The psychometric and cardiac effects on pseudoephedrine and antihistamines in the hyperbaric environment.

Abstract

STUDY OBJECTIVES: Pseudoephedrine (Sudafed®) and dimenhydrinate (Dramamine®) are often used by recreational scuba divers to avoid ear barotrauma and to control seasickness, respectively. However, these drugs have been little studied in the hyperbaric environment. This study examines the psychometric and cardiac effects of pseudoephedrine and dimenhydrinate at one (100 kPa, sea level) and three (300 kPa, 20 m) atmospheres absolute (bar). METHODS: A double-blind, placebo-controlled, crossover trial was carried out in the monoplace hyperbaric chamber of a university hospital. Thirty active divers (mean age 38 years) were studied. A bank of seven tests was used to assess cognitive function during four different dive combinations: placebo/ 1 bar (100 kPa, sea level), placebo/3 bar (300 kPa, 20 m depth) , drug/1 bar (100 kPa, sea level)and drug/3 bar (300 kPa, 20 m depth). Heart rate and cardiac rhythm were recorded during all compressions (dives). Repeated measures ANOVA was used to analyse the effects of drug, depth and the drug-depth interaction. RESULTS: There were no significant, independent effects of pseudoephedrine on any of the seven psychometric tests scores (p>0.05), although the drug tended to increase Anxiety scores (p=0.092). Increased depth (pressure) resulted in a significant increase in Anxiety scores (p=0.021) and a significant decrease in Verbal Fluency test scores (p=0.041). Pseudoephedrine caused a significant increase (p=0.036) in mean subject heart rate while depth (3 bar) caused a significant decrease (p=0.013). Dimenhydrinate resulted in a significant decrease in scores of mental flexibility (Trail Making, part B) (p<0.05). It had no effect upon mean subject heart rate (p>0.05). Depth resulted in a significant decrease in Verbal Memory test scores (p=0.001) and a significant decrease in mean subject heart rate (p<0.001). CONCLUSION: Pseudoephedrine does not cause significant alterations in psychometric performance at 3 bar pressure (300 kPa, 20 m) that might increase the risk of diving. Dimenhydrinate adversely effects mental flexibility at depth. This effect, when added to the adverse effect of depth on memory, may contribute to the dangers of diving. Depth causes significant adverse effects upon anxiety levels and semantic memory at 3 bar.