The Measurement of Arterial Pressure in Man. 



523 



Finally the first length of artery flattened (fig. 6, A). On repeating the 

 experiment upon the first length of artery by itself we found it began to 

 flatten and give a maximal pulse at 38 cm. H 2 ; the pressure then fell in the 

 manometer and reached zero as the compression was increased (fig. 6, B). 



Experiment III. 



We varied Experiment I by arranging the outlet in a U-tube containing 

 mercury, so that the resistance to outflow and diastolic pressure increased 

 pari passu with the compression (fig. 7). The diastolic pressure being thus 



Fig. 7. 



raised pari passu with the compression, the maximal pulsation appeared just 

 before the point at which the artery was flattened in systole. The result 

 under these conditions was, of course, the same whether one length or two 

 lengths of artery (or artery, tissue schema, and vein) were used. Their walls 

 were equally stretched and made more and more rigid by the rising diastolic 

 pressure. There was thus little loss of systolic force as the pulse passed along 

 the tubes. On the other hand, the pulse transmitted to the compression 

 chamber and recorded by the manometer became less as the arterial wall 

 became more rigid. When the diastolic pressure which pertained in the 

 schema was over-topped, the length or lengths of artery began to flatten, and 

 a maximal pulse resulted. 



Mac William and Melvin* conclude from their study of the simple schema 

 that the diastolic pressure and maximal pulse do not always coincide. By 

 our experiments we bring into play the effect on the artery of obstructed 

 venous outflow, and find the diastolic pressure and maximal pulse in 

 agreement. 



* 'Heart/ vol. 5, p. 153 (1914). 



