BLOOD PRESSURE 131 



sion and decompression of the artery ; that is, the pulse may reappear on 

 decompression at a lower pressure than that at which it disappeared on 

 compression, the difference being most marked when the decompression 

 is done quickly. This difference is owing to the fact that the full force 

 of the pulse does not reach the forearm until all the vessels have become 

 distended with blood. (3) There are often discrepancies in the systolic 

 readings taken from different limbs; thus, it is not uncommon to find 

 that the systolic pressure in the leg is higher than that in the arm even 

 when the observed person is in the horizontal position. These differences 

 are most commonly observed in patients suffering from aortic regurgi- 

 tation or thickened arteries. In aortic regurgitation the pulse is of the 

 water-hammer variety, and the greater systolic pressure observed in the 

 leg vessels in such cases seems to depend on differences in the phys- 

 ical conditions concerned in the transmission of this exaggerated pulse 

 wave to the vessels of the two extremities. 



The reason for the discrepancies in cases of hardened arteries is no 

 doubt that the hardening is likely to be more pronounced in the ves- 

 sels of the thigh than in those of the arms. When a hardened vessel is 

 compressed it does not collapse uniformly that is, it does not become 

 completely closed but its walls come together at the middle part while 

 chinks still remain at the sides. The blood continues to pass through 

 these chinks, and a very considerably higher pressure in the cuff is re- 

 quired to obliterate them. That this is probably the correct explanation 

 is supported by the observation that, although in such patients the pulse 

 does not disappear in the vessels of the foot at the same pressure as it 

 does at the wrist, a distinct change is nevertheless perceptible in the 

 pulse of the foot at a cuff pressure equal to that producing obliteration 

 in the wrist. In a patient showing a systolic pressure of 115 mm. for the 

 upper arm and 198 mm. for the leg, at 116 mm. the pulse in the leg, 

 although not obliterated, became notably cut down in volume. There- 

 after it persisted at a small volume with little alteration until the pressure 

 became sufficient to obliterate it. It is said that repeated compression 

 and decompression of the hardened arteries greatly reduces the dis- 

 crepancy in the systolic readings. Differences in systolic readings are 

 also sometimes observed in normal individuals, particularly after mus- 

 cular exercise, but for these no satisfactory explanation can be given. 



While palpating the radial artery, it will often be noticed, as the 

 pressure in the cuff is gradually raised from zero, that the force of the 

 pulse increases perceptibly until a pressure of about 50 mm. is reached. 

 This paradoxical behavior of the pulse can also be demonstrated by the 

 sphygmograph (see page 201). Its cause is not understood, but it is 

 of significance that the greatest augmentations occur at a cuff pressure 



