Abstract

The range and ability to fix CO2 of soda lime employed in the oxygen aqualungs used by Naval commandos (n=20) have been assessed as a function of different underwater swimming speeds. A fictitious and very low value was set for the threshold concentration of CO2 of 5000 ppm (0.5%) and measurements were taken of the time taken to reach this value depending on what activity was being carried out. It is well-know that inspiratory concentrations of up to 1.5% can be tolerated for days at a time. The initial stage of the study included simulation of ventilation by means of a pump which introduced a flow of pure CO2 (1.5 l min-1) into the soda lime capsule; the threshold was reached on average in 2 hrs 15 min. Thereafter a number of operators (n=3) were studied during swimming in a pool against the current at a speed while at the higher the subject completed the test in 30 min owing to muscular exhaustion, without reaching it; 2.4 knots is, however, a speed that is rarely reached. Having prolonged the test, after 3 hrs 15 min swimming the concentration value of CO2 was 0.8%. A third test stage in the open sea (n=14) highlighted that after 4 hrs 30 min swimming underwater the concentration was still tolerable at around 1.5%. Further, at the end of two underwater swims, of respectively 3000 and 5000 m, the soda lime capacity was still such as to halve the concentration at the end of the test in 5 min: in the first case at a value of 0.03%, in the second 0.1%. No hypercapnic symptom was reported. A number of comments are made regarding CO. The paper closes by considering possible the programming of an oxygen immersion at constant speed with intervals of faster speeds once each single operator's capacity ''curve'' is known. Verf.-Referat