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