THE RELATION BETWEEN ALVEOLAR CARBON DIOXIDE TENSION AND SUSCEPTIBILITY TO DECOMPRESSION SICKNESS

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Abstract
The relation between alveolar CO2 tension and susceptibility to decompression sickness was investigated by comparing the CO2 tension in alveolar air collected shortly before decompression with the ability of the subject to remain for 2 hrs. in an altitude chamber at a pressure equivalent to 38,000 ft. The following results show that susceptibility increases with alveolar pCO2- Subjects were forced to descend whenever the alveolar pCO2 was more than 43 mm. Hg (7 cases). In contrast, no subject was forced to descend when his alveolar PCO2 was less than 38 mm. Hg (5 cases). Between 38 and 43 mm. Hg subjects were forced to descend on 57% of their tests (61 cases). Each subject whose tolerance varied during the course of these expts. passed fewer tests when his alveolar CO2 tension was high than when it was low. This was true both of spontaneous variations in tolerance and changes produced by ingestion of NH4C1. The latter substance was effective in reducing the susceptibility to decompression sickness of some subjects, but not all. The avg. alveolar CO2 tension tended to be low for both of 2 subjects who were always resistant to decompression and high for 4 of 8 subjects who were always forced to descend. The CO2 tension tended to be normal or low in the,4 remaining consistently susceptible subjects. Two of these may have been inadequately studied, and 2 were characterized by the recurrence of pain in some particular region. This suggests that the latter were individuals with special local conditions which caused unusual sensitivity to decompression. A similar circumstance appeared to exist in 2 other individuals who always had severe symptoms even when their alveolar CO2 tension was markedly lowered by NH4C1.

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