Does inert gas narcosis have an influence on perception of pain?

The effect of an increased nitrogen partial pressure under hyperbaric conditions is known as nitrogen narcosis (NN). At an ambient pressure of about 4 bar, reduced cognitive performance as well as euphoric effects are reported. We examined the effect of NN on pain perception. 22 subjects completed an experimental (50 meters = 6 bar) and a simulated control dive (0 m = 1 bar) in a hyperbaric chamber. Before and during each dive a standardized cold pressure test was performed. The intensity of pain perceived was assessed with the help of a visual analogue scale; additionally, subjects assessed the subjective effect of NN. The study showed that the perceived pain intensity is significantly reduced under nitrogen narcosis conditions (F1.21 = 5.167, p < 0.034) when compared to the perceived pain intensity under the control dive conditions (F1.21 = 0.836, p = 0.371). A connection between perceived pain intensity and subjects experience of the NN was not found under the experimental dive condition (r = 0.287, p = 0.195). We could show that even relatively moderate hyperbaric conditions may have an influence on the perception of pain. The results are highly relevant since nitrogen narcosis occurs in divers as well as in medical personnel or construction workers, working under hyperbaric conditions.

Neuropsychological deficits in scuba divers: an exploratory investigation.

OBJECTIVE: To investigate whether divers with varying levels of experience and without a history of reported decompression sickness (DCS) show neuropsychometric alterations possibly as a result of so-called repetitive "silent" paradoxical gas embolisms. METHODS: Using reaction time as a psychometric measure, 17 experienced military divers (ED, logging between 150 and 1,200 diving hours) and eight very experienced military divers (VED, logging between 2,800 and 9,800 diving hours) with no decompression sickness (DCS) in their medical histories were compared to 23 healthy controls without any diving history, matched as closely as possible with respect to age for the two diving groups. Motor reaction time, decision reaction time and error rates were measured during completion of both simple and complex reaction time tasks. RESULTS: Compared to their control group, VED showed significantly higher motor reaction times on both tasks and significantly higher decision reaction times in the complex task. ED were not found to be different from their respective controls. No changes in performance quality in terms of increased errors were observed in any of the tasks for either diving group. CONCLUSIONS: The findings support the proposed possibility that minimal cerebral lesions occur after diving even without DCS. Further studies with this highly selective population of very experienced divers using more elaborate neurocognitive and neuromotor tasks seem warranted.