Macklin and Macklin 363 



it may be well demonstrated by lateral X-ray films; the effect of its presence 

 may be listened to with a stethoscope, and it may be operatively removed. 



Airblock is localized mainly, and frequently altogether, in the mediastinum 

 and limg, and involves the pulmonary circulation primarily. It is the com- 

 bined effect of the interference of aberrant air with the circulation of the blood 

 and the respiratory movements of the lung. It results (a) from impingement 

 of bubbles of air on the pulmonary arteries and veins, and upon the heart 

 and great vessels in the mediastinum, which is particularly serious when the 

 pressure in that space rises above that of the atmosphere; and (b) from im- 

 mobilization of large areas of the lung by air bubbles locked in the connective 

 tissue. It is relieved naturally, to some extent at least, by escape of air from 

 the mediastinum into adjoining regions, including the pleural cavity. When 

 the pressure of the extravasated air in the metamediastinal parts, as the root 

 of the neck, or retroperitoneal region, becomes raised, there is interference 

 with the blood flow in these regions, and the airblock field is thus extended. 

 This field may be, therefore, in its most expansive form, subdivided into three 

 parts: pulmonic, mediastinal, and metamediastinal. Airblock is clinically 

 sensed by the airblock syndrome, which includes dyspnea, cyanosis, and in- 

 spiratory thoracic fixation. It may be confused with heart disease. There may 

 be accompanying signs of spread of air beyond the confines of the medias- 

 tinum. Retroperitoneal air may cause abdominal pain, simulating abdominal 

 disease. Airblock may be overcome by the bodily defense powers, the air being 

 absorbed into the blood stream, but, on the other hand, it may weight the 

 scales in favor of death. 



A special survey of the literature has revealed a multitude of human cases 

 of different kinds which show evidence of PIE and sequelae, with airblock. 

 All of these are regarded as arising from overstrained nonpartitional alveolar 

 bases which are subjected to unbearable pressure. Alveolar ectasia (usually 

 called alveolar "emphysema") is a very potent exciting cause, since it produces 

 attenuation and weakening of these vulnerable bases. Sudden overstrain is 

 regarded as more important than gradual, as in the latter sort there is time for 

 protective circulatory and other compensatory adjustments to be made. Local 

 alveolar ectasia is regarded as more serious than general, as there is, in the 

 former, more scope for excessive stretching of the nonpartitional bases to 

 take place. Increased intra-alveolar air pressure is also an important exciting 

 cause, and may be set up in a number of ways, all, excepting those of environ- 

 mental induction, coming under the heading of strong expiratory effort, par- 

 ticularly when the glottis is closed. The important predisposing cause is 

 diminution in volume of part of the lung, as the remaining part must then 

 become overexpanded, with overstretching of the nonpartitional bases. Atelec- 

 tasis is the most common volume-reducing condition, and may be single or 

 multiple, large or comparatively small. It may follow occlusion of the bronchi 

 from within or from without. The type due to impaction of foreign bodies 

 is serious because of its sudden production. Atelectasis is frequent in diseases 



