Aerospace PhysiologistAerospace Physiologist

MSC SymposiumMSC SymposiumLT Yniguez LT Yniguez

MCAS, Cherry PTMCAS, Cherry PT

G-TOLERANCE G-TOLERANCE IMPROVEMENT IMPROVEMENT PROGRAMPROGRAM

GTIP Goals andEnabling Objectives

understand your personal type of light loss learn when to utilize the anti-G ‘hook’ understand daily variations in relaxed G-

tolerance respect the 6 sec “buffer period” appreciate the potential “GLOC trap” understand the one-sided light loss that

may occur in the check-six position

Terminal ObjectiveG-TIP

Be familiar with Gz acceleration forces, the causes and

symptoms of (G-LOC), and the methods to

improve G-tolerance.

G-LOC A DEADLY THREAT

AIRCRAFT NO. G’sFA-18 8 5.5-8.0F-14 1 4.0AV-8B1 5.5EA-6B3 3.0-4.0S-3 1 3.0T-2 3 3.5T-34 35 1.5-9.0

Why pull Gs? 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

Anatomical/Physiological effects of

G-Forces

Cardiovascular Respiratory Sensory Cerebral

Cardiovascular Effects of +Gz:

BP above the heart BP below the heart blood pooling lower extremities CO and BV 10 sec delay in reflex Petechial hemorrhages

Cardiovascular system your BP forces blood up to your brain high Gs force the blood down away from your

head ‘Hook’ maneuver is designed to raise the BP and

keep blood flowing up to your brain– the muscle strain keeps blood from pooling in your

legs or arms, trapping it in your chest– the “hook” closes your glottis so you can strain

against it– the deep breath and strain raises pressure in the

chest to squeeze blood up to your head

G-warm up maneuver, or

G-awareness turn1. press-to-test G-suit2. pull about _ Gs for at least 10 sec

no strain3. OPTIONAL: gradually increase Gs

without straining until you see some light lossdetermines your relaxed G-tolerance consider it might be a low-G day

The Cardiovascular Reflex, or

“Why do I do the G-warm up maneuver?” the carotid bodies in your neck sense a

change in BP and initiate the cardiovascular reflex to maintain blood flow to your head

with increased Gs you see lower BP in your neck, and– your pulse increases– blood vessels throughout your body tighten up

this raises your BP and increases your relaxed G-tolerance

G-warm-up maneuver ...

gives you about 3/4 G additional relaxed G- tolerance protection

but it takes 10-15 seconds to occur– might notice more light loss on first pull of

the day and lasts only about 10-15 minutes

– so might consider doing G-warm-up close to the time that you’ll be needing the extra help

Push-Pull Effect 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 but normally + Gs come on just as your BP

is falling and you can GLOC at 3Gs! So avoid +Gs after sustained -Gs

– won’t occur unless -Gs last over 3-4 sec.

Petechia polka-dot bruises in dependent areas

where there 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, but fades out in 3 - 5 days are not contagious!

Respiratory Effects

AtelectasisHard to inhale

Atelectasis chest tightness and feel short of breath

after breathing 100% oxygen– release one side of oxygen mask

makes you cough but is not because the oxygen is “dry”

– oxygen, unlike air, is absorbed from your lungs so quickly that the air cells actually collapse and stick closed

worse after sustained Gs the cough is the cure -- this re-inflates the

air cells and relieves the unpleasant feeling

Hard to inhale 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 in

performance, or increased likelihood of GLOC or ALOC

be efficient -- another reason not to work any harder than you have to!

Visual effects of +Gz: in retinal circulation in retinal perfusion grayout or blackout visual field

Vision Loss1. tunnel vision ==> in-from-the-sides 2. “dimmer switch effect”3. splotches4. curtain5. combination/variations over time.

Vision loss may be asymmetric.

One sided light loss when check-6, normally inadvertently

tilt our head a little, so one eye becomes higher than other

top eye loses light before lower eye but we tend to “use the good eye”

and ignore the light loss the light loss in the top eye is the

GLOC warning!

G-Excess Illusion head tilt during a turn is misunderstood

by the body, which thinks your head has tilted more than it really has

but since you know where your head is, you think that the plane experienced an uncommanded pitch-up

watch out during a sustained turn don’t go by your instruments!

Cerebral effects of +Gz: cerebral perfusion cerebrospinal fluid pressure

Buffer Period your brain functions normally

without any blood flow for about 6 seconds, then simply shuts down!– probably a self-protective mechanism

answer to today’s quiz question is:

6 sec

Stohl curve

GLOC Trap get in habit of waiting for light

loss before we start to strain but may have no light loss

warning before GLOC above 6 Gs

Neurological Effects 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

GLOC -- A Continuumfully consciouslight lossblackoutcognitive impairment = ALOCunconscious = GLOC

More about GLOCG-induced loss of consciousness1. 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 mental functions and return to near normal capabilities

– may lose SA

If you GLOC you may ... have some tingling or numbness have some twitching or jerking have a pleasant dream not realize that you GLOCed! be a little confused or disoriented be aware that you have lost your

hearing feel a little “off” the rest of the day

Does Physical Training help G-tolerance?

before we can answer, we must understand the terms:– Relaxed G-tolerance– Endurance G-tolerance– Straining G-tolerance

Relaxed G-Tolerance the G level at which you have

significant light loss without 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

your relaxed G tolerance is increased

by 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”

your relaxed G-tolerance is decreased

by: fatigue alcohol dehydration illness medication layoff from G exposure

Straining G-tolerance the highest G-level you can stand

when doing your best straining maneuver

but is hard to measure and study does relate to physical strength, and

is improved by working out physical training improves your ability

to repeatedly strain without wearing out

Endurance G-tolerance the time you can keep straining

against varying G levels until you are exhausted

hard to measure, hence hard to use reliably in research

improved by both aerobic and anaerobic training!

Aerobic Training was once thought to decrease your

relaxed G-tolerance; probably not true

aerobic training actually improves your “staying power” by allowing rapid recovery from the straining– avoid extreme training -- keep your

resting heart rate above 45

So, Physical Training ... does not affect your relaxed G-

tolerance does improve your strength and

endurance G-tolerance– pays off on long, difficult

engagements, and on frequent flights

Physical Training So, train the muscles you strain

– your goal is sustained, repeated straining with rapid recovery

include aerobic training my personal view is that you are

better served by understanding Gs, and doing what you have to effectively and efficiently

Neck Strengthneck pain is #1 cause of down time for

high-G aviatorsmovement under Gshelmet, mask, NVGs, etc.

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

less likely to be injuredso, include neck strength training in your

weight workout!

Neck Pain/Injury leading cause of down time for high-G

aviators associated with high rate of G onset

(“snatching on the Gs”) non-pilot can’t anticipate G onset

head movement under Gs additional head mounted equipment good neck strength training minimizes

injury potential

The “Det Effect”or, “Where’d my G-tolerance

go?” Training Effect

– G-tolerance increases when you fly Gs Layoff Effect

– and drops off again when you don’t

Training Effect relaxed G-tolerance will increase all

by itself with 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 it 6. So training effect can push it up to 8! You don’t ever have to strain.

You get used to not having to strain

Engineering changes to improve G tolerance

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 -- esp before high Gs– gives a 1G increase in relaxed G-tolerance

positive pressure breathing with chest jerkin and Eagle anti-G suit

can sustain 8 Gs without straining! can keep talking and breathing throughout

high Gs so increases your endurance too

– less straining– better breathing

high Gs still suck, though....

Navy Combat Edge

Proper G suit fit ... G-suit helps you by doing some of the work strain first, then slack off after the G-suit fills fit should be snug, not tight

too loose just takes longer to fill up– while standing, should easily slip:

two fingers down by the thigh and calf, and open hand down the front

release G-suit when you need to (spring, fall)

AGSM M-1 classic grunt L-1 glottis closed completely “Hook” maneuver I say it’s OK to use your own combination

of leg strain/abdominal strain/hook maneuver as you need to.– Do what you have to do, but no more– understand what to do and why– know and respect the traps!

Hook maneuver1. tighten all muscles before G onset

“Get a Jump on the Gs!” above 62. deep breath, close glottis (say “hook”)3. bear down and strain for 3 seconds

strain harder for higher Gs; slack off at lower Gs4. while maintaining continuous muscle

strain, rapidly exchange full lung of airit’s hard to inhale under high Gs

5. work only as hard as you have to