ARTERIAL PRESSURE. 269 



ly abolished, on account of the stoppage of the action of the 

 heart. If respiration be resumed before the heart has become 

 arrested, the pressure soon returns to its normal standard. 



Muscular effort considerably increases the arterial press- 

 ure. This is due to two causes. In the first place, the chest 

 is generally compressed, favoring the flow of blood into the 

 great vessels. In the second place, muscular exertion pro- 

 duces a certain amount of obstruction to the discharge of 

 blood from the arteries into the capillaries. Numerous ex- 

 periments upon animals have shown a great increase in press- 

 ure in the struggles which occur during severe operations. 

 Bernard has shown that galvanization of the sympathetic in 

 the neck and irritation of some of the cerebro-spinal nerves 

 increase the arterial pressure, probably from their effects on 

 the muscular coats of some of the arteries, causing them to 

 contract, and thereby diminishing the total capacity of the 

 arterial system. 1 



Effects of Hemorrhage. Diminution in the quantity of 

 blood has a remarkable effect upon the arterial pressure. If, 

 in connecting the instrument with the arteries, we allow even 

 one or two jets of blood to escape, the pressure will be found 

 diminished perhaps one -half, or even more. It is hardly neces- 

 sary to discuss the mechanism of the effect of the loss of blood 

 on the tension of the vessels, but it is wonderful how soon the 

 pressure in the arteries regains its normal standard after it has 

 been lowered by hemorrhage. As it depends upon the quan- 

 tity of blood, as soon as the vessels absorb the serosities in suf- 

 ficient quantity to repair the loss, the pressure is increased. 

 This takes place in a very short time, if the loss of blood be 

 not too great. 



Experiments on the arterial pressure with the cardiometer 

 have verified the fact stated in treating of the form of the pulse, 

 namely, that the pressure in the vessels bears an inverse ratio 

 to the distention produced by the contractions of the heart. 



1 BERNAKD, Liquides de T Organism*, tome i. 



