BLOOD PRESSURE 133 



tion 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 physical 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 vessels 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 required to obliterate them. 

 That this is probably the correct explanation is supported by the observation that, al- 

 though 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 that of 

 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. Thereafter it persisted at a small volume with little 

 alteration until the pressure became sufficient to obliterate it. It is said that re- 

 peated 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 muscular 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 202). Its cause is not un- 

 derstood, but it is of significance that the greatest augmentations occur at the same 

 cuff pressure as that at which a sound first comes to be heard by listening over the 

 artery at the elbow. 



With regard to the diastolio pressure, there has been some controversy as to whether 

 it is more accurately gauged by the oscillatory or the auscultatory method. If both 

 methods are employed it will usually be found that the oscillatory gives a higher read- 

 ing than the auscultatory. The consensus of opinion seems to be that the latter 

 method is the more accurate, and certainly it is the easier to apply, for with the 

 oscillatory there is often great difficulty in deciding just exactly when the maximum 

 oscillation occurs. 



The strongest evidence supporting the conclusion that the auscultatory readings are 

 more reliable than the oscillatory has been gained by experiments with an artificial 

 schema, consisting of a wide glass tube representing the armlet, filled with Ringer's 

 solution and closed by rubber stoppers pierced by tubes, which are connected with a 

 fresh artery, which therefore runs from end to end inside the tube. Through tubing 

 connected with the artery a pulsatile flow of oxygenated Ringer's solution' is made 

 to flow at varying pressures, which are indicated by valved manometers (see page 152) 

 connected with the artery tubing just beyond the compression tube. The pressure in 

 the latter is also measured by a manometer, and it is caused to vary by a suitable 

 compressor. By comparing the behavior of the artery with the pulsating movement of 

 a spring manometer connected with the compression chamber, under different degrees 

 of pressure inside and outside the artery, it has been observed that the maximal oscilla- 

 tion occurs when the artery is actually somewhat flattened between the pulse beats; that 

 is, it occurs at an outside pressure above the diastolic pressure, at which of course the 

 vessel should retain its circular shape. When a stethoscope is applied to the tube 



