352 Pulmonic Interstitial Emphysema 



by accessory causes, may lead to PIE arid its sequelae. The accessory causes 

 already outlined are regarded as important. They may, indeed, be the deter- 

 mining factors in the precipitation of any given case of PIE, in the presence 

 of alveolar-base overstrain. Thus cough, straining at stool, etc., by raising 

 the intra-alveolar pressure in a region of alveolar ectasia, particularly if the 

 bases of the alveoli are weakened by an inflammatory process, may produce a 

 rupturing of the alveolar bases and leakage of air into the interstitium. In- 

 creased pressure in the alveoli is of great moment in this connection. Can it 

 alone cause PIE? That seems possible, as will appear from the discussion of 

 later cases. Certainly the combination of increased alveolar pressure and over- 

 distention of alveoli is a dangerous one. 



Again it is brought home that the functional anatomy of the lung is neces- 

 sary to an understanding of the response of the parts of the organ to abnormal 

 conditions. Aided by the data from experimental work we are enabled to 

 understand the origin and course of PIE, and even to predict in what type 

 of disease condition PIE may be expected. The testimony of recorded clinical 

 experience sustains our predictions. 



PIE FROM General Alveolar Overstrain 



So far we have dealt with clinical reports of human cases in which there may 

 be presumed to have been a PIE resulting from some local overstrain of the 

 alveolar bases, with complications. Even in these there may have been some 

 general overstrain as well as the predominating local one. In them elevation 

 of alveolar pressure, even though momentary, was regarded as very important. 

 We now wish to consider cases in which it is reasonable to assume that there 

 has been a general overstrain of alveolar bases on account of elevated pressure. 

 It is convenient to divide these into two categories: (i) Natural, and (2) 

 Artificial. 



Natural Overstrain Cases.~^he natural overstrain cases all show a severe 

 muscular effort characteristically for a short period, but one which may be 

 repeated; and when presumably the glottis is closed, so that the intrathoracic 

 pressure is raised and blood is prevented from entering the thorax, so that the 

 blood volume of the pulmonary vascular system is lowered and Factor "B" 

 is produced. Manifestations of PIE have been found in individuals who have 

 held their breath while lifting heavy weights," or tugging at heavy objects.^ 

 If strong expiratory efforts are made while the breath is being held the intra- 

 alveolar pressure is augmented; we have evidence of PIE occurring in women 

 during childbirth,^"' ^^ or in persons straining violently at stool.^^ Closely an- 

 alogous are the cases which occur even if the glottis is not completely closed 

 yet where there is sufficient obstruction in the airway to raise the intra-alveolar 

 pressure as expiratory efforts are made; then this pressure, combined with the 

 reduction in caliber of the pulmonary blood vessels arising through the pro- 

 longed interruption of venous return to the heart, will cause PIE. Thus we 

 find that PIE has been reported in patients with asthma;^^ with congenital 



