EFFECTS OF DIMENHYDRINATE ON GASTRIC TACHYARRHYTHMIA AND SYMPTOMS OF VECTION-INDUCED MOTION SICKNESS

Background: Previous research in our laboratory has shown that symptom s of motion sickness are accompanied by the loss of normal 3 cpm activ ity and the development of tachyarrhythmia in the electrogastrogram (E CC). Hypothesis: We hypothesized that dimenhydrinate would prevent the development of gastric tachyarrhythmia and reduce symptoms of motion sickness. Methods: Twenty healthy volunteers were tested in a counter- balanced, within-subject, double-blind design. Subjects were exposed t o a rotating optokinetic drum to induce vection after receiving either dimenhydrinate (100 mg) or a placebo on two separate occasions. EGG'S were recorded immediately before ingestion of capsules, 1 h after ing estion, and during rotation. Motion sickness symptom reports (SSMS) we re obtained prior to and during rotation. Results: The average SSMS sc ore was 5.9 points higher after placebo administration than after dime nhydrinate administration (t[19] = 4.87, p < 0.001). Significantly mor e subjects requested early termination of the rotating drum due to sev ere symptoms after placebo administration than after dimenhydrinate ad ministration (McNemar's chi(2)[1] = 6.00, p < 0.05). Drowsiness report s were significantly higher after dimenhydrinate administration than a fter placebo administration (t[19] = 2.65, p < 0.05). Analysis of ECC' s showed a significant decrease in normal 3 cpm and tachyarrhythmic ac tivity after dimenhydrinate, but no change after placebo (SR[19] = 53, p < 0.02 and SR[19] = 68, p < 0.01 respectively). During drum rotatio n gastric tachyarrhythmias increased significantly in the placebo cond ition (SR[18] = -0.61.5, p < 0.01), but not in the dimenhydrinate cond ition. EGG's were not significantly different between conditions. Conc lusions: We conclude that dimenhydrinate reduced motion sickness sympt oms at least in part by depressing central nervous system activity and possibly by suppressing abnormal gastric myoelectric activity.