128 THE VASCULAR SYSTEM 



exhausting bouts of boxing the pressure fell from 160 at the end 

 of the first bout to below 100, and rose to 130 after three minutes 

 rest. Inhalation of oxygen, then, lowers the pulse-rate and raises 

 the blood pressure, changes the respiration from the thoracic pressure 

 to the abdominal type, and restores the vigour of the athlete. 

 The heart seems to be poisoned by unoxidised products such 

 as lactic acid during extreme efforts, and therefore the com- 

 pressive action of the diaphragm is held in check (L. Hill and 

 M. Flack). After exercise the brachial pressure falls, while the 

 phalangeal pressure remains higher owing to vaso-dilatation and 

 for some time particularly if the subject is heated by exercise 

 (Oliver). 



THE VENOUS PRESSURE 



Oliver presses the pad of his haemodynamometer on a selected vein 

 of the back of the hand placed at heart's apex level ; next empties 

 the blood by stroking it on past the next valve ; then relaxing the 

 pressure, notes the point when the vein just refills. The writer 

 and M. Flack have tested the method by applying the armlet to the 

 upper arm, and raising the pressure within it to say 60 mm. Hg. 

 The pressure in the veins below the armlet must then rise to 

 60 mm. Hg. Employing small bags in accordance with Oliver's 

 method to test the pressure in the superficial veins, they have found 

 that they cannot be used accurately. A second armlet, however, 

 can be so used. This is placed round the forearm, and the pressure 

 raised above that in the veins, say to 70. The pressure in this 

 is then relaxed till some selected vein above this armlet, which 

 has been stroked empty up to the next valve, just refills ; thus an 

 accurate reading of the venous pressure is obtained. Employing 

 the two armlets, they found the venous refilling pressure exactly 

 corresponded to that in the upper armlet which was obstructing 

 the venous return. A convincing proof of the general accuracy 

 of the armlet method can be gained by this method thus find 

 the obliteration pressure for the brachial artery say it is 150 

 lower the pressure to 145 so that blood can get through, and then 

 find whether there is the same pressure, viz. 145, in the superficial 

 veins. If so, it is clear the arterial reading is correct within 5 mm. 

 They have done this in several cases, and in one where the 

 arterial wall felt full of stiff sclerosed patches, and have found no- 

 evidence that the arterial wall influences the readings. 



