Poor Pilot Recall of Loss of Consciousness


When I read papers by flight surgeons estimating the incidence of acceleration-associated loss of consciousness (G-LOC) in their pilot population as 15% to 30% in modern fighter jets, I smile at their naivety as I vividly recall my work with Sem Jacobsen, 40 years ago.

As a USAF flight surgeon, I was newly assigned to Wright-Patterson then as research scientist at the Aeromedical Research Lab. Jacobsen, a brilliant and gregarious Norwegian, was looking for subjects for his study of recall of loss of consciousness in the pilot population. The prevailing opinion among most flight surgeons then was that if you wanted to know if a pilot had a history of loss of consciousness, you asked him. Allowing for an understandable tendency to stretch the truth in order to get on or maintain flight status, the pilot seemed to be the best resource for personal information of this kind. Jacobsen was testing this hypothesis.

I was using bed rest and water immersion analogues to study the deconditioning effects of prolonged space flight. Getting away for a few hours to participate in Jacobsen's two-seater jet study was a perfect opportunity to break the monotony. Since EEGs would be recorded during the test procedure, I first had to have some twenty electrodes glued to my scalp with colloidion, then a needle was inserted through the hole in the small metal disc to abrade the skin until the desired level of skin impedance was achieved. Finally a few drops of electrolyte solution were added and the electrode disc was sealed with more colloidion. I was ready for the flight helmet.

The pilot of the F-100 sat in the front seat wearing his G-suit. We "guinea pigs" would sit in the back seat without G-suit, brains monitored by the in-flight EEG recorders, face and body monitored both by camera and the pilot, using his rear view mirror, and all conversations were recorded. We were to climb to 12,000 feet then roll the sleek jet into a high-speed dive to 7,000 pulling out at 7G, a level pre-selected to induce a rapid transition from gray-out to blackout to sustained G-LOC in the unprotected test subject. Each volunteer was subjected to two runs then brought back to base for debriefing.

I was delighted with my two runs and absolutely certain that I had passed the test with flying colors and had maintained consciousness throughout. As a flight surgeon I knew I had cheated somewhat for I had employed the M-1 maneuver by forcibly exhaling against \my partially closed glottis during the high G phase to improve my G tolerance.

Having seen the results, Sem had a twinkle in his eye when he began the debriefing. This should have alerted me that perhaps I had overstated just how well I had done. He asked me if at any time during the high G runs I had experienced gray-out and I replied, "Of course." He asked me if I had experienced blackout and I admitted, "Yes," to that also. He then asked if I had experienced loss of consciousness at any time or the "shakes". The shakes are involuntary twitching or rhythmic shaking of the extremities or head under high G maneuvers. I told him, "No" on both counts. He asked, "Are you sure?" and I said, "Yes."

He then played back the movie of the first of my two runs. It showed me, obviously unconscious with head bent forward, nearly in my lap for the first twenty seconds, followed by a period of wild gyration of head and extremities flailing about in the "shakes" for another twenty seconds or so and finally coming to and gazing out the canopy as if having the time of my life. The film was an extraordinary shock. I was in complete disbelief and challenged the identity of the subject in that film clip for that person could not have been me.

It was a thoroughly shattering experience to see my unconscious body involved in this alien shaking about without the slightest recall. The second run was a duplicate of the first.

The playback of the EEG tracings was less informative to me than the film but there was no mistaking the sudden transition from an unconscious brain wave pattern to the spiking waves heralding motor cortex activation and the "shakes", a form of seizure activity much too close to Grand Mal to suit me.

And my case was no exception, Jacobsen later reported to me when we reviewed all the test data. All of the test subjects experienced loss of consciousness. The shakes varied considerably from subject to subject. A few had no motor activity, some others experienced obvious "shakes" like mine and most showed only occasional twitching. None had the slightest recall for unconsciousness or of the "shakes". All were totally surprised and dismayed at their films during debriefing.

There it was - proof that I had not the slightest recall for some 30 to 40 seconds of my life during those high G pullouts. The precious history, so important to a clinician in determining a patient's status, completely irrelevant when one is asking about loss of consciousness. What if I had been piloting the damn thing was the first thing to come to mind when the reality of G-LOC finally entered my consciousness.

Later in life I had the opportunity to observe two instances where individuals fell to the ground unconscious when their heads inadvertently hit an electric fence wire serving my garden. In both cases they got up immediately and continued viewing the garden, completely oblivious to the fact that moments before they had been lying on the ground, unconsciousness. I thought of my military fighter pilots then, unconscious at the controls of their wayward aircraft, oblivious to everything.

Later still, I was to add my observations that the statin class of drugs can cause abrupt transient global amnesia without the slightest warning, further reinforcing my growing concerns that our brains are definitely fallible. Under certain conditions of altered awareness associated with acceleration, electric shock and chemical exposure, our brains have no power of recall and a patient's history abruptly becomes irrelevant.

Duane Graveline MD MPH
Former USAF Flight Surgeon
Former NASA Astronaut
Retired Family Doctor

 

 

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