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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



arteries, but rather it keeps flowing in a curve from 

 the main direction of the inflow tract toward the 

 outflow tract. This translocation of blood within the 

 ventricle during the isovolumetric phase is energy pre- 

 serving. In fact, there seems to be rather little turbu- 

 lence and not always complete mixing of blood during 

 this "intraventricular" streaming from the inflow side 

 to the outflow region. This explains why the streamlin- 

 ing of flow in the venous circulation is not always com- 

 pletely interrupted by the passage of blood through the 

 ventricle. For example, the systemic venous blood is 

 transferred into the pulmonary arteries in such 

 manner that superior caval blood reaches predomi- 

 nantly the right lung and inferior caval blood the left 

 lung [see also Bucher et al. (27)]. Obviously, the 

 possibility of incomplete mixing deserves attention 

 when samples of so-called mixed venous blood are 

 drawn. 



How much does the velocity of the blood flow 

 decrease during the transit in the ventricle? In the 

 resting organism with a slow heart rate, the velocity 

 of blood streaming into the ventricle toward the end 

 of diastole is rather small, as may be surmised from 

 the fairly flat portion of the ventricular volume curve. 

 When the cardiac output is elevated, the velocity of 

 the intraventricular flow during isovolumetric con- 

 traction will probably increase for two reasons: /) 

 the velocity of end diastolic ventricular inflow in- 

 creases through a shortening of diastole due to high 

 heart rates and through a more forceful atrial con- 

 traction; 2) the transit time through the ventricle is 

 shortened by the more powerful and often shorter 

 myocardial contraction. Such higher intraventricular 

 flow velocities under sympathetic activity could then 

 result in a better energy conservation by not letting 

 the speed of blood flow slow down too much before 

 ventricular ejection begins again. 



[It is the feeling of the editors that there is not 

 sufficient evidence to show that continued transloca- 

 tion of blood within the ventricular cavity during iso- 

 volumetric contraction could contribute significantly 

 to the subsequent ejection. Ed.] 



2-4: Rapid and reduced ventricular ejection. As soon as 

 the pressure in the ventricular cavities exceeds that 

 in the aorta or the pulmonary artery, the blood is 

 suddenly ejected. Although flow is created by a 

 difference between the intraventricular and arterial 

 pressures, an inspection of pressure curves alone, 

 simultaneously recorded from the ventricle and the 

 root of the artery, furnishes only meager information 

 about the rate of volume flow and its time course. 

 However, from simultaneously recorded flow and 



fig. 15. Phase relationships between pressure and flow as 

 revealed by simultaneously recorded curves from the ascending 

 aorta of a conscious dog. Upper tracings: rate of volume flow 

 measured with a permanently implanted electromagnetic 

 flowmeter. Lower tracings: aortic pressures obtained through a 

 permanently implanted cannula leading to a strain gauge 

 manometer. A: curves from the quiet reclining animal. B: 

 curves from the animal running behind a car during moderate 

 exercise. [Original curves by the courtesy of Frederick Olm- 

 stead, Cleveland Clinic, Cleveland, Ohio (personal communi- 

 cation, 1961 ).] 



pressure curves in the aorta or in the pulmonary 

 artery, the process of ventricular ejection is now 

 fairly well understood [VVetterer (155)]. The ejection 

 starts abruptly (fig. 15). The blood column in the 

 root of the aorta, which is practically stationary at the 

 end of diastole and during isovolumetric contraction, 

 is rapidly accelerated and pushed toward the periph- 

 ery. The greatest flow acceleration occurs during 

 the steeply ascending limb of the aortic pressure 

 curve, so that the highest flow rate (peak of the 

 flow curve) is actually reached prior to the summit 

 of the pressure curve. When the flow then becomes 

 less rapid, the phase of reduced ejection is said to 

 begin. The border between rapid and reduced 

 ejection is quite arbitrary. When only pressure and 

 cardiometer curves were available [Wiggers (156)], 

 it was difficult to determine from the gradual leveling 

 off of the downward limb of the volume curve when 

 the rapid ejection started to slow down. The summit 

 of the ventricular pressure curve was thought to 

 indicate the end of rapid ejection (fig. 14). It is now 

 known that the flow slows down earlier, since the peak 

 of the flow curve definitely precedes the peak of the 

 ventricular or aortic pressure curve (upper tracings 



