BLOOD VESSELS 



449 



B. In the intact Animal. — 1. To measure the systolic 

 pressure it is necessary to find the pressure which must be 

 apphed to an artery in order to prevent the pulse from passing. 



This may be done with Riva Rocci's apparatus (fig. 189, 

 {B.) by applying a bag round the limb so that it rests upon 

 the brachial artery. The bag is firmly strapped on by 

 means of a broad supporting belt, and it is connected with a 

 pump, by which the pressure within it may be raised, and 

 with a mercurial manometer by which the pressure applied 

 may be measured in mm. of mercury. The pressure is then 

 raised either (a) till the pulse beyond the band is no longer 

 felt, or (6) till no sound is heard with each pulse wave through 

 a stethoscope applied to the artery beyond the band. The 

 pressure is then gradually relaxed till (a) the pulse is again 



Fig. 190.— To show the Difference between Systolic, Diastolic, and Mean 

 Blood Pressure throughout the Arterial System. S., systolic pressure ; 

 D., diastolic pressure ; M., mean pressure. 



felt or (6) the sound with each pulse wave heard through the 

 stethoscope reappears. The column of mercury, at this 

 moment, indicates the systolic pressure in the artery 

 {Practical Physiology). 



2. The diastolic pressure may be measured by further 

 relaxing the pressure and noting the point at which the 

 pulse sound again disappears. 



(2) Normal Arterial Pressure. 



By these methods it has been found that the systolic 

 pressure in the brachial artery of man is about 120 mm. of 

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