The correlation dimension of rat hearts in an experimentally controlled environment

The electric response of several isolated rat hearts in a controlled environment was studied experimentally. The correlation dimension D-2 was estimated and was found to be between 4 and 6.5 when the response was nearly periodic. The variation of D-2 with the concentration of calcium was studied and a general trend of its increase with increasing concentration was found. Two types of ventricular fibrillation (VF) were observed, one that corresponds to a stochastic signal where D-2 is unbounded and the other to a low dimensional dynamical system with 3.5 less than or equal to D(2)less than or equal to 4. It was found also that for the heart the correlation dimension is only an approximate concept. A new method for the estimation of D-2, that is suitable for the case when it is only approximate was introduced. A surrogate data method suitable for the analysis of nearly periodic series was implemented. (C) 2000 American Institute of Physics. [S1054-1500(00)00201-9].