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Measurement of deformation of canine epicardium in vivo during cardiac cycle.

A new accurate method to determine the deformation of the epicardial surface during the cardiac cycle in vivo is described. Epicardial deformation is determined by a circumferential strain, a base-to-apex strain, and a shear angle. In the measuring setup, one magnetic field-generating coil (MFGC) and two sensor coils are attached to the epicardium, thus forming an approximately right-angled triangle with the MFGC at the right-angled corner and the sides containing the right angle, parallel to the circumferential and base-to-apex direction, respectively. The MFGC generates a magnetic field that rotates around the axis of the coil. The strength of that field decreases with increasing distance. Both strains and the shear angle are derived from the amplitudes of the voltages induced in the sensor coils and their phase difference. In the experimental situation the accuracy of the measurement of strain and shear angle is +/- 0.005 and +/- 1 degree, respectively. The device has a frequency response of 100 Hz (-3 dB) and practically no zero drift. In four open-chest dogs during left ventricular ejection, circumferential natural strain, base-to-apex natural strain, and shear angle at the epicardium of the left ventricular free wall ranged from -0.06 to -0.13, from -0.02 to -0.08, and from 6.8 degrees to 11.5 degrees, respectively.