428 C. R. BARDEEN 



studies of twenty-three boys in the supine and sitting positions 

 ('08) show an average difference of 7.6 per cent between the su- 

 pine and the sitting positions (extremes 2.6 per cent to 22.7 per 

 cent). For the average normal individual we may therefore 

 take 5 to 7 per cent as a conservative estimate of the reduction 

 in area which we may expect in the heart shadow area between 

 pictures taken in the prone and sitting positions when the patient 

 leans slightly forward in the latter position. These changes in 

 size of the heart associated with change in posture are due chiefly 

 to changes in hydrostatic pressure in the inferior vena cava. 

 To a large extent they may be overcome by binding the lower 

 extremities. As a rule but not always the pulse rate is faster in 

 postures in which the heart is relatively small. 



The effects of the respiration on the size of the heart seem to 

 be less constant. According to F. M. Groedel ('11) the heart 

 does not as a rule change in size during quiet respiration al- 

 though there is a slight fall of blood pressure during inspiration. 

 In forced inspiration there is a marked fall of blood pressure 

 which may be followed by a passive rising of the diaphragm and 

 a rise of blood pressure. At the height of deep inspiration the 

 heart, or at least the heart shadow, may be smaller than normal 

 owing to the pull of the pericardium. In three experiments in 

 the sitting position I found a decrease in the area of the heart 

 silhouette in expiration as compared with inspiration in two 

 instances (—2 per cent, —2.5 per cent), an increase in one in- 

 stance ( + 5 per cent), average +0.2 per cent. In the prone 

 position I found a decrease in the cardiac area during expiration 

 in two instances ( — 5 per cent, + 6 per cent) and an increase in 

 one instance, +4 per cent), average -2.3 per cent. In the 

 standing position I found an increase during expiration of 6.6 

 per cent and 9 per cent in two instances, average +7.8 per cent. 

 From these few experiments it would appear that in the prone 

 position, when the heart is relatively large in size, it tends to be 

 smaller during expiration, while in the standing position, in 

 which the heart is relatively small, the heart tends to be larger 

 during expiration than during deep inspiration. We need a 

 much more extended series of observations before this can be 



