FUNCTIONAL ANATOMY OF CARDIAC PUMPING 



785 



fig. 22. Effect of spontaneous respiration on right ventricu- 

 lar stroke volume, measured by the directly recorded pulmonary 

 blood flow in an anesthetized normal dog. The simultaneously 

 recorded pattern of right atrial filling (represented by superior 

 vena cava flow), arterial, venous, and intrathoracic pressures 

 permit a time correlation. Tracings from top to bottom: time 

 and base line, aortic pressure in mm Hg, pulmonary artery, 

 superior vena caval and intrathoracic pressures in mm water, 

 pulmonary arterial and superior vena caval flows in ml/min. 

 A = beginning of inspiration; S = acceleration of superior 

 vena caval flow during ventricular systole; D = acceleration 

 of superior vena caval flow during ventricular diastole. Stroke 

 volume (in ml) entered under pulmonary arterial flow curve. 

 Flow (in ml) through superior vena cava during each cardiac 

 cycle entered at bottom of record. Electrical frequency re- 

 sponse of both flowmeters reduced from 400 to 40 cycles/sec. 

 Superior vena caval pressure curve damped. [From Brecher & 

 Hubay (21).] 



estimates of Holt (77) with dye dilution techniques, 

 which range from 30 to 76 ml for a dog of 1 5 to 1 6 kg 

 in weight. This enormous discrepancy cannot be 

 reconciled at present. Simultaneous determinations 

 under rigidly controlled conditions with both methods, 

 the cineangioradiography and the indicator dilution 

 technique, may elucidate this point. 



That the situation is equally unsettled for measure- 

 ments in man is shown by the work of Rushmer 

 (139), Chapman et al. (32), Nylin (122), Reindell 

 et al. (134), Folse et al. (47), Luthy (personal com- 

 munication, and 106). Generally, determinations 

 using roentgenologic technique furnish smaller values 

 for the functional residual capacity than measure- 

 ments with dye dilution techniques. For instance, 

 Folse et al. (47), employing radio-iodinated Diodrast, 

 found in 20 resting persons that the left ventricular 



stroke volume averaged 42.2 ± 8.8 ml per m 2 of body 

 surface area. The diastolic capacity averaged 90 ± 

 26 ml per m 2 (functional residual capacity 48 ml/m 2 ). 

 On the other hand, Luthy (106) found with thermo- 

 dilution techniques that in normal patients the left 

 ventricular stroke volume amounted to 45 ml per 

 m 2 of body surface (range 39-57 ml/m 2 ) but the 

 diastolic capacity to 145 ml per m 2 (range 128-173 

 ml/m 2 ). According to these data the stroke volume 

 would be only one-third of the diastolic capacity 

 [39 %, Folse et al. (47); 31 ';, Luthy (106)] whereas, 

 in the dog it is apparently about two-thirds (60%, 

 Gribbe). 



The problem is further complicated by the fact 

 that the ratio of stroke volume to functional residual 

 capacity changes markedly under various normal and 

 pathological conditions. This is well illustrated by 

 the observation that a great increase in resistance to 

 ventricular ejection (e.g., in extreme hypertension) 

 causes the heart size to become much larger while 

 the stroke volume decreases. This implies a large 

 increase in the functional residual capacity. Direct 

 evidence for an increase in functional residual 

 capacity under this condition is the observation that, 

 when the aortic resistance is suddenly reduced by 

 opening of an arteriovenous shunt, the first stroke 

 volume is twice the normal size [Hamilton (61)]. 

 From the foregoing it is obvious that much more 

 information based on direct measurements of heart 

 volumes under various conditions is needed. 



Atrial Volume 



The volume of blood contained in the atrium at 

 any time has evoked much less interest than the 

 ventricular volume. No quantitative information 

 has been available until recently. Even the termi- 

 nology of atrial blood volumes is more difficult to 

 define than that of ventricular volumes. During two 

 phases of the cardiac cycle (isovolumetric contraction 

 and isovolumetric relaxation), the ventricle contains 

 a definite volume because the atrioventricular and 

 semilunar valves lock the ventricular content. The 

 atria, however, are always open on the venous inflow 

 side. On the outflow side they are closed only from 

 the beginning of isovolumetric ventricular contraction 

 to the end of isovolumetric ventricular relaxation. 

 Consequently, the volume contained at any one 

 instant represents the balance of almost continuously 

 changing inflow and outflow. 



The changes in atrial volumes can be understood 

 by following the atrial volume curves (open circles) 



