The Nervous System, Ear, Hearing and Balance — Page 72, Lesson 107

I want to walk you through three important topics that connect the nervous system, the ear, and how we maintain balance in flight. Let's start with the Coriolis effect. If you're in a steady turn and you suddenly move your head — and I mean a movement faster than about three degrees per second — your brain will interpret that as a change in the turn rate. That's a false sensation. This is called a cross-coupled stimulation of the semicircular canals, and it's the technical definition of the Coriolis effect. Your semicircular canals are the fluid-filled loops in your inner ear that detect rotation. When you're already turning and you add a head movement, the fluid in one canal sloshes into another canal's plane, and your brain gets a completely wrong signal about what your body is doing. Now, here's the critical rule that I cannot overemphasize: whenever there is a conflict between what your eyes tell you and what your inner ear tells you, visual reference will provide the more accurate picture of orientation. As a pilot, the most important sense for spatial orientation is sight. Always remember that. Let's move to alcohol and flying. Alcohol has a lower specific gravity than water. Specific gravity is a measure of density compared to water — alcohol is lighter. When alcohol gets into the fluid of your inner ear, it changes that fluid's specific gravity. That causes erroneous results for certain head movements, leading to disorientation. But there's an even longer-lasting problem. Alcohol can persist in the fleshy stalk of the otoliths — those are the structures in your inner ear that detect linear acceleration and gravity — for days after all traces of alcohol have vanished from your blood. It is not unusual for even small head movements to cause disorientation or motion sickness up to three days after alcohol was last consumed. So the effects outlast your blood alcohol level by a long margin. Now, motion sickness. The term is actually a misnomer — it's not a sickness in the pathological sense. It is a normal and direct manifestation of sensory functions. It is probable that no one with a normal vestibular apparatus — that's your balance system in the inner ear — is completely immune. Motion sickness has been referred to since the times of Hippocrates. It arises when you are exposed to real or apparent motion of an unfamiliar kind. It occurs not only in normal flying but also in space or at sea. Some individuals experience it in a car or on a train. The cause is a mismatch between the visual and vestibular signals. Your eyes tell your brain one thing; your inner ear tells it another. The brain cannot reconcile the two, and you get symptoms. Those symptoms are: nausea, hyperventilation, vomiting, pallor — that's paleness — cold sweating, headache, and depression. It can be severely incapacitating, but it is a normal response to perceived stimuli. Anyone with a normal sense of balance will suffer motion sickness if stimulated enough. Its symptoms are observed in up to eight percent of passengers on board modern aircraft. Motion sickness can even be generated without any real motion — for example, in a simulator when an expected movement does not occur. That mismatch alone can trigger it. Motion sickness can cause problems with flying training programmes. To avoid the problem, all progress should be gradual. For example, gradual progress from gentle turns to steep turns, and avoidance of aerobatics during early training. Any prolonged break from training may lead to a recurrence of the problem. Many pilots experience motion sickness when they fly, but most can adjust or be conditioned to avoid symptoms. For a pilot suffering from chronic motion sickness, it is most important that his or her organization's aviation specialist is consulted.