseased heart valves with mechanical prostheses may be related to fluid dynamic disturbances. Magnetic resonance velocity mapping may allow quantitative, non-invasive, serial assessment of the blood velocity distribution around prosthetic heart valves in patients. MATERIAL AND METHODS: Velocity mapping was performed in six patients with aortic St. Jude Medical valves. Axial velocity components were measured at three positions near the valve and correlated with earlier in vitro results and with earlier invasive measurements. RESULTS: The velocity profiles downstream of the valve prostheses reflected the valve design and thus confirmed previous findings. In the one diameter downstream position blood flow velocities accelerated initially through the lateral orifices of the valve. Later in the acceleration phase the velocity profile became skewed and the antegrade velocity components increased in the part of the vessel corresponding to the central slit of the valve. Retrograde velocities occurred in part of the lateral orifice regions. CONCLUSIONS: MR velocity mapping provides valuable information on velocity fields around prosthetic bileaflet aortic valves. The velocity fields from the present study disclose qualitative similarity to those previously obtained. The present study, however, suggests a more skewed velocity profile than predicted from former studies. More extensive studies on larger patient groups should be performed, also with other valve types in order to establish a bank of reference data.

Adult↗

PubMed1995

A new control volume method for calculating valvular regurgitation.

BACKGROUND: The purpose of the present study was to develop a new method of measuring heart valvular regurgitation based on control volume theory and to verify its accuracy in vitro and in vivo. Current methods of quantifying valvular regurgitation rely too much on assumptions about the flow field and therefore are difficult to apply in vivo. In particular, the proximal isovelocity surface area (PISA) method oversimplifies the proximal velocity field by assuming hemispherical isovelocity contours proximal to the orifice. This severely limits the applicability of the PISA method. Use of the basic control volume theory, however, removes the need to assume the manner in which the proximal flow accelerates toward the regurgitant orifice, the shape and size of the orifice, the shape of the orifice plate, and the non-newtonian behavior of the fluid. Apart from a correction that is necessary if the orifice plate is moving, the control volume method assumes only the incompressibility of the fluid and therefore is a potentially more accurate approach. In addition, the use of magnetic resonance imaging (MRI) precludes the need for an acoustic window. METHODS AND RESULTS: MRI has been used to measure the three-dimensional velocity field proximal to regurgitant orifices, including single and multiple orifices and a cone-shaped orifice plate. Both steady (0 to 7.5 L/min) and pulsatile (2 and 3 L/min) flows were used. By intergrating this velocity over a control volume surrounding the orifice, we calculated the flow rate through the orifice. As a validation, the cardiac output of a 50-kg pig also was measured and was compared with thermodilution measurements. It was found that MRI could be used to measure the three-dimensional flow proximal to regurgitant orifices. This enabled the calculation of the flow rate through the orifice by integrating the velocity over the surface of a control volume covering the orifice. This flow rate correlated well with the actual rate (0.992; correlation line slope, 1.01). Care had to be taken, however, to exclude from the integration regions of aliased velocity. The cardiac output of the pig measured using MRI was in close agreement with the themodilution measurements. CONCLUSIONS: Our new method of measuring valvular regurgitation has been shown to be very accurate in vitro and in vivo and therefore is a potentially accurate way to quantify valvular regurgitation.

Animals↗

PubMed1995

Left ventricular blood flow patterns in normal subjects: a quantitative analysis by three-dimensional magnetic resonance velocity mapping.

OBJECTIVES: Magnetic resonance velocity mapping was used to investigate the hypothesis of a vortex motion within the left ventricle interacting with mitral valve motion and inflow velocity. BACKGROUND: In vitro flow visualization studies have suggested the presence of a large anterior vortex inside the left ventricle during mitral inflow. However, to our knowledge the occurrence of this phenomenon has not been demonstrated in the human left ventricle. METHODS: Magnetic resonance velocity mapping was performed in 26 healthy volunteers using a flow-adjusted gradient sequence for three-dimensional flow velocity acquisition in the long-axis plane of the left ventricle. By computer processing, the flow vectors in the left ventricle were visualized and animated dynamically. RESULTS: The early diastolic mitral inflow was apically directed, and a large counterclockwise anterior vortex was created within the left ventricle shortly after the onset of the mid-diastolic semiclosure of the anterior mitral leaflet. During mid-diastolic diastasis, mitral inflow ceased until the flow accelerated again at atrial systole. The final closure of the mitral valve was preceded by a smaller vortex seen at the tips of the mitral leaflets. At systolic ejection, all flow vectors were directed toward the left ventricular outflow tract. The anterior vortex had a radius of 1.62 +/- 0.24 cm (mean +/- SD), and the average angular velocity (i.e., the rotation of an element about the center of the vortex within the central core) was 30.08 +/- 9.98 radians/s. The maximal kinetic energy of the anterior vortex was 4.3 x 10(-4) +/- 7.1 x 10(-5) J. CONCLUSIONS: The hypothesis of a diastolic vortex formation in the human left ventricle was confirmed, and its close temporal relation to the motion of the anterior mitral leaflet was demonstrated.

Adult↗

PubMed1995

The anastomosis angle does change the flow fields at vascular end-to-side anastomoses in vivo.

PURPOSE: The purpose of this article was to study the influence of the anastomosis angle on the flow fields at end-to-side anastomoses in vivo. METHODS: Polyurethane grafts of similar internal diameter to that of the abdominal aorta (8 mm) were implanted from the suprarenal to the infrarenal level in 10 pigs. Three angles of standardized distal end-to-side anastomoses (90 degrees, 45 degrees, and 15 degrees) were studied. The anatomic position of the anastomoses was constant, the proximal outflow segment was occluded, and the flow rate through the graft was controlled. Flow visualization was accomplished by a color-flow Doppler ultrasound system. RESULTS: The angulation was reproduced within 10%. Gross hemodynamic parameters were stable, and the similarity parameters were typical for peripheral bypasses (mean Reynold's number is 424 and Womersley's parameter is 5.9). The flow fields were clearly dependent on the anastomosis angle. A zone of recirculation (approximately 5% of the flow area), extending from the toe to one diameter downstream, was found in the 45-degree and 90-degree anastomoses. No flow disturbances were detected at the toe and one diameter downstream with an anastomosis angle of 15 degrees. At the heel different recirculating flow patterns were found in the different anastomoses. CONCLUSION: The anastomosis angle does change the flow fields at vascular end-to-side anastomoses in vivo.

Anastomosis, Surgical↗

PubMed1995

Dynamic quantification, visualisation and animation of blood velocities and flows in infrarenal aortic aneurysms in vivo by three-dimensional MR phase velocity encoding.

OBJECTIVES: Nuclear magnetic resonance (MR) phase velocity encoding techniques were developed for assessment of three-dimensional blood flow patterns and regional blood flows in infrarenal aortic aneurysms in vivo. METHODS: Twenty patients with abdominal aortic aneurysms were investigated before elective surgery with a 1.5 Tesla MR-scanner. Standard multislice spin-echo sequences were used for aneurysm imaging. A flow-adjusted gradients sequence (FLAG) provided three-dimensional vector plots depicting local blood flow velocities as functions of time and anatomical position. Computer-generated animated presentations of the vectors were developed to ease data analysis and interpretation. RESULTS: The blood flow patterns in infrarenal aortic aneurysms were much more complex than previously believed. Their main characteristics were simultaneous breakdown of the antegrade flow and creation of major retrograde flow components. Major pattern determinants included inlet geometry and lumen morphology, especially presence or absence of a thrombus. CONCLUSIONS: The frictional forces generated within the lumen as a result of the breakdown of laminar flows are probably translated to the aneurysm wall and contribute to thrombus formation, aneurysm growth and risk of rupture.

Aged↗

PubMed1995

An in vivo model for studying the local haemodynamics of end-to-side anastomoses.

OBJECTIVES: To develop an in-vivo model to study the anastomotic flow patterns. DESIGN: Prospective, open, animal study. METHODS: Polyurethane grafts with an internal diameter equal to the abdominal aorta (8 mm) of 90 kg pigs were implanted as bypass grafts from the supra-renal to the infra-renal level. A novel technique for constructing anastomoses with different anastomosis angles and only slight dilatation was used. The proximal outflow segment was occluded and the flow rate through the graft controlled by clamping the iliac arteries. Visualisation of the flow-fields at the distal end-to-side anastomosis was achieved by a comprehensive colour Doppler mapping protocol. RESULTS: The angulation of the anastomoses was controllable and reproducible. Gross haemodynamic parameters were stable within physiological ranges and were typical for peripheral bypass grafts. The flow fields at the distal end-to-side anastomosis were visualised and found to be in accordance with those reported by in vitro studies. Using different angles of Doppler insonation the same flow field characteristics were found. CONCLUSIONS: The model is an appropriate tool for studies of the effects of anastomotic geometry on local flow fields in vivo.

Anastomosis, Surgical↗

PubMed1995

In vivo analysis and three-dimensional visualisation of blood flow patterns at vascular end-to-side anastomoses.

OBJECTIVES: The aim of this study was to describe the velocity fields at distal vascular end-to-side anastomoses with different anastomosis angles in vivo. MATERIALS AND METHODS: The abdominal aorta of ten 90 kg pigs was exposed from the superior mesenteric artery to the trifurcation. A segment of the aorta was bypassed using a polyurethane graft. Three anastomosis angles: 90 degrees (n = 3), 45 degrees (n = 3) and 15 degrees (n = 4) were studied. The bypass length, the anatomical position and the geometry of the anastomoses were standardised. During measurements, the proximal outflow segment was occluded and the flow rate was controlled by reversible iliac artery cross-clamping. Using a colour Doppler system the velocity fields were measured at various positions in the anastomosis. The colour Doppler velocity data were transferred to a computer for dynamic three-dimensional visualisation of the velocity profiles. RESULTS: The angulation was reproduced within 10%. During the experiment, the flow rate was kept constant with Reynold's numbers typical for peripheral arteries. In the 90 degrees anastomoses very disturbed flow fields were seen. The 45 degrees anastomoses were characterised by: (1) low antegrade and retrograde velocities at the heel and (2) a zone of reverse and oscillating velocities at the toe and at one diameter downstream of the toe (1DDD) during deceleration. In the 15 degrees anastomoses no flow disturbances were seen either at the toe or at 1DDD. The velocity profiles were close to parabolic at peak flow at both positions. CONCLUSIONS: It is concluded that the 15 degrees anastomosis is preferable from a haemodynamic point of view.

Anastomosis, Surgical↗

PubMed1995

Magnetic resonance velocity imaging: a new method for prosthetic heart valve study.

The aim of this study was to compare different (long/short echo time, whole body/small bore scanner) magnetic resonance velocity measurement techniques and their applicability to the measurement of blood velocity downstream of prosthetic heart valves. In-vitro magnetic resonance velocity measurements were performed downstream of four normal and stenotic prosthetic heart valves (St. Jude Medical bileaflet, Monostrut tilting disc, Ionescu-Shiley Pericardial and Starr-Edwards caged-ball) under steady flow conditions in an aortic test chamber. Cross-sectional and longitudinal velocity images were obtained downstreamed of the valves. Magnetic resonance was able to measure all three components of fluid velocity downstream of the valves under normal and stenotic conditions except in regions of turbulence. The velocity was measured across the tube cross-section in 10-15 minutes producing a good visualization of the axial velocity profile. High velocity regions, shear layers and reversed/stagnant regions were identified. The flow rate calculated by integration of the magnetic resonance velocity across the cross-section of the tube was accurate to 5-6% in normal cases and slightly less accurate for stenotic valves. Although signal loss on the modulus image was adverse to the velocity images, it was found that these regions could be used to identify areas of flow disturbance. The high magnetic field, small bore scanner was able to produce images with a resolution of 0.2 x 0.2 x 1.0 mm and was less affected by turbulence producing more detailed flow images. Magnetic resonances has been shown to be a useful new tool in the measurement of the velocity downstream of prosthetic heart valves. In particular it's short data acquisition time and the possibilities to reproduce the same measurements in-vivo make it an attractive alternative to traditional methods.

Biophysical Phenomena↗

PubMed1995

MARIAN: an analysis tool for the assessment of left ventricular function measured by velocity encoding MRI.

Velocity encoding MRI is a new non-invasive technique for measuring cardiac blood flow velocities. Flow in the three directions of space can be measured during the entire heart cycle. However, the analysis of large amount of data obtained from this technique requires specialized computational software packages to provide physicians with efficient analysis tools. A data visualization software package named Magnetic Resonance Imaging Analyzer (MARIAN) was developed. This software package uses visualization, animation, analysis, and computational tools adapted to time series of cardiac MRI data files, all accessible through a sophisticated graphics user interface. MARIAN was used as a tool for the analysis of the left heart blood flow patterns in two groups of human subjects: ten volunteers and eight patients. The patients were diagnosed with incapacitating angina pectoris and previous left ventricular myocardial infarction. Vector plot animations of the left atrial flow were realized for all volunteer examinations. The temporal flow velocity profiles were sampled at the tips of the mitral leaflets and in the lumen of the right upper pulmonary vein, when possible. The isovolumic relaxation time (IVRT) was estimated. The following flow parameters were obtained from the velocity profiles: at the mitral valve, the early diastolic E-wave, the late diastolic A-wave, the time of occurrence of the E- and A- waves; at the right upper pulmonary vein, the systolic S-wave, the early diastolic D-wave and the reverse late diastolic R-wave. The results obtained were consistent with previous studies using similar MRI techniques. Compared to the control group, the patient group exhibited higher isovolumic relaxation time, a lower peak E-wave, and a lower D-wave. MARIAN thus provided a fast, efficient and accurate data visualization tool for the analysis of human data.

Adult↗

PubMed1994

A new perivascular multi-element pulsed Doppler ultrasound system for in vivo studies of velocity fields and turbulent stresses in large vessels.

A pulsed Doppler ultrasound (PDU) multi-element system was developed for perivascular registration of velocity fields and turbulence in large vessels. In vivo evaluation and comparison with hot-film anemometry (HFA) was performed. C-shaped shells were designed with holes to fit five small 10 MHz ultrasonic probes directed at five measuring points along a diameter perpendicular to the vessel axis. By rotating the shell in 45 degrees steps, blood velocities were measured in 17 points covering the entire cross-sectional vessel area. Measurements were performed in the ascending aorta and at three axial locations in the descending thoracic aorta in pigs. Simultaneous PDU and HFA measurements were performed distal to induced vascular stenoses of different degrees. Three-dimensional visualisation of velocity profiles was made, and Reynolds normal stresses (RNS) were calculated for different levels of turbulence intensities based on the simultaneous PDU and HFA measurements. The velocity profiles in the ascending aorta were skewed at top systole with the highest velocities towards the posterior wall. In the descending thoracic aorta at the ligmentum of Botalli, the velocity profiles were skewed throughout the entire systole with the highest velocities at the right anterior vessel wall. Further downstream in the descending aorta the velocity profiles appeared blunter. The frequency response of the modified PDU system was determined by a 'random noise test' revealing an upper -3dB cut-off frequency of approximately 200 Hz. Regression analysis showed a linear relationship between RNS measured with PDU and RNS measured with HFA (r = 0.93). Two vessel diameters distal to a 75% stenosis RNS up to 28 N m-2 were measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Three-dimensional visualization of velocity profiles in the human main pulmonary artery with magnetic resonance phase-velocity mapping.

Detailed data on blood velocity fields in the normal human main pulmonary artery are an essential platform for discriminating physiologic from pathologic pulmonary flow patterns. Over the years, many studies have revealed quite inconsistent data mainly because of lack of suitable measuring techniques. By using combined cardiac- and respiratory-triggered magnetic resonance phase velocity mapping, very consistent data were obtained in 12 volunteers. In all subjects the location of the highest axial velocities was shifted from the inferior-right toward the superior-left part of the vessel area during the right ventricular contraction, with rapidly decreasing velocities to the inferior right evolving into retrograde flow in the deceleration phase. The mean temporal velocity profile was consistently skewed with a low flow region also toward the inferior-right vessel wall. The magnetic resonance phase shift method used in this study provided remarkably consistent high-quality data about human pulmonary artery velocity fields. This is most likely because of the use of combined cardiac and respiratory triggering.

Adult↗

PubMed1994

Two-dimensional mitral flow velocity profiles in pig models using epicardial Doppler echocardiography.

OBJECTIVES: This study investigated the velocity distribution across the natural mitral valve. BACKGROUND: Information about the blood velocity distribution across the mitral valve is of interest in basic fluid dynamic studies of the natural mitral valve and is needed for precise cardiac output estimates by Doppler echocardiography. METHODS: The velocity distribution across the mitral valve was measured by epicardial Doppler echocardiography in ten 90-kg anesthetized pigs. By rotating the ultrasound transducer in 30 degrees intervals from the apical position, we constructed two-dimensional velocity profiles across the left ventricular inflow tract from diameters from each rotation arranged around a reference point. The time-averaged mitral velocity profile was calculated to estimate the error in cardiac output calculations that may occur with pulsed Doppler ultrasound when a single sample volume is used to record the mean velocity across the mitral orifice. RESULTS: The time-averaged diastolic cross-sectional mitral velocity profiles at the level of the mitral annulus and leaflet tips were variably skewed because of the development of a large anterior vortex in the left ventricle during the deceleration of early diastolic inflow and atrial systole. The ratio of the time-velocity integral of the center sample volume to the spatially averaged time-velocity integral was 1.13 +/- 0.15 (mean +/- SD) (range 0.80 to 1.32). Using regression analysis, we found a correlation between the degree of nonuniformity of the cross-sectional velocity distribution and the peak velocity of the anterior vortex (r = 0.65, p < 0.01). CONCLUSIONS: The assumption of a flat mean velocity profile across the mitral valve can introduce errors of +13 +/- 15% (mean +/- SD) in cardiac output measured with pulsed Doppler ultrasound when one is interrogating a single center sample volume.

Animals↗

PubMed1994

Studies by pulsed Doppler ultrasonography of velocity fields downstream of graded stenoses on the abdominal aorta in pigs.

PURPOSE: To investigate local hemodynamics downstream of arterial stenoses, a perivascular five-element Doppler ultrasound transducer was used for registration of one-dimensional velocity profiles and estimation of Reynolds (turbulent) normal stresses downstream of smooth, graded stenoses on the abdominal aorta in six 90 kg pigs. METHODS: Blood velocities were registered by a 10 MHz pulsed Doppler velocimeter that used a modified zero-crossing detector with an upper -3 dB cutoff frequency of 200 Hz. Signal analysis included ensemble averaging, turbulence analysis, and dimensional visualization of velocity profiles. RESULTS: Velocity profiles downstream of minor (< or = 40%) and moderate (40% to 65%) stenoses were skewed with the highest systolic velocities toward the anterior vessel wall and diastolic flow reversal occasionally present at the posterior vessel wall. Immediately downstream of severe (> or = 65%) stenoses a prominent poststenotic jet and systolic recirculation zones were present. Further downstream, vortices and eddies dominated the flow field. Reynolds normal stresses were highest at locations in the velocity field with high-velocity gradients corresponding to the parajet zone. CONCLUSIONS: The present study demonstrated that pulsed Doppler ultrasonography can provide detailed and quantitative information of flow phenomena such as jetlike flow, vortices, and recirculation zones in a poststenotic flow field in the abdominal aorta.

Animals↗

PubMed1994

Dose-dependent cardiotoxic effect of amiodarone in cardioplegic solutions correlates with loss of dihydropyridine binding sites: in vitro evidence for a potentially lethal interaction with procaine.

Increasing evidence suggests that amiodarone treatment may represent a potential risk in patients exposed to cardiac surgery. Conversely, amiodarone has been suggested to be beneficial as an additive to cardioplegic solutions, but its use has not been tried in vivo. We evaluated hemodynamic, ECG, and possible toxicologic effects of amiodarone when added to the cardioplegic solution. Pigs weighing (70 +/- 2 kg, n = 24) were exposed to cardiopulmonary bypass (CPB) and hypothermic cardiac arrest for 1 h with Bretschneider's (BS) or St. Thomas' Hospital (St. Th.) cardioplegic solution. Amiodarone or the solvent was added to the solutions. Only pigs receiving the lowest dose of amiodarone (0.028 mg/g tissue) could be weaned from bypass. Higher doses resulted in graded myocardial contractures without recovery of electrical activity. Electron microscopy showed severely disintegrated myocytes and swollen mitochondria in amiodarone-exposed hearts. No changes in equilibrium binding characteristics were observed for beta-adrenoceptors, whereas maximum binding capacity (MBC) and receptor affinity for voltage-operated Ca2+ channels were dose-dependently decreased (mean 73%, p < 0.0005; 105%; p < 0.05). Ca2+ paradoxlike findings similar to those in pigs were inducible in isolated, in vitro perfused rat heart exposed to normothermic or hypothermic chemical arrest with BS and amiodarone. This model was therefore used to evaluate whether the observed myocardial damage was associated with excessive tissue Ca2+ accumulation. Addition of amiodarone to BS was associated with a significant increase in 45Ca2+ content in the heart, irrespective of temperature. Only 2 of 13 hearts recovered some degree of mechanical activity during reperfusion. When procaine (an antiarrhythmic drug with membrane-stabilizing properties, an effect that is potentiated by amiodarone) was removed from BS, 45Ca2+ accumulation did not differ from that in controls and mechanical activity recovered fully in 7 of 8 hearts. In conclusion, amiodarone added to Ca(2+)-free as well as Ca(2+)-containing cardioplegic solutions led to dose-dependent myocardial damage at reperfusion, irrespective of temperature. In parallel with clinical features was a reduction in maximum binding capacity and a decrease in affinity for the Ca2+ channel antagonist. Removal of procaine from BS prevented excessive Ca2+ accumulation and mechanical deterioration in isolated heart. We hypothesize that amiodarone administered under the conditions described may change the configuration of the Ca2+ channel, rendering it more permeable to Ca2+. Pharmacologic interaction between amiodarone and procaine apparently is at least partly responsible for the increased Ca2+ uptake and the stone-heart phenomenon during reperfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiodarone↗

PubMed1994

Influence of abdominal aortic curvature and resting versus exercise conditions on velocity fields in the normal abdominal aortic bifurcation.

Local hemodynamics are considered an important atherogenetic factor in the abdominal aortic bifurcation. This study addresses the quantitative flow fields in a pulsatile flow model of a normal abdominal aortic bifurcation when encountering realistic upstream anatomy, realistic inlet flow conditions and different physiologic flow conditions (rest vs. exercise). Two-dimensional laser Doppler anemometry measurements gave axial as well as radial velocities. The localization and magnitude of peak velocities, retrograde flow and secondary velocity patterns were found to be determined to a great extent by the curvature of the abdominal aorta, the triphasic flow wave form and the inlet velocity profile. Significant changes were also seen when simulating different physiologic flow conditions. Thus retrograde velocities were present at both the flow divider and the lateral vessel wall for the rest condition but not for the exercise flow conditions, and the location of low and retrograde velocities during diastole were as much determined by abdominal aortic curvature as by the bifurcation for nearly all flow conditions and locations. In conclusion, the anatomy and hemodynamics in the abdominal aorta cannot be neglected when studying the hemodynamics in the abdominal aortic bifurcation.

Aorta, Abdominal↗

PubMed1994

Turbulent stresses downstream of three mechanical aortic valve prostheses in human beings.

High levels of turbulent stresses resulting from disturbed blood flow may cause damage to red blood cells and platelets. The purpose of this study was to evaluate the spatial distribution and temporal development of turbulent stresses downstream of three mechanical aortic valve prostheses in human subjects: the St. Jude Medical, the CarboMedics, and the Starr-Edwards silicone rubber ball. Blood velocity measurements were taken at 17 measuring points in the cross-sectional area of the ascending aorta 5 to 6 cm downstream of the aortic anulus with the use of a perivascular pulsed Doppler ultrasound system. Turbulence analysis was done for each of the 17 measuring points by calculating the radial Reynolds normal stresses within 50 msec overlapping time windows during systole. By coordinating the calculated Reynolds normal stress values for each time window and for all measuring points, computerized two-dimensional color-coded mapping of the turbulent stress distribution during systole was done. For the St. Jude Medical valves the highest Reynolds normal stress (27 to 63 N/m2) were found along the central slit near the vessel walls. The temporal development and spatial distribution of Reynolds normal stresses for the CarboMedics valves were quite similar to those of the St. Jude Medical valves with maximum Reynolds normal stress values ranging from 19 to 72 N/m2. The typical Reynolds normal stress distribution for the Starr-Edwards silicone rubber ball valves was asymmetric, revealing the highest Reynolds normal stresses (11 to 56 N/m2) at various locations in the annular region between the ball and the vessel wall. The spatial distribution and temporal development of turbulent stresses downstream of the three investigated mechanical aortic valve prostheses correlated well with the superstructure of the valves. The maximum Reynolds normal stresses for the three valve types were in the same order of magnitude with exposure times sufficient to cause sublethal damage to red blood cells and platelets.

Adult↗

PubMed1993

Velocity profiles in the ascending aorta in pigs: axial development and influence of changes in left ventricular contraction pattern.

Earlier studies using hot-film anemometry in pigs have revealed skewed tangentially rotating velocity profiles in the ascending aorta during systole. The reason for this phenomenon has been postulated to be caused by the left ventricular contraction pattern. Therefore, the aim of this study was to investigate the influence of the left ventricular contraction pattern on the velocity fields in the ascending aorta of pigs. We used a 10 MHz perivascular pulsed Doppler ultrasound system to measure point blood velocities at two axial locations over the entire cross sectional area in the ascending aorta of 90 kg pigs. The axial component of the velocity profiles was visualized dynamically by computerized 3-dimensional animation techniques. Changing left ventricular contraction patterns were accomplished by reversible occlusion of either the left anterior descending or right posterior descending coronary artery. The axial development of the systolic rotating and skewed velocity profiles in the ascending aorta was described. The appearance of the systolic velocity profiles were virtually unaffected by changes in left ventricular contraction pattern.

Animals↗