Pilot incapacitation? Who me? Im in great shape!
Though the greatest threats to pilots still remain alcohol, hypoxia, carbon monoxide and likely side effects of medication, these are conditions over which the pilot essentially has good control.
Among causes in the other category, are vertigo and anxiety. Vertigo is among the most frightening and most completely incapacitating sensations a pilot can experience. Though relatively rare, it is regarded with such seriousness that some types of recurrent vertigo are grounds for denial even of a special issuance medical. Anxiety attacks are subtler but are equally incapacitating. Neither of these conditions gets much press and misinformation abounds.
To understand vertigo, one first has to understand how the brain processes sensations that result in the notion of balance. All mammals from the platypus on up have a structure buried in bone at the base of the skull called the labyrinth. Buried at right angles, these three rings of fluid-filled tubes, lined with sensory hair cells, are constantly sensing the relative direction of movement of the tubes around the fluid contained within.
The situation is rather like that seen when spinning a raw egg on a kitchen counter: When the egg is spun, the innards tend to remain at rest and resist the eggs rotation. But once the fluid is moving, it tends to continue to. When the egg is stopped, the innards continue and tend to drag the egg back into rotation.
Similarly, the three tubes in the labyrinth, being oriented in the three separate planes, detect rotational acceleration in any axis. Two other adjacent inner ear structures, the saccule and the utricle appear to act as linear accelerometers.
This ingenious system of three biologic turn co-coordinators oriented at 90-degree angles works well, but is vulnerable anywhere along its path. The amount and composition of the fluid bathing the hair cells (which are after all, the sensors) must be absolutely correct. When the hair cells degenerate, its rather like losing rpm on a gyro, or on all three turn coordinators.
Because there is another threesome of tubes behind the other ear, loss of one serves to bias the system information heavily in favor of one-sided acceleration. The sense of the room spinning becomes overwhelming.
The brainstem is constantly being bombarded by communication from the hair cells that line these circular tubes, containing information as to which way the contained fluid is turning relative to the eggshell. It is the hair cells signal that makes us able to determine that we are turning, or ceasing to turn.
To make matters worse, in humans there is an eyeball-to-ear interconnection. Ever wonder how it is that we track rapidly moving targets? Our eyes fixate, follow, and rapidly transit back to pick up the next one moving in the same direction. When this motion becomes involuntary, it is called nystagmus.
If the central processor is getting heavy were turning right information, the eyes track slowly to the left, and then jump rapidly to the right, then repeat the cycle over and over. The resulting jumping visual images are not difficult to interpret if we really are turning. But when the environment is stable, this slow-left fast-right motion of our visual imagery is nauseating. Vertigo follows.
Vertigo-inducing conditions range from benign paroxysmal vertigo of Barany, which is characterized by the occurrence of episodes of nystagmus and vertigo with the head in certain critical positions, to labyrinthitis, due to infection of the middle ear or due to alcohols effects, quinine, streptomycin, gentamicin and other antibiotics.
The duration of episodes generally is longer in inflammatory illnesses, and the toxic effects of some antibiotics can cause a permanent disorder especially in older patients. Interruption of the blood supply to one labyrinth is thought to cause a particularly dramatic picture of severe vertigo, nausea and vomiting – without other symptoms such as ringing in the ear or hearing loss. This can last for days and weeks.
Disorders of the wiring harness, the nerve from the labyrinth to the brain may also affect left/right signal balance, and if the perpetrator is large enough may also affect the adjacent auditory portion of the nerve, resulting in hearing loss.
The most feared form of vertigo, however, is Menieres disease. This is most common in ones 50s, and consists of a dilation of the tubes and associated plumbing, leading to degeneration of the hair cells. The attacks are progressive, and when associated deafness progresses, the attacks cease. It is utterly and completely disqualifying to flight.
Many of the symptoms are similar to another illness called vestibular neuronitis, which does not progress and is less likely to recur.
Once in the cockpit, about the only thing a pilot can do to prevent vertigo is to avoid the 30-degree head forward and down position, which orients one of the circular canals exactly about the vertical axis of the aircraft. I believe this is a reason why head down is so effective in disorienting an instrument pilot doing unusual attitude practice.
Unfortunately, this is precisely the position involved in looking at parts of the instrument panel, reaching for a fuel selector, or reading charts. And, certainly anyone with a viral illness resulting in any sort of balance disturbance, no matter how minor, shouldnt go anywhere near a PIC seat.
High Anxiety
Pilots have equally little control over anxiety. Humans deal with anxiety in different ways and in some instances it raises your performance levels to new heights. Its when anxiety rises to the point of altering decision making, or impairing perception, that pilots get into trouble.
The very first thing not to do is to hyperventilate. We move about seven liters of air in and out of the chest in a minute. If we double that (easy to do unconsciously when under severe stress), we set off a chain of acid-base changes that make blood vessels constrict and can make the fingers numb and the lips tingle, which in turn causes alarm and even more respiration, thereby worsening the alkalosis even further. Its a vicious cycle that eventually will impair cognition as the brain blood supply constricts with alkalinization of the blood.
At the first symptoms of anxiety – tingling and numbness – the pilot will be faced with the added distraction of controlling both the rate of respiration and its depth. If you can control your respiratory rate to four breaths per minute, it is genuinely difficult to hyperventilate. There is some value to the old brown bag over the mouth and nose trick, which recycles and prevents loss of the exhaled carbon dioxide, but the bag makes being PIC very, very difficult.
Finally, consider your passengers. We all can take a cue from the airlines and use politically correct phraseology so as not to alarm even the most nervous of passengers. However, when a passenger experiences a panic attack, it is distracting at best and can even be fatal.
Some years ago I had a passenger in the number 3 seat kick out the oxygen plumbing below the pilots seat, forcing a descent into a VMC hole north of Montrose, Colo., to sort it out. Thank goodness I was not the only pilot aboard. Without the assistance of the other pilot/passenger, I would have been unable to re-ascend on-top and maintain the MEA.
After a good preflight briefing, after avoidance of anxiety, and after good passenger selection, crew resource management can be an invaluable tool. Delegate someone else to look after the panicked; be certain the panicked person isnt also hypoxic. Add oxygen (or use your pulse oximeter) if you havent already.
Descend gently and dont add eardrum pain to the picture. Dont ever raise your voice. If there are multiple passengers, you may consider unplugging the panicked passengers microphone, which limits spread of the contagion. If the panicked person is in the copilot seat, move the seat to the rearmost position possible and be certain his lap belt is buckled, reducing the exposure of the flight controls.
If a nonpanicked nurse or doctor is in the cabin, the brown paper bag over the head trick may help. Lastly, an old CFI trick: The best way to break a grip on the yoke is with a sharp stroke from the lap up to the headliner. Stay in control, and this too will pass.
-by Bruce Chien
Bruce Chien is a CFII, MEI and AME and owns a Piper Seneca.
