Assessment of the interaction of hyperbaric N2, CO2, and O2 on psychomotor performance in divers

Abstract

Diving narcosis results from the complex interaction of gases, activities, and environmental conditions. We hypothesized that these interactions could be separated into their component parts. Where previous studies have tested single cognitive tasks sequentially, we varied inspired partial pressures of CO2, N2, and O2 in immersed, exercising subjects while assessing multitasking performance with the Multi-Attribute Task Battery II (MATB-II) flight simulator. Cognitive performance was tested under 20 conditions of gas partial pressure and exercise in 42 male subjects meeting U.S. Navy age and fitness profiles. Inspired nitrogen (N2) and oxygen (O2) partial pressures were 0, 4.5, and 5.6 ATA and 0.21, 1.0, and 1.22 ATA, respectively, at rest and during 100-W immersed exercise with and without 0.075-ATA CO2. Linear regression modeled the association of gas partial pressure with task performance while controlling for exercise, hypercapnic ventilatory response, dive training, video game frequency, and age. Subjects served as their own controls. Impairment of memory, attention, and planning, but not motor tasks, was associated with N2 partial pressures >4.5 ATA. Sea level O2 at 0.925 ATA partially rescued motor and memory reaction time impaired by 0.075-ATA CO2; however, at hyperbaric pressures an unexpectedly strong interaction between CO2, N2, and exercise caused incapacitating narcosis with amnesia, which was augmented by O2. Perception of narcosis was not correlated with actual scores. The relative contributions of factors associated with diving narcosis will be useful to predict the effects of gas mixtures and exercise conditions on the cognitive performance of divers. The O2 effects are consistent with O2 narcosis or enhanced O2 toxicity.