Biomedical subjects

J Hopmeyer

Publications and source records attributed to J Hopmeyer.

8 recordsLinked to original sources

PubMed1998

Mechanism of mitral regurgitation in hypertrophic cardiomyopathy: mismatch of posterior to anterior leaflet length and mobility.

BACKGROUND: In hypertrophic cardiomyopathy, a spectrum of mitral leaflet abnormalities has been related to the mechanism of mitral systolic anterior motion (SAM), which causes both subaortic obstruction and mitral regurgitation. In the individual patient, SAM and regurgitation vary in parallel; clinically, however, great interindividual differences in mitral regurgitation can occur for comparable degrees of SAM. We hypothesized that these differences relate to variations in posterior leaflet length and mobility, restricting its ability to follow the anterior leaflet (participate in SAM) and coapt effectively. METHODS AND RESULTS: Different mitral geometries produced surgically in porcine valves were studied in vitro. Comparable degrees of SAM resulted in more severe mitral regurgitation for geometries characterized by limited posterior leaflet excursion. Mitral geometry was also analyzed in 23 patients with hypertrophic cardiomyopathy by intraoperative transesophageal echocardiography. All had typical anterior leaflet SAM with significant outflow tract gradients but considerably more variable mitral regurgitation; therefore, regurgitation did not correlate with obstruction. In contrast, mitral regurgitation correlated inversely with the length over which the leaflets coapted (r= -0.89), the most severe regurgitation occurring with a visible gap. Regurgitation increased with increasing mismatch of anterior to posterior leaflet length (r=0.77) and decreasing posterior leaflet mobility (r= -0.79). CONCLUSIONS: SAM produces greater mitral regurgitation if the posterior leaflet is limited in its ability to move anteriorly, participate in SAM, and coapt effectively. This can explain interindividual differences in regurgitation for comparable degrees of SAM. Thus, the spectrum of leaflet length and mobility that affects subaortic obstruction also influences mitral regurgitation in patients with SAM.

Adult↗

PubMed1998

Estimation of mitral regurgitation with a hemielliptic curve-fitting algorithm: in vitro experiments with native mitral valves.

To date, studies on the mitral flow convergence method have used rigid, circular, or slit orifices to represent the regurgitant orifice. In this study, explanted porcine mitral valves, with the entire mitral apparatus preserved, were mounted in an in vitro model to reproduce the three-dimensional regurgitant orifice geometry while permitting close control and measurement of the experimental conditions. This experimental setup permitted the evaluation of the hemispheric and hemielliptic formulas under realistic physiologic conditions. In this study, a heart rate of 70 beats/min was used with cardiac outputs between 1.5 and 6 L/min. Peak regurgitant flow rates ranged from 7 to 16 L/min (regurgitant jet velocities ranged from 2 to 5.5 m/sec); peak aortic flow rates ranged from 9 to 30 L/min. Four native mitral valves were used for these studies for a total of 28 stages. Although the hemielliptic modification has previously shown success in vitro and computationally, it has not been used clinically because of difficulty imaging the flow convergence region in three orthogonal planes. A curve-fitting algorithm was developed to extract the hemielliptic dimensions from two standard ultrasound views by rotating the transducer 90 degrees. Improved agreement was obtained between true and calculated flow rates by the hemielliptic formula (y = 1.02 x + 0.29; r = 0.91) compared with the hemispheric formula (y = 1.18 x - 2.2; r = 0.66). This method provides accurate results with a realistic three-dimensional regurgitant orifice geometry and has the capability of being incorporated as a function key on an ultrasound machine for clinical application.

Algorithms↗

PubMed1998

Pulsatile flow computational simulations of mitral regurgitation.

The noninvasive quantification of mitral regurgitation remains an important clinical goal. Recently, the flow convergence method was developed to estimate the regurgitant flow rate. This study used three-dimensional pulsatile flow computational simulations to evaluate the accuracy of the flow convergence method in the presence of complicating factors such as ventricular confinement, noncircular orifice shape, and the presence of aortic outflow. Results showed that in the absence of aortic outflow and ventricular confinement, there was a plateau zone where the calculated flow rate by the hemispheric formula approximated the true flow rate, independent of the orifice shape. In the presence of aortic outflow and in chambers of physiologic dimensions, there was no longer a clear zone where the hemispheric formula was valid. The hemi-elliptic modification of the flow convergence method worked in all cases, independent of the degree of ventricular confinement or the presence of aortic outflow. Therefore, application of the hemi-elliptic formula should be considered in future clinical studies.

Aorta↗

PubMed1997

Importance of leaflet elongation in causing systolic anterior motion of the mitral valve.

BACKGROUND AND AIMS OF THE STUDY: There is growing evidence for mitral leaflet elongation in patients with hypertrophic cardiomyopathy. Such elongation could predispose to systolic anterior motion (SAM) of the mitral valve by increasing leaflet mobility and providing a geometry that promotes this condition. METHODS: To test this postulate, five porcine mitral valves were studied in a physiologic left heart pulsatile flow duplicator. They were elongated with patches sutured to the basal posterior leaflet (three sizes per valve) or anterior leaflet (basal, middle, or distal). Each geometry was studied with normal papillary muscle position and with anterior and inward displacement, as seen in hypertrophic cardiomyopathy, to shift the leaflets into the outflow stream. RESULTS: Four points became clear. 1) Leaflet elongation promoted the development of SAM in response to papillary muscle displacement by creating long overlapping residual leaflets capable of moving anteriorly. 2) Posterior leaflet elongation also promoted SAM by shifting leaflet coaptation anteriorly, with progressive increases in SAM. 3) Basal and mid-anterior leaflet elongation caused SAM with prolapse; distal anterior leaflet elongation created SAM with a mobile flap (leaflet elongation without papillary muscle displacement created prolapse). 4) Residual leaflet length correlated well with total leaflet length (r = 0.87-0.98 for each valve), and the degree of SAM in turn correlated well with residual leaflet length (r = 0.62-0.98 for individual valves). CONCLUSIONS: Mitral leaflet elongation, by increasing the residual leaflet length and leaflet mobility, can play an important role in promoting SAM in response to outflow forces, as demonstrated by prospectively altering leaflet length. These findings are consistent with recent observations that reducing leaflet redundancy and posterior leaflet height can reduce obstructive SAM following mitral valve repair in patients with mitral valve prolapse and help relieve obstruction in patients with hypertrophic cardiomyopathy and enlarged leaflets.

Cardiomegaly↗

PubMed1996

How sensitive are jet centerline velocities to an opposing flow? Implications for using the centerline method to quantify regurgitant jet flow.

A method for quantifying peak mitral and tricuspid regurgitant jet flow rate that utilizes a measure of jet orifice velocity (Uo, m s-1), a distal centerline velocity (Um, m s-1), and the intervening distance (X, cm) was recently developed. This method, however, modeled the regurgitant jet as a free jet, whereas many atrial jets are counterflowing jets because of jet opposing intra-atrial flow fields (counterflows). This study evaluated the feasibility of using the free jet quantification equation in the atrium where ambient flow fields may alter jet centerline velocities and therefore reduce the accuracy of jet flow rate calculations. A 4 cm wide chamber was used to pump counterflows of 0, 4, and 22 cm s-1 against jets of 2.3, 4.8, and 6.4 s-1 originating from a 2 mm diameter orifice. For each counterflow-jet combination, jet centerline velocities were measured using laser Doppler anemometry. For free jets (no counterflow), flow rate was calculated with 98% mean accuracy. For all jets in counterflow, the calculation was less accurate as (i) the ratio of jet orifice velocity to counterflow velocity decreased (Uo/Uc, where Uc is counterflow velocity), i.e. the counterflow was relatively more intense, an (ii) centerline measurements were mad further from the orifice. But although counterflow lowered jet centerline velocities beneath free jet values, it did so only significantly in the jet's distal portion, while the initial portion (X/D < 16, where D is jet orifice diameter) of a jet in counterflow behaved essentially as a free jet. Therefore, regurgitant jets, although not classically free because of systolic atrial inflow, will decay in their initial portions as free jets and hence are candidates for quantification with the centerline technique.

Feasibility Studies↗

PubMedDate not supplied

Computational simulations of mitral regurgitation quantification using the flow convergence method: comparison of hemispheric and hemielliptic formulae.

Mitral regurgitation results from the incomplete closure of the mitral valve, and the noninvasive diagnosis of this disease remains an important clinical goal. In this study, steady flow computer simulations were used to evaluate flow convergence method for flow rate estimation. The hemispheric and hemielliptic formulae were compared for accuracy in the presence of complicating factors such as ventricular confinement, orifice shape, and aortic outflow. Results showed that in the absence of aortic outflow and ventricular confinement, there was a plateau zone where the hemispheric formula approximated the true flow rate, independent of orifice shape. However, in the presence of complicating factors such as aortic outflow and ventricular confinement, there was no clear zone where the hemispheric formula could be applied. The hemielliptic formula, however, worked in all cases, regardless of chamber size or magnitude of aortic outflow. Therefore, application of the hemielliptic formula should be considered in future clinical studies.

Aorta, Thoracic↗

PubMedDate not supplied

The effect of aortic outflow on the quantification of mitral regurgitation by the flow convergence method.

The effect of aortic outflow on the quantification of mitral regurgitation by the flow convergence method was investigated by both in vitro experiments and computational simulations. Digital analysis of the color Doppler M-mode images was compared with results obtained with laser Doppler anemometry, an engineering gold standard, and three-dimensional computational simulations. Regurgitant orifices of 3.2 and 6.4 mm in diameter were used with instantaneous aortic flow rates from 0 to 500 ml/sec, corresponding to net cardiac outputs of 0 to 5 L/min. In the absence of aortic outflow, a clear plateau was observed in plots of the calculated flow rate as a function of the distance from the orifice, indicating that there was a zone in which the hemispheric assumption was valid. As the aortic outflow was increased, the length of this plateau region decreased and then disappeared at high aortic flow rates. Farther from the orifice, beyond the plateau zone, the flow rate was overestimated and this overestimation increased with increasing aortic flow rate. Results showed excellent agreement between in vitro experiments and computational stimulations. This study demonstrated that aortic outflow has a dramatic effect on the flow convergence region and therefore must be considered in flow rate calculations.

Aorta↗

PubMedDate not supplied

Identification of peak stresses in cardiac prostheses. A comparison of two-dimensional versus three-dimensional principal stress analyses.

This study assessed the accuracy of using a two-dimensional principal stress analysis compared to a three-dimensional analysis in estimating peak turbulent stresses in complex three-dimensional flows associated with cardiac prostheses. Three-component, coincident laser Doppler anemometer measurements were obtained in steady flow downstream of three prosthetic valves: a St. Jude bileaflet, Bjork-Shiley monostrut tilting disc, and Starr-Edwards ball and cage. Two-dimensional and three-dimensional principal stress analyses were performed to identify local peak stresses. Valves with locally two-dimensional flows exhibited a 10-15% underestimation of the largest measured normal stresses compared to the three-dimensional principal stresses. In nearly all flows, measured shear stresses underestimated peak principal shear stresses by 10-100%. Differences between the two-dimensional and three-dimensional principal stress analysis were less than 10% in locally two-dimensional flows. In three-dimensional flows, the two-dimensional principal stresses typically underestimated three-dimensional values by nearly 20%. However, the agreement of the two-dimensional principal stress with the three-dimensional principal stresses was dependent upon the two velocity-components used in the two-dimensional analysis, and was observed to vary across the valve flow field because of flow structure variation. The use of a two-dimensional principal stress analysis with two-component velocity data obtained from measurements misaligned with the plane of maximum mean flow shear can underpredict maximum shear stresses by as much as 100%.

Heart Valve Prosthesis↗