Fig. 4
From [71] with permission
Ventricular fibrillation as a possible seizure-induced condition that cannot self-terminate. a Segment of the full schematic shown in Fig. 9. b Spontaneous entry into ventricular fibrillation (VF) with a combination of bilateral vagal transection, isoproterenol, and systemic hypoxemia as a result of breathing with an extended dead space of 4 ml. c Segment from a period of asystole caused by 50-Hz vagal stimulation where a short spontaneous run of ventricular tachycardia developed, but did not persist or devolve to VF because the vagal stimulation continued. d Isoproterenol doses needed to enable VF were greater than the doses that caused maximal increases in heart rate and thus may have been producing local effects, including vasospasm, in the heart. e The contributions of dead space conditions and isoproterenol dose when added to bilateral vagotomy illustrating the very narrow range of conditions favoring VF. f The rate and extent of hypoxemia were critical for VF (red). Too small a change (black) or too great a change (blue) produced either sinus or non-sinus bradycardia, respectively, but never VF.