| 1. |
- Carlhäll, Carljohan, 1973-, et al.
(författare)
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Contribution of mitral annular dynamics to LV diastolic filling with alteration in preload and inotropic state
- 2007
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 293:3, s. G1473-H1479
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Tidskriftsartikel (refereegranskat)abstract
- Mitral annular (MA) excursion during diastole encompasses a volume that is part of total left ventricular (LV) filling volume (LVFV). Altered excursion or area variation of the MA due to changes in preload or inotropic state could affect LV filling. We hypothesized that changes in LV preload and inotropic state would not alter the contribution of MA dynamics to LVFV. Six sheep underwent marker implantation in the LV wall and around the MA. After 7–10 days, biplane fluoroscopy was used to obtain three-dimensional marker dynamics from sedated, closed-chest animals during control conditions, inotropic augmentation with calcium (Ca), preload reduction with nitroprusside (N), and vena caval occlusion (VCO). The contribution of MA dynamics to total LVFV was assessed using volume estimates based on multiple tetrahedra defined by the three-dimensional marker positions. Neither the absolute nor the relative contribution of MA dynamics to LVFV changed with Ca or N, although MA area decreased (Ca, P < 0.01; and N, P < 0.05) and excursion increased (Ca, P < 0.01). During VCO, the absolute contribution of MA dynamics to LVFV decreased (P < 0.001), based on a reduction in both area (P < 0.001) and excursion (P < 0.01), but the relative contribution to LVFV increased from 18 ± 4 to 45 ± 13% (P < 0.001). Thus MA dynamics contribute substantially to LV diastolic filling. Although MA excursion and mean area change with moderate preload reduction and inotropic augmentation, the contribution of MA dynamics to total LVFV is constant with sizeable magnitude. With marked preload reduction (VCO), the contribution of MA dynamics to LVFV becomes even more important.
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| 2. |
- Kindberg, Katarina, et al.
(författare)
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Spatial and Temporal Inhomogeneity of Left Ventricular Myocardial Transmural Strains During Diastole
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Rapid early filling requires a rapid shift to a very compliant left ventricle immediately after systole, allowing filling at low driving pressures. This compliance shift is manifested as changes in transmural strains: however its mechanistic basis is incompletely understood. Seven adult Dorsett hybrid sheep were anesthetized and radiopaque markers were surgically implanted to silhouette the LV chamber. Three transmural columns of four beads each were implanted into the lateral equatorial LV wall. Eight weeks after surgery, biplane videofluoroscopic images of all radiopaque markers were acquired at 60 Hz horn dosed-chest anesthetized animals. After data acquisition, hearts were arrested at the end-diastolic pressure aud quantitative hist.ology was used to determine fiber and sheet angles. Lagrangian strains in cardiac and liber-sheet coordinates were computed at end of early filling and end diastole with filling onset as reference at three transmural depths. Rapid early filling was dominated by subepicardial circumferential stretching (ECC=0.08±0.02) and fiber lengthening (Eƒƒ=0.03±0.01), midwall circumferential stretching (ECC=0.07±0.02), and subendocardial wall thinning (ERR=-0.05±0.01). Subepicardial strains achieved their ED values during early diastole, while mid wall and subendocardial straius reset during late diastole. Sheet-normal shear strain was a dominant contributor to wall thinning during diastole.
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| 3. |
- Kindberg, Katarina, et al.
(författare)
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Transmural Strains in the Ovine Left Ventricular Lateral Wall During Diastolic Filling
- 2009
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Ingår i: JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME. - : ASME International. - 0148-0731. ; 131:6
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Tidskriftsartikel (refereegranskat)abstract
- 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 (E-CC) had reached its final value already at EOEF, while longitudinal and radial strains were nearly zero at this time. Subepicardial E-CC and fiber relengthening (E-ff) at EOEF were reduced to 1 compared with 8 weeks after surgery (E-CC:0.02 +/- 0.01 to 0.08 +/- 0.02 and E-ff:0.00 +/- 0.01 to 0.03 +/- 0.01, respectively, both P < 0.05). Subepicardial E-CC 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.
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| 4. |
- Krishnamurthy, G., et al.
(författare)
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Material properties of the ovine mitral valve anterior leaflet in vivo from inverse finite element analysis
- 2008
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 295:3
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Tidskriftsartikel (refereegranskat)abstract
- We measured leaflet displacements and used inverse finite-element analysis to define, for the first time, the material properties of mitral valve (MV) leaflets in vivo. Sixteen miniature radiopaque markers were sewn to the MV annulus, 16 to the anterior MV leaflet, and 1 on each papillary muscle tip in 17 sheep. Four-dimensional coordinates were obtained from biplane videofluoroscopic marker images (60 frames/s) during three complete cardiac cycles. A finite-element model of the anterior MV leaflet was developed using marker coordinates at the end of isovolumic relaxation (IVR, when the pressure difference across the valve is ~0), as the minimum stress reference state. Leaflet displacements were simulated during IVR using measured left ventricular and atrial pressures. The leaflet shear modulus (Gcirc-rad) and elastic moduli in both the commisure-commisure (Ecirc) and radial (Erad) directions were obtained using the method of feasible directions to minimize the difference between simulated and measured displacements. Group mean (±SD) values (17 animals, 3 heartbeats each, i.e., 51 cardiac cycles) were as follows: Gcirc-rad = 121 ± 22 N/mm2, Ecirc = 43 ± 18 N/mm2, and Erad = 11 ± 3 N/mm2 (Ecirc > E rad, P < 0.01). These values, much greater than those previously reported from in vitro studies, may result from activated neurally controlled contractile tissue within the leaflet that is inactive in excised tissues. This could have important implications, not only to our understanding of mitral valve physiology in the beating heart but for providing additional information to aid the development of more durable tissue-engineered bioprosthetic valves. Copyright © 2008 the American Physiological Society.
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