288 TEXT-BOOK OF PHYSIOLOGY 



the ventricle and though there is at this moment a rapid fall of intra- 

 ventricular pressure, on opening of the auriculo-ventricular valves and a 

 descent of blood into the ventricle, the fall of auricular pressure seldom 

 amounts to more than 0.5 mm. of Hg. 



A Graphic Record of the Auricular and Ventricular Contractions 

 of the Human Heart. From the similarity of the anatomic arrangement 

 of the human heart to that of mammals in general it is permissible to assume 

 that a graphic record of the auricular and ventricular contractions of the 



human heart would resemble in its general 

 features that of the hearts of mammals hereto- 

 fore experimented on, and that the same series 

 of events present themselves in the human heart 

 during each cycle, though by reason of the 

 difference in the rate of the beat, the duration 

 of each event in the cycle is somewhat different. 

 The nearest approach to obtaining a graphic 

 record of the auricular and ventricular con- 

 tractions of the human heart by the direct ap- 

 plication of exploratory tambours was made by 

 FIG. 126. TRACINGS OF THE Francois Franck on a woman whose heart was 

 cSS^^JfTw congenitally displaced into the abdominal cavity. 

 WITH ECTOPIA or THE HEART, a, An investigation revealed the fact that this 

 Auricular; v, ventricular. (Fran- woman had a large opening in the anterior 



portion of the diaphragm through which the 



ventricle had passed and formed a large protrusion in the epigastric 

 region. Through thin and relaxed abdominal walls the ventricular pul- 

 sations could be distinctly felt as well as the pulsation of what ap- 

 peared to be the inferior portion of the right auricle. A fibrous ring 

 around the edge of the opening in the diaphragm supported the heart 

 at the auriculo-ventricular groove. On the application of exploratory 

 tambours in connection with recording tambours one to the right 

 ventricle, the other to the right auricle, the record shown in Fig. 126 was 

 obtained of which the upper line represents the contraction of the auricle 

 and the lower line the contraction of the ventricle. A comparison of the 

 record with that obtained from the horse, Fig. 118, p. 277, shows that the 

 relation of the auricular to the ventricular systole is the same in the former 

 as in the latter and that in their general features the two records correspond, 

 from which it may be inferred that in the human heart the events occurring 

 during the cycle are practically identical with those occurring in the hearts 

 of other mammals. The small size of the auricular curve and the absence of 

 undulations are probably due to the fact that the tambour was placed on 

 only a portion of the auricle. 



A Schematic Representation of the Events of a Cardiac Cycle in 

 Man. From graphic studies of the cardiac impulse, of the pressure changes 

 in the auricle and ventricle as indicated by pressure changes in the jugular 

 vein and carotid artery respectively it has become possible to construct a 

 diagram of the cardiac cycle of the human heart, to designate on the ventricu- 

 lar curve the time of the opening and closing of the valves, as well as the 

 time relations of the entire series of events. A scheme of this character is 

 shown in Fig. 127, based on that constructed by Fredericq. 



