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Study Objectives: To examine the psychometric and cardiac effects of pseudoephedrine at 1 and 3 atmospheres (atm) of pressure (0 and 66 feet of sea water, respectively), and to make recommendations about the agent's safety in the diving environment., Design: Double-blind, placebo-controlled, crossover study., Setting: Monoplace hyperbaric chamber of a university hospital., Subjects: Thirty active divers (mean age 38 yrs)., Intervention: A bank of seven tests was used to assess cognitive function during four different simulated dive combinations: placebo-1 atm, placebo3 atm, pseudoephedrine-1 atm, and pseudoephedrine-3 atm., Measurements and Main Results: Heart rate and cardiac rhythm were recorded during all dives. Repeated-measures analysis of variance was used to analyze the effects of pseudoephedrine, depth, and drug-depth interaction. No significant, independent effects of pseudoephedrine were seen on any of the seven psychometric test scores (p>0.05), although the drug tended to increase anxiety scores (p=0.092). Depth resulted in a significant increase in anxiety scores (p=0.021) and a significant decrease in verbal fluency test scores (p=0.041); it had no significant effects on the other five psychometric tests (p>0.05). Pseudoephedrine caused a significant increase (p=0.036) in mean heart rate, and depth caused a significant decrease (p=0.013). Neither pseudoephedrine nor depth affected cardiac rhythm., Conclusion: Pseudoephedrine does not cause significant alterations in psychometric performance at 3 atm of pressure that might increase the risk of diving. Depth causes significant adverse effects on anxiety levels and semantic memory at 3 atm. Pseudoephedrine and depth have significant but opposite effects on heart rate; although, these effects are unlikely to be clinically significant during diving. It is unlikely that pseudoephedrine adds significant risk to the diver.

Study Objectives: To examine the psychometric and cardiac effects of dimenhydrinate at 1 and 3 atmospheres (atm) of pressure (0 and 66 feet of sea water, respectively), and to make recommendations about the drug's safety in the diving environment., Design: Double-blind, placebo-controlled, crossover study, Setting: Monoplace hyperbaric chamber of a university hospital., Subjects: Thirty active divers (mean age 38 yrs)., Interventions: A bank of seven tests was used to assess cognitive function during four different dive combinations: placebo-1 atm, placebo-3 atm, dimenhydrinate-1 atm, and dimenhydrinate-3 atm., Measurements and Main Results: Heart rate and cardiac rhythm were recorded during all dives. Repeated-measures multivariate analysis of variance was used to analyze the effects of dimenhydrinate, depth, and drug-depth interaction. Dimenhydrinate resulted in a significant decrease in scores of mental flexibility (trail-making, part B, p<0.05) but had no effect on scores in the six other psychometric tests (p>0.05). It had no effect on mean heart rate (p>0.05), although frequent unifocal ventricular ectopic beats occurred in two subjects after ingestion of the drug. Depth resulted in a significant decrease in verbal memory test scores (p=0.001) and mean heart rate (p<0.001)., Conclusion: Dimenhydrinate adversely affects mental flexibility. This effect, when added to the adverse effect of depth on memory, may contribute to the dangers of diving.