1Aviation Medicine CHAPTER 12 SPATIAL DISORIENTATION 136 2 study card

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  1. SENSORY ORGAN systems are used to determine position in space are?
    • a) Vision,
    • b) Vestibular System, and
    • c) Proprioceptors.
  2. Dominant sense organ for orientation?
    • -providing up to 80% of the information needed.
    • -inputs to the brain tend to organise and dominate other sensory inputs
    • -allowing the individual to remain aware of aircraft position/attitude with reference to the Earth?s surface.
    • -comprise three fluid?filled tubes,
    • -orientated at right angles to each other,
    • -in the three planes of motion.
    • -detect angular accelerations.
    • -no movement, the fluid and canals remain stationary with respect to each other (A).
    • -As the head rotates, so do the bony canals.
    • -The endolymph fluid will tend to remain at rest (in accordance with Newton?s laws of motion) due to inertia.
    • - A flap valve, called the Cupula, is connected to sensitive nerve hair cells at the base of each canal which send nerve impulses to the brain when the Cupula is deflected (B).
  4. Acceleration required for semicircular canal to detect movement?
    If acceleration is less than 2? per sec2, the acceleration will not be detected by the semicircular canals. This is because the viscosity of the endolymph fluid and the frictional force from the canal wall is sufficient to move the fluid and canal together. This is referred to as ?sub?threshold? stimulation.
    • -are small sacs (one horizontal and one vertical) located in the utricle and saccule of the inner ear.
    • -Each sac has nerve hair cells that support calcium crystals (otoconia) embedded in a gelatinous membrane.
    • -These hair cells change position when subjected to linear acceleration
    • - or changes of the gravitational force vector,
    • - hence they measure head tilt under normal circumstances. (Figure 12?3).
    • -contributes only about 10% of the total information required by the brain to interpret orientation.
    • -includes all the skeletal and muscular nerve endings enabling awareness of the position of limbs and posture.
    • -There are sensory nerves around joints, in tendons, and pressure and vibration sensors in the skin.
    • The system is virtually useless for maintaining orientation while airborne as the application of G can easily be confused with the force of normal gravity, even when inverted.
  7. Vestibular illusions are described as follows?
    • a) Gyral ? refers to angular acceleration and affects the semi-circular canals;
    • b) Gravic ? refers to linear acceleration or G and affects the otolith organs;
    • c) Somato ? refers to the body; and
    • d) Oculo - refers to vision
  8. Vestibular illusions?
    • -somatogravic illusion (body affected by an illusion induced by the otolith organs),
    • -oculogyral illusion (vision affected by inputs from the semi-circular canals).
  9. Disorientation types?
    • Type 1, Unrecognised.
    • Type 2, Recognised
    • Type 3, Incapacitating.
  10. Type 1, Unrecognised?
    • -This is the worst situation!
    • - CFIT continues to be a major accident type.
    • - No avoidance action is taken as the pilot is unaware of the danger.
    • - is the greatest cause of fatality due to spatial disorientation.
  11. Type 2, Recognised?
    • - the most favourable situation.
    • -pilot knows that he/she is spatially disoriented
    • - can apply learned techniques to ensure safety until reoriented.
    • - situation is uncomfortable, relatively common, and is unlikely to result in an accident.
  12. Type 3, Incapacitating?
    • -pilot is aware that he/she is spatially disoriented,
    • -however is unable to correct the situation.
    • - Panic, or ?disorientation stress?, causes a breakdown in all the skills the pilot could use to rectify the problem.
    • - They give up trying to resolve the sensory conflict and accept their fate.
    • -constant turn or spin-sensation of rotation will cease-fluid(semicircular)canals has stabilised
    • -stop-fluid inertia-causes motion (standing on a accelerating truck(move back wards)-constant speed(stable)-stop(body moves foward)
    • -with a resultant sense of entering a turn in the opposite direction.
    • -subsequent incorrect ?recovery? action may put the aircraft back into a turn/spin in the original direction.
    • -visual system-track moving objects.
    • -brain thinks an object is moving/moving in relation to the object-eyes will move by an amount sufficient to maintain tracking.
    • - If this motion is only apparent, eg severe vertigo, this reflex eye movement will be interpreted as object movement.
    • -eye does not register detail very well while in motion.
    • -head turns,
    • -eye fixates on an object until the limit of the visual field is reached,
    • -then the eye flicks ahead rapidly to acquire another object for fixation,
    • -and so on as rotation continues. This is called saccadic vision.
  16. vestibular-ocular reflex
    • - movement of the fluid in the semicircular canals
    • - sends inputs to the brain to register angular accelerations.
    • - also generates a signal from the brain to the muscles of the eye to start them tracking in a flicking motion.
    • - normal reflex connection (called the vestibular-ocular reflex)
    • - allows the vestibular system to stabilize visual fixation and allow eye tracking within the moving platform of the head,
    • much like a gyroscopic missile targeting system.
    • -fluid motion continue in the canals nystagmus will occur and persist -blurred vision and inability to fixate on stationary targets.
  17. Vestibulo-ocular reflex ?
    • - stabilize gaze by countering movement of the head
    • -semicircular canals measure rotation of the head
    • - signal for the oculomotor nuclei of the brainstem- innervate the eye muscles.
  18. Alcohol is known to induce nystagmus?
    • Even moderate intake of alcohol has been shown to increase the duration and severity of nystagmus and may occur up to 48 hours after the alcohol intake.
    • Alcohol is absorbed into the endolymph fluid in the semicircular canals decreasing its viscosity.
    • Exaggerated differential movement of fluid within the canals can cause vertigo (dizziness) and nystagmus.
  19. The four basic types of eye movements?
    • -saccades
    • -smooth pursuit movements
    • -vergence movements
    • -vestibulo-ocular movements.
    • -sustained linear acceleration sa take-off(eg in the plane taking off pitch up attitude)
    • -otolith-interpret motion as a pitch up attitude
    • -no visual confirmation-horizontal otoliths cannot tell the difference between true horizontal linear acceleration
    • and acceleration due to gravity with the head tilted backwards (see Figure12.3).
    • -the effect oc acceleration is the same effect as tilting the head.
    • -pilot may compensates for this perceived attitude by lowering the nose of the aircraft-danger of flying into the ground
    • -pitch changes may be reinforced visually by the oculogravic illusion, where the eyes are forced down in their orbits by a reflex associated with the tilting back of the otoliths.
    • -This exacerbates the impression of the nose rising.
    • -This illusion typically occurs when visual references are poor, such as at night at isolated airfields.
    • -been termed the ?Dark Night Take-off Illusion? for this reason.
    -illusion experienced with deceleration -perception of a nose down pitch change.
  22. Sloping down runway?
    appear shorter
  23. Sloping Up Runway?
    - appear longer
    • -abrupt leveling from a climb-negative G (otolith organs)-sensation of being inverted.
    • -Confusion from stars and ground lights may reinforce this illusion.
    • -Dark Night Take-off Illusion may result in this sensation.
    • -sudden upward linear acceleration as in turbulence will cause a reflex where the eyes move down.
    • -This is also an oculogravic illusion
    • -can be interpreted as the aircraft pitching up.
    • - is a strong sensation of tumbling induced by the movement of the head from the plane of rotation.
    • - caused by ?cross?coupling? of the semicircular canals,
    • -different and conflicting information is sent to the brain by each of the three canals.
    • -rotation begins, let?s say in the horizontal plane, the horizontal (yaw) canal is initially stimulated by the acceleration.
    • - Movement of the head out of one plane of rotation and into another, for example by looking downwards at your feet,
    • -results in the yaw canal tipping out of the plane of rotation,
    • -so due to inertia the fluid keeps moving in the now stationary canal.
    • -However the ?roll? canal is brought into the plane of rotation by the movement,
    • -so this now detects the acceleration it could not previously feel.
    • -In addition, the ?pitch? canal detects the acceleration of the forward rotation of the head in looking down.
    • -All three semicircular canals are therefore being stimulated in different ways,
    • -which is confusing to the vestibular system resulting in severe disorientation, and frequently nausea.
    • -In addition, lateral displacement of the otolith organs in a rotating environment subjects them to Coriolis Force,
    • -which stimulates the otoliths and creates a sense of lateral displacement.
    • -makes this such a confusing tumbling sensation.
  27. Prevention of disorientation in aviation?
    • -Cockpit ergonomic design
    • -placement of switches
    • -Radios and other equipment
    • -prevent unnecessary head movements
  28. THE LEANS?
    • -semicircular canal and otolith inputs
    • -both somatogyral and somatogravic components
    • -slow rate of roll below the detection threshold of the semicircular canals (less than about 2?/sec2) it will not be detected.
    • -When the angle of bank is detected (on instruments) by the pilot
    • -and the attitude returned to the wings level position,
    • -fluid movement inside the semi-circular canals sends nerve impulses to the brain
    • -which are interpreted as movement in the roll axis.
    • -Consequently, the pilot will feel as though the aircraft has entered a bank in the opposite direction
    • -even though the aircraft instruments indicate straight and level flight (Figure 12.7).
    • dditionally, if the aircraft flies a prolonged coordinated turn, the semicircular canals will eventually
    • cease sending signals once the endolymph motion has stabilized within the canals.
    • The banked turn feels like the new wings level position.
    • On rolling out of the turn, the canals sense the roll to wings level, giving the sensation that the wings level position is actually a roll in the opposite direction.
  29. VISUAL ILLUSIONS discussed in detail in Chapter 8?
    • Perceptual disturbances and feelings of remoteness, detachment, and even ?out-of-body? experiences have been described by some pilots and are also known as central errors.
    • The exact cause of these phenomena is unclear although anxiety, sensory deprivation and a low level of arousal are undoubtedly contributing factors.
    • -one such illusion that usually occurs in single-seat aircraft at high altitude where there is very little sensory stimulation.
    • The pilot may feel isolated, anxious, or in extreme cases feel like they are outside their body looking back at themselves flying the aircraft.
    • - causes feelings of instability and anxiety as if the aircraft is balanced on a knife?edge.
    • -The perception is that any small control input will send it tumbling out of the sky.
    • Alternatively, the pilot may feel that the control column is unable to move due to some external force having control of the aircraft.
    • The source of the problem is the pilot?s own involuntary and unconscious movements and may lead to fighting the controls. This is called the ?Giant Hand Illusion?.
    • Disorientation may range from
    • -a mild case of the leans
    • -to a catastrophic breakdown of normal behaviour.
  34. Preventing Diorientation?
    • A thorough knowledge of the mechanisms of perception is paramount along with good instrument flying techniques.
    • Minimising environmental or self-imposed stress factors are also very important.
  35. Cockpit Design?
    • -One of the main causes of false sensory inputs is head movement out of the plane of rotation.
    • -Cockpits should be designed so as to avoid unnecessary head movements, especially during critical flight phases.
  36. Visual/Instrument Flight?
    • - vision provides up to 80% of orientation, visual flying will usually be adopted.
    • -poor visual cues along with a natural tendency to fly visually, disorientation will often occur.
    • -Transition between visual and instrument flying or vice versa may also increase the risk of disorientation.
    • -It is advisable to commence flying on instruments prior to entering areas of reduced visibility to allow the pilot to adjust to the instrument scanning technique.
    • -This will also confirm the instruments are presenting correct attitude information and give the pilot confidence in the serviceability of the equipment.
  37. Alternobaric Vertigo?
    • - will occur if there is a pressure difference in each middle ear cavity.
    • -This pressure differential is transmitted unequally to the endolymph fluid within the semicircular canals
    • -resulting in a sensation of dizziness.
    • - most likely to occur if suffering an upper respiratory tract infection where one Eustachian tube is blocked more than the other.
    • -can also occur momentarily during the Valsalva manoeuvre or blowing the nose when one ear clears before the other.
  38. Factor that increase the susceptibility to disorientation and impair the ability to recover>
    • Psychological and Stress Factors:
    • a) alcohol and its after-effects;
    • b) hypoglycaemia;
    • c) hypoxia;
    • d) dehydration;
    • e) drugs (prescription and non?prescription);
    • f) high temperature;
    • g) sleep deprivation; and
    • h) psychological stress factors.
  39. Landing Expectancy?
    • -During conditions of reduced visibility
    • -likelihood of flying an instrument approach to land is increased.
    • - workload is particularly high with head movements being more common.
    • -the close proximity of the ground, disorientation during this critical phase of flight may prove disastrous.
    • -the pilot must be prepared to carry out the missed approach from the minima (or any part along the approach path) if the landing requirements cannot be met.
    • -Abrupt power and pitch changes during the missed approach can lead to confusing vestibular inputs which may result in a total loss of situational awareness and subsequent impact with the ground.
    • Depends on the three Ps of:
    • Pre-flight preparation:
    • -Thorough planning, briefing and checking serviceability of equipment are essential.
    • -Knowledge of the expected flight conditions will alert the pilot to the possibility of disorientation.
    • -Good cockpit layout and design of instruments will help prevent disorientation but, if there are particular ergonomic hazards in your aircraft type, make sure you brief these before flight.
    • -A thorough knowledge of the mechanisms of disorientation and conditions in which it may occur will assist in the prevention of becoming disorientated.
    • Proficiency
    • -the more experience one has with instrument flying, the less chance of disorientation.
    • -does not mean that the experienced pilot will not become disorientated.
    • - Maintaining currency with instrument flying allows for correct interpretation of information presented by instruments. --practicing the correct instrument scanning technique will minimise the chance of the aircraft entering an unusual attitude.
    • -Once familiar with instrument flying, it is important to maintain a high standard by practicing.
    • - Don?t push visual criteria.
    • -If visual cues are poor, transition onto instruments and obey the appropriate safety procedures regarding aircraft manoeuvres and terrain clearance.
    • Physical fitness:
    • -minor illness can increase susceptibility to disorientation.
    • -Do not fly when sick or when taking medications of any kind unless in consultation with a medical practitioner qualified in aviation medicine.
    • -Alternobaric (pressure) vertigo is quite common with any ear problems and over the counter medications are likely to cause visual and cognitive decrements which also compromise safety.
    • -It is important to include fatigue in your evaluation of your well?being.
    • 1. Recognise the problem early:
    • -Take immediate action, do not defer. Always aviate first.
    • -Defer non-essential tasks.
    • 2. Re-establish visual dominance:
    • -Get on instruments, make them ?read right?. Believe the instruments and use correct instrument flying techniques. Do not be tempted to switch between instrument and visual flight.
    • -Avoid unnecessary head movements.
    • Any head movement will aggravate the disorientation,
    • and likely induce Coriolis.
    • 3. Beware of persistent symptoms:
    • -Maintain straight & level flight. Flying straight and level will reduce vestibular inputs. Additionally, less workload is required to maintain straight and level flight and more time can be spent concentrating on correct orientation
    • -Advise ATC. Advising other crewmembers within the same aircraft, or crew of another aircraft (in formation) will allow corrective actions to be adopted (flying straight and level, handing over control etc.). Advising Air Traffic Control of the problem and intended actions will allow facilitation of your requirements (assignment of a height block, radar vectors, etc.).
    • -Declare an emergency.
    • 4. Try to resolve sensory conflicts:
    • -Inability to resolve may lead to panic and psychological incapacitation.
    • -Abandon aircraft. If control is not regained and there is a chance of ground impact, ejection should be considered.
    • This does not mean throw away the aircraft every time you are spatially disoriented.
    • Recognising and treating the situation should ensure safety.
    • However, there have been cases where spatial disorientation has led to aircraft abandonment being the only safe option. Have a firm idea in your head before you go flying when you will need to take this option due to spatial disorientation.
    • 5. Transfer aircraft control:
    • -Utilise your co-pilot. In an aircraft with two pilots, handing over control to the other pilot is advisable. It is unlikely that both pilots will be disorientated at the same.
    • -Switch on the Autopilot
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1Aviation Medicine CHAPTER 12 SPATIAL DISORIENTATION 136 2 study card
2017-02-24 12:35:34
AVMO 2017

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