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1 Department of Biomedical Engineering, Washington University, St. Louis, MO, USA
2 Department of Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, MO, USA
* To whom correspondence should be addressed. E-mail: sjk{at}wuphys.wustl.edu.
For diastolic function (DF) quantification, transmitral flow velocity has been characterized in terms of the geometric features of a triangle (heights, widths, areas, durations) approximating the E-wave contour, whereas mitral annular velocity has only been characterized by E'-wave peak amplitude. The fact that E-waves convey global DF information, whereas annular E'-waves provide longitudinal DF information, has not been fully characterized, nor has the physiologic legitimacy of combining fluid motion (E) and tissue motion derived (E') measurements into routinely used indexes (E/E') been fully elucidated. To place these Doppler echo measurements on a firmer causal, physiologic and clinical basis, we examined features of the E'-wave (and annular motion in general), including timing, amplitude, duration, and contour (shape), in kinematic terms. We derive longitudinal rather than global indexes of stiffness and relaxation of the left ventricle (LV) and explain the observed difference between E- and E'-wave durations. Based on the close agreement between model prediction and E'-wave contour for subjects having normal physiology, we propose damped harmonic oscillation (DHO) as the proper paradigm in which to view and analyze the motion of the mitral annulus during early filling. Novel, longitudinal indexes of LV stiffness (k'), relaxation/viscosity (c'), and stored (end-systolic) elastic strain (xo') can be determined from the E'-wave (and any subsequent waves) by modeling annular motion during early filling as DHO. A subgroup exploratory analysis conducted in diabetics (n=9) and non-diabetic controls (n=12) indicates that longitudinal DF indexes differentiate between these groups on the basis of longitudinal damping (p<0.025) and longitudinal stored elastic strain (p<0.005).
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