Time-varying effective mitral valve area: prediction and validation using cardiac MRI and Doppler echocardiography in normal subjects

American Journal of Physiology-Heart and Circulatory Physiology

2006

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Stiffness- and relaxation-based diastolic function (DF) assessment can characterize the presence, severity, and mechanism of dysfunction. Although frequency-based characterization of arterial function is routine (input impedance, characteristic impedance, arterial wave reflection), DF assessment via frequency-based methods incorporating optimization/efficiency criteria is lacking. By definition, optimal filling maximizes (E wave) volume and minimizes "loss" at constant stored elastic strain energy (which initiates mechanical, recoil-driven filling). In thermodynamic terms, optimal filling delivers all oscillatory power (rate of work) at the lowest harmonic. To assess early rapid filling optimization, simultaneous micromanometric left ventricular pressure and echocardiographic transmitral flow (Doppler E wave) were Fourier analyzed in 31 subjects. A validated kinematic filling model provided closed-form expressions for E wave contours and model parameters. Relaxation-based DF impairment is indicated by prolonged E wave deceleration time (DT). Optimization was assessed via regression between the dimensionless ratio of 2nd (Q2) and 3rd flow harmonics (Q3) to the lowest harmonic (Q1), i.e., (Q2/Q1) or (Q3/Q1) vs. DT or c, the filling model's viscosity/damping (energy loss) parameter. Results show that DT prolongation or increased c generated increased oscillatory power at higher harmonics (Q2/Q1 = 0.00091DT + 0.09837, r = 0.70; Q3/Q1 = 0.00053DT + 0.02747, r = 0.60; Q2/Q1 = 0.00614c + 0.15527, r = 0.91; Q3/Q1 = 0.00396c + 0.05373, r = 0.87). Because ideal filling is achieved when all oscillatory power is delivered at the lowest harmonic, the observed increase in power at higher harmonics is a measure of filling inefficiency. We conclude that frequency-based analysis facilitates assessment of filling efficiency and elucidates the mechanism by which diastolic dysfunction associated with prolonged DT impairs optimal filling.

Section: Discussionmentioning

confidence: 99%

Frequency-based analysis of the early rapid filling pressure-flow relation elucidates diastolic efficiency mechanisms

American Journal of Physiology-Heart and Circulatory Physiology

2006

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“…The conservation of volume for an arbitrarily shaped object of variable volume V(t), containing an incompressible fluid and having an inlet and an outlet, requires that V͑t͒ ϭ V 0 ϩ ͐inflow ⅐ area dt Ϫ ͐outflow ⅐ area dt (1) where V 0 denotes the constant of integration. Specifically, Marino et al postulated that ͓LA͑t͒ Ϫ LA min ͔ ϭ PVA͐PV flow ͑t͒dt Ϫ MVA͐MV flow ͑t͒dt (2) where LA(t) refers to the LA volume as a function of time (t), LA min is the minimum LA volume (at ventricular end diastole), PVA is the (constant) PV area, PV flow (t) is the velocity of blood flow through the pulmonary veins as a function of time, MVA is the (constant) mitral valve area, MV flow (t) is the velocity of blood flow across the mitral valve, and time t ϭ 0 ms refers to the peak of the ECG QRS complex. Consequently, ͐PV flow (t)dt was calculated as the continuous velocity-time integral (VTI) of the Doppler flow profile of the right superior PV, and ͐MV flow (t)dt was calculated as the continuous VTI of Doppler transmitral flow.…”

mentioning

confidence: 99%

Prediction and assessment of the time-varying effective pulmonary vein area via cardiac MRI and Doppler echocardiography

Bowman

American Journal of Physiology-Heart and Circulatory Physiology

2005

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Accurately estimating left atrial (LA) volume with Doppler echocardiography remains challenging. Using angiography for validation, Marino et al. (Marino P, Prioli AM, Destro G, LoSchiavo I, Golia G, and Zardini P. Am Heart J 127: 886-898, 1994) determined LA volume throughout the cardiac cycle by integrating the velocity-time integrals of Doppler transmitral and pulmonary venous flow, assuming constant mitral valve and pulmonary vein areas. However, this LA volume determination method has never been compared with three-dimensional LA volume data from cardiac MRI, the gold standard for cardiac chamber volume measurement. Previously, we determined that the effective mitral valve area is not constant but varies as a function of time. Therefore, we sought to determine whether the effective pulmonary vein area (EPVA) might be time varying as well and also assessed Marino's method for estimating LA volume. We imaged 10 normal subjects using cardiac MRI and concomitant transthoracic Doppler echocardiography. LA and left ventricular (LV) volumes were measured by MRI, transmitral and pulmonary vein flows were measured by Doppler echocardiography, and time dependence was synchronized via the electrocardiogram. LA volume, estimated using Marino's method, was compared with the MRI measurements. Differences were observed, and the discrepancy between the echocardiographic and MRI methods was used to predict EPVA as a function of time. EPVA was also directly measured from short-axis MRI images and was found to be time varying in concordance with predicted values. We conclude that because EPVA and LA volume time dependence are in phase, LA filling in systole and LV filling in diastole are both facilitated. Application to subjects in select pathophysiological states is in progress.

“…4). Because filling is governed by the resultant effect of elastic recoil overcoming relaxation forces, we can make better predictions regarding how molecular changes might impact the Constant volume allows for derivation of effective mitral and pulmonary valve area (7,10). Impacts modeling of volumes/flow using MRI Myocardial imaging Myocardial integrated ultrasonic backscatter is associated with the initial pressure gradient (kxo) and the balance between the elastic and relaxation properties (c 2 Ϫ 4k) (66) LV, left ventricle; LVEF, LV ejection fraction; CHF, congestive heart failure; PDF, parametrized diastolic filling; c, index that characterizes relaxation; k, term that characterizes stiffness; HFpEF, heart failure with preserved ejection fraction; DASH, Dietary Approaches to Stop Hypertension; E=, maximum velocity of the mitral valve annulus during early filling; dP/dV, change in pressure over change in volume; LVEDP, LV end-diastolic pressure; xo, initial displacement of load; HR, heart rate; IVR, isovolumic relaxation; , time constant of isovolumic relaxation.…”

Section: Early Rapid Fillingmentioning

confidence: 99%

What global diastolic function is, what it is not, and how to measure it

Chung

Shmuylovich

American Journal of Physiology-Heart and Circulatory Physiology

2015

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Leonardo da Vinci's observation (circa 1511) that "the atria or filling chambers contract together while the pumping chambers or ventricles are relaxing and vice versa," the dynamics of four-chamber heart function, and of diastolic function (DF) in particular, are not generally appreciated. We view DF from a global perspective, while characterizing it in terms of causality and clinical relevance. Our models derive from the insight that global DF is ultimately a result of forces generated by elastic recoil, modulated by cross-bridge relaxation, and load. The interaction between recoil and relaxation results in physical wall motion that generates pressure gradients that drive fluid flow, while epicardial wall motion is constrained by the pericardial sac. Traditional DF indexes (, E/E=, etc.) are not derived from causal mechanisms and are interpreted as approximating either stiffness or relaxation, but not both, thereby limiting the accuracy of DF quantification. Our derived kinematic models of isovolumic relaxation and suction-initiated filling are extensively validated, quantify the balance between stiffness and relaxation, and provide novel mechanistic physiological insight. For example, causality-based modeling provides load-independent indexes of DF and reveals that both stiffness and relaxation modify traditional DF indexes. The method has revealed that the in vivo left ventricular equilibrium volume occurs at diastasis, predicted novel relationships between filling and wall motion, and quantified causal relationships between ventricular and atrial function. In summary, by using governing physiological principles as a guide, we define what global DF is, what it is not, and how to measure it. diastolic function; echocardiography; hemodynamics; mathematical modeling; suction pump LEFT VENTRICULAR (LV) DIASTOLIC dysfunction is typically reported and indexed as either an increase in myocardial stiffness or a slowing of relaxation (i.e., cross-bridge dissociation). In actuality, diastolic function (DF) is the result of the continuous interaction between the restoring force of elastic recoil and the opposing force generated by cross bridges that have yet to uncouple from the previous systole. The restoring forces seek to lengthen the muscle, while the cross-bridge forces previously acted to shorten the muscle. The simultaneous action of these two opposing forces during both isovolumic relaxation (IVR) and filling result in wall motion, constrained by pericardial sac volume, and simultaneous generation of pressure gradients. This review discusses the governing physical laws and the constraints of DF, as well as which indexes of DF are consistent with diastolic physiology. Deriving and evaluating indexes of DF using this conceptual framework both clarifies and advances our understanding of DF and diastolic dysfunction in health and disease. Physiology of DiastoleCardiovascular physiology is taught using the Wiggers diagram, which segments the cardiac cycle into systole and diastole ( Fig. 1) (49, 124). Systole begins...