Macklin and Macklin 353 



stenosis of the larynx, or in obstruction to the outflow of air from the bronchial 

 tree of any variety whatever;'^ with violent cough whatever its origin;"' '■•*^ 

 and also in patients who have been blowing against an obstruction, as into 

 a wind instrument or a blow gun.'* In all of these, elevated intra-alvcolar pres- 

 sure associated with Factor "B" may be postulated. The possibility of atelec- 

 tasis with compensatory emphysema exists in some of these cases with lung 

 disease, as indeed it does in any of these cases; biu it seems reasonable to 

 assume that such simple conditions as weightlifting, childbirth, etc., would be 

 unassociated with it as a general rule. 



The cases of prolonged muscular exertion, but without the holding of the 

 breath or any obvious elevation of the intra-alveolar pressure, should be men- 

 tioned here. Scott"' found pneumomediastinum, or pneumothorax, in athletes 

 who had run a long hard race, some hours after the race was over, and here, 

 we feel, PIE must have been the precursor. Failing heart, with supervening 

 Factor "B," can hardly be ruled out here. The lungs had been ventilated to 

 the full for a long period. There was no suggestion of atelectasis, though we 

 think this a possibility. 



Abrupt Decompression.— On the borderline between the natural and arti- 

 ficial overstrain cases are those which show PIE from too abrupt a decompres- 

 sion, as in leaving caissons'^ or escaping from submarines. The latter is of 

 particular naval importance at the moment of writing, and is an accident 

 which occurs in men being trained in the technique of ascending from deep 

 levels of water, when they fail to obey orders.™"' The recruits are taught to re- 

 lease themselves from diving bells at various levels, and to ascend with relative 

 slowness to the surface, pausing at different depths, and all the while to breathe 

 in and out of a bag attached to the mouth. The nose is held by a clip, and the 

 bag has a flutter-valve attachment which permits adjustment of pressure wathin 

 the bag and thus within the lungs as the person ascends. This prevents the 

 overexpansion of the air in the alveoli as the pressure on the outside of the 

 chest lessens during the ascent, as would be the case if the man held his breath. 

 Now this impulsion to hold the breath during the ascent is said to be over- 

 mastering in some men, and when this is done during rapid ascent the air in 

 the lungs expands, causing generalized increase in pressure and such over- 

 inflation as is possible in the confines of the thorax. At the same time the pul- 

 monary blood-vessel caliber is reduced on account of the obstruction to inlet 

 of blood into the thorax. Factor "B" would thus be in operation, as w^ell as 

 Factor "A" to some extent. In these cases, not only does air make its way into 

 the interstitial connective tissue of the lungs (PIE) but also into the pulmonary 

 capillaries in the form of fine bubbles,"' so that cerebral gas embolism results. 

 Blood likewise makes its escape into the alveoli, and bloody frothy sputum 

 may emerge from the mouth and nostrils. If the amount of air escaping into 

 the pulmonary blood vessels is large it gets churned into a frothy mass in the 

 left side of the heart and the victim succumbs rapidly. 



The important thing for us is that PIE is present, and that it is produced 



