Author/Editor		Kirn, Borut
Title		Določanje ekvatorialne ravnine levega prekata z optičnimi epikardialnimi označevalci pri budrah
Type		monografija
Place		Ljubljana
Publisher		Medicinska fakulteta
Publication year		1999
Volume		str. 47
Language		slo
Abstract		Dynamic mechanical properties of left ventricle (LV) are often analysed using epicardial deformations obtained by markers positioned on the LV surface. There is a lack of well defined coordinate system for presenting measured epicardial deformations. The self LV's coordinate system basing on its physiological properties, geometry and biaxial properties of myocardial tissue, can be defined using a model where epicardial deformations due to LV volume change are described as combination of three transformations: radial symetrical extension, torsion and elipticalization. For experiments six isolated guinea pig hearts were arrested in diastole and a catheter was inserted through the aorta into the LV chamber for the controlled injection and withdrawal of saline. Five acrylate crystals (0.1 mm in diameter) were anchored into the epicard of free LV wall in the form of the crux, visually oriented along estimated axial and circumferential directions of the LV. The protocol consisted of cycles of loading and unloading of the LV in steps of 100 q.l up to the maximal volume of 1000 micro l. Computer analysing of picture recorded by CCD camera was used for markers tracing. We assumed coordinate systems of transformations to coincide and that they have common centre in the marker located in the centre of the crux. Parameters of the model: elongation coefficients kx and ky, coefficient of torsion t and the angle alpha which part the self LV's coordinate system from the reference one, were reckoned up on three ways. In the first we used couples of noncentral markers for the calculations (six possible combinations), in the second we used minimal square list method for obtaining the best fitting set of parameters to all markers for one volume step and in the third we improved the second one by fitting parameters to all volume steps of one cycle at once and by assuming coefficients kX, ky and t to be linearly dependent of LV volume. (Abstact truncated at 2000 characters).
Descriptors		HEART VENTRICLE PERICARDIUM CARDIAC VOLUME VENTRICULAR PRESSURE STROKE VOLUME GUINEA PIGS MYOCARDIAL CONTRACTION MODELS, THEORETICAL