CH. XXVII.] ASPHYXIA 389 



sists in making a forced expiratory effort with the mouth and nose 

 shut ; the effects are most marked in people with an easily compres- 

 sible thorax. By such an act the intrathoracic and abdominal 

 pressures rise so greatly that the outlets of the veins of the limbs, 

 head, and neck into the thorax are blocked. At first, the blood in 

 the abdominal veins is drawn on into the right heart ; this produces 

 a slight rise of arterial pressure ; but soon, if the effort is continued, 

 the lungs are emptied of blood, the filling of the right heart is 

 opposed, and the blood is dammed back in the peripheral veins, where 

 the pressure rises to mean arterial pressure. The arterial pressure 

 begins then to fall; but before any considerable fall occurs, the 

 expiratory effort ceases from exhaustion of the subject of the experi- 

 ment, and a deep inspiration is taken. During this inspiration, the 

 blood delivered by the right heart is all used in the filling of the 

 comparatively empty pulmonary vessels ; thus several beats of the 

 left ventricle become abortive, and produce no effect on the radial 

 artery ; the face blanches, and the subject becomes faint from cerebral 

 anaemia. 



Asphyxia. 



Asphyxia may be produced in various ways: for example, 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 roughly divided into three 

 stages : (1) the stage of exaggerated breathing ; (2) the stage of con- 

 vulsions ; (3) the stage of exhaustion. 



In the first stage the breathing becomes more rapid, and at the 

 same time deeper than usual, inspiration at first being especially 

 exaggerated and prolonged. The muscles of extraordinary inspiration 

 are called into action, and the effort to respire is laboured and painful. 

 This is soon followed by a similar increase in the expiratory efforts, 

 which become excessively prolonged, being aided by all the muscles 

 of extraordinary expiration. During this stage, which lasts a vary- 

 ing time from a minute upwards, according as the deprivation of 

 oxygen is sudden or gradual, the lips become blue, the eyes are 

 prominent, and the expression intensely anxious. The prolonged 

 respirations are accompanied by a distinctly audible sound; the 

 muscles attached to the chest stand out as distinct cords. This stage 

 includes the two conditions hyperpncea (excessive breathing) and 

 dyspnoea (difficult breathing), which follows later. It is due to the 

 increasingly powerful stimulation of the respiratory centre by the 

 increasingly venous blood,. 



