Period doubling bifurcations in cardiac systems

Adams et al. (1981), observed in their experiences with dogs, a decrease in the Electrical Fibrillation Threshold (EFT) by hypothermal conditions and coronary arterial ligament. In this paper, it is proved that there appears also a decrease in the EFT, produced by the intravenous injection of Ketalar in concentrations larger than 9 mg/Kg of weight of the animal. Under these conditions, it is observed that the cardiac system presents a period doubling bifurcations dynamics, that is, the first “chaos” onsets represented by Ventricular Fibrillation (VF). Frequency spectra show this behavior by the appearance of the components of frequency one half and one fourth. This quantitative method is proposed to determine the proximity to chaos (VF) by measuring the Alternance Degree (AD).