566 



HANDBOOK OF PHVSIOLOGV 



CIRCULATION I 



DOG 65 KILOS MAY 4 1904- INSPIRATION EXPIRATION 



FIG. 12. Henderson's cardioineter, left, with calibrated record below. [From Henderson (73).] 



INSPIRATION 



ments in the method of recording the cardiometer 

 curve (though they neglected the consequences of 

 pressure change mentioned above) and, by taking 

 simuhaneous optical records of intraventricular, 

 aortic, and atrial pressure pulses, worked out the basis 

 for widely published diagrams of the relations between 

 these records. These diagrams are of inestimable value 

 in understanding and teaching cardioclynamics. 



The cardiometer cannot be used in measuring the 

 stroke volume of a heart beating normally within the 

 closed thorax. This, of course, limits its usefulness. 

 Nonetheless, the instrument has served very im- 

 portantly in analyzing the inechanism of cardiac 

 regulation. 



X-RAY CARDIOMETRY 



It has been thought possible to gain information 

 concerning cyclic changes in the size of the heart by 

 the use of the X ray. At first, timed short exposures 

 were made during diastole and systole (97). From the 

 corrected systolic and diastolic shadow areas the cor- 

 responding volumes were calculated (3, see also 70). 

 The differences in the two volumes should give the 

 summated stroke volumes of the two ventricles. Un- 

 fortunately, the resulting figure was nearer the stroke 

 volume of a single ventricle, a circumstance which 

 illustrates the essential weakness of the method. The 

 X ray cannot visualize the ventricular roof and the 

 pumping action which this partition does is consider- 

 able (67). 



Another radiological technique which has been 

 proposed is rontgen kymography . The outline of the 



heart is photographed through a set of narrow hori- 

 zontal slits I cm apart. During the time of one or two 

 cardiac cycles, the slits move down i cm. The move- 

 ment of the walls of the heart are traced on the film 

 much as would be those of a writing point on a kvmo- 

 graph. Connecting the systolic and diastolic points on 

 the film permits outlining the systolic and diastolic 

 areas and, from these areas, calculating the volumes 

 as outlined above. This procedure, though more 

 elegant, suffers from the same handicap in not visu- 

 alizing the A-V septum. An empirical constant can, 

 however, be applied to the kymographic movements 

 of the left ventricular wall which gives reasonable 

 agreement with the stroke volume as measured by 

 dye injection (79). 



The fluoroscopic image of the heart differs not only 

 in size but also in intensity during the cardiac cycle. 

 The intensity varies inversely with the amount of 

 blood contained in the heart, which acts as a filter 

 between the .source of the rays and a small fluorescent 

 screen, the luminosity of which is inxersely propor- 

 tional to the effective thickness of the heart. The 

 changes in luminosity of the screen can be sensed by 

 a photomultiplier and the proper circuity so that a 

 graphic record is obtained of the changing volume of 

 blood in a sector between the X-ray tube and the 

 small fluorescent screen. The record is of admirable 

 clarity and has a similar appearance to the mechani- 

 cally recorded ventricular plethysmogram. However, 

 the record must be calibrated empirically against 

 known stroke volumes with the use of a phantom 

 which produces deflections similar in amplitude to 

 those produced by the heart (i 14-1 16). 



Rushmer has pointed out that an approach to the 



