BLOOD PRESSURE 373 



and diastolic pressures by the pulse rate. When added to one another, the values 

 so obtained give the so-called S. D. R. index, for example: 



Systolic pressure 120 mm. Hg X 72 = 8,640 mm. Hg 

 Diastolic pressure 70 mm. Hg X 72 = 5,040 mm. Hg 



190 mm. Hg X 72 = 13,680 mm. Hg 



By combining in this way the pressure with the cardiac frequency, it is possible 

 to obtain an estimate of the vascular energy for longer periods of time. The high- 

 est S. D. R. index which has been observed in normal persons is close to 20,000. 

 Thus, a person with a total energy index of 30,000 may be said to show a 50 per 

 cent, increase, and so on. The lower limit seems to lie at about the figure 12,000. 

 The efficiency test described by Barringer^ consists in determining the cardiac 

 rate and blood-pressure before and after a graded exercise which may be determined 

 in foot-pounds. 



The Venous Blood Pressure. — It has been stated aoove that the 

 venous pressure may be determined in any vein of convenient size 

 and location by connecting it by means of a T-tube with a U-shaped 

 manometer containing normal saline solution. In this way, the lateral 

 pressure is obtained which prevails in this vein at the point of insertion 

 of the tube. By simultaneously registering the pressure in different 

 veins of the dog, Burton-Opitz^ has obtained the following average 

 values : 



Saphenous vein (left) 7 . 42 mm. Hg 



Femoral vein (left) 5. 39 mm. Hg 



Femoral vein (right) 5. 42 mm. Hg 



Facial vein (left) 5.12 mm. Hg 



Brachial vein (right) 3 . 90 mm. Hg 



Renal vein 10.9 mm. Hg 



Mesenteric vein 14.7 mm. Hg 



Splenic vein 10.1 mm. Hg 



Portal vein 8.9 mm. Hg 



External jugular vein (left) . 52 mm. Hg 



External jugular vein (right) — . 08 mm. Hg 



Superior cava (per. portion) — 1 . 38 mm. Hg 



Superior cava (centr. portion) —2. 96 mm. Hg 



Inferior cava at hep. vein . 00 mm. Hg 



This compilation shows that the pressure decreases gradually 

 from the periphery to the center at the rate of about 1 mm. Hg for 

 every 35 mm. of distance. The zero-line is reached in close proximity 

 to the chest. Centrally to this point, the pressure becomes negative 

 and eventually attains its lowest value in the auricular portion of the 

 heart, namely — 10 to — 15 mm. Hg. As the pressure in the peripheral 

 veins is only 10 to 15 mm. Hg, the total fall in the venous system 

 amounts to no more than 30 mm. Hg. It should also be remembered 

 that this fall is had only because the soft walls of the venous channels 

 are constantly exposed to the elastic pull of the lungs which becomes 

 greatest during inspiration. This can readily be proved, because 



1 Arch, of Int. Med., March, 1916. 



2 Am. Jour, of Physiol., ix, 1903; also Pfliiger's Archiv, cxxix, 1908. 



