Fall from Grace

Years ago, before I became a neurologist, I was a Naval Flight Surgeon.  That position will probably always be my favorite.  Better even than the year I worked the concession at the movies during high school.  True, working at the theater meant free movies and all the nacho cheese and broken chips I could eat, but thanks to poor impulse control and vats of canned cheese, there was a bonus 20 lbs weight gain.  Over my years as a Flight Surgeon, I was able to log flight time in all sorts of aircraft, from pointy go fasters to whistling s&*!cans of death;  I even had the good fortune to work with the space shuttle program towards the end of both of our careers.   Never had I ever been expected to, been paid to do things like fly in a H3 down the beach, or head a few states over for lunch.  For a few years I was really cool.  Life moves on though, now my fod walk downs are through the living room for legos.

 First things first however. Before any of that, before I could become super cool flight surgeon version of me, loomed ground school.  Officially known as Aviation Preflight Instruction, or API, it was a month of aeronautics didactics and physiology training.  Having gone through med school (the first two years being solid lectures) I have an advanced degree in passive learning.  My trepidation lay in the other part of API, the physiology and survival training, which was more than just bookwork.   The other half of API was survival training, anxiety inducing sweaty palm sort of stuff.  Like learning how to escaping aircraft (emergency egress) that are doing things they are not designed to do, for example, falling out of the sky or burning or falling out of the sky and burning.  And with the Navy being the Navy, much of that involved getting wet.

Survival training started out with the basics.  We began by reviewing swim strokes, then swimming a lap, then two laps.  For the first two weeks I did fine, kept my head above water so to speak.  With every small accomplishment my confidence grew and I was beginning to think I might pass.  That came to an abrupt end the beginning of the third week when I found myself standing atop a dive platform which, though it completely dominated one side of the pool, and I had in fact walked around it several times, I had been able to completely mentally block up until that point. I think I was in a minor fugue state climbing to the top, I don’t really remember it, but suddenly I was just an arm’s length beneath the steel I beams of the ceiling, nauseous and a little panicky, staring down past my toes to the pool hundreds of feet below getting ready to jump fig 1.(maybe about 15 feet, but this is my story, so I call it like a see it).   After that, I was supposed to swim underwater for about 45 feet without breaking the surface.  You know, just in case the whole falling out of the sky burning thing became a horrible reality. 

They say that pride goeth before the fall, but sometimes the opposite holds true.  After an internal struggle with self-preservation, my pride forced us off the platform towards the pool.  Having watched the composure with which I accomplished that part of the exercise, my pride slunk down the ladder and hid in the locker room.  It was a controlled fall, but exclusively by gravity.   I managed to hit the water and in the proper entry position (feet and arms crossed, one hand pinching my nose), so, props to me.  I even made it the 45 feet underwater, but it was not easy.  I surfaced, just past the 45 ft mark and looked at the instructor.  And, nope, that was a fail.  My heel, my Achilles heel, broken the surface, once.  I was devastated, and I had to go again.

Back up to the top, still anxious.  Toes on the edge.  Arms crossed, nose pinched.  Step off into space.  Fall, cross feet.  Hit water.  World spinning, violently.  Nope, what, no.  This was not good.  I could see the line but I couldn’t figure out where it was, it kept moving.  And my right ear was hurting.  A lot.  And I was nauseous.  And so much spinning, did I mention that?  I mean, I know the earth is rotating, but that isn’t even background noise in my daily routine.  Nothing wanted to stay in the same place. Afraid to fail in front of my classmates and desperately not wanting to jump again, I started out in what I thought was the right direction and pushed on.    I surfaced just on the far side of the line, desperate for air, ear hurting, the pool spinning, nauseous, and looked in what I hoped what the direction of the instructor for the sign that I passed.  (I’d say I was waiting with baited breath, but that was the opposite of my state at the time).   As far as I could tell, I got the nod from the instructor.  I waded through the shallow end in the general direction the rest of the would be pilots, flight officers, and flight surgeons to watch the next hapless jumper. 

Fig 1. The ear. The tympanum or tympanic membrane seperates the middle and inner ear from the ear canal.The middle ear houses the ossicles, which transmit sound from the ear drum or tympanic membrane to the cochlea in the inner ear. The inner ear contains the cohlea which processes sound and the vestibular labyrinth, which processes head position and acceleration. The information is transmitted to the brainstem via the 8th cranial nerve also called auditory or vestibulocochlear nerve.

What happened to me?  Vertigo.  So. Much. Vertigo.  Triggered ultimately by the vestibular labyrinth in my right ear, but the story starts at the top of the platform.  After a jump from that height, not only is there have the weight of the atmosphere (1 atm or 14.7 pounds/ sq inch), but the weight of the water, and that increases quickly.  At 10 ft underwater that increases to 1.3 atm or 19 psi.  That doesn’t seem like much of a change, for bones and muscles and our bits that are not air filled, it isn’t.  But, for hollow spaces like sinuses, ears, guts and lungs those changes are a lot more significant.  At 10 ft underwater, the very compressible air in those spaces now wants to take up about 75% of its previous volume.  Organs like guts and lungs that are surrounded by soft tissue can easily adjust, like a balloon.  (Going up, decreasing pressure can be an issue, scuba divers - have to exhale on the way up because at 33 ft lungs can hold twice as much air, and lungs do have a finite volume they can expand before something pops.  Same for intestines, had a flight instructor who joked that he could fart going over a bridge). Bony cavities- ears and sinuses, are fixed spaces, so expanding and contracting gases are a bit more problematic.  They have openings into our pharynxes (back of the throat and nose), which allow them to equilibrate. If the openings are blocked for some reason, like a cold or allergies, they can’t.  If the pressure gradient is small, it is painful, because lucky us, these areas are innervated, or might impair hearing or bleed a little.  If the gradient becomes large enough, something else has to give.  In the ears, the eustachian tube, (fig 1) is what allows the middle ear to equilibrate, and if this is blocked, then under enough pressure, the ear drum can perforate.

Fig 2, An enlargement of the inner ear. The tympanic membrane, vestibular apparatus, the ear drum, middle ear, and inner ear. The inner ear contains the cohlea which processes sound and the vestibular labyrinth, which processes head position and acceleration. We have two vestibular labyrinths, one in each ear, and they are mirror images of each other. Each contains 5 fluid filled (endolymphatic fluid) receptor organs. Three semicircular canals, oriented at 90 to each other which measure angular acceleration, each one oriented to pick up movement in a different plane. The urticule and saccule which measure linear acceleration. The utricle and saccule sense linear movement via small stones or crystals called otoconia floating embedded in gel in the endolymph which contact specialized hair cells embedded in the walls of the two sensory apparatus ( Image courtesy of Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=29025011)

We have two vestibular labyrinths, one in each ear, and they are mirror images of each other.  Each contains 5 fluid filled (endolymphatic fluid) receptor organs.  Three semicircular canals, oriented at 90 degrees to each other which measure angular (rotational) acceleration, and the urticule and saccule which measure linear acceleration.  The utricle and saccule sense linear movement via small stones or crystals called otoconia floating embedded in gel in the endolymph which contact specialized hair cells embedded in the walls of the two sensory apparatus (fig 3).  With linear acceleration- moving forwards backwards, up, or in my case, down, the embedded hair cells move immediately, but the free floating otoconia lag due to inertia.  That bends the hair cells (which causes them to depolarize), and sends a signal down the 8th cranial nerve to the brain.  The semicircular canals work similarly, except instead of crystals embedded in a gel, they use a diaphragm called a cupula (fig 4) With angular (rotational) acceleration, fluid starts circulating around the canal and again, due to inertia, displaces the diaphragm, which depolarizes the hair cells and sends a signal down the 8th cranial nerve to our brain.

Fig 3. Drawing of the the utricle and saccule. They sense linear movement via small stones or crystals called otoconia floating embedded in gel in the endolymph which contact specialized hair cells embedded in the walls of the two sensory apparatus.

So the vestibular labyrinths uses fluid filled channels to detect linear acceleration via the utricle and saccule and rotational acceleration via the semi circular canals.   The paired vestibular labyrinths in each ear are supposed to send complimentary information via the 8th cranial nerve, the vestibulocochlear nerve aka auditory nerve, to the brainstem, where one of its functions is to direct and stabilize eye movements. When we detect rotational acceleration via our vestibular labyrinths, it drives a reflex called the vestibulocochlear reflex that attempts to compensate for the rotation by driving our eyes slowly in the opposite direction and allows us to stabilize our vision. It is a good system, but not completely fail-proof, to which as anyone who has ever had positional vertigo can attest.  If the rotation, or sense of rotation- remember inertia, persists then when our eyes have moved as far to the side as they can, as they can they reset quickly to a mid position- basically straight ahead position, then drift again in an attempt to maintain a fixed image or stable gaze. That process is called nystagmus. When we are rotating or moving, this is useful.  When we are not, it can be debilitating. Vertigo is the spinning sensation that happens when the inputs from one or both of the vestibular labyrinths are faulty, or we perceive motion that is no longer there, like spinning on an office chair or stepping off a tilt-a-whirl and end up with vertigo thanks to inertia within the semicircular canals.  Once the stimuli is gone, ie the acceleration, vertigo is typically self-limiting.

Temperature changes in one ear can also trigger the vestibulocochlear reflex by heating or cooling the endolymph and triggering a small current. In medicine, we make use of this in a test called cold (or warm) calorics.   By infusing cold water into one ear, we can activate the lateral semicircular canal.  It is used typically in comatose patients to help assess brainstem function. We don’t use this in conscious people often, because it triggers not only the VOR but vertigo, which rapidly leads to nausea, and vomiting.  I didn’t go into neurology because I enjoy being vomited on. 

Back to my ill-fated jump. My left ear has very dependable anatomy, a fully functioning Toyota level dependency eustachian tube, runs smoothly every time.  My right ear has the K car equivalent and decided not to work that jump, so when I hit the water I perforated my ear drum and infused my middle ear directly with cold water. I essentially self administered the cold caloric test, which is still the only time I have performed it on a conscious patient. 10/10 Would not do again.

Please email or connect through social media us with questions or comments!

fig 4, Drawing of a semicircular canal, with the cupula in the ampulla, the widest region of the canal. Due to inertia, the fluid lags with angular acceleration and displaces the cupula.