DETERMINATION OF SIZE OF HEART BY X-RAYS 467 



manner all that would be necessary to determine the heart v.ol- 

 ume from a given silhouette would be the knowledge of a constant 

 to multiply into cube of a given diameter, just as we may quickly 

 estimate the volume of a sphere from a knowledge of vr and the 

 radius of the sphere. The hearts of different individuals differ 

 somewhat in shape and vary also under different conditions in 

 the same individual. Furthermore it is difficult to place two 

 different individuals so that the heart will obstruct the x-rays 

 in an exactly equivalent manner. The best we can do is to use 

 methods which will give approximately equivalent heart sil- 

 houettes and make use of a formula for volume which will give 

 approximate volume. 



After considerable experimenting not only on the living but 

 on cadavers the position described above, sitting down, leaning 

 forward, and with the breath held at the end of a moderately 

 deep inspiration, was selected as that giving the most uniform 

 heart-silhouette with relation to heart volume. Study of the 

 volume of moderately distended hearts in cadavers in relation 

 to the areas of heart outlines drawn as described above so as to 

 correspond with the silhouette areas of x-ray plates led to the 

 establishment of the following formula for heart volume based 

 on silhouette area : 



0.53 A^'" A = silhouette area 



The estimates of heart volume given in tables A and B are 

 based upon this formula. For the sake of convenience the vol- 

 ume is given in round numbers in cubic centimeters. While 

 there is no direct method of testing the accuracy of this formula 

 in the living, dissecting room data may prove of interest in show- 

 ing how closely area and volume correspond. The method of 

 estimating the area in the dissecting room has already been de- 

 scribed, p. 438. The volume is determined by plugging the 

 orifices of the heart and then measuring the amount of water 

 or oil displaced by the heart. If the cavities of the heart are 

 empty they are filled with the fluid used for measuring the dis- 

 placement before the orifices are plugged. The aorta and pul- 

 monary artery are included in the volume to a level which 



