168 



THE VASCULAR MECHANISM. 



FIG. 55. 



d 



AU 



Simultaneous Tracings from the 

 Right Auricle and Ventricle of the 

 Horse. (After Chauveau and Marey.) 



itself give any information as to the relative amounts of pressure ex- 

 erted by the auricle and ventricle respectively. 

 In the curve the auricular lever rises about 

 half as high as the ventricular lever ; but we 

 must not infer from this that the auricular 

 stroke is half as strong as the ventricular 

 stroke ; the former is arranged so as to move 

 much more readily, to be much more sensitive 

 than the latter. The instrument, it is true, 

 may be experimentally graduated, and may 

 then be used to determine the actual amount 

 of pressure ; but for this purpose is not wholly 

 satisfactory. We may add that the irregu- 

 larities seen on the ventricular curve during 

 the ventricular systole, and on the auricular 

 curve at the same time, have given rise to 

 much debate, and need not be discussed here. 

 On the whole, the method, though useful for 

 giving a graphic view of the series of events 

 within the cardiac cavities during a cardiac cycle, the short auricular 

 pressure, the long-continued ventricular pressure, lasting nearly half the 

 whole period, and the subsequent pause when both parts are at rest or in 

 diastole, cannot with safety be used for drawing more detailed conclusions. 

 Perhaps the least untrustworthy method of recording the changes of 

 endocardiac pressure is that recently introduced by Roy and Rolleston, 

 though difficulties present themselves in the interpretation of the curves 

 obtained by it. 



By means of a short canula introduced through a large vessel, or directly, as 

 a trocar, through the walls of the ventricle (or auricle), the blood in the cavity is 

 brought to bear on an easily moving piston. The movements of the piston are 

 recorded by a lever, and the evils of inertia are met by making the piston and 

 lever work against the torsion of a steel ribbon, the length of which, and conse- 

 quently the resistance offered by which, and hence the excursions of the piston, 

 can be varied at pleasure. 



The curves obtained by this method vary according to circumstances. 

 We may take as fair examples two curves from the left ventricle, one (Fig. 

 56, A) of a rapidly beating, and the other (Fig. 56, H) of a slowly beating 

 heart. 



122. In attempting to interpret these curves with the view of learning 

 the changes of pressure taking place in the heart, it is desirable to study 

 them in connection with the tracing of which we have already spoken 

 (Fig. 57), taken .by means of a light lever placed on the exposed ventricle, 

 and which, as we have seen, is a curve of the changes taking place in the 

 front-to-back diameter of the ventricle ; or we may use what is very nearly 

 the same thing, viz., a cardiographic tracing (Fig. 58) ; that is to say, a 

 tracing of the cardiac impulse which is a curve of changes in the pressure 

 exerted by the apex of the heart on the chest-wall. 



Various forms of cardiograph have been used to record the cardiac impulse. In 

 some the pressure of the impulse, as in the sphygmograph, is transmitted directly 

 to a lever which writes upon a travelling surface. In others the impulse is, by 

 means of an ivory button, brought to bear on an air-chamber, connected by a 

 tube with a tambour, as in Fig. 54 ; the pressure of the cardiac impulse com- 

 presses the air in the air-chamber, and through this the air in the chamber of the 

 tambour by which the lever is raised. In such delicate and complicated move- 

 ments as those of the heart, however, the use of long tubes filled with air is liable 

 to introduce various errors. 



