Suffocation and related problems.

Experiments were carried out on rats, rabbits and dogs to investigate the course of respiration and circulation during various types of suffocation. From the results of dogs, the course of respiration on obstructive asphyxia consists of three stages; the stage of dyspnea, of apnea, and of terminal respiration. The respirations in the stage of dyspnea and the stage of terminal respiration are generally inspiratory. In typical hanging, the course of respiration is characterized by shorter stages of dyspnea and apnea and a longer stage of terminal respiration as compared with that in obstructive asphyxia. In non-obstructive asphyxia, the course of respiration has the initial stage before the stage of dyspnea. The results of experiments simulating deficiency of oxygen in the external atmosphere suggested that the lethal oxygen percentage is approximately 2.2%. In drowning, the course of respiration consisted of four stages: initial stage (surprise-respiration and initial apnea), stage of dyspnea, stage of apnea and stage of terminal respiration. The surprise-respiration is suggested to be induced by the contact of water with the mucus membrane of larynx or trachea. The respirations during the stage of dyspnea are essentially inspiratory, and do not always have a convulsive character. In a few dogs, the precipitous fall of blood pressure and flat electroencephalogram appeared immediately after aspiration of water. This seemed to be caused by the reflex vagal inhibition of the heart, which was induced by the contact of water with the mucus membrane of larynx or trachea. It is suggested that the reflex vagal inhibition of the heart is one of the causes of loss of consciousness and drowning during swimming.