CHANGES OF PRESSURE DURING CARDIAC CYCLE. 15 



vein and carotid artery, or directly through the auricular appendix into 

 the heart. These tubes have, in each case, been connected with mano- 

 meters of special construction, and all more or less adapted to the 

 recording of rapid changes of pressure. Xone of these methods 

 materially interfere with the circulation. After the introduction of 

 such tubes, the sounds of the heart remain the same as before. 1 

 Hiirthle has shown that the curve given by the cardiac impulse also 

 remains unaltered.' 2 Even if a semilunar valve be punctured during 

 the passing of a tube down the carotid, no harm results, since the tube 

 fills the hole it has made, the valves remain otherwise competent, and 

 the pressure curves are unaltered. 



The truth of the records obtained depends entirely on the perfection 

 of the registering apparatus employed. Chauveau and Marey did 

 not give any proofs of the capabilities of their instrument, and the 

 accuracy of their curves. These authors used air transmission, and 

 thus, no doubt, most rapid variations of pressure could be conducted 

 to the recording tambours. Bonders 3 has since proved that a 

 sensitive Marey tambour gives readings of considerable accuracy, 

 although the lever has a swing of its own, due to the momentum of its 

 mass, which in rapid variations of pressure tends to make the excursions 

 too great. 



It is an extremely difficult problem to contrive a manometer which 

 answer, without much inertia, to extremely quick changes of in tra ventricular 

 pressure. A mercury manometer is useless, because of the momentum of its 

 mass. Thus this instrument gives a lower reading of intraventricular pressure 

 than of aortic pressure, simply because it has not time to follow the rise of 

 intraventricular pressure. Such a result is, of course, absurd. 



FIG. 7. Fick's straight spring manometer. 



The manometer must, in all its moving parts, be made of the smallest 

 mass, and the object in hand is best attained by the use of some form of elastic 

 counterpoise to resist the moving part of the instrument. Fick's straight 

 spring manometer, in which air is employed as the agent of transmission, 

 satisfies most of the conditions required. 4 



It consists of a tube a a, which opens into a very small chamber, the floor 

 of which is formed by a rubber membrane. In the middle of this membrane 

 is fixed an ivory knob, which presses against a strong steel spring/" The 

 exceedingly small movements of this spring are greatly magnified by the long 

 lever /<. This instrument has been proved to be accurate by the following 

 experiment. 



1 Chauveau and Marev, loc. cit., p. 301. 



*Arch.f. d. ges. Physiol., Bonn, 1891, Bd. xlix. S. 93. 



3 Onderzoek. ged. in h. physiol. Lab. Utrecht, Hoogesch., Tweede Reeks, 1S67, vol. i. 

 pp. 11-1S. 



4 Fick, Arch. f. d. gts. Physiol. , Bonn, 1883, Bd. xxx. S. 597. v. Frev's tonometer 

 is constructed essentially on the same principle, air being used as the medium of trans- 

 mission. 



