Motion Sickness

Motion sickness, or seasickness, ruins diving trips, vacations and travel for many. Everyone is susceptible; it can happen to anyone if the circumstances are right. A lot is known about motion sickness, but our understanding of the cause is not perfect. There are people who are resistant to motion sickness, but sufficient angular acceleration will induce motion sickness in anyone in nearly any means of travel.

Even astronauts are annoyed by this problem: Approximately 70 percent of all crew members experienced some degree of motion sickness during the first 72 hours of orbital flight in the space shuttle.

Mechanisms of Injury

The vestibular balance apparatus of the ears detects motion and is stimulated by the repeated angular acceleration that occurs on a moving boat. If you are below decks or have otherwise lost visual contact with the water/horizon, your eyes signal the brain that there is no motion. The sensors of body position, however, send a different signal, and the brain may struggle to resolve the conflict. Anxiety, confusion and dismay can result, leading to symptoms of yawning, pallor (paleness) and headache. These are often followed by nausea and vomiting.

There is more to motion sickness than a mismatch of sensory inputs. Other possible factors include the role of Coriolis forces (forces due to the earth’s rotation), other nonphysiological stimuli, cerebrospinal fluid and the cerebellum.

Manifestations

If you have experienced motion sickness, you probably think of nausea as the primary symptom. Other symptoms include dizziness, fatigue, burping, sweating, vomiting, excessive salivation and headaches.

The reverse can occur, too. “Land sickness,” or mal de débarquement, occurs when you return to dry land after becoming adapted to an environment in constant motion. The brain becomes accustomed to the new input from increased motion, and upon returning to land the motion is no longer present. The abrupt change can produce the same symptoms originally experienced upon going to sea.

Prevention

To manage motion sickness, find the part of the vessel with the least up and down movement and stay there — usually that will be in the center of the vessel. Stay as low as possible while maintaining eye contact slightly above the horizon. If visual contact is not possible, try keeping your eyes closed.

There are a variety of medications that a diver could take to minimise symptoms and reduce risk. Before taking a medication, read the information provided to understand potential side effects.

• The most commonly used medications are antihistamines, which are available without a prescription and share common side effects. These medications include Dramamine® (dimenhydrinate), Bonine® (meclizine), Benadryl® (diphenhydramine) and Marezine® (cyclizine). A common side effect of this group is drowsiness, which might seriously impair a diver’s ability to perform safely.
• Phenergan® (promethazine) is a prescription drug chemically related to tranquilizers, and it also has antihistamine properties. Drowsiness is a prominent side effect, and it can be used as a sedative-hypnotic. The drug may impair the mental and physical abilities required to perform potentially hazardous tasks. Alcohol and similar drugs accentuate the sedative effects of promethazine.
• Scopolamine-dextroamphetamine is a combination of oral scopolamine and oral dextroamphetamine, and it has been studied for use in the space program. These are very potent medications and the combination has not been approved by the U.S. Food and Drug Administration (FDA) for motion sickness. A physician prescribing this combination for motion sickness would be outside the scope of the FDA.
• Trans-Derm SCOP® (scopolamine patch) has been used by many divers who found it beneficial and reported few problems. Side effects include hallucinations, confusion, agitation and disorientation.

There are possible non-pharmacological interventions available to divers, but some may not have been tested in trials. Possible remedies include the ingestion of ginger and the use of a band that applies pressure to a particular spot on the wearer’s wrist.

Complications

Dehydration, anxiety and depression are common complications of motion sickness. Although motion sickness usually goes away once the motion stops and causes no lasting harm, people who have prolonged exposure, such as crew members on ships, may have exacerbated symptoms.

Implications in Diving

For the Diver

• Before a dive, ensure you are adequately rested, nourished and hydrated. If you are apprehensive, avoid eating two hours before you embark.
• If you choose to take a medication, take note of potential side effects and be on the lookout for them.
• If symptoms continue, contact a physician

For the Dive Operator

• Before boarding, let divers know the best place for them on the vessel to help them avoid motion sickness.
• Most people adapt to motion, so motion sickness often resolves after a few hours.

For the Physician

• Be sure to communicate to the patient the potential side effects of the prescribed medication.
• Intramuscular injection of certain drugs can provide great relief for severely motion-sick individuals.