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Methods of Raising a Low Arterial Pressure. 

 By W. M. Bayliss, F.K.S. 



(Received August 29, 1916.) 



(From the Physiological Laboratory, University College, London.) 



CONTENTS. 



PAGE 



Loss of Blood 381 



Loss of Vascular Tone 388 



Accommodation of the Vascular System 391 



Summary 393 



References 393 



In the course both of physiological experiments and of clinical practice a 

 low arterial pressure may be due to two different causes, apart from failure of 

 the heart. 



After haemorrhage, the blood pressure is low on account of deficiency of 

 blood in circulation, so that the output of the heart is decreased and is 

 insufficient to keep up a due supply in the arteries to take the place of that 

 flowing through the capillaries. Now, while it is obvious that constriction of 

 the arterioles would raise the pressure in such cases, by diminishing the rate 

 of outflow through the capillaries, the result would be to decrease the supply 

 of blood to all organs whose arterioles are affected, so that no real gain would 

 be obtained. In such cases, what is needed is to increase the volume of blood, 

 without constricting arterioles. 



But the arterial pressure may be low, although the volume of the blood is 

 normal. Supposing that the heart is beating efficiently, the low pressure is, 

 in such cases, due to peripheral vaso-dilation. Such a condition is met with 

 when the spinal cord is cut high up, as in the " spinal animal," and also in 

 cases which are called " shock." Here, what is required is clearly to restore 

 the normal tonic contraction of the arterioles. An increased volume of blood 

 may be useless or even harmful, if the heart cannot correspondingly increase 

 its output. 



It is, nevertheless, the usual practice to treat both kinds of state by the 

 intravenous injection of saline solutions, sometimes by transfusion of blood. 

 But the unsatisfactory effect of saline injections suggested that a more 

 efficient fluid might be found and the following investigation was undertaken 

 with that object. 



