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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



ously as soon as ventricular ejection ceases. It is 

 likely that contractions of muscle fibers in the conus 

 arteriosus tend to make the valve rings more narrow 

 during ejection, as discussed in an earlier section. In 

 this manner axial velocity of flow is increased and 

 turbulence, which may prepare the valves for closure, 

 is enhanced. At the end of systole when ejection 

 ceases, the forward movement of blood in the root 

 of the artery continues for a very brief period. Then, 

 the action of the eddies on the upper surface of the 

 valves prevails over the force exerted from below 

 (rapidly falling intraventricular pressure). Hence 

 the retrograde surge of blood toward the ventricle 

 (see fig. 15) is arrested by valve closure, and marked 

 pressure differences between the relaxing ventricle 

 and the elastically distended aorta can develop. 



VENTRICULAR AND ATRIAL VOLUMES 

 IN VARIOUS ACTIVITIES 



Certainly one of the most important features of a 

 pump is the volume which can be propelled per 

 stroke. This is easy to measure in a mechanical pump, 

 but it requires complex and sophisticated instru- 

 mentation to determine the stroke volume of the 

 intact heart. Successful attempts in this direction have 

 recently been reported, e.g , by Rushmer ( 1 39) and 

 his school, by Hawthorne (67), and by Olmstead 

 (personal communication). Nevertheless, numerous 

 questions remain still unanswered, namely, a) the 

 quantitative correlation of the stroke volume with the 

 other parameters of cardiac activity, and b) the 

 relationships of the ventricular stroke volume to the 

 volumes remaining in or passing through the atria, 

 the ventricles, and the large vessels. At the present 

 time most of these questions can only be approached 

 under highly controlled situations which limit the 

 significance of the experiment. Discrepancies are 

 therefore encountered depending upon the method of 

 approach used. At this point, it must also be re- 

 marked that heart volumes have traditionally been 

 measured by X-ray or cardiometer techniques which 

 include the volumes of the walls. Only recently have 

 radiopaque dyes and other media been developed 

 which permit measuring the content of the cardiac 

 cavities and not their over-all volumes (56). Conse- 

 quently a large part of the data incorporated in the 

 literature require critical attention. In this chapter, 

 the word "volume" refers exclusively to the liquid con- 

 tent of the cardiac cavities and excludes the volume oc- 



cupied by the walls and by the blood-filled vessels or 

 channels in the walls. 



I 'entricular Volume 



To describe the changes in ventricular volumes 

 under dynamic conditions, it is advisable to review 

 the modern terminology introduced bv Rushmer 

 (139). This terminology is illustrated and somewhat 

 expanded in figure 20 by drawing a parallel between 

 the familiar lung volumes (left) and the ventricular 

 volumes (right). 



The stroke volume of the organism at rest corre- 

 sponds to the tidal volume of respiration. In exercise 

 the ventricle can also eject some of the blood which 

 at rest would remain in the ventricular cavity at the 

 end of systole. Rushmer suggests the term "systolic 

 reserve volume" for that additional amount of blood 

 which is not ejected under resting conditions, but can 

 be maximally ejected with a more forceful contrac- 

 tion. This corresponds to the expiratory reserve 

 volume of the lungs. The volume of blood left in the 

 ventricle after a normal systole used to be called 

 "residual volume." Rushmer restricts the term 

 residual volume to that amount of blood remaining 

 in the ventricle after maximal ejection. Then the 

 term corresponds truly to the lung residual volume. 

 The ventricle can also increase its stroke volume by an 

 augmented venous return during diastole and sub- 

 sequent ejection of this extra volume in addition to 

 the resting stroke volume. The term "diastolic 

 reserve volume" defines the maximal amount of 

 blood which the ventricle can receive and then eject 

 in addition to the normal diastolic inflow. This 

 volume corresponds to the inspiratory reserve volume 

 of the lungs. The resting stroke volume, systolic 

 reserve volume, and diastolic reserve volume together 

 define the maximal stroke volume, which corre- 

 sponds to the vital capacity of the lungs. 



The parallelism can be carried even further (fig. 

 21). In the resting organism, the amount of blood 

 remaining in the ventricle at the end of ejection 

 (called by some authors the "end-systolic volume") 

 would best be referred to as functional residual capac- 

 ity since it is now customary to use the term capacity 

 for the sum of two or more "volumes." ("Capacity" 

 does not imply something that is absolute or fixed, 

 despite the unfortunate analogy suggested by the 

 age-old and uneradicated expression "vital capacity.") 

 The functional residual capacity of the ventricle 

 comprises the systolic reserve volume plus residual 



