Behavioral effects of increased CO2 load in divers

The behavioral effects of elevated PACO2 were examined to clarify risks due to CO2 retention in diving. In two separate laboratory studies, experienced divers breathed 6% CO2 mixtures under normobaric conditions. Normoxic study: Subjects (n = 8) first breathed air (control); then 6% CO2, 21% O2, balance N2 (exposure); and then air again (postexposure). Hyperoxic study: Subjects (n = 10) first breathed 100% O2; then 6% CO2 in O2; and then O2 again. Subjects performed a test battery in each condition. In the control and postexposure conditions, tests consisted of simple and choice reaction time, postural sway, tremor, and hand steadiness. In the exposure conditions, only the simple and choice reaction time tests were performed. No significant performance decrements during CO2 exposure were found in either study. However, regression analyses indicated that changes in postural sway, tremor, and decision-making time after normoxic CO2 exposure were proportional to decrements in individual end-tidal PCO2 levels following CO2 exposure. We conclude that divers may be at risk for performance impairment immediately after a period of CO2 retention.