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NAWC ASTC Cherry Point GTIP 95

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American Osteopathic College of Occupational and Preventive Medicine2014 Annual Meeting, Seattle, Washington

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“Nothing to Disclose!”

24.0 IDENTIFY Gz acceleration forces, thecauses and symptoms of (G-LOC), and themethods to improve G-tolerance.

24.1 IDENTIFY effects of +/- Gs.

24.2 IDENTIFY different types of Loss ofConsciousness (LOC).

24.3 LIST physical and physiological factors thatmay effect G-tolerance.

24.4 IDENTIFY physiological and mechanicalmechanisms used to increase G-tolerance.

• On 13 July 1977 British racing driver David Purley survived adeceleration from 173 km/h to zero in a distance of about0.66 m, enduring 180 G.

• The beak of the red-headed woodpecker hits the bark of atree with an impact velocity of over 21 km/h, subjecting thebird’s brain to a deceleration of approximately 10 G whenits head snaps back.

It’s fun

It builds character

So you can kill the other guy

So you don’t get killed

Actually only pull Gs to change direction

The current capabilities of trained individuals to maintainclear vision during sustained exposures to 9 Gz is a result of:

• Use of a G suit

• Very effective self-protective straining maneuvers suchas the M-1, L-1

• Pressure breathing

All of which are variants of the Valsalva maneuver

developed in the 1940s


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The most plausible causes are:

1) Increased capability of jet-powered fighters tosustain, with minimal pilot effort, accelerations inthe 7-10 gz range for periods longer than thesymptom-free 3-8 second cerebral ischemic anoxicperiod which precedes GLOC.

2) Improperly performed valsalva-type strainingmaneuver.

3) Development of a hypotensive vasovagal typereaction.

Poor anti-G straining maneuver was cited in70+% of the mishaps

Fatigue / G-suit malfunction is 20%

Low G-tolerance at 14%

40% were student pilots

Aviation, Space, and Environmental Medicine, Volume 76, Number 4, April 2005 , pp. 370-374(5)

Within pilot characteristics, only two factors werefound to be statistically significant: the time in theaircraft and pilot age.

There was a 3.5-9.5 times greater chance ofexperiencing a G-LOC mishap if the pilot had less than600 h in the aircraft.

There was a 3 - 4.5 times greater chance ofexperiencing a G-LOC mishap if under the age of 30.

Human body has minimal tolerance to right or leftaccelerations.

Most aircraft do not apply accelerative forces in thelateral direction.


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Curve A is the case of water immersion, that is the human body in water. In this case,tolerable G levels are higher than 10 and tolerable time is 4 minutes for 10G.

• Tilt back seat (30 deg tilt)– Gives < 1 G additional relaxed tolerance

– Standard seat is 13 deg; this raises your head and lets you see out better

• Anti-g suit– Always lags the G onset

Start your muscle strain before the gs come on – especiallybefore high gs

– Gives a 1G increase in relaxed g-tolerance

• Protection may also be augmented with positive pressurebreathing during +gz.

• Intensity

• Duration

• Rate of onset

• Body area and site

• Acceleration direction

Cardiovascular

Respiratory

Sensory

Cerebral

BP ~ 120/80 mm Hg at chest

Reduced by ~ 22 mm Hg per G

Drops to 98 mm Hg at eye level

~ 18 mm Hg inside eye

“Do the math”

Blackout at < 4.0 G

G-LOC at < 5.0 G

30 cm


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BP above the heart

BP below the heart

blood pooling lower extremities

CO and BV

10 sec delay in reflex

Petechial hemorrhages

BP forces blood up to your brain

High Gs force the blood down away from yourhead

AGSM maneuver is designed to raise the BP andkeep blood flowing up to your brain– Muscle strain keeps blood from pooling in your legs or

arms, trapping it in your chest

– AGSM closes your glottis so you can strain against it

– Deep breath and strain raises pressure in the chest tosqueeze blood up to your head

Atelectasis

Hard to inhale

Atelectasis Chest tightness and feel short of breath after

breathing 100% oxygen

– release one side of oxygen mask

Makes you cough

Is not because the oxygen is “dry”

– oxygen, unlike air, is absorbed from your lungs soquickly that the air cells actually collapse and stickclosed

Worse after sustained Gs

The cough is the cure -- this re-inflates the aircells and relieves the unpleasant feeling

May feel like you can’t get enough air in

Due to physical forces compressing your chest

– breathing is usually rather easy -- this isn’t

You just have to work at it

Hypoxia may contribute to decrease inperformance, or increased likelihood of GLOC orALOC

Be efficient -- another reason not to work anyharder than you have to!

in retinal circulation

in retinal perfusion

Grayout or Blackout

Visual field


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1. Tunnel vision ==> in-from-the-sides

2. “Dimmer switch effect”

3. Splotches

4. Curtain

5. Combination/variations over time.

Vision loss may be asymmetric.

When check-6, normally inadvertently tilt ourhead a little, so one eye becomes higher thanother

Top eye loses light before lower eye

But we tend to “use the good eye” and ignorethe light loss

The light loss in the top eye is the GLOCwarning!

Head tilt during a turn is misunderstood bythe body, which thinks your head has tiltedmore than it really has

Since you know where your head is, you thinkthat the plane experienced an uncommandedpitch-up

Watch out during a sustained turn

Don’t go by your instruments!

Polka-dot bruises in dependent areas wherethere is no counter-pressure

Caused by high, sustained Gs

Worse when you haven’t flown for awhile

Like a bruise, looks worse the next day, butfades out in 3 - 5 days

Are not contagious!

Cerebral effects of +Gz:

Cerebral perfusion

Cerebrospinal fluid pressure Brain functions normally without any blood flow forabout 6 seconds, then simply shuts down!

– probably a self-protective mechanism

Answer to today’s quiz question is:

6 sec


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+Gz

Time (seconds)

0 5 10 15 20 25

CardiovascularReflex

9

7

5

3

1

G-induced Loss ofConsciousness(G-LOC)

Blackout

Greyout

Pilot gets into habit of waiting for lightloss before we start to strain

But may have no light loss warning beforeGLOC above 6 Gs

Cognitive changes -- error making

– Some fatigue related, some ALOC

ALOC -- “almost GLOC”

– Impairment but not LOC

– Typical “almost lost it” scenario

GLOC -- G induced loss of consciousness

– LOC is all-or-none, but

– G effects are a continuum

fully conscious

light loss

blackout

cognitive impairment= ALOC

unconscious = GLOC

G-induced loss of consciousness

1. Absolute incapacitation period

– Classic LOC -- out cold

– Varies 1-18 sec, mean 12 sec

Typical in-flight GLOC is short: 1-6 sec

As pilot lets go of the stick, plane goes to 1G

– Flailing is common

Blood flow returns in watershed pattern

2. Relative incapacitation period

– 1-24 sec additional

– Lights are on, but no one is home

Subject is upright, looks OK, but

Incapable of thinking or responding

– Terminates abruptly with reintegration of mentalfunctions and return to near normal capabilities

– May lose SA


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Have some tingling or numbness

Have some twitching or jerking

Have a pleasant dream

Not realize that you gloc’d!

Be a little confused or disoriented

Be aware that you have lost your hearing

Nauseous, sleepy or apathetic

Feel a little “off” the rest of the day

Two unique EEG waveforms found, one precedingunconsciousness and the other preceding the return toconsciousness during G-LOC episodes.

Even though the supply of oxygen to the brain was rapidlyrestored (within approximately 15 s), the EEG andperformance data showed that approximately 60 s wererequired for the brain to regain functional integrity.

Aviat Space Environ Med. 2005 Jan;76(1):19-27.

The delay in performance and EEG recovery following G-LOCdemonstrates that the recovery of brain activity to supportcognitive function requires more than just the restoration ofnormal oxygen levels.

Aviat Space Environ Med. 2005 Jan;76(1):19-27.

The subjects often reported:

Difficulty in thinking

Loss of memory

Visual changes other than gray- and

Black-out

Hearing loss


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Frequency

Difficulty thinking, could not concentrate, did notremember.

34

Visual changes – flashing colors, rotating visualfield with vection.

21

Hearing loss/impairment. 16

Twitching of the face, hands, or feet. 12

Impaired motor control; inability to act, maintaincontrol.

5

Felt ‘slow’; i.e., temporal distortion. 4

Lightheaded. 3

Any factor that reduces overall efficiency of the body,especially the circulatory system

Blood volume decrease

- Varicose veins

- Hemorrhage

Blood pressure decrease

- Hypotension

- Fatigue/illness

- Alcohol abuse

Any factor that increases overall efficiency of the body,especially the circulatory system

Hypertension

Fear & excitement

Tensing of muscles

Short stocky build

AGSM

M-1 classic grunt

L-1 glottis closed completely

“Hook” or “Hick” maneuver

It’s OK to use your own combination of legstrain/abdominal strain/hook maneuver as youneed to.– Do what you have to do, but no more

– Understand what to do and why

– Know and respect the traps!


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Balldin UI, Sporrong A,Tesch PA. Rehydration and Gtolerance,

psychomotor performance and muscle function. Aerospace MedicalAssociation Annual Scientific Meeting. Aviat. Space Environ. Med. 1984;55:467

A 3% dehydration may decrease G endurance measured as theability to withstand repeated 15-s periods at +3.5 and 5 G withnormal body temperature by about 40%.

Max attained relaxed gradual onset G

Before heat stress 7.1 g±0.8

After heat stress 6.3 g±0.9

(P<0.001)

• Time at increased g with relaxed rapid onset g

Before heat stress 55 s ±16

After heat stress 48 s ±20

(P<0.001)

The pilot should be aware of the dangers of heat load.

Be encouraged to maintain hydration.

Avoid excessive heat exposure during pre-flighttransportation to the aircraft and during pre-flight walk-around inspections of the aircraft.

Use hangars or sun shades to protect the aircraft whenparked before take-off in hot climate.

Training Effect

– G-tolerance increases when you fly Gs

Layoff Effect

– And drops off again when you don’t

With sustained negative gs Push over, or level inverted flight

– BP rises in your head and your carotid bodies compensate by: Slowing your pulse, and

Dilating your blood vessels

– This lowers your BP in about 10-15 sec

Normally + gs come on just as your BP is falling and you canGLOC at 3gs!

Avoid +gs after sustained -gs

– Won’t occur unless -gs last over 3-4 sec.


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Before we can answer, we must understand the terms:

– Relaxed G-tolerance

– Endurance G-tolerance

– Straining G-tolerance

The G level at which you have significant light losswithout doing a straining maneuver.

Relates to heart-to-eye distance

– Body shape

– Seat-back angle

Varies

– From person to person

– From day to day

Same for women and men

4 to 6 gs for most people

Obviously different with or without an anti-g suit

Does not relate to physical training

Relaxed G-Tolerance

Tilt-back seat

– Lowers shortens heart-to-eye distance

– Less than 1G improvement seen in F-16

Anti-g suit

– Onset delayed until after the gs come on

Recent G exposure -- the “training effect”

Fatigue

Alcohol

Dehydration

Illness

Medication

Layoff from G exposure

Highest g-level you can stand when doing your beststraining maneuver.

But is hard to measure and study.

Does relate to physical strength, and is improved byworking out.

Physical training improves your ability to repeatedlystrain without wearing out.


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Time you can keep straining againstvarying G levels until you are exhausted

Hard to measure, hence hard to usereliably in research

Improved by both aerobic and anaerobictraining!

Epperson WL, Burton RR,Bernauer EM. The influence of differentialphysical conditioning regimes on simulated aerial combat maneuveringtolerance. Aviat. Space Environ. Med. 1982 ; 53:1091-7

and

Tesch PA, Hjort H, Balldin UI. Effects of StrengthTraining on G Tolerance.Aviat. Space Environ. Med. 1983; 54:691-5, :

SACM time in 11-12 weeks of strength training in centrifuge subjects or 11fighter pilots increased by 20-40%

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Rusko H, Kuronen P, Tesch P, Balldin U. The effects of a training programon physical fitness and G-tolerance of pilots. Ann Med Milit Fenn 1990;65:61-68:

SACM time increased from the second controls in 17 fighter pilots by 24%after 6 months of physical training and by 38 % after 12 months oftraining

Balldin UI, Myhre K, Tesch P, Wilhelmsen U, AndersenHT. Isometric abdominal muscle training and G-tolerance. Aviat. Space Environ. Med. 1985; 56:120-4:

No increase in G-tolerance of fighter pilots was foundwith muscle strength training of abdominal musclesonly.

Was once thought to decrease your relaxed g-tolerance; probably not true

Aerobic training actually improves your“staying power” by allowing rapid recoveryfrom the straining

– Avoid extreme training -- keep your resting heartrate above 45

Relaxed g-tolerance will increase all by itselfwith frequent exposure to gs

– It’s not flight time, but “g-time”

Can increase up to 2 gs within a week

– Say usual relaxed g-tolerance is 5; g-suit makes it6. So training effect can push it up to 8! You don’tever have to strain.

You get used to not having to strain


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Does not affect your relaxed G-tolerance

Does improve your strength and endurance G-tolerance

– Pays off on long, difficult engagements, and onfrequent flights

So, train the muscles you strain

– Your goal is sustained, repeated straining with rapid recovery

Include aerobic training

You are better served by understanding gs, and doingwhat you have to effectively and efficiently

Neck pain is #1 cause of down time for high-gaviators Movement under gs

Helmet, mask, nvgs, etc.

Great Benefits come with neck strength Better control (don’t want to kiss your belly button!)

Less likely to be injured

So, include neck strength training in yourweight workout!

Leading cause of down time for high-G aviators

Associated with high rate of G onset (“snatchingon the Gs”)

Non-pilot can’t anticipate G onset

Head movement under Gs

Additional head mounted equipment

Good neck strength training minimizes injurypotential

1. A correct Muscle and Respiratory Straining Maneuver.

2. Anti-G suit, especially with full coverage of the lower body and

possibly with a continuous ready pressure.

3. Pressure breathing during G, unassisted for short G exposures

and assisted pressure breathing for endurance.

4. Muscle strength training program and physical endurance

training (however, evidence difficult to scientifically prove).

5. Avoid physical and mental fatigue before flying.

6. Avoid heat stress and dehydration.

7. Avoid low blood sugar concentration.

8. Regular high G-exposures.

9. Good health before flying.

10. Tilted seat back angle and elevated legs.

1. Not used to high G exposures.

2. Poorly timed anti-G straining maneuver.

3. Not properly fit anti-G suit.

4. Mask leakage when pressure breathing during G.

5. High body temperature and dehydration.

6. Low blood sugar concentration.

7. Fatigue and minor illness.

8. Tall body length with long heart-brain distance.

9. Upright seat position.

10.Hang-over.


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