A Blood Pressure Apparatus. 
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A blood pressure apparatus with pith-ball attachment 
indicating diastolic pressure. 
By Nathan ael fedde. 
[From the Laboratory of Physiology of the Cornell University Medical 
College.] 
Of the many factors governing blood pressure, the most impor- 
tant, namely the force of the heart beat, receives least attention. 
A knowledge of the systolic pressure is of value in warning of 
certain dangers, but gives no clue as 
to the amount of work the heart 
does. In order to estimate this we 
must know the difference between the 
pressure during the heart beats and 
that in the intervals. The maximum 
pressure is easily ascertained by any 
one of the numerous sphygmomano- 
meters. Only a few have means, in 
any way satisfactory, for determining 
diastolic pressure, and these are pro- 
hibitive in price and of tremendous 
bulk. To overcome these obstacles 
we have devised a small instrument 
that can be attached to any sphyg- 
momanometer. This consists in an 
air chamber communicating by means 
of a glass tube containing a pith-ball 
with the tube leading from cuff to 
manometer. Any increase of pressure in the cuff is equalized in 
the chamber by a rush of air passing the pith-ball and moving 
it. With a steady slow exhaust of air the ball moves exactly as the 
point of Erlanger's lever, but without the fling. An average pulse 
throws Erlanger's lever about 3 cm., while the pith-ball flies about 
three times that distance. The movements of the ball are inter- 
preted just as the movements of the lever in Erlanger's instru- 
ment. That point of pressure is read at which the oscillations 
begin to fall off from the maximum. 
