Hematologic changes after two exposures to 6.7 ATA air at three-day intervals.

Hematologic parameters were studied in human subjects exposed to various diving regimens. A series of exposures in a dry chamber to a simulated depth of 188 ft of seawater gauge (fswg), 6.7 ATA, utilizing compressed air, were carried out according to standard Navy diving tables. The subjects were serially followed for a control period prior to diving and subsequently for up to 1 wk. Little significant change occurred except for alterations in some platelet factors. In another series of experiments, the single excursion was followed by a second dive to 188 fswg 3 days later, again with appropriate hematologic monitoring. A pronounced eosinopenia and increased clotting times were observed soon after reaching the surface. Platelet depletion associated with increased clumping and elevated megathrombocyte levels persisted long after the second excursion. A latent hemodilution also developed 3--5 after the second dive. These findings clearly demonstrate that repeated hyperbaric exposures produce additive effects and further suggest that no diving procedure is completely innocuous.