Space motion sickness symptoms are similar to motion sickness on Earth. About 70 percent of first-time space travelers develop the condition during the first few hours in space with symptoms peaking around 10 hours into the flight. The condition can recur when returning to Earth's gravity, which, along with takeoff, is one of many critical events during space flight.
The medications currently available affect a person's cognitive ability.
"Astronauts typically take promethazine, a medication used to treat nausea. It's a good medicine, but it causes sedation," said Dr. John L. Dornhoffer, a researcher on the National Space Biomedical Research Institute's (NSBRI) neurovestibular adaptation team. "Astronauts have worked all their lives to do this job, and they want to avoid taking something that makes them sleepy."
The drugs can impair the ability to react quickly, think clearly and recall information, so spacewalks are out of the question. And, extravehicular activity is never an option when a crewmember feels nauseous.
An ear, nose and throat specialist, Dornhoffer is researching four drugs - lorazepam, meclizine, promethazine and scopolamine - to determine what drug is most effective at reducing space motion sickness without impacting cognitive and physical ability. His team is also researching the most effective way to administer the medications.
"These drugs are used to treat balance disorders, and all have central nervous system side effects. We are using cognitive tests to determine which medication causes the least impairment," said Dornhoffer, associate professor of otolaryngology at the University of Arkansas for Medical Sciences and executive director of the Prosper Meniere Society.
Seventy-five healthy study participants are undergoing different tests to overstimulate the inner ear, creating symptoms of vertigo, similar to what may be felt in space. Vertigo sufferers often feel their surroundings are moving or they are spinning around and cannot get their bearings. Others feel like they are being pulled toward the floor or to one side of the room. Other than nausea and vomiting, symptoms include difficulty focusing, sweatiness and heart palpitations.
A rotating chair spins subjects starting at five revolutions per minute (rpm). The speed is increased by two rpm every five minutes until a total of 30 rpm is achieved in an hour. While spinning, participants are cued to make head movements that create significant stimulation of the inner ear.
"A healthy individual can do that for about 15-25 minutes before feeling sick. The subject then does the test a second time after taking a drug countermeasure or placebo to test the response," Dornhoffer explained.
An Operant Test Battery, developed by a co-investigator at the National Center for Toxicological Research, is being used to measure cognitive impairment as a result of drug administration and induced vertigo. The test measures specific tasks including time perception, short-term memory and learning.
A custom-designed off-axis rotating chair, located at the University Hospital in Antwerp, Belgium, is being used to validate the rotating chair results. By spinning subjects off axis, the inner ear's otolith organ is stimulated and then analyzed. The otolith is the inner ear's gravity-sensing organ. While in the chair, subjects wear a three-dimensional eye-tracking device, which measures horizontal, vertical and rotational eye movements. This combination of devices allows the inner ear's three semicircular canals to be studied separately.
Once the testing is completed and the data analyzed, the group will test the best way to administer the drug or drug combination.
The study results will have benefits to patients on Earth suffering from balance disorders such as vertigo, disequilibrium or Meniere's disease. The rotating chair model is already being used to test patients on Earth suffering from undiagnosed balance problems.
The NSBRI's consortium members include Baylor College of Medicine, Brookhaven National Laboratory, Harvard Medical School, The Johns Hopkins University, Massachusetts Institute of Technology, Morehouse School of Medicine, Mount Sinai School of Medicine, Rice University, Texas A&M University, University of Arkansas for Medical Sciences, University of Pennsylvania Health System and University of Washington. The NSBRI is funded by NASA.