PHENOMENA OF ASPHYXIA. 1 97 



The phenomena of asphyxia are usually divided into several stages : 1. During 

 the first stage there is hyperpncea, the respirations being deeper, more frequent, 

 and laboured. The extraordinary muscles of respiration both those of inspiration 

 and expiration ( 118) are called into action, dyspnoea is rapidly produced, and the 

 struggle for air becomes more and more severe. At the same time the oxygen of 

 the blood is being used up, while the blood itself becomes more and more venous. 

 The venous blood circulating in the medulla oblongata and spinal cord stimulates 

 the respiratory centres, and causes the violent respirations. This stage usually lasts 

 about a minute, and gradually gives places to 



2. The second stage, when the inspiratory muscles become less active, while 

 those concerned in laboured expiration contract energetically, and indeed almost 

 every muscle in the body may contract ; so that this stage of violent expiratory 

 efforts ends in general convulsions. The convulsions are due to stimulation of the 

 respiratory centres by the venous blood. The convulsive stage is short, and is 

 usually reached in a little over one minute. This storm is succeeded by 



3. The third stage, or stage of exhaustion, the transition being usually some- 

 what sudden. It is brought about by the venous blood acting on and paralysing 

 the respiratory centres. The pupils are widely dilated, consciousness is abolished, 

 and the activity of the reflex centres is so depressed that it is impossible to discharge 

 a reflex act, even from the cornea. The animal lies almost motionless, with flaccid 

 muscles, and to all appearance dead, but every now and again, at long intervals, it 

 makes a few deep inspiratory efforts, showing that the respiratory centres are not 

 quite, but almost paralysed. Gradually the pauses become longer and the inspira- 

 tions feebler and of a gasping character. As the venous blood circulates in the spinal 

 cord, it causes a large number of muscles to contract, so that the animal extends its 

 trunk and limbs. It makes one great inspiratory spasm, the mouth being widely 

 opened and the nostrils dilated, and ceases to breathe. After this stage, which is 

 the longest and most variable, the heart becomes paralysed, partly from being over- 

 distended with venous blood, and partly, perhaps, from the action of the venous 

 blood on the cardiac tissues, so that the pulse can hardly be felt. To this pulseless 

 condition the term " asphyxia " ought properly to be applied. In connection with 

 the resuscitation of asphyxiated persons, it is important to note that the heart con- 

 tinues to beat for a few seconds after the respiratory movements have ceased. 



The whole series of phenomena occupies from 3 to 5 minutes, according to the 

 animal operated on, and depending also upon the suddenness with which the trachea 

 was closed. If the causes of suffocation act more slowly, the phenomena are the 

 same, only they are developed more slowly. 



The Circulation. The post-mortem appearances in man or in an animal are 

 generally well marked. The right side of the heart, the pulmonary artery, the 

 vense cavae, and the veins of the neck are engorged with dark venous blood. The 

 left side is comparatively empty, because the rigor mortis of the left side of the 

 heart, and the elastic recoil of the systemic arteries, force the blood towards 

 the systemic veins. The blood itself is almost black, and is deprived of almost all 

 its oxygen, its haemoglobin being nearly all in the condition of reduced haemoglobin, 

 while ordinary venous blood contains a considerable amount of oxyhaemoglobin as 

 well as reduced Hb. The blood of an asphyxiated animal practically contains none 

 of the former and much of the latter. It is important to study the changes in the 

 circulation in relation to phenomena exhibited by an animal during suffocation. 



We may measure the blood-pressure in any artery of an animal while it is being 

 asphyxiated, or we may open its chest, maintain artificial respiration, and place a 

 manometer in a systemic artery, e.g., the carotid, and another in a branch of the 

 pulmonary artery. In the latter case, we can watch the order of events in the 

 heart itself, when the artificial respiration is interrupted. It is well to study 

 the events in both cases. 



