THE AURICULAR PRESSURE CURVE. 23 



by Porter with the Hlirthle manometer, agree fairly closely in the main 

 outlines. 



By means of a large cannula placed in the auricular appendix, and 

 connected with a Hiirthle tambour, Porter 1 took curves (Fig. 16), in 

 which the following points are to be observed : 



A, The systolic rise of the auricular pressure = + 9 mm. Hg. 

 A.B, A first diastolic fall 



B.C, A first diastolic rise = + 5 



C.D, A second diastolic fall = - 10 



E, A second diastolic rise = + 5 ,, 



F, A third diastolic fall = + 0-5 



G, A period of no pressure. 



Upon the second curve given in th % e figure the following relations are 

 marked : 



1. Beginning of the auricular systole. 



2. Beginning of ventricular systole. 



3. Opening of semilunar valves. 



4. The plateau stage of the ventricular systole. 



5. Beginning of ventricular downstroke. 



6. End of ventricular downstroke. 



A considerable negative pressure appears in the auricle during the 

 height of the ventricular systole (Fig. 16, D, 4), a negative pressure which 

 must materially aid in the filling of the auricle. This is given as follows : 



Chauveau and Marey - 2 to - 33 mm. Hg. 

 Goltz and Gaule . - 7 to - 10'4 

 Porter ... - 10 



By Chauveau and Marey the phenomenon was explained by the 

 supposition that the descent of the base of the ventricle during systole 

 pulls on the auricular wall, and thus dilates the auricular cavity. This 

 is scarcely probable, as the auricle is free to move as a whole, and 

 would therefore follow the ventricle, v. Frey, Krehl, and Fredericq 

 suggest a different explanation. During the ventricular systole, the 

 ventricles, by the expulsion of blood, become smaller ; by their diminu- 

 tion the negative pressure in the thorax is increased, and thus the 

 auricles, large veins, and lungs are dilated. So long, therefore, as the 

 thorax is closed, the heart can act in this way, not only as a force 

 pump, but also as a suction pump. Each systole of the ventricles 

 helps to fill the auricles. Porter has further put forward an ingenious 

 theory to explain the second diastolic fall. He supposes that when 

 the papillary muscles contract they pull down like a diaphragm the 

 auriculo-ventricular valves, which are closed and ballooned out 

 towards the ventricular cavity. Thus the cavity of the auricle is 

 increased. The commencement of the second diastolic fall agrees 

 closely with the beginning of the downward movement of the valves, 

 as determined by Eoy and Adami in their research on the papillary 

 muscles (see p. 10 and p. 39). 



Probably this, the most important fall in the auricular pressure, 

 is produced, not by one only, but by both of these factors combined. 

 With an increasing frequency of heart-beat, Porter has found that the 

 1 Journ. PhysioL, Cambridge and London, 1892, vol. xiii. p. 513. 



