American Osteopathic College of Occupational and Preventive Medicine 2014 Annual Meeting, Seattle, Washington
24.0 IDENTIFY Gz acceleration forces, the causes and symptoms of (G-LOC), and the methods to improve G-tolerance.
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• On 13 July 1977 British racing driver David Purley survived a 24.1 IDENTIFY effects of +/- Gs. deceleration from 173 km/h to zero in a distance of about 24.2 IDENTIFY different types of Loss of 0.66 m, enduring 180 G. Consciousness (LOC). • The beak of the red-headed woodpecker hits the bark of a 24.3 LIST physical and physiological factors that tree with an impact velocity of over 21 km/h, subjecting the may effect G-tolerance. bird’s brain to a deceleration of approximately 10 G when its head snaps back. 24.4 IDENTIFY physiological and mechanical mechanisms used to increase G-tolerance.
The current capabilities of trained individuals to maintain clear vision during sustained exposures to 9 Gz is a result of: It’s fun • Use of a G suit It builds character • Very effective self-protective straining maneuvers such So you can kill the other guy as the M-1, L-1 So you don’t get killed • Pressure breathing Actually only pull Gs to change direction All of which are variants of the Valsalva maneuver developed in the 1940s
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The most plausible causes are: Poor anti-G straining maneuver was cited in 1) Increased capability of jet-powered fighters to 70+% of the mishaps sustain, with minimal pilot effort, accelerations in the 7-10 gz range for periods longer than the Fatigue / G-suit malfunction is 20% symptom-free 3-8 second cerebral ischemic anoxic period which precedes GLOC. Low G-tolerance at 14% 2) Improperly performed valsalva-type straining maneuver. 40% were student pilots 3) Development of a hypotensive vasovagal type reaction.
Aviation, Space, and Environmental Medicine, Volume 76, Number 4, April 2005 , pp. 370-374(5)
Within pilot characteristics, only two factors were found to be statistically significant: the time in the aircraft and pilot age. There was a 3.5-9.5 times greater chance of experiencing a G-LOC mishap if the pilot had less than 600 h in the aircraft. There was a 3 - 4.5 times greater chance of experiencing a G-LOC mishap if under the age of 30.
Human body has minimal tolerance to right or left accelerations. Most aircraft do not apply accelerative forces in the lateral 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 < 1G additionalrelaxed tolerance • Intensity – Standard seat is 13 deg; this raises your head and lets you see out better • Anti-g suit • Duration – Always lags the G onset • Rate of onset Start your muscle strain before the gs come on – especially • before high gs Body area and site – Gives a 1G increase in relaxed g-tolerance • Acceleration direction • Protection may also be augmented with positive pressure breathing during +gz.
BP ~ 120/80 mm Hg at chest
Reduced by ~ 22 mm Hg per G 30 cm Drops to 98 mm Hg at eye level Cardiovascular ~ 18 mm Hg inside eye Respiratory “Do the math” Sensory Blackout at < 4.0 G Cerebral G-LOC at < 5.0 G
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BP forces blood up to your brain High Gs force the blood down away from your BP above the heart head AGSM maneuver is designed to raise the BP and BP below the heart keep blood flowing up to your brain blood pooling lower extremities – Muscle strain keeps blood from pooling in your legs or CO and BV arms, trapping it in your chest – AGSM closes your glottis so you can strain against it 10 sec delay in reflex – Deep breath and strain raises pressure in the chest to Petechial hemorrhages squeeze blood up to your head
Atelectasis Chest tightness and feel short of breath after breathing 100% oxygen – release one side of oxygen mask Atelectasis Makes you cough Is not because the oxygen is “dry” – oxygen, unlike air, is absorbed from your lungs so Hard to inhale 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
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 in retinal circulation You just have to work at it in retinal perfusion Hypoxia may contribute to decrease in Grayout or Blackout performance, or increased likelihood of GLOC or Visual field ALOC Be efficient -- another reason not to work any harder than you have to!
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1. Tunnel vision ==> in-from-the-sides When check-6, normally inadvertently tilt our 2. “Dimmer switch effect” head a little, so one eye becomes higher than 3. Splotches other 4. Curtain Top eye loses light before lower eye 5. Combination/variations over time. But we tend to “use the good eye” and ignore Vision loss may be asymmetric. the light loss The light loss in the top eye is the GLOC warning!
Head tilt during a turn is misunderstood by Polka-dot bruises in dependent areas where the body, which thinks your head has tilted there is no counter-pressure more than it really has Caused by high, sustained Gs Since you know where your head is, you think Worse when you haven’t flown for awhile that the plane experienced an uncommanded Like a bruise, looks worse the next day, but pitch-up fades out in 3 - 5 days Watch out during a sustained turn Are not contagious! Don’t go by your instruments!
Cerebral effects of +Gz:
Cerebral perfusion Brain functions normally without any blood flow for Cerebrospinal fluid pressure about 6 seconds, then simply shuts down! – probably a self-protective mechanism Answer to today’s quiz question is:
6 sec
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9 G-induced Loss of Consciousness Pilot gets into habit of waiting for light (G-LOC) loss before we start to strain 7 Blackout But may have no light loss warning before +Gz Greyout 5 Cardiovascular GLOC above 6 Gs Reflex
3
1
0 5 10 15 20 25 Time (seconds)
Cognitive changes -- error making fully conscious – Some fatigue related, some ALOC ALOC -- “almost GLOC” light loss – Impairment but not LOC blackout – Typical “almost lost it” scenario cognitive impairment GLOC -- G induced loss of consciousness = ALOC – LOC is all-or-none, but – G effects are a continuum unconscious = GLOC
2. Relative incapacitation period G-induced loss of consciousness – 1-24 sec additional 1. Absolute incapacitation period – Lightsareon, butno oneishome – Classic LOC -- out cold Subject is upright, looks OK, but Incapable of thinking or responding – Varies 1-18 sec, mean 12 sec – Terminates abruptly with reintegration of mental Typical in-flight GLOC is short: 1-6 sec functions and return to near normal capabilities As pilot lets go of the stick, plane goes to 1G – May lose SA – Flailingis common Blood flow returns in watershed pattern
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Have some tingling or numbness Two unique EEG waveforms found, one preceding Have some twitching or jerking unconsciousness and the other preceding the return to consciousness during G-LOC episodes. Have a pleasant dream Not realize that you gloc’d! Even though the supply of oxygen to the brain was rapidly Be a little confused or disoriented restored (within approximately 15 s), the EEG and Be aware that you have lost your hearing performance data showed that approximately 60 s were required for the brain to regain functional integrity. Nauseous, sleepy or apathetic Feel a little “off” the rest of the day
Aviat Space Environ Med. 2005 Jan;76(1):19-27.
The delay in performance and EEG recovery following G-LOC demonstrates that the recovery of brain activity to support cognitive function requires more than just the restoration of normal 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 not 34 remember. Visual changes – flashing colors, rotating visual 21 field with vection. Hearing loss/impairment. 16 Twitching of the face, hands, or feet. 12 Impaired motor control; inability to act, maintain 5 control. Felt ‘slow’; i.e., temporal distortion. 4 Lightheaded. 3
Any factor that reduces overall efficiency of the body, especially the circulatory system Any factor that increases overall efficiency of the body, especially the circulatory system Blood volume decrease - Varicose veins Hypertension - Hemorrhage Fear & excitement Blood pressure decrease Tensing of muscles - Hypotension Short stocky build - Fatigue/illness AGSM - Alcohol abuse
M-1 classic grunt L-1 glottis closed completely “Hook” or “Hick” maneuver 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!
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Max attained relaxed gradual onset G Balldin UI, Sporrong A,Tesch PA. Rehydration and Gtolerance, Before heat stress 7.1 g±0.8 psychomotor performance and muscle function. Aerospace Medical After heat stress 6.3 g±0.9 Association Annual Scientific Meeting. Aviat. Space Environ. Med. 1984; 55:467 (P<0.001) A 3% dehydration may decreaseG endurance measured as the ability to withstand repeated 15-s periods at +3.5 and 5G with • Time at increased g with relaxed rapid onset g normal body temperatureby about 40%. 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. Training Effect – G-tolerance increases when you fly Gs Avoid excessive heat exposure during pre-flight transportation to the aircraft and during pre-flight walk- Layoff Effect around inspections of the aircraft. – And dropsoff againwhen you don’t Use hangars or sun shades to protect the aircraft when parked before take-off in hot climate.
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 can GLOC 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: The G level at which you have significant light loss – Relaxed G-tolerance without doing a straining maneuver. – Endurance G-tolerance Relates to heart-to-eye distance – Straining G-tolerance – Body shape – Seat-back angle
Relaxed G-Tolerance Varies – From person to person Tilt-back seat – Fromdaytoday – Lowers shortens heart-to-eye distance Same for women and men – Less than 1G improvement seen in F-16 4 to 6 gs for most people Anti-g suit Obviously different with or without an anti-g suit – Onset delayed until after the gs come on Does not relate to physical training Recent G exposure -- the “training effect”
Highest g-level you can stand when doing your best straining maneuver. Fatigue But is hard to measure and study. Alcohol Does relate to physical strength, and is improved by Dehydration working out. Illness Physical training improves your ability to repeatedly Medication strain without wearing out. Layoff from G exposure
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Time you can keep straining against
varying G levels until you are exhausted Epperson WL, Burton RR,Bernauer EM. The influence of differential Hard to measure, hence hard to use physical conditioning regimes on simulated aerial combat maneuvering reliably in research tolerance. Aviat. Space Environ. Med. 1982 ; 53:1091-7 and Improved by both aerobic and anaerobic Tesch PA, Hjort H, Balldin UI. Effects of StrengthTraining on GTolerance. training! Aviat. Space Environ. Med. 1983; 54:691-5, : SACM time in 11-12 weeks of strengthtraining in centrifuge subjects or 11 fighter pilots increased by 20-40%
______ Balldin UI, Myhre K, Tesch P,Wilhelmsen U, Andersen Rusko H, Kuronen P,Tesch P, Balldin U. The effects of a training program HT. Isometric abdominal muscle training and G- on physical fitness and G-tolerance of pilots. Ann Med Milit Fenn 1990; tolerance. Aviat. Space Environ. Med. 1985; 56:120-4: 65:61-68: SACM time increased from the second controls in 17 fighter pilots by 24% No increase in G-tolerance of fighter pilots was found after 6 months of physical training and by 38 % after 12 months of with muscle strength training of abdominal muscles training only.
Was once thought to decrease your relaxed g- Relaxed g-tolerance will increase all by itself tolerance; probably not true with frequent exposure to gs – It’s not flight time, but “g-time” Aerobic training actually improves your “staying power” by allowing rapid recovery Can increase upto 2 gs within a week from the straining – Say usual relaxed g-tolerance is 5; g-suit makes it 6. So training effect can push it up to 8! You don’t – Avoid extreme training -- keep your resting heart ever have to strain. rate above 45 You get used to not having to strain
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Does not affect your relaxed G-tolerance So, train the muscles you strain Does improve your strength and endurance G- tolerance – Your goal is sustained, repeated straining with rapid recovery – Pays off on long, difficult engagements, and on Include aerobic training frequent flights You are better served by understanding gs, and doing what you have to effectively and efficiently
Neck pain is #1 cause of down time for high-g Leading cause of down time for high-G aviators aviators Associated with high rate of G onset (“snatching Movement under gs on the Gs”) Helmet, mask, nvgs, etc. Non-pilot can’t anticipate G onset Great Benefits come with neck strength Head movement under Gs Better control (don’t want to kiss your belly button!) Additional head mounted equipment Less likely to be injured Good neck strength training minimizes injury So, include neck strength training in your weight workout! potential
1. A correct Muscle and Respiratory Straining Maneuver. 1. Not used to high G exposures. 2. Anti-G suit, especially with full coverage of the lower body and 2. Poorly timed anti-G straining maneuver. possibly with a continuous ready pressure. 3. Not properly fit anti-G suit. 3. Pressure breathing during G, unassisted for short G exposures and assisted pressure breathing for endurance. 4. Mask leakage when pressure breathing during G. 4. Muscle strength training program and physical endurance 5. High body temperature and dehydration. training (however, evidence difficult to scientifically prove). 6. Low blood sugar concentration. 5. Avoid physical and mental fatigue before flying. 7. Fatigue and minor illness. 6. Avoid heat stress and dehydration. 8. Tall body length with long heart-brain distance. 7. Avoid low blood sugar concentration. 9. Upright seat position. 8. Regular high G-exposures. 9. Good health before flying. 10.Hang-over. 10. Tilted seat back angle and elevated legs.
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