Long-term intermittent exposure to high ambient CO2 causes respiratory disturbances during sleep in submariners

During most of the cruise, submarines are detached from their environment. Therefore, O(2) levels are relatively low (19 kPa, 144 mm Hg) and CO(2) levels are high (1 kPa, 7.6 mm Hg). There are, however, periods during ventilation of the submarine in which CO(2) levels drop and O(2) levels increase. The objective of this study was to determine whether these unique gas changes might result in sleep-disordered breathing in submariners.

The sleep of eight healthy soldiers was assessed three times: (1) control night, in submarine docking; (2) at the beginning of the cruise (reflecting acute exposure to gas changes); and (3) at the end of the cruise (chronic exposure to gas changes). Each night was divided to three parts because of different CO(2) levels (secondary to ventilation of the submarine). Sleep and breathing were measured using the portable Watch PAT100 device (Itamar Medical, Ltd; Caesarea, Israel) to detect breathing abnormalities during sleep.

Sleep and breathing data were categorized according to four CO(2) conditions: acute moderate (inhaled CO(2) levels of 2.3 to 5 mm Hg during first 1 to 2 nights of the cruise); acute high (inhaled CO(2) levels of 5 to 9.2 mm Hg during the first 1 to 2 nights of the cruise); chronic moderate (inhaled CO(2) levels of 2.3 to 5 mm Hg during nights 9 to 10 of the cruise); and chronic high (inhaled CO(2) levels of 5 to 9.2 mm Hg during nights 9 to 10 of the cruise). Respiratory disturbance index (RDI) was significantly higher in the chronic moderate CO(2) condition than the chronic high condition (18.9/h vs 8/h, p < 0.005). RDI did not correlate with CO(2) levels during the first nights of the cruise (R = - 0.2, not significant), but significantly negatively correlated with it during the last nights of the cruise (R = - 0.56, p < 0.05).

We conclude that during an 11-day cruise, submariners adapt to high CO(2) levels, as evidenced by the significant dependence of RDI on CO(2) during the final but not initial days of the cruise. This adaptation resulted in a significant increase in RDI when CO(2) levels declined during the later nights of the cruise.