278 TEXT-BOOK OF PHYSIOLOGY 



last 0.16 sec., the ventricular systole 0.32 sec. and the pause 0.32 sec. 

 approximately. 



The Curve of the Systole and Diastole of the Heart. In the study 

 of the volume changes of the heart by means of a specially devised cardi- 

 ometer, Henderson was enabled to record the contraction and relaxation 

 movements of the heart, obtaining thereby a curve that resembled the curve 

 of the contraction and relaxation of a skeletal muscle. If this curve is re- 

 versed and superposed on a curve of the intra-ventricular pressure, their 

 relation one to an other becomes apparent, Fig. 119. 



The chief characteristic of the systolic portion of the curve, viz.: its 

 steep ascent, though less than that of the pressure curve, shows that with 

 the opening of the semilunar valves, b, a large portion of the volume of the 

 blood in the ventricles, 90 per cent, according to Henderson, is quickly and 

 in a uniform manner discharged, after which the outflow slows and finally 

 ceases as indicated by the rounded apex of the curve. The chief character- 

 istic of the diastolic portion of the curve, viz. : its steep descent, though less 

 than that of the pressure curve, shows that with the opening of the auriculo- 



ventricular valves, d, a large portion of 

 the volume of the blood in the auricles 

 flows quickly into the ventricles during 

 the early part of the diastole, nearly, if 

 not entirely refilling them, a procedure 

 occupying a period of time approxi- 

 mately that required for the systolic 

 discharge. In some experiments the 



.2 .3 .* . f . 6 jr .B .j& portion of the curve, recording the in- 

 FIG. ii9-THE VOLUME CURVE OF crea se of volume does not reach the ab- 



scissa but runs off parallel with it. In 

 other experiments it gradually approxi- 

 mates the abscissa or shows a slight fall at the time of the succeeding auri- 

 cular contraction. According to Henderson blood has ceased to flow 

 from the auricles into the ventricles during the foregoing period and the 

 contraction of the auricles adds but little to the volume of the blood already 

 in the ventricles. Other investigators attach more importance to this 

 event. 



The portion of the volume curve between the apex and the beginning 

 of the succeeding ventricular systole, embracing the entire diastolic period, 

 has been subdivided into two portions, viz. : (a) from the apex to the be- 

 ginning of the horizontal portion, corresponding to the period of relaxation 

 and refilling the diastole proper and (b) the period of rest or the diastasis. 

 This latter period is of rather short duration in the normal rate of heart 

 beat. It lengthens if the rate decreases, and shortens if the rate increases. 



The Movement of the Blood During the Cycle. From the char- 

 acteristic features of the foregoing record it is apparent that with the re- 

 laxation of the auricular walls, blood at once flows from the venae cavae and 

 the pulmonic veins into the auricular cavities and continues so to do through- 

 out the entire auricular diastole. With the relaxation of the ventricular 

 walls, however, the blood that has accumulated in the auricles up to this 

 time, or its equivalent coming from the venae cavae and pulmonic veins, now 

 flows into the ventricles until they are nearly filled. Before they are filled, 



