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Research Papers

Transmural Strains in the Ovine Left Ventricular Lateral Wall During Diastolic Filling

[+] Author and Article Information
K. Kindberg, M. Karlsson

Department of Management and Engineering, Linköping University, Linköping SE-581 83, Sweden

C. Carlhäll

Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305; Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Palo Alto, CA 94305; Department of Clinical Physiology, Linköping University Hospital, Linköping SE-581 85, Sweden

T. C. Nguyen, A. Cheng, F. Langer, F. Rodriguez, D. C. Miller

Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305

G. T. Daughters

Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305; Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Palo Alto, CA 94305

N. B. Ingels

Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305; Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Palo Alto, CA 94305ingels@stanford.edu

J Biomech Eng 131(6), 061004 (Apr 21, 2009) (8 pages) doi:10.1115/1.3118774 History: Received June 11, 2008; Revised March 18, 2009; Published April 21, 2009

Rapid early diastolic left ventricular (LV) filling requires a highly compliant chamber immediately after systole, allowing inflow at low driving pressures. The transmural LV deformations associated with such filling are not completely understood. We sought to characterize regional transmural LV strains during diastole, with focus on early filling, in ovine hearts at 1 week and 8 weeks after myocardial marker implantation. In seven normal sheep hearts, 13 radiopaque markers were inserted to silhouette the LV chamber and a transmural beadset was implanted into the lateral equatorial LV wall to measure transmural strains. Four-dimensional marker dynamics were obtained 1 week and 8 weeks thereafter with biplane videofluoroscopy in closed-chest, anesthetized animals. LV transmural strains in both cardiac and fiber-sheet coordinates were studied from filling onset to the end of early filling (EOEF, 100 ms after filling onset) and at end diastole. At the 8 week study, subepicardial circumferential strain (ECC) had reached its final value already at EOEF, while longitudinal and radial strains were nearly zero at this time. Subepicardial ECC and fiber relengthening (Eff) at EOEF were reduced to 1 compared with 8 weeks after surgery (ECC:0.02±0.01 to 0.08±0.02 and Eff:0.00±0.01 to 0.03±0.01, respectively, both P<0.05). Subepicardial ECC during early LV filling was associated primarily with fiber-normal and sheet-normal shears at the 1 week study, but to all three fiber-sheet shears and fiber relengthening at the 8 week study. These changes in LV subepicardial mechanics provide a possible mechanistic basis for regional myocardial lusitropic function, and may add to our understanding of LV myocardial diastolic dysfunction.

FIGURES IN THIS ARTICLE
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Copyright © 2009 by American Society of Mechanical Engineers
Topics: Fibers , Surgery , Inflow
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Figures

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Figure 1

(a) Locations of LV epicardial markers (Nos. 1–13) and LV lateral equatorial transmural bead array (Nos. 15–26). At each time sampled, local circumferential (XC) and longitudinal (XL) axes are in the epicardial tangent plane, with the radial axis (XR) perpendicular to this plane and pointing away from the LV chamber. Origin (O) is the centroid of the epicardial bead Nos.15,19, and 23; (b) Schematic illustration of fiber and sheet geometry at three transmural levels from histological examination of a transmural tissue block. Shaded planes are sections perpendicular to the local fiber axis, shown as black bands on the right surface of each subblock. Black bands with white dots illustrate sheet orientations at each depth. The subendocardial subblock is shown magnified to illustrate the cardiac coordinate axes, the fiber (α) and sheet (β) angles, as well as the fiber (Xf), sheet (Xs), and sheet-normal (Xn) axes.

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Figure 2

Cardiac cycle timing in one representative heart. The start of the studied interval (filling onset: t=0), EOEF, and ED are indicated (vertical dashed lines). LVP, LV pressure (solid squares); LVV, LV volume (open triangles).

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Figure 3

Strains plotted against fractional percent LV filling volume at 1 week (solid triangles) and 8 weeks (solid circles) postoperatively: (a) subepicardial ECC, (b) subendocardial ECC, (c) subepicardial Eff, and (d) subendocardial Eff

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Figure 4

LV inflow rate (dV/dt) versus percentage LV filling volume at 1 week (solid triangles) and 8 weeks (solid circles) postoperatively

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Figure 5

Average (±SE) contributions to subepicardial, midwall, and subendocardial circumferential strain (ECC) from each of the fiber strains in Eq. 6 at EOEF: (a) 1 week postoperatively and (b) 8 weeks postoperatively

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