278 RESPIRATION 



respiratory movements. The reason for this partial cessation of respira- 

 tion, or apnea, is not that we overcharge our blood with oxygen, as was once 

 thought, for Hering has shown that animals in a condition of apnea may 

 have less oxygen in their blood than in a normal state, although the carbon 

 dioxide is less. It is probable that the cause of apnea is that by rapid in- 

 flations of the lungs impulses pass up by the vagi, by means of which in- 

 spiration is after a while inhibited; or that by the repeated stimulation of 

 the center by vagus impulses which result in rapid respiratory movements, 

 anabolism is at last arrested. Apnea is with difficulty produced, if at all, 

 when the vagi are divided. 



Asphyxia. The condition of stress in the respiratory apparatus brought 

 about by insufficient respiratory activity leads to a condition of asphyxia. 

 Progressive asphyxiation may be brought on by anything which interferes 

 with the normal interchange of the respiratory gases of the blood. 



Asphyxia may be produced by the prevention of the due entry of oxygen 

 into the blood, either by direct obstruction of the trachea or other part of the 

 respiratory passages, or by introducing instead of ordinary air a gas devoid 

 of oxygen, or, by interference with the due interchange of gases between 

 the air and the blood. 



The symptoms of asphyxia may be divided into three groups, which 

 correspond with the stages of the condition which are usually recognized; 

 these are: i, the stage of exaggerated breathing, hyperpnea; 2,. the stage of 

 convulsions, dyspnea; 3, the stage of exhaustion, asphyxiation. 



In the first stage the breathing becomes more rapid and at the same time 

 deeper than usual, the inspirations at first being especially exaggerated and 

 prolonged. This is soon followed by a similar increase in the expiratory 

 efforts being aided by the muscles of extraordinary expiration. This stage is 

 usually called hyperpnea. Hyperpnea soon passes into a condition of labored 

 breathing in which there is marked increase of the force of the expiratory 

 as well as the inspiratory act, a condition described as dyspnea. All the 

 muscles capable of aiding either directly or indirectly in respiration are ulti- 

 mately brought into action. These respiratory convulsions are followed by 

 rather sudden onset of paralysis of the respiratory center and death. 



The conditions of the vascular system in asphyxia are: i, more or less 

 interference with the passage of the blood through the systemic and the pul- 

 monary blood-vessels; 2, accumulation of blood in the right side of the heart 

 and in the systemic veins; 3, circulation of impure (non-aerated) blood in 

 all parts of the body, especially through the respiratory center. 



Cheyne-Stokes' breathing is a rhythmical irregularity in respirations which 

 has been observed in various diseases. Respirations occur in groups; at the 

 beginning of each group the inspirations are very shallow, but each succes- 

 sive breath is deeper than the preceding, until a climax is reached, after which 

 the inspirations become less and less deep, until they cease altogether for 



