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TEXT-BOOK OF PHYSIOLOGY 



resents the time of the diastole, during which the heart cavities are enlarg- 

 ing with the incoming of a new volume of blood in consequence of which 

 the heart is pressing against the chest walls. The systolic plateau is charac- 

 terized by one or more elevations and depressions, the true cause of which is 

 unknown. 



The Cardiac Cycle. The cardiac cycle is a period in the heart's activ- 

 ities embraced between the beginning of one auricular systole and the 



beginning of the next succeeding auricular 

 systole. During this period a series of events 

 occur which collectively constitute the physio- 

 logic activities of the heart as a whole. The 

 most striking of these events is the successive 

 activity of the auricular and ventricular walls. 

 An examination of the exposed heart shows 

 that the cycle is characterized by: 



a 



1. The auricular systole. 



2. The ventricular systole. 



3. The pause or period of 

 which both auricles and 

 at rest. 



repose during 

 ventricles are 



The Graphic Record of the Cardiac Cycle. For 

 the purpose of obtaining accurate information as to the 

 sequence of events, their time relations, as well as of the 

 pressure within the heart cavities during each phase of its 

 activity, it is necessary to obtain graphic records of the en- 

 tire cardiac cycle. 



This was first successfully accomplished by Chauveau 

 and Marey, by means of sounds or tambours (Fig. 117) in- 

 troduced through the jugular vein into the cavities of the right 

 heart. Each tambour consists of a metallic frame covered 

 by a thin rubber membrane. By means of flexible tubes, a. 

 v., the interior of each tambour can be placed in communi- 

 cation with the interior of a second tambour provided with 

 a recording lever. Pressure applied to the cardiac tambour 

 will be followed by a movement of the enclosed air toward 



FIG. 117. CARDIAC SOUNDS, the recording tambour indicated by an outward movement 

 v, Tambours to be ^inserted into of its mein brane and a rise of the lever; removal of the pres- 

 the ventricle; a, tambour to be in- sure will be followed by a movement of the enclosed air 

 serted into the auricle; w, rubber toward ^g cardiac tambour indicated by an inward move- 

 membrane surrounding metal ment of the membrane an d a fall of the lever. 

 frame-work; a, v ends of tubes in wj^ ^ ta mbours ^ introduced into, and carefully 

 connection with tambours. adjusted to the interior of the right heart, the auricular and 



ventricular contractions will exert pressure on their enclosed 

 tambours as indicated by the rise of the levers of the re- 



cording tambours, which continues so long as the pressure lasts. With the relaxation of the 

 auricular and ventricular walls the pressure is removed and the levers fall to their former posi- 

 tion. When the levers are [applied to the surface of a recording cylinder a record of auricular 

 and ventricular contractions is obtained such as that shown in Fig. 120. 



A similar r ecord would be obtained if the tambours were placed in the cavities of the left 

 side of the heart. 



In the graphic record, Fig. 118 obtained by the foregoing method, it 

 is apparent that during the period of repose there is a gradual ascent of 

 the tips of the recording levers, the result of a gradual increase of pres- 

 sure due to the accumulation of blood within the heart cavities. When this 

 reaches a certain level the auricular contraction occurs rather suddenly, 

 followed by an equally sudden relaxation, after which the auricular walls 

 remain at rest for a relatively long period, though the pressure within the 



