This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
This varies somewhat according as to whether the patient is wholly immersed in an atmosphere of air compressed to one-half to one atmosphere in a closed chamber for one or two hours, or whether he simply breathes it from a reservoir through a tube with closely fitting mouthpiece for twenty to sixty inspirations.
The former and older method, as carried out by Reichenhall, often caused oppression of head, tinnitus, and other disagreeable sensations, but had a sedative and equalizing effect on the circulation, slowing heart-action, raising arterial tension and altering the distribution of blood, lessening its amount in the veins and increasing it in the arteries. It increased also expectoration and excretion (Burdon Sanderson: Practitioner, vol. i.).
In the more recent method employed by Waldenburg and Biedert, the extra compression amounts to only 1/100 to 1/45 atmosphere, and the good results obtained are more clearly traceable to the extra amount of oxygen. Nutrition and blood-formation are improved, the "lesser circulation" is rendered freer and less congested, and at the same time the vital capacity of the lungs is increased. The alternate use of rarefied air, which induces rather opposite conditions, is employed in this method (Medical Times, ii., 1877). Certainly theory favors further trials of "pneumatic medicine," but we require more extensive experience before judging of its merits. Ducrocq, indeed, reports almost opposite conclusions to those of Burdon Sanderson (Archives Generale, September, 1876).
Mosso describes various anomalous results in the distribution of blood in the extremities under a pressure of two atmospheres, and explains them by changes in the innervation of the heart, or, with Paul Bert, by chemical, rather than by mechanical changes (Medical Record, 1879).
Workmen employed in making bridges, etc., under a pressure of two to three atmospheres, suffer from pains in the ears and joints, apparently due to "dilatation of superficial vessels," after leaving work. Among a large number of men no hemorrhage, heart disease, or serious disorder occurred (Medical Times, ii., 1877; cf. Moxon: British MedicalJournal, i., 1881, p. 496).