THE CIRCULATION 127 



radial pulse with the fingers of the right hand. Close the exhaust valve 

 and compress the rubber bulb rapidly to raise the pressure to about 

 140 mm. Hg. In a young person possessing an elastic vascular system 

 and in the sitting position, we would not expect to find a pressure higher 

 than this. Consequently, the pressure in the cuff overcomes at this 

 time the internal pressure. The brachial artery is fully compressed 

 and the radial pulse obliterated. Now gradually deflate until the radial 

 pulse just barely makes itself felt. Read the pressure and deflate rap- 

 idly. Be sure to compress the arm for only the shortest possible time. 

 Repeat again after intervals until you have acquired this technic thor- 

 oughly and are able to obtain correct results. This gives the systolic 

 blood-pressure. 



(b) Auscultation. Place the chest-piece of a stethoscope over the 

 region of the bifurcation of the brachial artery directly below the lower 

 edge of the cuff. Inflate rapidly as before, then deflate gradually. No 

 sound is heard when the brachial artery is obstructed. At the very 

 moment, however, when the arterial pressure just overcomes the out- 

 side pressure a sound is produced indicative of the systolic gushes of 

 blood through the constriction. Read the pressure, which, as has just 

 been stated, is the systolic. Practice this method a number of times. 

 Compare these results with those obtained previously by palpation. 



The estimation of the diastolic pressure may be attempted during 

 the process of palpation by carefully noting the amplitude of the oscilla- 

 tions of the mercury of the manometer. When the systolic pressure 

 breaks through the constriction these fluctuations are small, but become 

 much larger as the diastolic value is approached. Below this point 

 their amplitude again decreases. A better way is to ascertain this 

 value by the method of auscultation. Having determined the moment 

 when the systolic sound just appears, continue to deflate slowly. The 

 sound becomes louder; soon reaches a maximum, and then suddenly 

 disappears. Read the pressure at this point. It indicates the diastolic 

 pressure. 



Deduct the value of the diastolic pressure from that of the systolic. 

 This gives the pulse-pressure, which varies under ordinary conditions 

 between 35 and 40 mm. Hg. 



2. Effect of Posture. Determine the systolic and diastolic pressures 

 of the subject while resting horizontally upon the table with his head 

 upon a pillow. Repeat this test after he has assumed the sitting posi- 

 tion, and again after he has assumed the standing position. Tabulate 

 the results and determine the pulse-pressure. Explain the results. 

 What bearing do they possess upon the condition of the vascular system? 



Crampton has attempted to obtain an approximate estimate of the 

 condition or vascular tone of a person by balancing the increase in the 

 heart rate with the increase or decrease in blood-pressure resulting on 

 standing up. The range of the systolic pressure has been found to be 

 between +10 and 10 mm. Hg, and the increase in the frequency of 

 the heart between and 44. By assigning equal percentages to these 



