The "diving brain": cognitive effects of inert gas narcosis

Inert gas narcosis is a syndrome complained by scuba divers performing deep dives while breathing air. It is characterized by a severe dysfunction of cognitive abilities, leading to dangerous or lethal behaviors. Since symptoms get worse with depth, the gradual growing of partial pressure of nitrogen (PpN2), critical from 39 meters (PpN2> 4 atm), is considered the main causal factor. Herein, our aim is to evaluate inert gas narcosis effects on cognitive functioning at depth lower than 39 meters. Methods: Thirteen expert divers performed as dive at 1 and 30 metres. Visuo-spatial functions and short-term memory were evaluated with the Clock Drawing Test and the Digit Span Test, respectively. Tests were administered with an ad-hoc tablet inserted in an underwater self-equalized case. Data were analysed with repeated measures ANOVA, using depth level as within-subjects factor. Results: Clock Drawing Test (p< 0.05) and Digit Span Test (p< 0.05) scores showed a significant reduction during the 30 metres dive, compared to 1 metre. From a subjective standpoint, no divers reported having experienced narcosis symptoms during the dive. Conclusions: Herein, we demonstrate that inert gas narcosis is a more common and underestimated syndrome, characterized by an insidious onset of symptoms at depth lower than 39 meters (PpN2< 4 atm).