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Common Motion Sickness Drug Could Impair Divers' Judgment

From the WebMD Archives

Sept. 20, 2000 -- Scuba diving can be an intoxicatingexperience. But scientists at the University of Pittsburgh have found that acommon seasickness medication, Dramamine, taken just before a dive couldproduce the mental equivalent of "one too many," possibly impairingjudgment and raising the risk of an accident. A second study by the same team,however, shows that pseudoephedrine, a drug found in many sinus medicationssuch as Sudafed, has only modest effects on brain function and is probably safefor divers. Both studies appear in this month's issue of the journalPharmacotherapy.

Scuba divers are particularly vulnerable to the mind-alteringeffects of certain drugs because of the way air is delivered from the tank.Nitrogen makes up about three-quarters of the air we breathe. When compressedinto a scuba tank and inhaled under the high pressures encountered at depths of33 feet or more, it can have a disorienting effect -- kind of like taking a fewdrinks. Indeed, Kevin O'Toole, MD, one of the study authors, tells WebMD thatevery 33 feet a diver descends is the equivalent of drinking one martini in itseffect on the brain. Scientists call this condition "nitrogennarcosis," but divers know it by a more poetic name -- "rapture of thedeep."

To study the effects of two popular, over-the-counter drugswhen combined with nitrogen narcosis, the scientists placed 30 experiencedscuba divers in a hyperbaric chamber that simulated the pressure of a 66-footdive (two martinis). While in the tank, the divers breathed the same type ofcompressed air they would have in a scuba tank.

Forty-five minutes before going on the "dive," eachsubject took a pill containing pseudoephedrine, a decongestant many divers taketo relieve pressure in the sinuses or middle ear; dimenhydrinate, the activeingredient in most anti-seasickness products such as Dramamine; or a dummypill. The experiments were designed so that each person was tested with eachdrug.

The investigators chose these drugs because they are popularamong scuba divers, and because each has been associated with side effects thatcould distort a diver's judgment, especially when combined with nitrogennarcosis. Pseudoephedrine has been linked with nervousness, excitability, andrestlessness and may also cause a rapid or irregular heartbeat. Dimenhydrinatecan make people extremely dizzy or drowsy.

While in the chamber, the subjects performed various tasks ofmemory, verbal ability, and manual dexterity. Each person also wore a monitorthat recorded his or her heart rate and rhythm. They went through the samebattery of tests while resting in the chamber at normal atmosphericpressure.

Even without the drugs, the participants exhibited increasedanxiety and decreased verbal fluency at conditions simulating 66 feet underwater, the researchers found. Pseudoephedrine produced a slight increase inheart rate and interacted with the depth effect to increase the decline inverbal fluency, but overall, the authors write that "it is unlikely thatpseudoephedrine adds significant risk to the diver."

Dimenhydrinate, on the other hand, was associated with muchlower scores on a test that required the subjects to switch rapidly between twotasks and is a measure of mental flexibility. "We showed a definiteimpairment [from dimenhydrinate], especially in combination with narcosis, andthe deeper you go, the greater your decline," says O'Toole, an experienceddiver who directs the hyperbaric medicine program at the University ofPittsburgh. "I would not recommend that someone take this drug anddive."

Add dimenhydrinate to the effects of narcosis "and you'rereally zonked," says Murray Grossan, MD, a Los Angeles-basedotolaryngologist and a scuba diver since 1970. He tells WebMD that many fataldiving accidents occur because divers ignore or forget to watch the monitorsthat tell them they're low on air, which could be the result of impairedjudgment produced by narcosis. Grossan was not involved in the study.

However, the potential effects of pseudoephedrine on heartfunction should not be dismissed, warns Claes Lundgren, MD, PhD, director ofthe Center for Research and Education in Special Environments at the StateUniversity of New York in Buffalo. People diving at great depths may experiencean immersion effect, in which blood travels away from the limbs and into thechest, where it may distend the heart and render it more vulnerable to theeffects of drugs that affect heart rhythm. "This could be responsible for anumber of scuba deaths that remained unexplained," he tells WebMD.

Grossan says that his patients have found the scopolamine patchto be a good antidote to seasickness. They can remove it just before diving orwear it in the water if they dive with a hood. Some people also have had goodluck with wristbands that compress certain pressure points and are reported torelieve nausea.

"It's worth noting that neither of these drugs is permittedfor commercial pilots," says Lundgren. "Risk is a relative concept.[When it comes to diving after taking one of these drugs], it's really for theindividual to define for him- or herself what is acceptable."