Abstract
When respiration is arrested by a 50 c/s alternating current passed between the forelimbs of rabbits there may be a delay between the end of the shock and the spontaneous resumption of respiration. This paper examines the relation of such a delay with the duration of shock and the current magnitude independently and in terms of two physical concepts: (a) the product of shock duration and current magnitude, called here `charge equivalent'; and (b) a quantity proportional to the energy input. The influence of the shock duration apparently exceeded that of the current. Furthermore, delay was strongly associated with both `charge equivalent' and energy input. When temporary circulatory arrest due to ventricular fibrillation occurred, an additional mechanism appeared to operate. Although protracted, the delay showed similar associations with the shock duration and current magnitude. An interesting observation was that the interval between spontaneous defibrillation and the resumption of respiration also showed a strong association with shock duration. The restarting of respiration appears to depend on the circulation. It may be that when the circulation restarts, after a period of ventricular fibrillation, blood-borne inhibitory substances, which accumulated during the period of circulatory arrest, could affect the respiratory centre.