106 PULSE RECORDS IN THEIR RELATION TO 



systole (first negative wave or " x " depression). Porter states that 

 relaxation of the auricular appendix proceeds for a variable time, 

 terminating at the beginning or end of the second positive wave ; 

 but the observation is of little value, for under the conditions of his 

 experiment the relaxation would depend in the main on passive 

 filling. When the ventricle is inhibited by vagal inhibition in the 

 dog, or if clamped off from the auricle in the tortoise, a negative 

 wave is still present (Fran9ois-Franck) ; it also occurs in the 

 jugular pulse in certain cases of heart block when the ventricle 

 fails to respond to the auricular contraction (Wenckebach). 

 Morrow's tracing (Fig. 12) shows similar characteristics ; but while 

 the ventricle is inactive, the depression, though still present, is 

 reduced in size. While Franois -Franck found it abolished by irri- 

 tation of the auricle, Fredericq ( 12c ) has shown that this is not 

 the case, and states ( 12a ) that when the auricles have passed into 

 delirium, at each ventricular contraction the auricular appendices 

 diminish in volume, and are, as it were, aspirated towards the cavity 

 of the auricle, and the negative wave persists. 1 



From these observations it is clear that the systole of the 

 ventricle plays a considerable part in causing the depression, and 

 it has been attributed by many writers to an event occurring at 

 this time, namely, descent of the A-V line (Fredericq, Porter, 

 Wenckebach, &c.). 



In concluding this section it may be said that the two negative 

 waves which together form the most 'prominent depression of the 



1 Franc.ois-Franck's observations were carried out with the chest open. Fredericq 

 has controlled his own observations by repeating the experiments with the chest 

 intact, the advantages of which are obvious. 



There is a fact which is often insufficiently appreciated, namely, that the 

 circulation is completely obstructed at two points during approximately half the 

 cardiac cycle. The obstructions are situated at the auriculo-veutricular valves. 

 Nevertheless it is only during a small fraction of the cardiac cycle, during systole 

 of the auricles, that blood is not pouring into the heart. The main function of the 

 auricles is not to load the ventricles ; the ventricles fill well when the auricles are 

 paralysed, and by comparison the auricles are small chambers. They serve mainly 

 as reservoirs, and during their brief contraction the large veins in their vicinity 

 adopt this function. In contracting the auricles return to the state of potential 

 reservoirs. 



So the over-engorgement of the veins, which would otherwise occur, is prevented ; 

 and so it happens that in spite of the fact that the circulation of man is never an 

 open path, the flow of blood through peripheral vessels is constant and uniuter- 

 mitting. While in heart block venous stagnation is rare, clinical observations of 

 to-day point to its frequent origin in inefficient, ill-timed, or obstructed systole of 

 the upper chambers. 



