DEMONSTRATIONS. 

 CIRCULATION. RESPIRATION. ANIMAL HEAT. 



CHAPTER XXXIX. 

 INTRACARDIAC PRESSURE. BLOOD FLOW. 



Intracardiac Pressure. Owing to inertia the mercurial manometer 

 is unable to respond to the rapid changes of intracardiac pressure. The 

 pulse curves obtained by the mercurial manometer are also distorted by 

 the swings due to the momentum of the mass. To record the changes 

 of intracardiac pressure an instrument must be contrived which is able 

 to follow a change of pressure equal to 1500 mm. Hg per second. 



FIG. 247. HUrthle's spring manometer. 



Fio. 248. Spbygmoacope. 



Hurthle's spring manometer consists of a small tambour, 5 '5 in 

 diameter, covered with rubber membrane. A button attached to the 

 membrane works against a steel spring. The movement of the spring 

 is magnified by a light lever. Inertia is proportional to the mass and 

 the square of the velocity. By making the tambour very small and the 

 lever very light the errors due to the inertia of the fluid and lever are 

 reduced to a minimum. 



The sphygmoscope is an equally good instrument. One end of a 

 rubber finger-stall is drawn over the end of a rubber cork. The cork is 

 inserted into a short piece of wide tube. A glass tube passes through 



