study notes for exam human performance aviation medicine

8/6/2019 Study Notes for Exam HUMAN PERFORMANCE AVIATION MEDICINE

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Physics of the Atmosphere

o Functions of the atmosphere :1. Radiation Protection

y UVand sub-atomic articlesy Ozone layer

2. Thermal Protectiony Clouds reflect IR radiation (greenhouse)y Pollutants cause excess warming

1. Gaseous support of lifey O2, CO2,H2O

o Atmospheric Division: Troposphere weather convection Stratosphere ozone Mesosphere Thermosphere/Ionosphere charged particles.Temp can reach 1500

degrees

Exosphere space, particle collisions are rarePhysiological Zones

MSL 10000ft The physiological zone

10000-50000 ft The Physiologically Deficient Zone

50000ft+ The Space Equivalent Zone

Composition of the atmosphere

Oxygen 21% Nitrogen 78% Rare gases (methane, ozone, carbon dioxide) 1% Pressure/Altitude relationship

Gravity vs thermal expansion

Density and pressure both fall exponentially

ICAO standardatmosphere

Pressure 760 mmHG Density 1.225kg/m3Boyles Law

At a constant temperature, the volume ofa gas is inversely proportional

to the pressure

At constant T, V1/w P

Daltons Law

The total pressure ofa mixed gas = sum of partial pressures of the

constituent gases

Ptotal = p1+ p2+ p3+pn


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Charles Law

Pressure remaining constant, Volume ofa gas will vary with temperature

Volume remaining constant, pressure ofa gas will vary with temperature

Henrys Law

The amount of gas held in solution is proportional to the pressure of the

gas above the solution

The Law of Gaseous Diffusion

A gas will move from an area of higher pressure to an area ofLower

pressure


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Cardiovascular & Respiratory Physiology 9/11/

0101:0 :00 AM

AtmosphereTrachea &

BronchiAlveoli

Blood: CO 2carried in

solution as H+

and HCO3(carbonicacid)

Tissues

Oxygen + Glucose = energy 1 glucose = 38 aerobic = 2 anaerobicMetabolism

The process where cells use oxygen carbon dioxide (waste) Requires constant fuel : ( carbohydrate from food) + oxygen

Haemoglobin

Conjugated protein Haem (iron-porphyrin compound) + globin (4 polypeptide chain complex) Hb = 4O2 Normal Hb concentration = 15g/100mlOxygen Pathway:

Carbon Dioxide Pathway:

Chemoreceptors

Central chemoreceptors are located in the medulla.

Sensitive to CO2 Rise in pCO2/ Fall in pH (more acidic)Peripheral chemoreceptors located in the aorta and carotid arteries

Sensitive to O2 Fall in pO2A rise in pCO2 or fall in pO2will lead to an increase in rate and depth of breathing.

The Heart

4 chambered pump 2 atria, 2 ventricles valves ensure one-way blood flow Atria pump blood ventricles lungs (right ventricle) and rest of body (left

ventricle)

Contraction of ventricle = pulseBlood & Pressure

Resp ra o (exc a ge ofgases)

C rc la o (d str b tio ofgases)

Oxidatio in cells

Atmosp ereTrac ea &

Bronc iAlveoli

Blood: O2carried in redcells bo nd to

aemoglobin

Tissues


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Adu t s 6 L d 50% fluid (plas a) + 50% blood cells Red Cells carry oxygen White cells (5types) attack foreign cells produce antibodies kill bacteria Platelets are blood clotting Normal Blood pressure 120/ 0mmHg Stroke Volume = amountof blood ejected each beat Cardiac Output= Stroke volume x HeartRate = SV x HR Cardiac Output: 3-5L/minArt r

& V

Arteriestake blood AWAY from the heart

High pressure blood Elastic, muscular walls Regulate blood pressureVeinstake blood to the heart

Low pressure blood Inelastic Contains valves for one-way flowCapillaries allow diffusion in the tissues

Very thin wallso Cir tio Arterial driving pressure Venous return determines cardiac output Non-return valvesin veinshelps blood getbackto the hear to maintain CO Negative intrathoracic pressure during inspiration Peripheral muscle actionBaror f

x

Stretch receptors Monitors and adjusts blood pressure Fall in BP = less baroreflex activityIncrease cardiac contractility + Increase HR +

Vasoconstriction

BPtherefore rises 6-12 secondsto full activate


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Hypoxia

o Hypoxia isthe lack ofsuffiecientoxygen to meetthe needs ofthe body tissues The brainweighs only 2%butis responsible for a 20%oxygen uptake. Hence, the earliesteffects of

insufficientoxygen are the impairmentof cerebral functions.

o As altitude increases, pressure decreases and above 10,000ft, there isinsufficientoxygen tomaintain adequate cerebral function. Itishard to predictwhen hypoxia affects an individual

as each ofusis differentphysically and mentally to pinpointan exactmeasurementof

altitude where impairmentmay occur. Also, due to the nature ofhypoxia, the pilots

judgementisunaware ofitsinsidious effects.

oo Factors causing hypoxia:1. Altitude the greater the altitude, the more rapid the onset2. Time longer time of exposure greater effect3. Exercise increasesthe demand for oxygen4. Cold energy is required to generate heatto overcome lowtemperature, and thisincreases

demand for oxygen

5. Illnessillnessincreases energy demands ofthe body6. Fatigue lowersthe threshold for hypoxia symptoms7. Drugs/Alcohol depress brain functionsreduce the tolerance of altitude8. Smoking produces carbon monoxide which bindsto haemoglobin with a greater affinity

than oxygen, thus reducing the amountofhaemoglobin available for oxygen transport.

Also, lung disease affects air sacs and makesithard to breathe

Types of hypoxia

1. Hypoxic hypoxia- Low partial pressure of oxygen in the arterial blood- Mostcommon : exposure to high altitude, low pressure and no supplementof oxygen2. Anaemic Hypoxia- Reduction ofhaemoglobin circulating the body- Decreased red blood cell + excessive bleeding such ashaemorrhages- Iteffectively puts body ataltitude before leaving ground and cockpitaltitude gives boostto

more altitude.

3. Histotoxic Hypoxia- Happenswhen the appropriate amountof oxygen is reaching the cells butthere is a

disorder prohibiting the cellsto utilise oxygen effectively

- Carbon monoxide poisoning : inhibitsthe ability ofhaemoglobin to release the oxygenbound to it

- Excessive intake of alcohol4. StagnantHypoxia


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- Happenswhen blood failsto deliver oxygen to targettissues due to local restriction in theflow ofwell-oxygenated blood

- Blood pooling peripheral vision loss and loss of ability to focus, can also cause blackoutsand unconsciousness

- Extreme rapid accelerationSymptoms and signs

Euphoria slows brain down + relaxed feeling Personality change common sense is diminished Impaired thinking and judgement Slowed reaction Mental/muscular incoordination Diminished hearing and vision Severe headaches Blue discolouration ofskin Nausea Shortness of breath Fatigue Recovering from hypoxia substantial memory loss Ultimately, loss of consciousness, coma death

Stages of hypoxia

All individualswho normally live around sea level will experience symptoms ofhypoxia when

they are exposed to altitude of 10000ft+

Stages ofhypoxia can be classified by performance decrementwhichis dependentupon altitude

and the oxygen saturation of blood.

Indifferent stage

Occurswhen breathing air ataltitude of0-10,000ft arterial oxygen saturation is 98%to87%.

Dark adaptation is affected at5000ft visual sensitivity to the nightis reduced by 10%caused by mild oxygen starvation , hence the use of oxygen is required during nightflightat

high altitudes.

Performance of newtasks may be impaired. Slightincrease in heartand breathing rates.CompensatoryStage

10,000ft 15,000ft


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arterial oxygen saturation 87%to 80% Cardiovascular and respiratory physiological responses provide protection againsthypoxia Effects on central nervoussystem become perceptible after ashorttime ; drowsiness,

decreased judgementand memory, difficulty performing tasks requiring mental alertness or

discrete motor movements.

Effects of prolonged flightatthis altitude : persistentheadache & excessive fatigue 12,000ft+ ; shortterm memory loss Worstcase during climb 10k-15k ft: become hypoxic Hypoxic : person gets fixated to a particular task, during focus, loses all surroundings Loses judgement, decrease psychomotor skill, difficulty in simple tasks Sum up these reactions aviator losessense oftime and surroundings, spendsthe last

moments of consciousnessin a meaninglesstask

15000ft+ will cause lostof consciousness and death Dist rbance stage

15,000ft 20,000ft Arterial oxygen saturation 65%to 60% Mental performance deteriorates , confusion, dizziness occursin few mins Total incapacitation with loss of consciousness rapidly followswith little or no warning.Time of Useful consciousness

Maximum length oftime during which an individual can carry outpurposeful activity following

a loss of oxygen supply

EPT =Effective Performance Time isthe length oftime an individual is able to performuseful flying dutiesin an environmentofinadequate oxygen, EPT more accurately refersto

functional performance than TUC

Alveolar gases

Dry air is composed of 21% oxygen, 78%nitrogen and 1%other gases. Atthe barometricpressure of 760mmHg, partial pressure of oxygen would be 160mmHg. However, when a

gasisin contactwith a liquid and isin equilibrium with the liquid , the partial pressure of

oxygen will change.

Lungs & airways are always moist, air is rapidly saturated withwater vapour in the uppersegments ofthe respiratory system. Therefore, typical mixture of alveolar gas : oxygen,

nitrogen, carbon dioxide, water vapour

Atbody temp, water vapour has a partial temperature of 47mmHg. Hence total pressureremaining for the inspired gasesis 713mmHg giving the partial pressure of oxygen to be

150mmHg.


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As altitude increases, ambientpressure decreases butpartial pressure ofwater vapourremains as 47mmHg. This changesthe composition of gases. For every partof air atan

increased altitude, oxygen countis relatively lesser than oxygen atsea level.

OxygenSystems

For flights above 10,000fta supplementary oxygen supply mustavailable. Itmay consistof a

portable oxygen container and mask or a fixed installation adjacentto the crew and passengers.

Diluter Demand

Flightcrew oxygen system : close-fitting maskwith a regulator thatsupplies a flow ofoxygen according to cabin altitude.

Regulators are designed to provide an appropriate proportion of oxygen and air from a mixof0%oxygen and 100%cabin air ataltitude below 8,000ft. Itgradually increasesthe

proportion of oxygen until 33,000ftwhere 100%oxygen and 0%cabin air is delivered.

Oxygen issupplied atthe rate ofthe user when they inhale. Thisreducesthe amountofoxygen required.

Pressure demand

Similar to diluter demand equipment Oxygen is automatically supplied under slightpressure atcabin altitudes above 10,000ft

with full pressure breathing above 38,000ft.

Pressure Demand mask with mask mounted regulator

A pressure demand maskwith a regulator attached directly to the mask rather thanmounted on the instrumentpanel or elsewhere

Mask mounted regulator eliminatesthe problem of a long hose which mustbe purgedbefore oxygen is delivered to the mask.

Continuous flow oxygen system

For passengers Re-breather bag ( collectsusers exhaled air to be re-inhaled) The oxygen in the re-breather is replenished by a continuous flow of oxygen regulated as for

dilutor demand.

Only a portion of oxygen is consumed during each breath, air in the re-breather remainshighly saturated with oxygen and is drawinto the lungs atthe beginning ofinhalation. If bag

is depleted before breath, cabin air isused for remainder inhalation

Cabin Pressurisation


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Decompression is slow

body gases will escape withoutdifficulty. Middle ear and sinuses

will be ventilated fairly easilybecause the higher pressure within

the cavities will force open theEustachian tube ( connects the

middle ear to back of nose) and thesinus openings.

Decompression is rapid

Gases expanding inside theintesinal tract may cause pain but

instestines can stretch significantly

Same as lungs because lung gas isusually expelled through thetrachea with little resistance

For prolonged flights operating above 10000ft, using oxygen masks is exhilarating and

inefficient. Another method to maintain adequate supply of partial pressure of oxygen is to

pressurise the aircraft cabin to ensure the cabin altitude remains below10,000ft, irrespective of

the actual altitude of the aircraft.

Cabin air supple is provided by tapping bleed air from the aircraft engine or by using an

independent compressor, and the pressure within the cabin is controlled by an outflow valve.

Maintaining the cabin at sea level pressure would require a very strong and thus heavy

structure for the fuselage affects weight and fuel economy.

Normal individuals can tolerate altitudes of up to 10000ft but this is not true for elderly or the

diseased who are less tolerable to the effects of hypoxia. Hence pressurised cabins are to

maintain ,000ft to compromise physiological needs of the crew and economical needs of

aircraft operator.

Rapid Dec mpre

ion

If cabin pressure is suddenly lost during flight, pressure inside will equalise outside pressure of

air. Magnitude of the rate of decompression, physiological effects will be determined by:

Si e of cabin rupture or number of lost windows Aircraft altitude Pressure differential between cabin and external environment. Volume of cabin Position of the rupture or lost window venturi effect can lead to increase in cabin altitude

if cabin air is sucked out

The larger the rupture + smaller cabin + greater pressure differential between cabin and the

outside air more rapid the rate of decompression

Explosive decompression = extremely rapid loss of pressure .

When this occurs , mist will fill the cabinA sudden equalisation of pressure = strong blast of air outwards from cabin opening. This may

cause loose items / humans to be sucked out. Therefore, flying at high altitude in pressurised

aircraft , seat belt must be used and also provides restraint during unexpected turbulence.

Within the body cavities, free gases will expand and will be expelled wherever possible.


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Decompression sickness

In addition to the gases trapped in the body cavities, a considerable volume (primarilynitrogen) exists elsewhere within the body, not in normal gaseous state but in solution.

Decompression sickness usually occurs 18,000ft 25,000ft

Prevention and treatment

Decompression sickness can be prevented by pre-breathing 100% oxygen before flight inorder to wash out nitrogen dissolved in the body tissues

There is a risk of decompression sickness if flying within a 12-24 hr scuba diving ,dependent on the depth of dive

Following donning of100% oxygen rapid deceleration to 25,000ft and a slower descent tobelow 18,000ft should prevent decompression sickness

Decompression sickness should be treated with 100% and individual should be kept warmand still

Emergency post-flight treatment in a recompression chamber may be necessary on landingand medical advice should be sought by radio communication prior to landing.

Barotrauma

At high altitudes, the body is exposed to high pressure externally, but internally, the pressure

remains the same as it was on the ground and so the gases inside begin to expand in accordance

with Boyle s Law.

The human body contains a significant amount of gas which is largely air. Some is dissolved in

bodily fluids. Air also exists as a free gas in the intestinal tract, the middle ear and the sinuses

where it will expand as altitude increases.

Expansion of gases in sinuses headache Trapped gases in middle ear ear pain Trapped gases in stomache abdominal fullness Trapped gasses in small intestine considerable pain and expansion can cause faintingReduce barotrauma :


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Dontfly during a cold or congestion ofupper respiratory tract Avoid eating gas forming foods Avoid eating too quickly or too much because ofthe risks ofswallowing air Do notfly within 24 hrs of dental treatment Avoid drinking large quantities or gassy fluidsHyperventilation

Breathing in excess ofthe metabolic needs ofthe body. A waste productof metabolism is carbon

dioxide whichis carried to the lungs via the bloodstream. The respiratory centre ofthe brain

controlsthe rate of breathing and reactsto the amountof carbon dioxide in the bloodstream.

When there is exercise, the cellsuse more oxygen and thisinduces more carbon dioxide to be

produced. However , if a faster rate of breathing takes place and no physical exercise is

produced, no carbon dioxide is created. Hence, the excessive breathing removes carbon dioxide

from the bloodstream faster than metabolism , causing a chemical changesin the bloodstream.

Thisishyperventilation.

Causes of hyperventilation :

Anxiety Stress Excitement Motion sickness Vibration Heat Acceleration Pressure breathing Hypoxia

Symptoms of hyperventilation:

Dizziness Increased sensation of body heat Tingling sensation in fingers and toes Increased heartrate Nausea Blurred visionExtreme case: loss of consciousness breathing rate slows fastrecovery backto normal

Breathing in paper bag : inhaling carbon dioxide increases blood acidity to restore the normal

acid-base balance and decreasesthe breathing rate


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Vision

Why is vision important in aviation?

Provides 80%oforientationduringflight Importantincollisionavoidance Depthperception(takeoff,landing,formation) Importantforsituationalawarenessandcorrectorientation

Important eye components

C

:Majorityofthefocusingabilityoftheeye

Lens:finetunesthevisualimage

Retina:thelightsensitiveareawherelightisconvertedtoelectrical

impulses

Iris:controlstheamountoflightenteringeye,catersforlevelsof

illumination

Pupil:theapertureintheiristhroughwhichlightenterstheeye

Extra-ocularmuscles:co-ordinatedeyemovements

Visual Functions

Aimedatdetecting 3 majorcomponents:

1. Lightsense

2. Form Sense

3.Colour Sense

Thesearedetectedbytheretina.

Thecrudeimageisthenmanipulatedbythebraintoproducea

recognisableimage

Cones

Located in centre of theretina(fovea)

Detect detail , perceive colourand identify far-away objects

Used for day or high intensitylight vision

Best visual acuity (capacity ofeye to resolve detail)

3 diff types: red, green , blue

Each cone connects to asingle optic nerve fibre

High resolution & detail

Rods

Located in periphery of retina, an area that is 10000 timesmore sensitive to light thanfovea

Used in low light intensity

Poor visual acuity


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Visual Acuity

Measured via standard eye chart at 6m away Normal visual acuity 6/6 : subject sees 6m while rest of population

sees 6m

Poor vision 6/60 Subject sees 6m while rest of population sees 60mColour Perception

Cone (fovea) function Blue,red,green ratio 1:10:10 Variation in proportion and saturation of these colours gives any other

colour

Peak spectral sensitivities: Red cones 564nm Blue cone 420nm Green cone 534nmPhysiological blind spot

Caused by lack of rods and cones at optic disc Covers 2-6 degrees of visual field Sufficient to block18 m object at 200mDepth Perception

Binocular cues( up to 200m):

Convergence amount that the axes of the eyes converge to bringvisual target to each fovea

Stereopsis the fusion of signals from slightly disparate retinal points,measured in seconds ofarc ofdisparity

Accommodation if the eye observes a close object, the lens isthickenedand the pupil becomes larger, while to focus on a more

distant target, the lens flattens and the pupil becomes smaller

Monocular cues:

Retinal image/size constancy comparison of the object from pastexperience

Relative motion/motion parallax near objects appear to move againstthe oberservers motion, distant objects move in the same direction as

the observers motion

Obscuration nearer objects appear to cover distant objects Aerial perceptive


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Overlap Position in visual field Atmospheric perspective distant objects appear more blue and hazy

than near objects

Linear perspective parallel lines converge at adistancePerception time

Detect visualise,recognise : 1s

What to do? 2s

Muscle movement, change path 2.5s

Total time : at least 5s

Night vision

Function of the rods ( & therefore peripheral vision) Visual acuity is less than during the day Colour vision is poor Night environment consists ofdegraded visual cues Can be worsened by atmospheric conditionsDark Adaptation:

The process by which the eyes adapt for optimal night visual acuityunder conditions of low ambient illumination

Rapidadjustments from dark to light Slower adjustments from light to dark Each eye adapts independently 30min -45min to fully adapt depends on regeneration of photopigments in the rods and cones 5-7 min for cones 30-45 min for rods full adapted cones give very poor night vision therefore, best when

rods are fully adapted

To minimise dark adaption time:

Avoid inhaling carbon monoxide from smoking /exhaust Adjust instrument and lighting to low as possible Avoid exposure to bright lights Use supplementary oxygen at night flying above 5000ftThe night blind spot

At night, the fovea cannot be used for vision as it contains no rods This region of the eye is effectively another blind spot Each eye has 2 blind spots: The physiological blind spot ( optic disc )

and the night blind spot (fovea)


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Using eyes atnight

Awareness of limitations of eye Rods need to be used Looking off-centre ( not directly at an object) stimulates the peripheral

vision and rods

Keeping the eyes moving stimulates rods Increases the chances ofdetecting an object ( stationary or moving) Never fixate for more than 2-3 seconds Insure a15degree overlap when scanning This will counter the night blind spotMaximise Night vision prior to flight

Balance diet Plenty of rest Avoid bright lights Wear sunglasses No smoking, alcohol, drugsMaximise Night vision DURING flight:

Ensure complete darkadaptionTarget acquisition and object detection can be maximise by :

Use off centre viewing ( 10 to 15degrees) Keep gaze moving Scan pattern needs practise Exploit contrast if possible Maintain clean visors/screens Close one eye if flashed Minimise cockpit lighting Min external lighting Use supplementary oxygen


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Noise

o Effects ofaltitude change:o Boyles Law: the air in the cavity of the middle ear expands and

contracts depending on atmospheric pressure.

o During a change in altitude, if the pressure in the ear is not readilyequalised with outside pressure, the drum is disintended inflammation

+ pain + temporary deafness

o CLIMB: When air in the middle ear expands, small bubble ofair isforced out through the Eustachian ( connects middle ear to back of

throat) tube at frequent intervals. Hence, pressure equalisation occurs

automatically

o DESCENT: outside air pressure increases, the middle ear which hasaccommodated to the reduced pressure at altitude is at a lower

pressure than the external ear canal.Consequently, the increased

pressure forces the eardrum inwards.This is more difficult to relieve

because air must now go back up the Eustachian tube to equalise

pressure between the inner ear and the outside pressure.

oo Vestibular Apparatus:o 3 Semi-circular canals: form a motion sensing system andare right

angles to each other. Assists in the maintenance of balance and to

stabilise the eyes

o Otolith: sense gravity and linear accelerationoo Angular Acceleration:o When the head beings to turn, speed up, slow down or stops turning,

sensory hairs in the canal are temporarily deflecteddue to the motion

of the fluid lagging behind the motion of the canal wall.Nerve impulses

are sent to the brain turning motion is sensed.

oo


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Motion sickness

o Motion sickness is a response to real or apparent motion to which aperson is unfamiliar and hence, unadapted.

o Flying training: 23-39% of student pilotso Interfere with progresso Affect enthusiasm, performance and self-esteemo Operational flying: 10% of crewo Loss of performanceo Decresed effectiveness ofaircrafto Aborted flighto Flying safety hazardo Sea: Rough 90% , 55% in moderate seaso Potent stimulanto Vomiting causes dehydration and electrolyte disturbanceso Erodes will to liveo Must take tablets ASAPo Space flight : 40-50% ofastronauts experience SMSo Signs / symptoms appear in first few hrs of microgravity exposureo Worse with head movementsCauses of motion sickness

o Motion in flight, sea, in car generates patterns of sensory input whichconflict with those patterns based on land.Brain will be upset by this

conflict due to signals from vestibular system

o Anxiety & hyperventilationWhen someone is anxious and tense, the nervous system becomes

extra sensitive and if vestibular system is already sensitive, anxiety

can take it above critical level.

When someone hyperventilates, it increases ones arousal level

increase in sensitivity of vestibular system

o Alcohol diffuses from bloodstream to endolymph (semi-circular canal).Because it is less dense than water, alcohol does not become evenly

distributed within the endolymph, but creates a light spot which causes

the fluid to move within semi-circular canal as if the head was turning.

This increases sensitivity of the canal head spinning .Following the

removal ofalcohol, sensitivity of the canals remain the same.

o Visual/Vestibular Mismatchboth signs are contradictory

visual signals without expected vestibular signal


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o Canal/otolith mismatchBoth signals contradictory (coriolis effect)

canal signals without expected otolith signals (space sickness, head

movement in weightlessness, alternobaric vertigo)

Otolith without canal ( bow of ship in rough weather)

Signs Symptoms:

1. Pallor2.Cold sweats3.Nausea4.Vomiting5. Hyperventilation &air hunger6. Increased salivation, feeling of bodily warmth, light headed 7.Belching & flatulence8.Sighing and yawning9. Headache10. Drowsiness and lethargy

Earliest symptom is epigastric discomfortnauseaavalanche

phenomenonmultiple symptom signsvomit

Contributing factors:

o Ageo Sex : females more likely to suffer 1.7:1o Anxietyo Mental activityo Aircraft/environmental factors : control dynamicso Individual variationManagement approach

o MEDICAL:o History : motion stimulus : provocation, frequency, severity

Risk factors: susceptibility factors, anxiety,stress

o Clinical examination : evidence of other disease processeso MANAGEMENT :o Behavioural

Minimise head movement

Lie down

Close eyes

Keep mind occupied


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Stay in stable part ofaircraft

View horizon

o Adaptation: the more you fly the less likely you are to be motion sick o Medications:

Central anticholinergics( scopolamine (kwells), atropine,

cinnarizine,promethazine from avomine or phenergen)

o Sympathomimetics( ephedrine, pseudoephedrine,amphetamines)o Others ( calcium channel blockers, phenytoin)o Densitisation:o Used by most air forceso Program of frequet motion stimulation with a nauseogenic stimulus

(coriolis)

o May be supplemented by flying phaseo Leads to adaptation to motion stimulio Desensities individual to motion effectso 85% success rateo must go back to flying immediately


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Noise

o Noise = any sound that is unwanted, unpleasant or damagingo Sound = energy that produces the sensation of hearingo Vibration = inaudible acoustic phenomena that produces tactile

sensations

What is vibation?

o The alternating motion ofan object relative to a reference position (object at rest)

o Series of oscillations involving displacement andaccelerationo Usually transmitted thru direct contact between body anda vibrating

structure

Sound!

o Sound is a form of vibrationo Molecules in atmosphere vibrate causing alternating atmospheric

compression and rarefaction

o Oscillating fluctuations in local atmopheric pressure result whichemanate outwards from sound source

o Stimulation of the hearing mechanism generates a subjective auditorysensation

o Sound is propagated thru matter as a wave of fluctuating pressureAmplitude measure in decibels

THE DECIBEL :

o The decibel scale is a logarithmic scale calculated from actual soundpressures

o A 3 db rise means the sound energy at the ear has DOUBLEDo The scale is weighted to mimic the response of the human earSources of noise in aircraft:

o Aerodynamic noiseo Engine/propulsiono Cabin conditiono Avionicso Weapons systemo Auditory warnings/communicationo Direct voice inputProblem with noise

o Communication difficultieso Stresso Fatigueo Distraction


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o Deafnesso Compensation costsAircraft communication

o Communication essentialo Noise interferes with effective comm.Ways to overcome noise

o Intercom syso Noise-cancelling headphoneso Noise-attenuating headseto Standard phraseologyo Phonetic alphabetHearing damage

o Related to noise levelo Duration of exposureo Individual susceptibilityTemporary threshold shift

o Reduced sensitivity to soundo Due to acute noise exposureo Often associated with tinnitus ( ringing in ears, persistent firing of

auditory nerve)

o Rapid recovery after exposureo Timing ofaudiogramsNoise induced hearing loss

o Consequence of continued exposureo Permanent threshold shifto Initial high tone sensorineural deafnesso Physical damage to hair cellso Affects both earsHearing conservation program

o Assessment of workpaceo Early detection of hearing deterioration is keyo Oh&sAcceptable noise level

o 85Db for 8 hrs. 88Db = 4 hrs. 82Db = 16hrsProtective equip:

o aircrew helmetso aircrew headsetso earmuffs


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o insert earplugso active noise reduction has electronic 180degree phase adjustment


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Visual illusions

Oculogravic illusion

o When aircraft accelerates and there is a backward rotation of theresultant force vector, the pilot may experience a pitch up illusion.

Accompanied by apparent upward movement anddisplacement of

objects, such as line of lights.

Auto-kinesis

o In the dark, static light will have motion when staredat for severalseconds & will increase in movement if it becomes the prime focus

o At night, shift the gaze to not stare at single light sourceIllusion of level flight ( false horizon)

o In absence of clearly defined horizon, the pilot may choose mistakenlyanother pt of line as a reference.Eg.Flying parallel to a sloping cloud

bank instead of earths surface

The landing errors

o The visual approach and landing ofan aircraft requires the pilot toperceive and respond to a number of visual cues. When flying a 3

degree approach, the angle between the horizon and the visual impact

point on the runway is also 3 degree.Thus the approach is flown using

suitable control inputs to maintain a constant angle subtendedat the

horizon.

o Large aircraft: touchdown pt will be shot of the visual aiming pto Visual texture in the peripheral field will assist final judgement of

height and speed.

o Surface feature andatmospheric conditions can create illusions ofincorrect height anddistance from runway.Can be avoided by

approach angle guidance lights

Ground lighting illusions

o Lights along a straight path such as a road or lights on moving vehiclescan be mistaken for runaway lights

o Bright runway where few lights illuminate the surrounding terrain maycreate the illusion of there being less distance to the runway threshold.

o Flying over terrain which has few lights to provide height cutes maylead to a lower than normal approach being flown.

Atmospheric condition

o Haze, mist or fog can lead to refraction of light illusion of greaterheight or greater distance from runway

o Penetrating mist or fog illusion of pitch up may cause pilot to steepenthe approach


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o Rain on windscreenrefraction of light illusion of greater height ordistance pilot makes shallower than normal approach rain also

gives blooming effect to perception of runway lights gives perception

that approach is faster and runway is closer than it actually is.

Runway and terrain slope illusion

o Unsloping runway or terrain illusion that aircraft is higher altitudeand runway is shorter lower than normal approach

o Runways which slopes down have opposite effectRunway width illusion

o Approaching a narrow runway aircraft may seem higher lowerapproach than normal.

o Approaching wider runway aircraft seems lower higher approachthan normal landing beyond runway threshold

Featureless terrain ( black hole)

o Absence of ground features eg.Land over water, darkenedareas,terrain with snow creates illusion that aircraft is at higher altitude

than reality leading to lower approach.

o Landing at night at aerodome with no surrounding lights pilots faceblack hole excessively low approach with risk of undershooting

runway .Cause: runway edge light is only visible cue and there is

nothing to provide dimension of scale leading to false perception of

distance andangle.

Prevention ofdisorientation:

o Illusions can be overcome by believing instruments>sensationso Never continue flying in bad weather conditions unless suitably

qualified in instrument flying

o In poor visibility : do not mix instrument flying with visual flying ,constant switching may lead to disorientation

o Never fly into dusk or darkness unless very competent withinstruments

o Avoid sudden head movements in flight, especially when manoeuvringo Ensure outside visual reference are used they are reliable fixed pts on

earths surface

o Do not fly with cold or other illnesso Do not drinkalcohol within 12 hrs of take offo Do not fly when tiredo Maintain practice and proficiency in instrument flying

study notes for exam human performance aviation medicine

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