VENOUS PRESSURE 



79 



point they first become still more intense and then suddenly- 

 become faint. The reading of the manometer at which 

 the sounds are loudest is the diastolic pressure. 



The mean pressure is the mean between the systolic and 

 the diastohc pressure. The pulse-pressure is the difference 

 between the systolic and diastolic pressures. It is a 

 measure of the output of the heart. 



A rough indication of the arterial pressure can be obtained 

 by placing two fingers upon the radial artery. The 

 proximal finger exerts the pressure and the distal finger 

 detects whether the pulse comes through or not. Certain 

 characteristics of the pulse are recognised clinically. The 



Fig. 19. — (From Starling's Princi'ples of Physiology.) 



volume is the difference between the diastohc and systohc 

 pressure ; it is therefore identical \vith pulse-pressure. 

 The tension is the pressure during diastole. 



The Measurement of Venous and Capillary Pressure 



A rough estimate of the pressure in the subcutaneous 

 veins of the upper hmb can be obtained by raising the 

 arm and noting the height above the heart level at which 

 they become blanched. Another method is by means of 

 the apparatus shown in Fig. 19. It consists of a rubber 

 bag, on the opposite sides of which are two holes. The 

 bag is placed on the skin so that one hole is opposite a 

 vein. Over the other hole is placed a plate of glass. The 

 junction between bag and skin and between bag and 



