92 



shock, and according to Jex-Blake^* it is operative in death 

 from lightning. There is convincing evidence — experi- 

 mental and clinical — that the same mechanism is respon- 

 sible for sudden death during overdosing with bodies of the 

 digitalis series. 



Sudden Death in Aortic Regurgitation. 

 The frequency of absolutely sudden death in this con- 

 dition has long been recognized. In view of the usual 

 coronary and myocardial involvements, the causation of the 

 fatal issue — sometimes occurring without antecedent signs 

 of cardiac failure — may naturally be ascribed to ventricular 

 fibrillation. There seem to be no good grounds for the 

 assumptioii of protracted vagus inhibition as an effective 

 cause. 



Tteflex Cardiac Inhibition. 

 Reflex vagus inhibition has in the past been freely invoked 

 to account for sudden death in many diseased conditions 

 and even in healthy persons — for example, from a violent 

 blow on the epigastrium, etc. On the experimental side 

 extended investigations on a great number of healthy 

 animals and a considerable number of diseased ones have 

 failed to lend support to the hypothesis ; it has usually been 

 found impossible to stop the heart long enough to kill by 

 reflex inhibition or even by strong direct stimulation of the 

 vagus, escape of the heart or the ventricles usually occurring 

 much too soon for death to be caused by circulatory arrest. 

 The conclusion has been reached by different observers that 

 the possibilities of a fatal issue in this way have, to say 

 the least, been greatly exaggerated, and that there is no 

 sufl&cient ground for assuming reflex inhibition per se to be 

 a frequent or important mode of death.* In some instances 

 where the vagal hypothesis had met with a large measure of 

 acceptance — for example, in cases of sudden death during an 

 early phase of ordinary chloroform anaesthesia — the view has 

 not proved to be tenable, since such deaths have been shown 

 to be essentially due to an altogether different mechanism — 

 ventricular fibrillation. 



On the other hand, the possibility of increased sus- 

 ceptibility to vagus inhibition under certain abnormal con- 

 ditions must be borne in mind. In Embley's^* work on 

 chloroform it was found that under special conditions, in 

 dogs after a large dose of morphine, the inhalation of strong 

 chloroform vapour may cause great slowing of the heart, 

 fall of blood pressure, and stoppage of respiration — conse- 

 quences evidently depending on excessive vagus action, and 

 obviated or removed by exclusion of such action by section 

 of the vagi or by atropine. But the conditions present in 



* Sudden death during operative procedures in the thoracic cavity 

 (thoracocentesis, etc.) seems, in the light of the work of Capps and D. D. 

 Lewis, to depend on fall of hlood pressure due to vasomotor changes rather 

 than to reflex cardiac inhibition (,Arch. of Int. Afedicme, 1907, cxxxiv, 868). 



