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G Induced Loss of Conciousness Part 3
Gjunkie1
#1 Posted : Thursday, April 14, 2011 5:49:02 PM(UTC)
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Part III.
To stop the Rot: anti-GILOC or extend your (+Gz) envelope.

The object of the exercise is to maintain CBF, Cerebral Blood Flow despite high +Gz. The object of maintaining CBF is to maintain the continuous supply of Oxygen (O2) and Glucose upon which our brains depend to acrobat effectively (and thereby stay alive, which we have to do to WIN, pay our taxes, worship our Maker or do anything else worthwhile. This is the First and ABSOLUTE Law of Aerobatics. No NESTEROV’s here, please). >5 seconds failure to do this means >15 seconds coma, minimum. The characteristics of GILOC as previously discussed are summarised here below:

GILOC salient features:
1. Common.
2. No discomfort (you don't know what's hit you).
3. Amnesia: you often don't remember anything (if you are still alive).
4. Onset is variable:
i. +Gz level encountered.
ii. manner of onset: may be instantaneous and without warning.
5. Incapacitation prolonged:
<15 secs: unconscious.
<30 secs: relative.
< 3 mins: operational.
<30 mins: intellectual.
6. Convulsions common.
7. No long-term ill-effects described. But repeated GILOC on the same day extends the periods of incapacitation. (If it gets you, return to base, carefully. Don't do it again on the same day.)

In Part II we discussed the history of GILOC and methods introduced to avoid it. What are the systems involved? What do we have to work with? What can we manipulate for good or ill? Because by foolishness we CAN make matters worse. Factors involved are illustrated in Fig 1.

I. The CIRCULATING BLOOD VOLUME, cBV

cBV is annoyingly like the Cerebral Blood Volume, also CBV, the blood in the Brain at any one moment in time, so let us call it cBV. The Systemic Blood Volume, sBV, is the volume of blood in the body at any one time, but it may not all be available for the rapid changes in circulatory pattern we need. If we are hot, a large volume of blood will be shunted into our skins to keep us cool by radiating our heat to the environment. Meanwhile we will be sweating like mad and loosing water from the sBV, both processes reducing the cBV available for us to pump up into our heads. Whether leaving our bodies to their own (inadequate in GILOC) devices, or helping them along as we shall see.

GILOC antidotes:
1. Keep cool (as ever).This includes good cockpit design and insulation. Rearward hinging hoods are fine for ejection in jets, but the very devil in tractor propellor, single engined aircraft, unless one wants an excuse to get it blown off before you get airborne (probably without the benefit or your vertical tail surfaces).
2. Avoid de-hydration, keep well hydrated, that is drink enough water. The old KGB trick, when they were running World Championships to predetermined results, was to leave you sweating it out at the holding point in the blazing sun. Whilst we would be getting the wobblies about whether there was enough fuel left aboard to finish the sequence they would be laughing down their socks at what should have been worrying us - our progressive dehydration and developing hyper-pyrexia as our thickening blood sludged in our pink English skins (keep worrying, its just as bad in you non- English bronzed Adonises, we just look more ridiculous!).

II. PERIPHERAL VASCULAR RESISTANCE.

Because blood is so heavy, even under +1Gz, to keep our all-up weight low enough to move at all has required that our vascular systems be only partly filled with blood, which has then to flow only to where it is absolutely necessary. Keeping it only where we need it and to leave enough with which to perfuse our brains is a never-ending battle which keeps our Autonomic Nervous System constantly busy, every second, every day of our lives. It's knife-edge stuff at the best or times. Factors worth remembering indude:

i. The Sympathetic Nervous System (SNS), which, among other functions, constricts the small terminal arteries just before they become the capillaries from which the blood's goodies get to the cells. The higher the sympathetic activity the less the blood languishing out in the periphery, the more to maintain central blood pressure and CBF (though this is complicated by the effect the SNS has constricting cerebral blood vessels). Terror, apprehension, anticipation and even hard voluntary muscle contraction (as, for example, by hand grip or isometric leg muscle contraction) will increase it. (This is one reason why we all hate instructing in acrobatics: if you know exactly what’s coming, being Pl, it’s fun. If you don't, being P2, it’s hell, always being just behind the game. Similarly, always bounce your oppo in dogfighting,
don't give him a chance by waking him up. He should never know who hit him. Anonymous success is the name of the game).

ii. Temperature, both body and ambient (around about us). If we are hot, blood is shunted to the skin to cool us down. This blood is sequestered, leaving a smaller cBV with which to try and maintain the supply to the brain.

iii. Blood gases and acidity (pH). Many tissues' blood flow is effected by these. If they are deranged (as by prolonged gross muscle effort with lung blood flow patterns distorted by prolonged high +Gz) one should not be surprised if even less blood is left for the cBV.

iv. Toxins: poisons, including food poisoning. "Bombay belly”, carbon monoxide from cockpit contamination by engine exhaust fumes and alcohol all take their toll. Intoxication or ill-health are NO-NO’s for flying, let alone aerobatics. lf you are off-form, don’t fly. End of story.

v. Fatigue. If YOU are exhausted, don't expect your G-tolerance to be any better.

GILOC-antidotes:
3. Plan and anticipate each manoeuvre. Be calculating, careful and deli berate in all you do. Use your Entry and Exit Gates, your Targets and Way-Points through each and every manoeuvre.
4. Keep cool (again). In every sense of the term.
5. Limit the length of high-Gz details to the time you will be allowed in the next World competition so that you are always at one's best when in the air and not progressively getting worse. You always think that you are getting better as a long detail progresses. Unfortunately
it's pure delusion and an indication of the effect on one's brain and the progressive distortion of one's intellect by the cumulative effects of high Gz. It is also counter-productive. In competition you can only fly the sequence once - the first time. So you have to get the first run perfect. The second is a waste of time. 10 minutes in the box is probably all you can constructively use at anyone time. When learning and practising figures at altitude, before bringing them down into the box, be careful to monitor your performance objectively. You will be using your time better coming home sooner and using positioning lime constructively, such as gliding back inverted, rather than bashing on getting steadily worse. A major problem is that the longer you go on subjecting the lungs to high +Gz, the more lung blood flow is distorted and the amount of blood usefully exposed to the air in your lungs is reduced. Use your time constructively, often this will be to get back on the ground and let your lungs unwind while you de-brief and get set up to put the next detail to even better use.
6. Take great care over cockpit cooling, ventilation and exhaust gas isolation. Exhaust fumes flow everywhere: forward, aft, usually in exactly the opposite direction you would expect the air space to move in that part or the aircraft. Plan and check air movement in every part, especially along surfaces which lead to the cockpit. You will be surprised. Meanwhile that carbon monoxide detector in the cockpit is probably mounted in the only part of the cockpit not contaminated by noxious gases!

III. VENOUS RETURN, VR, of blood to the heart (Fig 2).



Several mechanism are at work, including:
i. The "muscle pump" in our legs. As we contract our leg muscles they expand transversely within the tight compartments of the Deep Fascia, compressing the deep veins running between them back to the abdomen. The veins have one-way valves so that the blood
they contain is squirted up into the abdomen at very high pressure (so long as we are using the leg muscles). As the muscles relax, blood in the superficial veins in the legs is sucked into the deep venous system through valved venous communications passing through the Deep Fascia. If the valves in the communicating connections fail one gets "varicose veins", the hideous expansion of which reflects the power of the leg venous pump.
ii. Gravity gets the blood back from the head under +Gz (some 20% of the total cBV).
iii. Intra-abdominal Pressure (IAP) forces blood up from the abdomen through the Diaphragm (the muscular division between chest and abdomen) and into the Heart whenever there is a pressure differential across the diaphragm. This is increased during inspiration, breathing-in. Expanding the chest and depressing the diaphragm to suck in air through the mouth also ejects blood from the abdomen up into the heart.
iv. Intra-thoracic Pressure (ITP). When it falls during inspiration, venous filling of the heart is enhanced by the increase in the pressure gradient from abdomen into chest as well as aiding the return of blood from head, arms and upper body.

GILOC -antidotes:
7. Make sure your rudder bar and pedals are stronger than you can break. Your are going to need them to enhance your venous return by vigorous compression of them by your legs against the back of your seat. Make this part of your pre-flight check. Better to break the rudder controls on the ground and be around to suffer the engineers wrath than to try to explain to St. Peter why you have arrived so soon.
8. Practise isometric abdominal straining on the ground. They are the means of getting the blood back into your heart. The problem is now simplified into getting it up to your head.
9. If you have an aircraft capable of sustained high +Gz then use a G suit. But to be effective to get the blood back to the diaphragmatic level requires not only gaiters but abdominal compression too. It has to be ultra reliable and very quick to inflate. The weight penalty of the associated gear means that at present this has to be a very high power-to-weight ratio machine. You still have the problem of getting the blood from Heart to head. We'll deal with that next.

IV. CARDIAC OUTPUT

Is what we depend on to shove the (under high Gz) lead-weight blood up to our brains. By "output” we imply both the volume and the pressure at which blood is pumped out by the heart each time it beats. We need an adequate volume as only 20% will go to the brain. We need high enough pressure to get the blood up to the head. Each cardiac ejection in its turn depends on:
i. The Venous Return (VR), above, to fill the now empty heart and supercharge it by an enhanced filling pressure reflecting a high pressure venous return ejected from abdomen up into the heart.
ii. The volume and pressure of each cardiac contraction. These in their turn depend on how "fit" we and our hearts are: whether the heart muscle has been stimulated by the Sympathetic Nervous System (SNS) and what is the Intra-thoracic Pressure, as the heart will pump up an ejection pressure above the pressure around it in the chest.

Skip to the second half...

John Firth, Queens Medical Centre, Nottingham
Steve Johnson
MX2
Nashville, TN
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