IV 



ASPHYXIA 163 



vulsions cease. After this stage is reached, a long-drawn 

 inspiration takes place at intervals ; but the intervals 

 become longer and longer and the inspiratory movements 

 more and more feeble until the last breath is taken and 

 breathing ends with an expiratory gasp.i 



After death by asphyxia the blood throughout the 

 whole body is of course venous. The right side of the 

 heart, the great (systemic) veins and the pulmonary 

 ' arteries are highly distended with blood, while the left 

 side of the heart is empty. This condition of the vascular 

 system is brought about largely by an obstruction to the 

 usually easy flow of blood through the lungs, which is due 

 to a constriction of their small arteries caused by the 

 stimulation resulting from the venosity of the blood. But 

 it is helped by the unusually forcible drawing of blood 

 into the great veins which results from the increased 

 force of the respiratory movements (see p. 166). 



Venous blood is distinguished from arterial by two 

 features, by ha\-ing less oxygen and more carbonic acid. 

 Hence, in asphyxia, two influences of a distinct nature 

 are co-operating ; one is the deprivation of oxygen, the 

 other is the excessive accximulation of carbonic acid in the 

 blood. Oxygen starvation and carbonic acid poisoning, 

 each of which is injurious in itself, are at work to- 

 gether. 



The respiratory centre is very sensitive to variations 

 in the normal quantity of carbonic acid in the blood. 

 We have already stated that the carbonic acid in the 

 alveolar air exerts a ])artial pressure of 40 mm. of 

 mercury, this corresponds very closely to the pressure of 

 carbonic acid in the blood leaving the lung and reaching 

 the respiratory centre. If this pressure of carbonic acid 

 be raised by even a few millimetres the respiration 



1 The tertQ asphyxia is sometimes used to include aU the above three 

 stages, from the onset of dyspnoea until death ensues. 



H 2 



