508 CIRCULATION OF BLOOD AND LYMPH. 



the point of systolic pressure is not satisfactory, since the pulse waves increase 

 gradually in amplitude without a sudden break, or perhaps there is more 

 than one place at which a sudden increase occurs. A more reliable method 

 according to Erlanger is to note the point at which the ascending and descend- 

 ing limbs of the pulse wave show a noticeable separation (Fig. 205). "At 

 the moment the pressure on the artery falls below systolic, blood succeeds in 

 making its way beneath the cuff. This must be squeezed out before the lever 

 can return to the base line, whereas at higher pressures the lever is raised 

 only through the hydraulic-ram action of the pulse wave upon the upper 

 edge of the cuff." After finding the systolic pressure the diastolic pressure 

 is obtained by allowing the pressure to drop still further. The pulsations 

 increase in height to a maximum size and then decrease. The pressure at 

 which the maximum pulse wave is obtained marks the diastolic pressure. 

 It is better perhaps in dropping the pressure for this last purpose to manipu- 

 late stopcock i so as to drop the pressure 5 mms. at a time, recording the pulse 

 wave at each pressure. In this way a record is obtained such as is given in 

 Fig. 202. It should be added, also, that in order to keep the lever of the 

 tambour horizontal while the pressure in the system is being lowered there 

 is a minute pinhole in the metal bottom of the tambour. Through this 

 pinhole the pressure in the tambour and chamber, /, is kept atmospheric 

 throughout, except during the quick changes caused by the pulse waves. 

 By means of this instrument one can determine within a minute or so the 

 amount of the systolic and diastolic pressure in the brachial artery, and also, 

 of course, the difference between the two, the pulse pressure, which may be 

 taken as an indication of the force of the heart-beat. 



The Normal Arterial Pressure in Man and Its Variations. 

 By means of one or other of the instruments devised for the 

 purpose, numerous results have been obtained regarding the 

 blood-pressure in man at different ages and under varying normal 

 and abnormal conditions. Unfortunately, the methods used have 

 not always been complete. Some authors give only systolic 

 pressures, for example. In such experiments also a troublesome 

 factor is always the psychical element. The mental interest 

 that the individual experimented upon takes in the procedure 

 almost always causes a rise of pressure and perhaps a changed 

 heart rate. Results, as a rule, upon any individual show lower 

 values after the novelty of the procedure has worn off, and the 

 patient submits to the process as an uninteresting routine. Under 

 normal conditions, Potain* estimated the systolic pressure in the 

 radial of the adult at about 170 mms. of mercury and the varia- 

 tions for different ages he expressed in the following figures: 



Age 6-10 15 20 25 30 40 50 60 80 



Pressure (systolic). 89 135 150 170 180 190 200 210 220 



Without the other side of the picture that is, the diastolic pres- 

 sure and the force of the heart beat (pulse pressure) it is difficult 

 to interpret these figures. The rapid increase up to maturity 

 probably represents chiefly the larger output of blood from the heart; 

 the slower and more regular increase from maturity to old age is 

 due possibly to the gradual hardening of the arteries, since the less 

 * "La pression arterielle del'homme/' Paris, 1902. 



