Compressed air, as a therapeutic agent, in the treatment of consumption, asthma, chronic bronchitis, and other diseases / by Archibald Simpson ; with a preface by William MacLeod.
- Simpson, Archibald, 1790-1847.
- Date:
- 1857
Licence: Public Domain Mark
Credit: Compressed air, as a therapeutic agent, in the treatment of consumption, asthma, chronic bronchitis, and other diseases / by Archibald Simpson ; with a preface by William MacLeod. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![]4 logous to the actions of a pair of bellows, which will, obviously, be opened and closed with equal ease, whatever be the ])ressure of the atmosphere. But it is otherwise with the respiratory movements, as a little consideration of the forces in action, and the relations of the parts concerned, will show. In inspiration we have, on the one hand, tending to expand the chest, the force exerted by the muscles, and the pressure of the air entering the lungs ; on the other, tending in an opposite direction, the elasticity of the thoracic walls, the at- mospheric pressure on their external surface, and the elasticity of the lungs and bronchi. From the relation of the lungs to their con- tahiing cavity, although, in ordinary circumstances, the costal and the pulmonary portions of the pleura3 are constantly in contact, without being, save at their points of reflexion, united, there is yet, from the elasticity of the pulmonary tissue, a constant tendency to the formation of a vacuum in the pleural cavity. We know, that if, after death, the thoracic walls being contracted as far as possible, an opening be made in them, the lung will contract still farther. In life, then, while the walls remain perfect, the formation of a vacuum between the lungs and the walls of their containing cavity is prevented by the pressure of the air in the lungs acting against their elasticity, and not counter-balanced by a similar pressure on the pleural surface of the lung, as it is when air is admitted by puncturing the thorax. The correct statement, therefore, of the conditions necessary for inspiration, is, that the force exerted by the inspiratory muscles, plus the difference between the atmospheric pressure and the elasticity of the lungs, should exceed the resistance offered by the elasticity of the thoracic walls and the pressure of the atmosphere on them. It follows, then, that if the atmospheric pressure be diminished (or the elasticity of the lung increased), although it would, at first sight, appear that the expansion of the chest would be facilitated, in consequence of the diminished pressure on its exterior, yet, from the increased tendency to vacuum in the pleural cavity, the act of inspiration becomes, in reality, more diffi- cult of performance, as we know to be the case when the atmospheric pressure is diminished, by ascending to any great elevation above the ordinary level. On the other hand, if the pressure of the air be increased, or the elastic force of the lungs diminished, we have an opposite effect—the tendency to vacuum becomes less, and the lung following moi-e readily the expansion of the thoracic cavity, the act of inspiration is facilitated, and the expansion of the lung is increased, the air entering more freely into its vesicles, within certain limits. During inspiration, the difference between the atmospheric pressure, and the resistance offered by the elasticity of the lung, is constantly diminishing, the latter increasing as the lung is expanded. From considerations such as these, then, Dr Pravaz draAvs the fol- lowing conclusion :— Si Ton reconnait que la reaction des divisions bronchiques est une resistance qui croit avec I'expansion de I'organe; siI est certain, d'un autre cote, que dans les conditions ordinaires de](https://iiif.wellcomecollection.org/image/b21478478_0016.jp2/full/800%2C/0/default.jpg)
