(i) Experiments have been made on the incidence and time of onset of decompression sickness in mice exposed in single or repeated exposures to raised pressures of nitrogen or helium . If a first (conditioning) exposure to pressure is followed 5 min later by a second (test) exposure, the incidence of sickness is considerably higher than that for either exposure alone, or for a single exposure equal in length to the sum of the other two exposures. The same result is obtained if the conditioning exposure is to saturation. Sickness produced by repeated exposures has a shorter latency of onset than after single exposures. These results are explicable on the basis of asymptomatic bubble formation after decompression. (ii) This latent susceptibility to decompression sickness, as revealed by the test exposure, initially increases with time after decompression, reaches a maximum, and then declines. The rate of decline is faster than can be accounted for on the basis of the decay and local reabsorption of bubbles. It is suggested that gas bubbles are also removed by passage from the tissues through the venous system to the lungs. (iii) The degree to which very short second exposures to pressure (lasting only a few seconds) give rise to the symptoms of decompression sickness cannot be explained on the basis of the kinetics of bubble growth. These symptoms could also arise from compression by the second exposure of bubbles in the tissues, allowing them to enter the venous system and pass to the lungs, where, if expanded by decompression before elimination, they give rise to severe decompression sickness. (iv) These observations are in direct conflict with the principles on which current decompression tables are based. The relative success of the latter must be attributed to the empirical manner in which the tables have been constructed and modified in the light of experience.The results support the theory that separated gas may be present in symptomless decompressions and raise the question of gas transport to the lungs as a factor which should be taken into account in the design of decompression tables.
Experimental simulations of gas-driven eruptions: kinetics of bubble growth and effect of geometry
