Die Doppler-echokardiographische Quantifizierung des regurgitierenden Blutvolumens bei Patienten mit Mitralinsuffizienz

Summary The purpose of this study was to assess the accuracy and clinical utility of pulsed Doppler echocardiography in determining the regurgitant fraction in patients with pure mitral regurgitation. In 30 unselected consecutive patients with mitral regurgitation and in 20 patients without valvular heart disease pulsed Doppler echocardiography was performed to measure blood flow at the mitral and aortic valve. The regurgitant blood volume was calculated as the difference of the stroke volumes measured at the mitral and aortic valve. The regurgitant fraction was computed as regurgitant blood volume/mitral flow. By cardiac catheterization regurgitant blood volume and regurgitant fraction were obtained from the left ventricular angiographic stroke volume and the stroke volume measured by thermodilution. Five patients were excluded because of technically poor left ventricular angiograms. In 4 patients with mitral regurgitation measurement of the regurgitant blood volume and regurgitant fraction was impossible by Doppler because of poor ultrasound signal quality. In 21 patients with mitral regurgitation the correlations between the invasive and the Doppler measurements were significant (regurgitant blood volume:r=0.89, SEE=20.9 ml; regurgitant fraction:r=0.91, SEE=7.1%). However, the mean percent error of the regurgitant fraction measurement (12.0±11.6%) was smaller than of the regurgitant blood volume measurement (24.9±17.0%). In the control group the regurgitant blood volume ranged between –25.1 ml and 11.6 ml and the regurgitant fraction between –17.7% and 12.4%.Thus, pulsed Doppler echocardiography is clinically useful in determination of the regurgitant fraction in 84% of unselected adult patients with pure mitral regurgitation. The Doppler method is limited in the diagnosis and quantification of mild regurgitation. However, the method is more accurate in determining the regurgitant fraction than measuring the regurgitant blood volume.

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Abkürzungsverzeichnis MI Mitralinsuffizienz - RBV regurgitierendes Blutvolumen - RF Regurgitationsfraktion - SV_Angio angiographisch berechnetes Schlagvolumen - SV_Ao Doppler-echokardiographisch an der Aortenklappe gemessenes Schlagvolumen - SV_Mi Doppler-echokardiographisch an der Mitralklappe gemessenes Schlagvolumen - SV_Thermo mittels Thermodilution bestimmtes Schlagvolumen     

The importance of slice location on the accuracy of aortic regurgitation measurements with magnetic resonance phase velocity mapping

Although several methods have been used clinically to evaluate the severity of aortic regurgitation, there is no purely quantitative approach for aortic regurgitant volume (ARV) measurements. Magnetic resonance phase velocity mapping can be used to quantify the ARV, with a single imaging slice in the ascending aorta, from through-slice velocity measurements. To investigate the accuracy of this technique,in vitro experiments were performed with a compliant model of the ascending aorta. Our goals were to study the effects of slice location on the reliability of the ARV measurements and to determine the location that provides the most accurate results. It was found that when the slice was placed between the aortic valve and the coronary ostia, the measurements were most accurate. Beyond the coronary ostia, aortic compliance and coronary flow negatively affected the accuracy of the measurements, introducing significant errors. This study shows that slice location is important in quantifying the ARV accurately. The higher accuracy achieved with the slice placed between the aortic valve and the coronary ostia suggests that this slice location should be considered and thoroughly examined as the preferred measurement site clinically.     

Quantification of heart valve regurgitation: a critical analysis from a theoretical and experimental point of view

A theoretical analysis is presented regarding factors of importance for the determination of distance of intrusion of the regurgitant jet in heart valve regurgitation. The analysis is based on hydrodynamic theory. In the idealized model situation, for a circular hole, the intrusion of the regurgitant jet is linearly related to the product of the fluid mean velocity in the orifice and the diameter of the orifice. This was also shown to be true in an experimental fluid model. Thus, volume regurgitation cannot be quantified by the measurement of distance of intrusion of the regurgitant jet alone. On the other hand, an estimate of volume regurgitation can, in the idealized situation, be obtained if mean fluid velocity in the orifice, distance of intrusion of the jet and regurgitation time are known.     

Quantitative evaluation of intra-aortic flow disturbance by the fluid momentum index: Effect of the left ventricular systolic function on the hemodynamics in the aorta.

The combined hemodynamics in the left ventricle and aorta were analyzed numerically to investigate how the hemodynamics in the aorta varies with changes in left ventricular systolic function quantified as the ejection fraction (EF). EFs of 0.3, 0.5, and 0.7 were defined by controlling the total volume ejected during systole, while maintaining the ventricular volume at the end of diastole. The results showed that although the variation in left ventricular systolic function resulted in a change in the magnitude of the flow velocity, the intraventricular and aortic flows, including the secondary flows at the aortic valve orifice, were essentially the same regardless of the EF. To evaluate the strength of the secondary flow relative to the axial flow, the flow momentum index, FMI, was proposed. Spatiotemporal maps of the FMI obtained with different EFs had similar topological patterns, suggesting that the left ventricular systolic function contributed less to the efficiency of conveying blood in the axial direction in the aorta. Systolic function had a minimal effect on the spatiotemporal distribution of the maximum wall shear stress (WSS). A comparison of the spatiotemporal maps of the FMI and WSS revealed that the spatiotemporal maximum of WSS that occur in peak systole did not correspond to that of the FMI, demonstrating that the spatiotemporal maximum WSS was not induced by the helical flow. These results demonstrated that the left ventricular systolic function is not reflected in the global hemodynamics in the aorta and addressed potential of the FMI as an index to quantify the aortic flow disturbances.     

Mean Velocity and Reynolds Stress Measurements in the Regurgitant Jets of Tilting Disk Heart Valves in an Artificial Heart Environment

Laser Doppler velocimetry, with a high temporal resolution (1 ms time windows), was used to measure the flow field in two regions (major and minor orifices) near the aortic and mitral valves (Bjork Shiley monostrut Nos. 25 and 27, respectively) of the Penn State artificial heart. The motion of each valve was also investigated using a 1000 frame/s video camera in order to estimate the valve's closing velocity. Fluid velocities in excess of and opposite to valve closing velocity were detected near the valve, providing evidence of squeeze flow. Maximum Reynolds shear stresses of approximately 20,000 dyn/cm² and time-averaged Reynolds shear stresses of approximately 2000 dyn/cm² were observed during the regurgitant flow phase. These elevated Reynolds shear stresses suggest that regurgitant jets play a role in the hemolysis and thrombosis associated with tilting disk heart valves in an artificial heart environment. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 4727Wg, 4279Qx     

Estimation of arterial compliance in aortic regurgitation: three methods evaluated in pigs

Three methods for measuring arterial compliance when aortic regurgitation is present are examined. The first two methods are based on a Windkessel model composed of two elements, compliance C and resistance R. Arterial compliance was estimated from diastolic pressure waveforms and diastolic regurgitant flow for one method, and from systolic aortic pressure waveforms and systolic flow for the other method. The third method was based on a three-element Windkessel model, composed of characteristic resistance r, compliance C and resistance R. In this method arterial compliance was calculated by adjusting the model to the modulus and phase of the first harmonic term of the aortic input impedance. The three methods were compared and validated in six anaesthetised pigs over a broad range of aortic pressures. The three methods were found to give quantitatively similar estimates of arterial compliance at mean aortic pressures above 60 mm Hg. Below 60 mm Hg, estimates of arterial compliance varied widely, probably because of poor validity of the Windkessel models in the low pressure range.     

Improved method for cardiac output determination in man using ultrasound Doppler technique

An existing ultrasound Doppler method for measuring cardiac output has been improved and refined, partly by locating the sampling volume higher up in the aorta while still using the aortic ring size as the effective transverse flow area. The basis for using this technique is the approximately rectangular systolic velocity profile in the aortic orifice in physiologically and anatomically normal subjects, and the fact that this profile velocity is conserved as the maximum velocity in the ascending aorta for some 3 to 4 cm above the valves. This higher location of the sampling volume improves Doppler signal quality, and does not reduce the accuracy of the method, as can be confirmed in each experimental subject. Together with automatic computer-based online signal analysis, the technique employed enables us to make continuous long-term beat-to-beat measurements of cardiac output in subjects without aortic valve disease or grossly deforming disease of the aortic root.     

Hemodynamic evaluation with TURBO BRISK--a rapid phase contrast angiography technique.

Hemodynamic imaging by phase contrast angiography was significantly accelerated by selective interpolation and segmentation in k-space using TURBO BRISK. The method was tested in vitro on three independent flowfields, representative of human blood rheology: a straight tube simulating the descending aorta, a curved tube simulating the aortic arch and a two-chamber orifice flow model simulating valvular regurgitation. The results were compared to data obtained by Laser Doppler Velocimetry (LDV) and showed good agreement. For the straight tube, the flow velocity obtained by five TURBO BRISK methods with increasing segmentation factors and corresponding time savings showed good agreement with LDV. For the curved tube, the velocity showed good general agreement with some differences in the decelerating part of the cycle, and in the low-velocity secondary flow structures. The orifice flow evaluation, the most time consuming case, was performed by the control volume method. It showed good agreement with actual flows through the orifice. Data acquisitions for TURBO-4 BRISK could be performed in 20s for each velocity component. The method shows promise for breath-hold acquisitions in clinical applications, including calculation of blood flow volumes through diseased arteries, measurement of blood backflow volumes through dysfunctional heart valves to time valve replacement operations, and evaluation of arterial wall shear stress, an important factor in the genesis of atherosclerosis.     

Developments in cardiovascular ultrasound. Part 2: Arterial applications

Many of the changes resulting from arterial disease can be measured, using Doppler ultrasound for measurement of blood velocity and B-scan imaging for measurement of tissue structure and composition. Wall thickness, the degree of arterial narrowing and plaque volume can be measured using B-scan imaging, and 3D ultrasound can be used to improve the accuracy of measurements of plaque volume and for improved visualisation of complex arterial geometries. Measurement of the dynamic properties of the arterial wall permits estimation of wall elasticity and plaque motion. From the Doppler signal, measurements of blood velocity are used to estimate the degree of arterial narrowing and volumetric flow, although measurement errors can be large. Wall shear stress can be estimated by measuring the velocity gradient at the vessel wall. The problems of inadequate spatial resolution and interference from overlying tissue are largely removed when intravascular systems are used, and these have superior capability in the assessment of arterial structure and tissue composition. However, measurement of quantities relating to blood flow is more difficult using the intravascular approach, as the indwelling cather disturbs the blood flow pattern, and currently, assessment of flow and vessel cross-section are not performed at the same site.     

Fast Measurements of Flow through Mitral Regurgitant Orifices with Magnetic Resonance Phase Velocity Mapping

Magnetic-resonance (MR) phase velocity mapping (PVM) shows promise in measuring the mitral regurgitant volume. However, in its conventional nonsegmented form, MR-PVM is slow and impractical for clinical use. The aim of this study was to evaluate the accuracy of rapid, segmented k-spaceMR-PVM in quantifying the mitral regurgitant flow through a control volume (CV) method. Two segmented MR-PVM schemes, one with seven (seg-7) and one with nine (seg-9) lines per segment, were evaluated in acrylic regurgitant mitral valve models under steady and pulsatile flow. A nonsegmented (nonseg) MR-PVM acquisition was also performed for reference. The segmented acquisitions were considerably faster (<10 min) than the nonsegmented (>45 min). The regurgitant flow rates and volumes measured with segmented MR-PVM agreed closely with those measured with nonsegmented MR-PVM (differences <5%, p>0.05), when the CV was large enough to exclude the region of flow acceleration and aliasing from its boundaries. The regurgitant orifice shape (circular vs. slit-like) and the presence of aortic outflow did not significantly affect the accuracy of the results under both steady and pulsatile flow (p>0.05). This study shows that segmented k-space MR-PVM canaccurately quantify the flow through regurgitant orifices using the CV method and demonstrates great clinical potential.     

Velocity measurements within confined turbulent jets: Application to cardiovalvular regurgitation

An expression for centerline mean velocity distributions for circular and noncircular confined turbulent jets has been obtained by assuming self-preservation of flow downstream of the jet potential core. It was assumed that the velocity decay was not only dependent on the streamwise distancex in terms ofx/d, as in the case of free jets, but also on the ratio of the orifice diameterd to the confining pipe diameterD. To validate the expression and to determine the empirical constants, measurements of the centerline velocities within the confined jets issuing from different size circular orifices and various noncircular orifices of different shapes were conducted. The results indicate that the validity of the expression is restricted tod/D≤0.25 and is weakly dependent on the particular orifice shape. It is suggested that, as for the case of free turbulent jets reported earlier, that this expression may be used potentially to predict the valvular lesion size or to estimate the volume of valvular regurgitation for confined jets provided the value ofD, which corresponds to the “atrial diameter”, is known or statistically available.     

In vitro velocity measurements down strem from the lonescu-Shiley aortic bioprosthesis in steady and pulsatile flow

Velocity measurements were made in vitro using laser Doppler anemometry (LDA) downstream from an lonescu-Shiley (IS) bioprosthetic aortic heart valve. Velocity measurements were made in both steady and pulsatile flow. A systematic, flow mapping approach to the measurement methodology showed that the IS valve generated a large jetlike flow constriction. The acceleration ratio, defined as the maximum mean velocity for the IS valve divided by that for no valve obstructing the flow, was as high as 2·4 for steady flow and 2·6 for pulsatile flow. It was concluded that the IS valve generated a flow quite unlike that observed by other in vestigators for the natural human aortic valve, after which the leaflet design of the IS valve was modelled. In addition, a comparative analysis of steady and pulsatile results was undertaken. It was found that the pulsatile flow results for the systolic ejection interval could be divided into three phases, denoted early, mid, and late systole, as defined by the flow structure at the data plane location. Only during midsystole were the pulsatile flow results approximated by the steady flow results. Also, it was found that the magnitude of the flow disturbance measured in steady flow tended to be an upper bound on that measured for pulsatile flow.     

Estimation of turbulent shear stress in free jets: Application to valvular regurgitation

In an attempt to better assess the severity of valvular regurgitation, anin-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m², corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.     

Echocardiographic characteristics of transprosthetic blood peak velocity in the Sorin Bicarbon bileaflet prosthetic heart valve

The Bicarbon prosthetic heart valve with two curved leaflets is designed so that the blood flows through the three orifices are parallel jets of equal size. This study was conducted to confirm that the Bicarbon valve functions clinically as designed. Forty-three patients underwent valve replacement with the Bicarbon valve. Forty-eight Bicarbon valves were implanted: 25 valves in the mitral position and 23 in the aortic position. Peak blood flow velocity through the three prosthetic orifices was measured postoperatively by Doppler echocardiography. The three flow jets through the prosthesis were parallel. The velocity through the lateral orifice was 2.33±0.38 m/min, and the velocity through the central orifice was 2.14±0.43 m/min at the aortic position (P>0.05). The velocity through the lateral orifice was 1.72±0.06 m/min at the mitral position, and that through the central orifice was 1.73±0.06 m/min (P>0.05). Serum lactic acid dehydrogenase values were also lower than those of patients or whom another bileaflet prosthesis had been implanted. The results confirm that the Bicarbon prosthetic heart valve performs clinically as designed, producing three parallel blood flow jets with equal flow velocity.     

Current development in Doppler echocardiography. The real-time two-dimensional Doppler flow imaging system

Recent advances in ultrasound instrumentations have provided a new Doppler modality capable of displaying the spatial distribution of blood flow velocities by colors on the monochromatic echo image on the real time basis, called the real-time two-dimensional Doppler flow imaging system. With this new Doppler technique, we can noninvasively relate the dynamic flow pattern to the anatomy and the motion of the cardiac structures and can further our understandings of flow dynamics in the circulatory system in health and disease. In clinical cardiology, the Doppler flow imaging technique offeres a quite sensitive approach to the detection of flow abnormalities caused by valvular insufficiency or stenosis and congenital shunt diseases. The spatial distribution of the regurgitant jet flow visualized by the Doppler flow imaging technique provides a semiquantitative approach to the evaluation of the severity of the valvular insufficiency. Furthermore, we can appreciate the spatial and angular orientation of the stenotic or regurgitant jet flow, which allows us to measure the velocity of the jet flow with the optimal beam direction. Though there are some limitations and pitfalls in the Doppler flow imaging system at present, it has provided the mapping of the dynamic distribution of flow velocities, which has never been available with the conventional Doppler technique, and has expanded Doppler capabilities and utilities in clinical cardiology. The Doppler flow imaging system is now widely used as a routine part of noninvasive cardiac examination and is improving its clinical significance.     

Hydrodynamic evaluation of a new dispersive aortic cannula (Stealthflow)

The aim of this study was to evaluate flow from a new dispersive aortic cannula (Stealthflow) in the aortic arch using flow visualization methods. Particle image velocimetry was used to analyze flow dynamics in the mock aortic model. Flow patterns, velocity distribution, and streamlines with different shape cannulas were evaluated in a glass aortic arch model. We compared flow parameters in two different dispersive type cannulas: the Stealthflow and the Soft-flow cannula. A large vortex and regurgitant flow were observed in the aortic arch with both cannulas. With the Stealthflow cannula, a high-velocity area with a maximum velocity of 0.68 m/s appeared on the ostium of the cannula in the longitudinal plane. With the Soft-flow cannula, ‘multiple jet streams, each with a velocity less than 0.60 m/s, were observed at the cannula outlet. Regurgitant flow from the cannula to the brachiocephalic artery and to the ascending aorta on the greater curvature was specific to the Soft-flow cannula. The degree of regurgitation on the same site was lower with the Stealthflow cannula than with the Soft-flow cannula. The Stealthflow cannula has similar flow properties to those of the Soft-flow cannula according to glass aortic model analysis. It generates gentle flow in the aortic arch and slow flow around the ostia of the aortic arch vessels. The Stealthflow cannula is as effective as the Soft-flow cannula. Care must be taken when the patient has thick atheromatous plaque or frail atheroma on the lesser curvature of the aortic arch.     

A bioenergetic assessment of mitral regurgitation: A new tool to assess severity?

Mitral regurgitation is frequently classified as mild, moderate or severe based on echocardiography. Patients with mild mitral regurgitation are usually managed medically. We hypothesise that mild mitral regurgitation as assessed volumetrically can in fact be severe when analysed from a bioenergetics point of view. The conservation of energy predicts that any regurgitant volume will require the heart to provide more work energy to support the circulation. Mitral regurgitation involves the left ventricle imparting potential energy, via blood pressure, and kinetic energy, via regurgitant velocity, to the regurgitant blood volume. This implies that regurgitant volume, regurgitant velocity, systolic blood pressure, heart rate, regurgitant orifice area and cardiac output are all important factors. We present limited data to demonstrate our hypothesis. A bioenergetic analysis of mitral regurgitation, may identify patients whose mitral regurgitation, assessed via echocardiography as mild, is actually clinically significant. In addition we identify the importance of blood pressure and heart rate control in patients with mitral regurgitation. The concept that a bit of mitral regurgitation in patients with poor left ventricles is a good thing, as it helps offload the left ventricle is from an engineering point fundamentally flawed.     

Three-component laser doppler velocimetry measurements in the regurgitant flow region of a björk-shiley monostrut mitral valve

Three-dimensional laser Doppler velocimetry measurements were acquired in a mock-circulatory loop proximal to a Björk-Shiley monostrut valve in the mitral position, and synchronous ensemble-averaging was applied to form an “average” beat. Two axial locations in the regurgitant flow region of the valve (in the minor orifice) were mapped, and maximum Reynolds shear stresses were calculated. A large spike in regurgitant flow was noted at the beginning of systole, which may be thesqueeze flow phenomenon computed by other researchers. A region of sustained regurgitant flow 50 msec later was the focus of this study. Maximum velocities of ～3.7 mps were noted, and maximum Reynolds shear stresses of ～10,000 dyne/cm² were calculated. Comparisons were made of two-dimensional (ignoring tangential component)versus three-dimensional shear stresses, and, in this case, in regions of high stress, the differences were insignificant. This suggests that the tangential component of velocity can probably be ignored in similar measurements where the tangential velocity is likely to be small.     

Impact of Diabetes Mellitus on Radial and Ulnar Arterial Vasoreactivity after Radial Artery Cannulation: A Randomized Controlled trial

Background: Endothelial dysfunction associated with diabetes mellitus (DM) may influence arterial vasoreactivity after arterial stimulus, such as cannulation, and cause changes in diameter and blood flow. Despite the frequent use of arterial cannulation during anesthesia and critical care, little information is available regarding vasoreactivity of the radial and ulnar arteries and its influence on underlying DM.Methods: Forty non-DM and 40 DM patients, who required arterial cannulation during general anesthesia, were enrolled. Using duplex Doppler ultrasonography, we measured the patients'' arterial diameter, peak systolic velocity, end-diastolic velocity, resistance index, and mean volume flow of both arteries at five different time points.Results: After radial artery cannulation, ulnar arterial diameter and blood flow did not significantly increase in DM group, as they did in non-DM group. Ulnar arterial resistance index significantly increased in both groups, but the degree of decrease in DM group was significantly less than non-DM.Conclusion: Ulnar artery''s ability to increase blood flow for compensating the sudden reduction of radial arterial flow in DM patients was significantly less than that in non-DM patients under general anesthesia. Such attenuated vasoreactivity of ulnar artery to compensate the reduced radial arterial flow may have to be considered in radial arterial cannulation for DM patients.     

Evaluation of extracranial blood flow in Parkinson disease

Decreased cerebral flow velocities in Parkinsonian patients were reported previously. Because of the limited data on vascular changes in Parkinson disease (PD), which may have a vascular etiology, we aimed to disclose any possible cerebral hemodynamic alteration in Parkinsonian patients. We prospectively evaluated 28 non-demented, idiopathic parkinsonian patients and 19 age and sex matched controls with Doppler sonography. Flow volumes, peak systolic flow velocities, and cross-sectional areas of vertebral and internal carotid arteries (ICA) were measured and compared between patients and controls. Correlation of patient age and disease duration with Doppler parameters was observed; and each Doppler parameter of patients within each Hoehn-Yahr scale was compared. There was no significant difference of measured parameters between groups. No correlation was found between disease duration and age with flow volume, cross-sectional area or peak systolic velocity. Hoehn-Yahr scale was not found having significant relation with Doppler parameters. Values of vertebral, internal carotid and cerebral blood flow volumes (CBF), peak systolic velocities, and cross-sectional areas were not significantly different between Parkinsonian patients and age and sex matched controls. Although regional blood flow decreases may be seen as reported previously, Parkinson disease is not associated with a flow volume or velocity alteration of extracranial cerebral arteries.