ASPHYXIA. 195 



the arterial blood pressure raised as a result of general vasocon- 

 striction. Because of its vasoconstricting properties, extract of 

 the adrenal glands ("adrenalin" or " epinephrin") is used 

 in k)cal anesthetics, as in cocain solution, to prevent bleeding and 

 to minimize the absorption of the cocain into the general circu- 

 lation (Fig. 26, No. IV). 



Asphyxia. Whenever the amount of oxygen which the blood 

 must supply to the tissue falls below the minimum amount re- 

 quired, a condition known as asphyxia develops. If the nervous 

 centers are intact, any interference with the respiratory function, 

 as by obstruction of the respiratory passages, lack of ogygen in 

 the atmosphere, or the presence of irrespirable gases in the at- 

 mosphere such as carbon monoxide, which reduces the oxygen 

 capacity of the haemoglobin, interferes with the blood supply of 

 the brain and will produce a train of phenomena in which the 

 respiratory and circulatory changes are prominent. In ordinary 

 asphyxia two factors may be involved, a deficiency of oxygen 

 and an excess of carbon dioxide in the blood. The phenomena 

 following each are essentially the same, and may be divided into 

 three typical stages. In the first stage, that of hyperpnoea, the 

 respirations are increased in rate and amplitude. This stage 

 merges into the second, which consists of exaggerated expiratory 

 efforts, loss of consciousness, stimulation of the vascular centers 

 in the brain causing general vasoconstriction accompanied with 

 vagus slowing of the heart. The net result is a rise in blood 

 pressure. In the third stage, the expiratory efforts give way to 

 slow deep inspirations followed by expiratory convulsions. The 

 pupils dilate widely, the heart becomes very weak from lack of 

 oxygen and overwork, and death occurs from cardiac failure. 

 The changes produced in the respiratory movements, as well as 

 those of the vascular system, are caused by the direct stimula- 

 tion of the respiratory (see p. 220) and vascular centers, by ex- 

 cess of carbon dioxide and by the lack of oxygen in the blood. 



Nitrous Oxide. The circulatory and respiratory changes ac- 

 companying the administration of nitrous oxide gas are very 

 similar to those produced in asphyxia. The asphyxia produced 

 by the lack of oxygen and the excess of carbon dioxide in the 



