120 DISEASES OF THE PARENCHYMA OF THE ^(JNG. 



merit of the heart by the lungs, or of depression of the diaphragm and 

 liver. If an emphysematous lung did indeed exercise a pressure inward 

 and downward, did it really dislocate the heart and the liver, it is to be 

 presumed that this pressure would also act outward upon the inner wall 

 of the chest, and oppose an obstacle to its contraction during expiration. 



The supposition of centrifugal pressure of an emphysematous lung 

 against its neighboring parts is due, partly to erroneous physiological, 

 pathological, and anatomical assumptions, and in part to confusion of 

 emphysema with that condition which we have described as permanent 

 inspiratory expansion of the air-cells, and upon whose distinctness from 

 emphysema we have already insisted.* 



This demonstration will serve to show that emphysema has no 

 influence in impeding either the inspiratory expansion or the expira- 

 tory contraction of the thorax proper. The respiratory movements of 

 the diaphragm, however, are very differently affected, in this respect, 

 from the movements of the ribs. The diaphragm, which descends dur- 

 ing inspiration upon relaxation of its muscles, returns to its inspiratory 

 position, partly through the upward pressure of the abdominal viscera, 

 partially by the traction of the elastic lung upon its upper surface ; but 

 it can easily be proved that the latter force plays the most important 

 part in this process. In those cases of very relaxed abdominal walls 

 occurring after repeated pregnancy, where all pressure upon the dia- 

 phragm on the part of the abdominal viscera is out of the question, the 

 diaphragm still ascends during expiration; nay, as long as the thorax 

 remains closed, it preserves this position in the cadaver, even after all the 

 viscera of the belly have been removed. It does not relax and sink until 

 the thorax is opened, because the suction of the lung upon its upper 

 surface does not cease until then. Hence it is clear that the loss of 

 elasticity, which the lung suffers by emphysematous attenuation of its 

 tissues, may considerably impede the return of the diaphragm to its 

 expiratory state, and sometimes may completely prevent it. Thus the 

 cooperation is lost of the most important muscle of respiration, upon the 

 free exercise of which the expansion and contraction of the chest, and 

 with it the renovation of air in the vesicles, mainly depend ; and we 

 may designate, as the second great factor of the dyspnoea of emphysem- 

 atous persons, the permanently inflated condition^ or, as more com- 

 monly is said, the permanently depressed state of the diaphragm. 



To these, however, in many cases, if not in all, a third cause is to be 

 added. In many emphysematous patients the structural alteration of the 



* In the permanent inspiratory expansion of the air-cells, resulting from obstruc- 

 tion of the more minute bronchi, the air, which is confined in the cells, and com- 

 pressed during expiration, does indeed hinder the thorax from returning to its normal 

 condition of expiration 



