1Topic 2.9 Disorientation AVMO 0019 study card 22022017

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  1. Learning Outcomes?
    • • Explain how various sensory systems contribute to spatial orientation.
    • • Describe the vestibular and proprioceptive systems in terms of:anatomy,function,limitations
    • • Categorise the types of vestibular and central illusions.
    • • Recommend strategies for the prevention of disorientation.
    • • Recommend strategies for overcoming disorientation in flight.
    • • Identify vestibular illusions experienced or observed using the Barany Chair.
    • • Describe situations in which aircrew can suffer spatial disorientation.
    • • Discuss the role of vestibular physiology in the genesis, prevention and management of disorientating vestibular illusions in flight.
  2. Spatial Disorientation SENSING ORIENTATION?
    • Eyes 80%
    • Proprioceptors 10%
    • Vestibular 10%
    • Integration and Interpretation
    • Perception of orientation
    • Peripheral Vestibular System
  3. Vestibular System?
    • • Mechanoreceptive sensory hair cells
    • • Afferent traffic via the vestibuloacoustic nerve (CN VIII)
    • • 3 ampullary nerves
    • • 2 saccular nerves
    • • 1 utricular nerve
    • • Nerve cell bodies lie in Scarpa’s ganglion in internal auditory meatus
  4. Semicircular Canals?
    • • 3 in each ear at right angles to each other
    • • Angular accelerometers
    • • Stimulation threshold of 2o/sec2
  5. Semicircular Canals?
    • • Prolonged rolls and turns reach steady state –no further acceleration
    • • Cupula returns to resting position
    • • Subsequent change in angular acceleration (eg cease turn, move head) sensed as a NEW movement
    • • Acceleration less than 2deg/sec not sensed at all
    • • Basis for SOMATOGYRAL, CORIOLIS, LEANS
  6. Visual Control?
    • • Medial longitudinal fasciculus
    • • Extraocular muscles linked to vestibular system
    • • The vestibulo-ocular reflex (VOR): stabilisation of retinal image
    • • Conjugate eye movements coordinated with head movements
    • • Prevents smearing of visual image
  7. Vestibulo-ocular reflex?
    • 1. Detection of rotation
    • 2. inhibition of extraocular muscles on one Side.
    • 2 Excitation of extraocular
    • 3. Compensating eye movement
  8. Otolith Organs?
    • • 2 in each ear - utricle and saccule
    • • Aligned in horizontal and vertical plane
    • • Linear accelerometers
    • • Vertical organ senses gravity under normal conditions
  9. Sensing linear acceleration?
  10. Otolith Organs?
    • • Deceleration and tilting head down give the same movement of the otolith membrane
    • • Confused messages basis of the SOMATOGRAVIC ILLUSION
  11. Semicircular canals Respond to?
    • Angular acceleration
    • Functions
    • Visual stability
    • Sense of turning/rotation.
  12. Otolith Organs Respond to?
    • •Linear acceleration
    • ` Functions
    • Tilt sensation
    • External force sensor.
  13. Proprioception?
  14. SPATIAL DISORIENTATION (SD)?
    The failure to correctly sense the position, motion or attitude of yourself, or your aircraft, in relation to gravity and the Earth’s surface.
  15. Prevalence Data?
    • 90% of SD related accidents are fatal.
  16. High risk flight environments?
    • • Flight in IMC Night
    • • High altitude
    • • Featureless terrain
    • • Prolonged accelerations
    • • Prolonged angular motion
    • • Subthreshold attitude changes
    • • High workload
    • • Cloud penetration
    • Low altitude in helicopters
  17. Experience does not confer immunity?
  18. Types of Disorientation?
    • • Unrecognised
    • • Recognised
    • • Incapacitating
    • Type 1
    • Type 2
    • Type 3
    • Incorrect perception
    • Correct perception
    • Conflict not resolved
  19. Somatogravic Illusion Caused by?
    • -Linear acceleration
    • -Otoliths and proprioceptors
    • -Poor visual cues
    • -False sensation of pitch (up or down)
    • -Dark Night Takeoff Illusion”
    • -Missed Approach
    • -Catapult launch
  20. Somatogravic Illusion Prevention?
    • -Stay on instruments
    • -May be accompanied by the oculogravic illusion 223 kt, 15CO fl
  21. Somatogyral Illusion Caused by?
    • • False sensation of rotation
    • • Semi-circular canals
    • • Graveyard spin or spiral
    • • Accompanied by the oculogyral illusion
  22. Somatogyral Illusion occurs When?
    • • Spin recovery
    • • Extended turns
    • • Poor visual cues
  23. Somatogyral Illusion Prevention?
    • • Avoid prolonged spinning
    • • Trust your instruments.
  24. G-excess Illusion Caused by?
    • • False sensation of rolling off bank during a turn
    • • Pulling G during a level, banked turn and looking into the turn.
  25. G-excess Illusion Prevention?
    • • Don’t look into turn
    • • ‘Snapshot view’ only.
  26. G-excess Illusion?
  27. The Leans?
    • • A false sensation of roll attitude when flying level
    • • Pilots can lean in order to dispel the sensation
    • • Not usually dangerous
    • • The most common illusion of all
  28. Coriolis Illusion Caused by?
    • • Tilting one’s head out of the plane of angular motion,
    • • ‘cross-coupling’ that transfers the motion percept from one semicircular canal to another
  29. Coriolis Illusion Result in ?
    • • Strong, unpleasant sensation of tumbling
    • • Nausea is common
  30. Coriolis Illusion Prevention?
    • Minimise head movements when turning
  31. Flicker Vertigo?
    • • Rotating or flickering light
    • • False sense of rotation in a direction opposite to the moving light.
  32. Alternobaric Vertigo?
    • • Spinning sensation caused by a difference in pressure between the left and right middle ear “Central” Errors
    • • Break-off phenomenon - feelings of detachment, isolation or physical separation while flying
    • • Variations:
    • • Knife edge - increased awareness of aircraft movement
    • • Giant hand - inability to make control inputs
  33. PREVENTION OF SPATIAL DISORIENTATION?
    early use of instruments don’t lie
  34. What can AVMOs do?
    • • Assess fitness to fly
    • • Subtle symptoms and signs cause significant SD risk
    • • Advise aircrew
    • • Medications, conditions, alcohol, fatigue, operational factors
    • • Advise Command
    • • Awareness of increased risk of SD in operations helps determine risk
  35. What can be done pre-flight?
    • • Pre-flight preparation
    • • SD Training
    • • Awareness of mission and flight conditions
    • • Recognise a problem early and take immediate action
    • • Maintain proficiency in instrument flying
    • • Don’t fly by ‘seat of the pants’
    • • Early and clear transition to instruments
    • • Fly only if physically & mentally fit
    • • Avoid alcohol and self-medication
  36. If disorientation occurs?
    • 1.Recognise the problem early
    • • Take immediate action
    • • Defer non-essential tasks
    • 2.Re-establish visual dominance
    • • Get on instruments, make them “read right”
    • • Avoid unnecessary head movements
    • 3.Beware of persistent symptoms
    • • Maintain straight & level flight
    • • Advise ATC
    • • Declare emergency
    • 4.Try to resolve sensory conflicts
    • • Inability to resolve may lead to panic and psychological incapacitation
    • • Abandon aircraft
    • 5.Transfer aircraft control
    • • Co-pilot
    • • Autopilot.
    • Make the instruments “read right”
  37. Quiz question 14?
    • • The semicircular canals detect:
    • a. Angular acceleration
    • b. Linear acceleration
    • c. Movement of the eyes
    • d. Acceleration due to gravity
  38. Quiz question 15?
    • A somatogravic illusion generally produces a false sense of:
    • a. Roll attitude
    • b. Yaw attitude
    • c. Pitch attitude
    • d. Rotation
  39. Please note:?
    • • All major Aviation Medicine reference texts categorise Somatogyral Illusion and The Leans as separate entities.
    • • Semantics in terminology is not important, but understanding what it feels like is essential.
  40. Somatogyral Illusion?
    • • “…a false sensation of rotation (or absence of rotation) that results from misperceiving the magnitude and direction of an actual rotation…result from an inability of the semicircular canals to register accurately a prolonged rotation.”
    • • Examples:
    • • Graveyard spin
    • • Graveyard spiral
    • • Gillingham illusion
  41. The Leans?
    • • :…a false percept of angular displacement about the roll axis…often associated with a vestibulospinal reflex appropriate to the false percept..”
    • • Caused by subthreshold rolls or prolonged bank
    • • Involves both otoliths and semicircular canals in prolonged turns
    • • Feeling banked turn dissipates (somatogyral)
    • • G vector gives false vertical cue (somatogravic)

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david_hughm
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1Topic 2.9 Disorientation AVMO 0019 study card 22022017
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2017-02-25 12:42:58
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