CO2 retention during hyperbaric exercise while breathing 40/60 nitrox
Kerem, D.; Daskalovic, Y.I.; Arieli, R.; Shupak, A.
Undersea and Hyperbaric Medicine Journal of the Undersea and Hyperbaric Medical Society Inc 22(4): 339-346
1995
ISSN/ISBN: 1066-2936 PMID: 8574121 Document Number: 452425
We evaluated CO-2 retention in 24 Navy construction divers breathing air at 1 atm abs (101.3 kPa) and 40% O-2 (40/60) nitrox at 4 atm abs (PO-2 of 162.1 kPa) inside a pressure chamber. The divers sat immersed to the sternal notch and exercised against pneumatically loaded pedals at a ovrhdot V-O-2 of approximately 1.3 liter/min. The mean end-tidal CO-2 tension (PET-CO-2) at 1 atm abs (45.7 +- 5.0 SD torr) was significantly higher than that of nondivers and diving trainees (40 +- 5.0) but did not increase significantly at depth (47.1 +- 6.3). The ranking of CO-2 retention was not maintained at depth. Unpredictable upward and downward shifts of up to 10 torr occurred in some divers. The PET-CO-2 of six of the divers at pressure was greater than 50 torr, which based on animal studies markedly increases the risk of central nervous system oxygen toxicity. We translated their values into individual depth limits with 40/60 nitrox: three with 50 lt PET-CO-2 lt 55 torr were forbidden to dive beyond 25 m and three with values gt 55 torr were restricted to 20 m. We propose that whenever possible, PET-CO-2 during exercise at pressure be measured in potential nitrox users and that the above PO-2 limits be enforced on moderate and extreme CO-2 retainers, respectively.