Learn More
We study the response of a model neuron, driven simultaneously by noise and at least two weak periodic signals. We focus on signals with frequencies components kf(0),(k+1)f(0),...(k+n)f(0) with k>1. The neuron's output is a sequence of pulses spaced at random interpulse intervals. We find an optimum input noise intensity for which the output pulses are(More)
By means of a selfadjusting experimental protocol based on the evaluation of the cardiac impedance, peak current thresholds were determined to defibrillate canine hearts with transventricular capacitor discharges. From 346 successful defibrillations performed on 20 mongrel dogs, an average value of 0·82 A/kg (s.d.=0·3) was found. The energy showed(More)
Toad ventricles were externally driven by periodic pulses while monophasic action potential (MAP) signals were recorded in seven excised and seven in situ ventricles. As the frequency was slowly increased in steps, the stimulated tissue displayed several dynamic characteristics. Hierarchies of periodic behavior, like phase-locking and period-doubling(More)
Fibrillation is more likely to occur in animals showing a high degree of cellular differentiation. Lower species, with cardiac tissue histologically and electrophysiologically more uniform, very rarely, if ever, can fall into this uncoordinated activity. We describe experiments during which two specimens of the South American toad, Bufo paracnemis (body(More)
It is difficult to design electronic nonlinear devices capable of reproducing complex oscillations because of the lack of general constructive rules, and because of stability problems related to the dynamical robustness of the circuits. This is particularly true for current analog electronic circuits that implement mathematical models of bursting and(More)
GEDDES and TACKER (1971) and GEDDES et al. (1974) suggested that the peak current is a better descriptor than the energy for specifying ventricular defibrillation. ARMAYOR et al. (1979) and ARREDONDO et al. (1980) found empirically that the coefficient of variation Cw of the energy W of the defibrillating shock was nearly twice as big as the coefficient of(More)
THE vulnerability of the heart (either atria or ventricles) to the fibrillatory process can be assessed by means of the socalled electrical fibrillation threshold, i.e. the minimum magnitude able to trigger the phenomenon or, in other words, a stimulus amplitude with 50 per cent probability of success under some specified conditions (VALENTINUZZ1 et al.,(More)
  • 1