Manuscript received September 29;
1987;
revised April 21;
1988. This work was funded by the Medical Research Council of Canada;
the Natural Sciences and Engineering Research Council of Canada;
and the Nova Scotia Heart Foundation. C. J. Purcell and G. Stroink are with the Department of Physics;
Dal-housie University;
Halifax;
N.S;
Canada B3H 3J5. B. M. Horacek is with the Department of Physiology and Biophysics;
Dalhousie University;
NS;
Canada B3H 3J5. IEEE Log Number 8822275;