|Ph.D Student||Ankri-Eliahu Galit|
|Subject||Characterization of the Effects of Changes in Cardiac|
Matrix Properties on Heart Function and
Development of a Novel Technique for
Cardiac Fiber Isolation
|Department||Department of Biotechnology||Supervisors||Professor Amir Landesberg|
|Professor Emeritus Ofer Binah|
|Full Thesis text|
Background: The myocardium consists of multiple sheets that connected by arrays of radial collagen fibers. Previous studies have demonstrated that the viscous force within the myocardium is negligible relative to the elastic force. However, the effects of changes in the extra cellular matrix elasticity were not well defined.
Cardiac systolic and diastolic functions on the macro-scale are determined by both cellular functions and intercellular interactions. Thus, to understand cardiac pathologies, there is a need to study the cellular function.
Hypotheses: (a) Dismantling of the collagenous "scaffold" of the myocardium leads to decreased passive myocardial stiffness or (b) development of edema leads to significant increase in the viscous forces and the passive myocardial stiffness. (c) Increased mechanical shear stresses between the myocardial sheets can facilitate in fiber isolation from the myocardium.
Methods: Experiments were performed in 57 healthy rats' hearts. The normal myocardium was gradually dismantled with collagenases while isovolumic contractions at varying preloads were imposed.
Isolated fibers were anchored on the isolated fiber setup at the base of an inverted microscope and mounted between a force transducer and a motor arm.
Results: A unique vertical Langendorff setup was developed with computer controlled preload and afterload. The main observations were: (I) Peak systolic pressure decreased rapidly (II) The left-ventricular (LV) cavity volume decreased and the LV wall width increased at the expense of the cardiac cavity. (III) Hysteresis evolved in the diastolic pressure volume relationship. (IV) There were no significant changes in the slopes of the end-systolic pressure-area relationship and end-diastolic pressure-area relationship. (V) The extracellular fluid volume significantly increased.
We developed a new technique to isolate fibers from the midwall of the myocardium. The novelty of this technique is the application of electrical stimulation to separate between myocardial sheets and to obtain long, thin fibers. The isolations' success rate was 73%.
Discussion: All the novel observations can be clarified by the development of significant viscosity that deteriorates both cardiac diastolic and systolic functions. The dismantling of collagen tends to increase the oncotic pressure, which leads to swelling of the ECM in parallel to a decrease in ECM elasticity. Our results indicate that the dominance of myocardial elasticity is crucial for proper systolic and diastolic functions.
In addition, we have proved that the simultaneous work of the collagenases and the mechanical shear stresses between the myocardial sheets facilitate the dissection of the myocardial sheets.