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Modelling of strain tensors in cardiac kinematics
Linköping University, Department of Biomedical Engineering, Biomedical Modelling and Simulation. Linköping University, The Institute of Technology.
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The heart wall consists of three distinct layers: the inner endocardium, the middle myocardium and the outer epicardium. The myocardium is the functional tissue that endows the heart with its ability to pump blood, and consists primarily of locally parallel muscle fibers. The orientation of these muscle fibers change with position in the wall. The myofibers have been shown to be arranged parallel in sheets that are rotated around the fiber direction relative to the radial direction of the left ventricle. During a cardiac beat there are local shortenings and lengthenings in the myocardium, both within and between myolaminar sheets. The mechanism by which the local shortening or lengthening is translated into the large and complex motions of the ventricle has to be studied on a local level, by studying deformation. A parameter that describes deformation is strain. The scope of the current project is to perform detailed studies of cardiac strain, particularly during diastole. There exist several definitions of strain tensors and the focus in this project is on the Lagrangian strain tensor.

The myocardial bead array gives kinematic measures of the myocardium toestimate strain in the left ventricular wall of the pumping heart. During surgery, radiopaque beads are inserted into the myocardium along three transmural columns, with typically four to six beads in each column. The 4D coordinates of the beads are acquired with high resolution using time-resolved biplane cineradiography.

This thesis presents a method for strain estimation from myocardial coordinate data. This strain estimation method is tailored for the transmural bead array and fits a polynomial to the bead coordinates. A benefit with the polynomial method is its ability to avoid loss of accuracy for the case of a missing bead, e.g. due to problems sometimes encountered during surgery or during the recovery period. The polynomial strain estimation method is applied to coordinate data from a transmural bead array to quantify diastolic myocardial strain in the ovine heart. This reveals transmural strain inhomogeneities during diastole in the ovine heart.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2006. , 36 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1269
Series
LIU-TEK-LIC, 50
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-35139Local ID: 25032ISBN: 91-85643-89-0 (print)OAI: oai:DiVA.org:liu-35139DiVA: diva2:255987
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-12
List of papers
1. Nonhomogeneous strain from sparse marker arrays for analysis of transmural myocardial mechanics
Open this publication in new window or tab >>Nonhomogeneous strain from sparse marker arrays for analysis of transmural myocardial mechanics
2007 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 129, no 4, 603-610 p.Article in journal (Refereed) Published
Abstract [en]

Background: Knowledge of normal cardiac kinematics is important when attempting to understand the mechanisms that impair the contractile function of the heart during disease. The complex kinematics of the heart can be studied by inserting radiopaque markers in the cardiac wall and study the pumping heart with biplane cineradiography. In order to study the local strain, the bead array was developed where small radiopaque beads are inserted along three columns transmurally in the left ventricle. Method: This paper suggests a straightforward method for strain computation, based on polynomial least-squares fitting and tailored for combined marker and bead array analyses. Results: This polynomial method gives small errors for a realistic bead array on an analytical test case. The method delivers an explicit expression of the Lagrangian strain tensor as a polynomial function of the coordinates of material points in the reference configuration. The method suggested in this paper is validated with analytical strains on a deforming cylinder resembling the heart, compared to a previously suggested finite element method, and applied to in vivo ovine data. The errors in the estimated strain components are shown to remain unchanged on an analytical test case when evaluating the effects of one missing bead. In conclusion, the proposed strain computation method is accurate and robust, with errors smaller or comparable to the current gold standard when applied on an analytical test case.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-41891 (URN)10.1115/1.2746385 (DOI)000248737000016 ()59323 (Local ID)59323 (Archive number)59323 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
2. Spatial and Temporal Inhomogeneity of Left Ventricular Myocardial Transmural Strains During Diastole
Open this publication in new window or tab >>Spatial and Temporal Inhomogeneity of Left Ventricular Myocardial Transmural Strains During Diastole
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword
cardiac strains, fiber-sheet strains, sheep, LV filling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-100800 (URN)
Available from: 2013-11-12 Created: 2013-11-12 Last updated: 2013-11-12

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Kindberg, Katarina

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