294 



THE MECHANICS OF THE HEART 



rod which carries a writing outfit. The latter consisted originally of a small 

 capillary glass pen which was connected with a tiny receptacle filled with ink. 

 The record was made upon white paper revolved with a certain speed. At the 

 present time, however, smoked paper is used most frequently, the writing needle 

 consisting simply of a delicate crosspiece situated upon the free end of the vertical 

 rod. 



One difficulty encountered in registering changes in pressure is presented by 

 the great inertia of the mercury. In the heart, the fluctuations are extreme and 

 are developed with such rapidity that the mercury is quite unable to follow them 

 accurately. To begin with, its sluggishness causes it to lag behind, while when 

 once set in motion,, it tends to continue in the same direction, surpassing the 

 actual pressure, often very considerably. For this reason, it is practically im- 



FiQ. 149. — Schema to Show the Connection Made Between the Aetert and 



Manometer. 



M, manometer; H, mercurial column; F, float; D, recording needle; K, kymograph; 

 B, tube leading to reservoir filled with solution of sodium carbonate; R, rubber tubing 

 filled with sodium carbonate solution; C, glass cannula in artery; A, clip upon artery; 

 V, maximal-minimal valve (Frank) to be inserted in this circuit; 1, maximal; 2, minimal 

 side; Vi, maximal valve of Hurthle. A minimal valve is obtained by inverting the 

 central tube. 



possible to obtain an exact record of the intracardiac pressures by means of this 

 instrument. It may be used, however, to register either the lowest or highest 

 degrees of pressure, as weft as the mean pressure. To accomplish this end, a 

 so-called maximal-minimal valve must be interposed between the heart and the 

 manometer.^ In its simplest form this valve consists of a 'short cannula which is 

 surrounded by a wide jacket of glass (Fig. 14971). The free end of the cannula is 

 bevelled and is equipped with a flap of rubber membrane fastened to it in the 

 manner of a door. As the dififerent waves of systolic pressure traverse the cannula 

 this flap is raised, so that the column of mercury in the manometer is constantly 

 forced upward until it accurately counterbalances the pressure. At this level it is 



1 Hurthle, Pfliiger's Archiv, xliii, 1888, 399. 



