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.
Remedially, oxygen may be considered as it exists diluted in the atmosphere, or as prepared artificially for inhalation with a definite proportion of air.
Pure fresh air of the elevated country or the coast is of well-known efficacy in all conditions of debility, of chronic catarrh and chronic dyspepsia; sea-air especially contains more ozone than the air of land, and is of value to those who have lived in towns and followed sedentary occupations. On the other hand, patients with weak chests and readily congested lungs are better in a less rare and less ozonized atmosphere, since a large proportion of ozone may excite in them irritation of mucous membrane (Cornelius Fox). During epidemics of influenza an unusual amount of ozone has been verified in the air, while in cholera epidemics it has been almost absent. The choice of a climate for any given case is, however, generally influenced by other considerations than the mere amount of oxygen to be obtained; the subject need not, therefore, be fully considered in this place. The chief cases in which theory indicates, and experience justifies, the use of oxygen-inhalation, are those of asphyxia and of venous congestion occurring in the course of phthisis, asthma, or emphysema.
It has been proposed to utilize nitrogen by adding a larger than normal proportion of it to ordinary air for inhalation in irritable and inflammatory lung-condition, but no definite results have been obtained in this country. Steinbruck (Vienna) has, however, lately recommended nitrogen-inhalations in the first and second stages of phthisis in young persons, stating that "they lower the circulation and allay nerve-irritability, give great relief, and sometimes cure;" in the third stage they are injurious (Dobell's Reports, 1876). I have not seen any confirmation of these results. The power of nitrous oxide as an anaesthetic has been largely developed in recent times (v. Anaesthetics).