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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 1 6. Phase relationships between aortic 

 pressures, Ao; left ventricular volume, LV, 

 (dots); atrial volume, LA, (open circles); 

 and electrocardiogram, ECG, in an anesthe- 

 tized normal dog with a spontaneous heart 

 rate of iio/min. The pressure tracings were 

 simultaneously recorded and correlated with 

 the volume measurement from the kinemato- 

 graphic frames. [Original curves and labeling 

 by courtesy of Peo Gribbe, Wenner-Gren 

 Research Laboratory, NorrtulPs Hospital, 

 Stockholm, Sweden (personal communica- 

 tion, 1 961).] 



PROTODIASTOLE 



EJECTION 



ISOMETRIC 

 CONTRACTION 



ISOMETRIC RELAXATION 

 RAPID INFLOW 



DIASTASIS 

 / ATRIAL SYSTOLE 



ORMOTHERMIA 36C 

 EART RATE 110 



0.5 sec 



the intraventricular pressure drops to the level of 

 the atrial pressure. The pressure decline, like the 

 pressure rise, is more rapid under the action of 

 epinephrine (158, 124) and apparently also in 

 exercise. Therefore, with epinephrine and during 

 exercise the duration of the isovolumetric relaxation 

 phase is shorter for the same pressure difference 

 between the incisura and atrial pressure. Neither the 

 precise moment of the valve opening at the end of 

 isovolumetric relaxation nor the pressure difference 

 necessary to actuate them has been satisfactorily 

 determined as yet. One usually takes the decline in 

 atrial pressure after the V point as an indication that 

 the atrioventricular valves have just opened and flow 

 through the orifice has begun. The crossing over of the 

 atrial and ventricular pressure tracings is therefore 

 taken as the end of isovolumetric relaxation. How- 

 ever, even with the most careful recording, it is 

 difficult to establish such a crossing over without 

 artifacts. Since at this part of the cardiac cycle the 

 heart has become a low-pressure system, instru- 

 mentation errors are commonly experienced with 

 positioning of pickup devices, movement artifacts, lack 

 of sensitivity, Bernoulli effect, and lack of a common 

 and reliable reference zero pressure level. 



5-7 : Rapid and slow ventricular filling. There is no 

 satisfactory procedure to measure directly the inflow 

 of blood from the atrium into the ventricle. The best 

 information stems from X-ray kinematographic 

 studies such as those of Rushmer (139), Chapman 

 et al. (31, 32), Gribbe et al. (56). A good time resolu- 

 tion was obtained by Gribbe, who took 40 to 50 frames 

 per sec using an image intensifier. The individual 

 frames of film were projected and the volume was 



calculated from the contrast silhouette of the left 

 atrium and ventricle, assuming that the left ventricu- 

 lar cavity resembles an ellipsoid of rotation. Figure 16 

 illustrates the steep upward slant of the curve during 

 the phase of rapid ventricular filling. The incline of 

 this part of the curve is even steeper than the decline 

 of the curve during rapid ventricular ejection, 

 indicating that blood actually rushes into the ven- 

 tricle faster than it is ejected from the ventricle. This 

 observation has an important bearing upon the 

 concepts of the forces which bring about ventricular 

 filling (see later section). After the rate of ventricular 

 inflow has reached its maximum, it begins gradually 

 to slow down until finally the curve tends to level 

 off. There is no distinct break which could serve as a 

 criterion for precise determination of the end of the 

 rapid filling phase and the beginning of the slow 

 phase. Nevertheless, the distinction between these 

 two phases remains useful at slow heart rates, as for 

 instance under strong vagotonic influence, because 

 the slow phase of ventricular filling then lasts much 

 longer than depicted in figure 16. 



7-1 : Filling by atrial contraction. With the contraction 

 of the atrial myocardium an additional volume of 

 blood is pushed into the ventricle, as shown by the 

 sudden final incline of the curve in figure 16. The 

 contribution of atrial contraction to ventricular 

 filling has been much debated [see Mitchell et al. 

 (113)]. According to the measurements of Gribbe 

 et al. (56), it should amount to about 20 to 25 per cent 

 of the volume entering the ventricle. Atrial pressure 

 drops after the peak of atrial systole but seemingly 

 without a measurable decrease in ventricular volume 

 by backflow through the atrioventricular valves. 11 



