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Aviation Medicine Seminar SeriesAviation Medicine Seminar Series

• Bruce R. Gilbert, M.D., Ph.D.

• Associate Clinical Professor of Urology• Weill Cornell Medical College

• Stony Brook University Medical College

• Head, Section of Male Reproduction• North Shore University Hospital

• Aviation Medical Examiner (AME)

• (1) How to Ace the Medical ExamDecember 13, 2003

• AME training

• How to find a Medical Examiner

• What the exam involves

• The 15 disqualifying conditions…

• (2) Spatial Disorientation-January 10, 2004• Vestibular based disorientation: What it is,

How to deal with it• Vision based disorientation: What it is, How

to deal with it

• (3) Common Aeromedical Problems-• February 14, 2004

• Motion Sickness• Hyperventilation• Hypoxia• Carbon Monoxide• Trapped gas• Self imposed stress

• (4) Advanced TopicsMarch 13, 2004

• Hypoxia/Oxygen use and abuse• Altitude induced decompression

sickness• Trapped gas• Cabin pressurization

INTRODUCTIONINTRODUCTION

• We possess the natural ability tomaintain body orientation and posturein relation to the surroundingenvironment whether at rest or inmotion

• Good spatial orientation is due to effective perception and/or interpretation of your

senses - Visual

- Vestibular(organs of equilibrium located in the inner ear)

- Proprioceptive

- Auditory

• Under certain conditions, your flightenvironment can create sensoryconflict and illusions that makeorientation difficult, and in some casesimpossible to achieve

• Spatial disorientation is the loss of your orientation in relation to the earth’s surface caused by a lack of or misinterpretation of sensory cues from - Visual

- Vestibular

- Proprioceptive

• Visual references provide the dominate sensory information to maintain spatial orientation• Changes in acceleration are detected by the

the vestibular system

Visual IllusionsVisual Illusions

DefinitionsDefinitions

• Sensory Illusion: A false or misinterpretedsensory impression; a false interpretation of a realsensory image

• Vertigo: A hallucination of movement. Asensation of rotary motion of the external world orthe individual

• Spatial Disorientation: Loss of proper bearings;state of mental confusion as to position, locationor movement relative to the position of the earth.

Number of Spatial DisorientationAccidents Resulting in FatalitiesNumber of Spatial DisorientationAccidents Resulting in Fatalities

Spatial Disorientation Accidents byPilot Certificate and Weather Certificate

Basic PhysiologyBasic Physiology

• Vision• Vestibular System

VisionVision

An Inside View of the EyeAn Inside View of the Eye

AMBIENT

CENTRAL

Visual FieldsVisual Fields

Visual illusionsVisual illusions

Visual IllusionsVisual Illusions

Landing IllusionsLanding Illusions

• RUNWAY WIDTH / LENGTH• RUNWAY SLOPE• SURROUNDING TERRAIN• HAZE• SMOOTH, SOLID SURFACES• BLACK HOLE• RUNWAY LIGHTING

Surrounding TerrainSurrounding Terrain

Runway Width-LengthRunway Width-Length

Runway SlopeRunway Slope

Terrain SlopeTerrain Slope

Haze or Sloping Cloud BankHaze or Sloping Cloud Bank

Sensory Illusions-VisualSensory Illusions-Visual

• False Horizon

• Confusing groundand star lights

• Autokinesis• At night, a stationary dim light against a dark

background will appear to move if a pilot fixates on thelight for 6 to 12 seconds. Can be mistaken for anapproaching aircraft.

Vestibular SystemVestibular System

• The vestibular system is located in theinner ear and is the size of a pencil eraser

• Comprised of 2 distinct structures - Semicircular canals (detects changes in angular acceleration)

- Otolith organs (detects changes in linear acceleration)

Vestibular SystemVestibular System

• Otolith Organs-Linear acceleration• Semicircular Canals-Angular acceleration

SEMICIRCULARCANAL

EUSTACHIANTUBE

MIDDLE EAR

OUTEREAR

EAR DRUM(TYMPANIC MEMBRANE)

OTOLITH ORGAN

Ear AnatomyEar Anatomy

Otolith Organ: Utricle & SacculeOtolith Organ: Utricle & Saccule

Otolith OrganOtolith Organ

• The Otolith organs are in each ear at thebase of the semicircular canals

• The otoliths detect changes in linear acceleration in the horizontal plane and

changes in the position of the head inrelation to gravitational forces

OtolithOtolith

• The structure consist of small sacscovered by hair cells

• These filaments project into anoverlying gelatinous membrane tippedby tiny calcium stones

OtolithOtolith

• Sensory hairs will deflect with achange with a change in your headposition

• Hairs will also deflect with sufficientlinear acceleration or deceleration

OtolithOtolith

• During take-off with forward linear acceleration , the fluid will flow over

the otolith and send a signal to thebrain inducing a false sensation of overrotation

OtolithOtolith

• This illusion would tell you to pushforward with the controls regardless ofaircraft attitude

• This could cause the aircraft to nose-over…potentially ruining your day!

Semicircular CanalsSemicircular Canals

• The semicircular canals are made up ofthree half circular interconnected tubeslocated at 90 degree angles from each other

• Monitors angular acceleration and senses rotation in 3 dimensions - Roll

- Pitch

• Each canal is filled with a thick fluidand contains hair cells

• The hair cells moves as the fluidmoves inside the canals

Vestibular Hair CellVestibular Hair Cell

Angular Acceleration and SemicircularCanal Fluid Movement

Time 0 sec > 25 sec StopConstant rate turn > 2 degrees/sec

• If your head is kept still and the airplane is flying straight and level, the fluid in the canals will not move and the hair cells

remain erect - No rotation is felt or detected

• The somatagyral illusions concerns false sensation about the magnitude and or false perception of rotation in its actual absence

• Graveyard spiral• Coriolis Illusion• Inversion Illusion• Leans

ProprioceptorsProprioceptors

• Another sensory input that plays a rolein maintaining spatial orientationcomes from the proprioceptors locatedin:

- Skin

- Tendons and Muscles

- Joints

• Proprioceptors provide informationabout body position and movements

• By sensing points of contact betweenthe body parts and the surroundingenvironment it makes it possible foryou to know your relative posture

• The problem with seat-of-the-pantsflying is that in IFR conditions, they donot differentiate between straight andlevel and performing a 1g turn

Sensory Illusions-VestibularSensory Illusions-Vestibular

• Otolith Organ (Linear Acceleration)• Semicircular Canals (Angular Acceleration)

• Subthreshold accelerationLeans

• Graveyard Spiral• Vertigo/Coriolis• Inversion Illusion

An abrupt change from climb to straight and level canexcessively stimulate the sensory organs for gravity andlinear acceleration, creating the illusion of tumblingbackwards.

The LeansThe Leans

• The leans is the most common illusionrelated to stimulation of thesemicircular canals

• The leans can caused by 2 differentsituations while flying instruments

• - Subthreshold turns (under 2 degrees per second)

• - Rapid changes in aircraft attitude

The LeansThe Leans

• Pilot’s failure to detect angular or banking motion.• If a bank is entered slowly (<2 degrees/sec) or

maintained long enough for fluid in thesemicircular canals (SSC) to stabilize, and theaircraft is quickly returned to straight and level.The motion of fluid in the SSC will give thesensation the aircraft is banking in the oppositedirection. The pilot will try to correct thisperception by banking the aircraft into an attitudepreviously perceived to be straight and level.

LeansLeans

RECOVERY FROMLEFT ROTATIONALSPIN

RIGHT ROTATION SENSATIONAFTER RECOVERY

TURNING BACK INTO LEFTROTATIONAL SPIN TRYINGTO COUNTER RIGHT ROTATIONSENSATION

Graveyard SpiralGraveyard Spiral

• The semicircular canal is activatedwhen you accelerate rapidly into a turn

• The fluid in the canal lags behind theaccelerated canal walls and bends thehair cells• - The brain interprets the movement

of the hair cells as angular movement

• If the turn continues at a constant ratefor seconds or longer, the motion ofthe fluid catches up with the canalwalls

- The hair cells are no longer bent and the brain receives thecompletely false impression that turning has stopped

• When you return to level flight, thefluid inside the canal will continue tomove during roll-out and even forwhile after the turn has stopped

- This will send a false signal to the brain indicating that you areturning in the opposite direction

• If this sensory illusion is believed, you may try tocounteract it by inappropriately turning the aircraftin the original direction

• If the turn continues and descent occurs the decentis felt by the pilot who attempts to pull back on theyolk to prevent further altitude loss. This onlyserves to tighten the turn and increase the decentrate. Ultimately structural damage andcatastrophic failure occur prior to impact…reallyruining your day!

Coriolis IllusionCoriolis Illusion

• The Coriolis illusion is probably the mostdangerous of the vestibular illusions

• This illusion involves the simultaneousstimulation of two or more canals• As associated with a sudden tilting of your head while

the aircraft is turning

Coriolis IllusionCoriolis Illusion

• This illusion produces a veryincapacitating sensation that theaircraft is rolling, pitching, and yawingall at the same time

Preventative MeasuresPreventative Measures

• The best way to protect against spatial disorientation is to educate yourself

about the sensory illusions andrecognize your limits as a pilot

• Take the opportunity topersonally experiencesensory illusions in ademonstration device• Barany chair• Gyro• Virtual Reality Spatial

DisorientationDemonstrator

Gryo-2Gryo-2

•• PORTABLE SPATIALPORTABLE SPATIALDISORIENTION DEMONSTRATORDISORIENTION DEMONSTRATOR

Gryo-2Gryo-2

• By following a few precautions youcan prevent or cope with thesessensory illusions

- Obtain a thorough weather briefing - Correct interpretation of the briefing - The benefit of 180 degree turn before entering IFR

conditions

• If you find yourself in instrumentconditions, concentrate on flying basicinstruments and disregard body sensations• Concentrate on your instruments.

Remove yourself from the peripheralenvironment and its distractions

• Increase instrument cross-check rate• Ask ATC as soon as you recognize the

problem• Avoid head movements during turns

- Move your eyes rather than your head - Defer non-essential task - Relinquish control to the other pilot - Use your auto-pilot

SummarySummary

• Vestibular System

• Semicircular Canals

• Graveyard Spin/Spiral

SummarySummary

• The Leans

• Coriolis Illusion

• Otolith Organs

SummarySummary

• Proprioceptors

• Preventive Measures

WE ALL GET DISORIENTATION WHILE FLYING. THEREAL CONCERN IS HOW LONG YOU LET IT LAST.

IF YOU ARE AWARE OF THE TIMES ANDCONDITIONS THAT IT’S MOST LIKELY TO OCCURAND APPROPRIATELY INCREASE THE FREQUENCYOF YOUR REFERENCE (CROSS-CHECK) TO A VALIDHORIZON, YOU’LL CONVERT UNRECOGNIZED TORECOGNIZED DISORIENTATION.

DAYS ARE RUINED BY UNRECOGNIZEDDISORIENTATION BUT NOT OFTEN FROMRECOGNIZED DISORIENTATION

SummarySummary

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