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Diving, general meaning and difficulties

The collision of the «Andrea Doria» with a Swedish ship off New York harbor is still generally remembered as the biggest shipping disaster after the Second World War. Even today, four years after the sinking, the wreck of what was then the most beautiful ship of the Italian merchant navy lies at the bottom of the sea. Although the «Andrea Doria» still represents a value of several million Swiss francs, it has not yet been salvaged. After the First World War, the English were already able to lift the valuable ships of the German Imperial Navy, which had sunk itself in Scapa Flow, and thus to supply English industry for years with the best and cheapest steel scrap.

Report on the diving experiment in Toulon on the 4th of November, 1960

The effects of the increasing overpressure on the organism with increasing water depth can all be studied in overpressure chambers, which offers great advantages because of the direct observation possibilities and the elimination of all difficulties connected with the water itself, such as thermal insulation, visibility, etc. Thus, hyperbaric chambers were built and used already in the last century.

Respiratory Physiological Aspects of Diving

The medical-physiological difficulties of diving, especially deep diving, are closely related to respiration. The first to be mentioned is hyperoxia. Atmospheric air contains about 21% oxygen, giving an oxygen pressure in inspiratory air of about 140 Torr (mm Hg) at normal altitudes. In alveolar air the oxygen pressure is still 95, and in arterial blood about 90 Torr. This pressure is sufficient to saturate 95-97% of the hemoglobin of the red blood cells with oxygen. Therefore, in normal lungs, higher oxygen pressures do not allow much higher oxygen saturation of the hemoglobin.

Decompression, the safe resurfacing

The problem of greatest practical importance remains for diving, especially deep diving, decompression, the safe resurfacing. Most diving accidents and the so-called caisson disease are due to insufficient decompression. The problem is as old as diving and has always concerned divers' physiologists and medical advisors. What is it all about?

Experimental Decompression Research

Oxygen poisoning can be safely avoided by reducing the oxygen concentration in the gas mixture. The deep intoxication could be explained as carbonic acid retention, in extreme cases as carbonic acid narcosis. The increasing gas weight at overpressure makes breathing so difficult that when individually varying limits are exceeded, there is no longer sufficient ventilation. Hypoventilation, however, means an increase in carbonic acid tension in the alveoli and in the blood with all secondary effects on the circulation and consciousness.

The formula for the Bühlmann algorithm, which has been valid for years, is as follows:

pt tol i.g. = (p amb / b) + a
or
p amb tol = (pt i.g. - a) * b