362 TEXT-BOOK OF PHYSIOLOGY 



has been furnished by Erlanger. With a given speed of the drum, the up and 

 down strokes of the lever practically coincide. But if the speed of the drum 

 be slightly increased "so that each wave subtends about i to 2 mm. of smoked 

 paper (this speed is attained merely by removing the governor), the change 

 in form of the successive waves manifests itself usually as a more or less 

 abrupt separation of the ascending and descending strokes of the pulse record 

 (Fig. 164). The phenomenon may vary somewhat with the form of the 

 pulse wave and may even be obscured by fling, but there has been no great 

 difficulty in recognizing it in every case. It is often very clear when the 

 tracing shows no abrupt increase in amplitude whatsoever. It is just as 

 accurate an index to the systolic pressure as the ' sensory criterion ' and that 

 of v. Recklinghausen. The change in form occurs because, 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." 

 The conclusions of Erlanger regarding the results of his investigations 

 with this apparatus may be partially summed up in the following statements, 



and as they hold true for other forms of 

 apparatus which determine both systolic 

 and diastolic pressures, they are here ap- 

 pended: "The pressure that is deter- 

 mined by occluding an artery is probably 

 the maximum end pressure of the artery 

 occluded. The pressure determined by 

 the method of maximal oscillations is the 

 FIG. 164. TRACING SHOWING THE minimum lateral pressure of the artery 

 POINT, INDICATED BY THE ARROW, AT rnrrmrP H and therefore a Q the mini 

 WHICH THE SYSTOLIC PRESSURE is TO BE mpressea, ana, t re, as U 



NOTED. (Erlanger.) mum lateral pressure is the same in all of 



the larger arteries, the pulse pressure, 



determined when the pressures in the brachial artery are observed, tends 

 to approximate the lateral pulse pressure in the aorta." 



Any positive statement as to the numerical values of the different pres- 

 sures is somewhat difficult to make inasmuch as they will vary within physio- 

 logical limits in accordance with the position of the body, exercise, charac- 

 ter of psychic states, digestion, temperature, and other conditions. For 

 comparative investigations it is necessary, therefore, to place the subject of 

 the investigation in one and the same position, to apply the cuff to the corre- 

 sponding arm, to use always a uniform width of cuff and to select the same 

 time of day with reference to meals, etc. 



It may be stated, however, that in adult life the systolic pressure in the 

 brachial artery ranges from no to 135 millimeters of Hg. in men and about 

 10 mm. less in women; the diastolic pressure ranges from 65 to no mm. 

 Hg.; the pulse pressure ranges from 25 to 40 mm. Hg. 



The Auscultatory Method of Determining the Blood-pressure. 

 In 1905 a new method was introduced and described by Korotkow for the 

 determination of both the systolic and diastolic pressures, which in the 

 experience of clinicians is more accurate and satisfactory in both physiologic 

 and pathologic conditions than any of the other clinical methods. (See 

 papers by Goodman and Howell in the Univ. of Pa. Medical Bulletin, Nov., 



