Macklin and Macklin 365 



tory efforts, particularly against obstruction. In the discussion, an effort has 

 been made to visualize the vascular sheaths under the influence of what we 

 have termed "Factors 'A' and 'B.' " Factor "B" is important wherever it exists, 

 and seems to be particularly so in those cases of PIE arising after prolonged 

 muscular effort, as in young men who have just run a "marathon." 



There is a type of case where the chest is suddenly decompressed, causing 

 air in the alveoli to assume a plus pressure relative to that of the environment. 

 Faulty submarine escape is listed here. The decompression phase of bomb blast 

 may also produce overstrain from this cause, but authorities tend to regard 

 the compression phase as the more important. 



We have attempted to divide the cases of PIE into two groups depending 

 on whether the nonpartitional bases show local or general overstrain, but 

 it is difficult to draw a sharp line here. The important cases arising from 

 overstrain from too high pressure in intratracheal anesthesia and in arti- 

 ficial respiration may be more general than local in base involvement. Hered- 

 ity seems undoubtedly to predispose to PIE. 



We have found in the literature so much evidence of unsuspected PIE and 

 its sequelae, with airblock, that we are impelled to believe that the condition 

 is much more prevalent than is realized by the medical profession. We there- 

 fore urge that clinicians be on the lookout for evidences of airblock, that they 

 take all possible means to diagnose it, particularly by X ray, and that they 

 relieve it by surgical intervention whenever it is deleterious to the patient. 

 It seems more than possible, too, that preventive medicine can do something 

 to lower the incidence of PIE. We feel that our predictions of the widespread 

 occurrence of PIE and the types of disease in which it was to be found, made on 

 the basis of our knowledge of the functional anatomy of the parts concerned, 

 have been fulfilled, and that the light shed on the condition has already en- 

 abled clinicians to see their way more clearly and helpfully. Much remains to 

 be done, but we feel that the anatomical approach to such problems will in 

 the future, as in the past, lead to valuable kno^vledge. 



Final Note 



Anent our emphasis on atelectasis as a cause of PIE, the paper of Wyatt,^^ just 

 published, is of great interest. He finds, in a series of 135 cases of pneumonia 

 in children, that no less than 26, or 19 per cent, had atelectasis demonstrated 

 roentgenographically. Although he does not mention PIE, nor pneumo- 

 mediastinum, as being present in his atelectasis cases, four of the lateral 

 roentgenograms which he reproduces in his article are, in our opinion, sug- 

 gestive of air in the mediastinum, and, inferentially, of PIE. 



A letter has also just appeared in the Laiicet by E. Montuschi^ on the sub- 

 ject of airblock in lung blast, in which he refers to the technique of L. Con- 

 dorelli"' for entering the anterior mediastinum to remove air. "The approach," 

 he says, "is from the suprasternal notch, downward, with a curved needle slid- 

 ing behind the posterior aspect of the manubrium sterni." Montuschi states 



