U. Solimene, Vincenzo Condemi, Sergio Borghi, Angelico Brugnoli, Tullio Marzi

Centre for Research in Medical Bioclimatology, Biotechnologies, and Natural Medicines — State University of Milan, Osservatorio Meteorologico Milano Duomo, ITIS Molinari — Milan, Italy

Survival is possible for a few weeks without food, for a few days without fluids, but just for a few minutes without breathing. Hence the importance of studying the issues tied to the actual oxygen levels in the atmosphere.

Oxygen appeared in the atmosphere two billion years ago and reached the current rate approximately five-hundred million years ago. As is also well known, the oxygen concentration is a constant value, expressed as a 20,93% rate of all the other gases contained in air.

Based on specific temperature, relative humidity, and atmospheric pressure values, appropriately re-calculated, the oxygen concentration is subject to fluctuations that need to be considered in view of possible and potential biomedical applications. Using the status equation for dry air based on Dalton’s Law on partial gas pressures, different oxygen density values per cubic metre can be obtained, available to aerobic living organisms.

This paper is aimed at laying the foundations for the appropriate assessment of the possible physiological and pathophysiological effects of subsequent changes in pO2, using an interesting bioclimatic context — the City of Milan — as an example for a basic analysis.

The value of oxygen density, which is not constant in time and in space, has been assumed to have a biomedical significance.

Following preliminary studies carried out on sets of weather data for the October 2005/ September 2006 period, as observed by the Weather Station owned by the Milan State University and in accordance with important sector-specific studies carried out in Russia, typical seasonal trends in oxygen concentrations have been confirmed with a value range — for the studied period — of 305÷ 258 expressed in g/m3, with possible implications (either in the short or in the long term) for the pathophysiology of the respiratory tract.

The higher quantities of this gas available during the winter and its negative peaks during the three summer months tend to decline in the so-called urban heat isle, both in the summer and in the winter, generating a special bioclimatic effect that involves a sharp reduction in thermo-hygrometric ranges, with a clear shortening of the seasonal and annual oxygen density range. In a comparable bioclimatic environment, more interesting biomedical elements appear for the bioclimates that show clear and definite fluctuations of the physical magnitudes considered, both in an instant time range (few hours, one day, a few days) and in the comparison between the minimum and maximum annual temperature, relative humidity, and pressure values, and thus, by translation, in climatologically significant and wide enough time ranges. The range between the minimum and maximum oxygen density values, in these cases, clearly tends to expand significantly (consider, for example, continental climates) based on the climatological classification of W. Koeppen.

In order to ascertain significant correlations between different O2 concentration values and different diseases affecting the airways, and in view of a possible creation of climatotherapic basins, the processed oxygen density values were crossed with the Emergency Room data available for the City of Milan (ER Triage) for specific diseases involving the airways (allergic asthma, bronchial asthma, chronic obstructive bronchopneumopathy, etc.) and for a very interesting pilot symptom often observed in patients accessing the ER, namely dyspnoea, not confined to the respiratory tract but rather extended to other pathological forms. The cross-analysis between the environmental values and the clinical data does not seem to confirm the original assumption, thus including the variability of oxygen density among the secondary factors that require more in-depth studies built on an advanced statistical basis. For the observed diseases, on the other hand, environmental factors, such as sharp temperature changes and pollutant concentrations (in particular PM10, PM2.5, and ultrafine particles) seem to be more significant; for these, a statistically significant correlation has been demonstrated, in accordance with a wide international peer-review scientific literature.