THE INFLUENCE OF RESPIRATION 



123 



respiration, for a time lent support to the doctrine of Ludwig, but this 

 had to be abandoned so soon as the time relations of the respiratory 

 movements and the undulations of arterial pressure were definitely 

 settled. 



The synchronous records of respiration and arterial tension obtained 

 by Ludwig and Einbrodt, 1 showed that the rise of arterial pressure 

 takes place mainly in the inspiratory and not in the expiratory phase. 



Fig. 77. — Effect of respiration on arterial pressure. The numbers on 

 the left denote centimetres of mercury pressure. — Fredericq. 



The respiratory undulations of arterial tension have been recorded, not only 

 in mammals, but also in birds. 



By Einbrodt three different types of the respiratory effect are distinguished : — 



1. The respiration is quick and shallow. No marked effect either on the 

 frequency of the heart or the blood pressure is seen. 



2. The respiration is deep, the inspiratory movement is executed more 

 rapidly than the expiratory, and the periodicity is such that several heart-beats 

 occur during each complete act of respiration. The arterial pressure falls at 

 the beginning of inspiration, rises during inspiration until expiration has com- 

 menced, and falls during expiration. The heart-beat increases in frequency 

 during inspiration. 



3. The respiration is deep and slow, and the heart-beat is frequent ; these 

 conditions are established by vagotomy. The changes of arterial tension are 

 the same as in 2, but increased in amplitude. 



In order to explain the origin of the respiratory waves of arterial 

 tension, it is necessary to grasp the conditions which pertain to the 

 thoracic cavity. The heart and the large blood vessels which enter and 

 leave the heart lie in a closed and air-tight chamber, the thoracic cavity. 

 The remainder of this space is occupied by the lungs. The thorax is 

 formed of a bony and muscular wall, which possesses rigidity sufficient to 



1 Sitzungsb. d. h. Akad. d. Wissensch., inath.-naturw. CI., Wien, 1860, Bd. xl. S. 3C1. 



