G Tolerance and Physical Fitness

[UAM]

Do pilots who have higher than average blood pressure also have higher G tolerance? Thinking about it logically shouldnt this be the case, that higher blood pressure means more blood may be maintained in the head?
If so, would lowering your blood pressure by becoming a fitness fanatic have a negative effect on G tolerance?
Weird question, but its to resolve an argument!
Cheers

[Stan Evil]

I don't have any hard facts but here's personal experience and a crewroom story:

I've got quite low blood pressure and was fairly tall and skinny. I certainly found this gave me a low g tolerance and drove me to g-pants when others didn't bother. Some of the best fighter pilots I knew were little, fat, red-faced chaps.

When we started training Saudis in the 60s and 70s they had all sorts of problems with low g tolerance. Things got better in the 80s and 90s as 'civilisation' happened and their healthy eating habits became corrupted with the arrival of Big Macs and KFC causing their blood pressure to go up.

This may be apocryphal but it sounds logical.

[Whirlybird]

I'm not sure that that it is logical. Everyone's blood pressure goes up when it needs to, to pump more blood around the body. These times include during exercise, and under stress (left over from millions of years ago when we needed to fight or run away to survive). But it should go back to "normal" afterwards. In people with permanently high bp it doesn't. So presumably the healthy situation is a bp that can respond to what's needed. Does that mean it can go up when g forces require it to as well? I don't know. But I do gather that being tall, so the blood has further to go, makes it harder. So little 5ft 3in squirts like me would be the ideal fighter pilots, it seems. I wish I'd known that when I was younger.

[shifatur]

hey guys
been worrying about this thing lately........

am 19, bc is 135/96....now, thats unusual.............i know........but then again, i am one of the "coolest" of all guys and i never feel excited, overreactive or anything..........

how does that restrict my plan to get hold of j.a.a class one medical? am perfect at other things........would they refuse to issue me the medical just for that?

shifatur

[Whirlybird]

shifatur,

JAA limits, as someone said on the other thread, are 160/95. So you'd probably just about make it. The worst that would happen is that you'd have to take medication for it. HOWEVER, before that happens the AME might suggest you get a 24 hour reading. This is because it's normal for your blood pressure to go up when stressed, and most people are stressed during a medical, and some of us are whenever we see a doctor for ANYTHING. This is called White Coat Hypertension, and according to my AME is common among pilots - why am I not surprised. He told me to get a 24 hour reading when my BP was consistently high, right on JAA limits. You wear this weird gadget that takes your bp every half hour, and keeps you awake at night.:eek: Anyway, my 24 hr average was 122/80, and my bp never went over 140/90.

Back with the AME, he was getting readings of 170/100. He looked at me in despair. "Do I really scare you that much" , he asked. He tried 3 times then gave up: "OK, white coat hypertension; it's official". He wrote it on the form too.

So, shifatur don't panic! And incidentally, high bp rarely has anything to do with being over-excited or whatever; there's often no reason for it.

[ariel]

I also have the same problem as Whirly, (and countless others), which is elevated blood pressure when within 5 miles of a doctor of any kind!.

Incidentally, my 'normal' pressure is low - sometimes very low, (I've got one of those portable armband monitors, which proves very usefull to ones' sanity).

A tip, (or two), to help when going for the all important check: Take asprin a couple of hours before your appointment. Also, in some people, bp will lower if you have an empty stomach, so go easy on the fish & chips / big fry-ups, etc.. just before going to the doc!

At this point, it might be worth mentioning that high bp, (or what is 'deemed' to be high), is more of an issue in this country than some others. I may be wrong in saying this, (please feel free to correct me anybody), but Germany, for example, places much less importance on the 160/90 reading, (normal, NOT aviation). It apparently is not a serious issue over there, requiring treatment, unless the diastolic reading is in excess of 100.

Anyway, to the original question, I personally am not too keen on being exposed to 'G' forces myself - being 8.5 stone in weight, and 5ft 5ins.

Glad to see being overweight helps with some things ..... !

ariel

[Whirlybird]

ariel,

What constitutes "high" blood pressure, and whether it should be treated, is not generally agreed. It varies from doctor to doctor, never mind country to country. By itself high bp is not a problem; it's just a risk factor for things such as heart attacks and strokes. It's generally agreed that you need at least two risk factors before it's a problem. Other risk factors are smoking, high cholesterol, and...being male. Sorry guys, I don't make the rules. Anyway, while waiting between bits of my initial Class 1 medical at Gatwick (where for no good reason my bp reading was normal) I read their charts on the wall. What they seemed to prove was that if you were female, with no other risk factors, so long as your bp wasn't sky-high (about 180/110 if I'm remembering right), it wasn't likely to be a health risk. The trouble is, the CAA don't seem to have read their own charts. So I guess I'll have to keep on getting 24 hour readings now and then. Oh well, I suppose I can survive that.

[shifatur]

captain whirly!
thanks for the reply............though we have been deviating from the original point, it's worth mentioning that bp "is" related to the g force and therefore, i am not at all repentant to have changed the topic! :D

yea, i agree when u say that a pilots bp would shoot high above anywhere near the doctors boundary. the same thing happens to me.......but see, being 19, a bp of 135/96 "is" uncommon. both my parents have high blood pressure and it could well be passed to me as hereditery .

an aspirin with no fish and chips before the test should be enough to pass me the test. not into cigerrates and drinking, so, not worried about that at the moment.

anyways, would like to know the exact figures .........what is it that would disqualify me if that, god forbids, come over me? 160/110? please lemme know!

take care
shif

[Whirlybird]

shifatur,

Since you're in the US, I don't know exactly. However, I'm going there tomorrow for three weeks flying, so I may be able to find out, but I'll only have intermittent internet access till I get back. In the UK, I know 155/95 is OK, because I've had that "officially" before now, and there's been no problem. But one reading means nothing, and every doctor knows that. High bp is NEVER diagnosed on the basis of one reading.

Your bp is probably OK, and aspirin etc should do it if necessary. Another thing someone mentioned once on here is shutting your eyes and imagining yourself curled up in bed, lying in the sun, or some other relaxing place. If it's stress that's causing it to rise, that might help a bit. One other thing I gather is that the FAA are not as strict about what medications they allow as the CAA, if it should come to that.

But if you do have problems, get a 24 hour reading; then you'll know where you are. I was scared to, and only did so because the AME threatened to ground me if I didn't. I'm so glad I did. I'd been worrying, like you, for years. And my bp is LOW for my age (I'm the wrong side of 40), except in the doctor's surgery. And I had my 24 hour reading when I had a very stressful work day! So really, please try and stop worrying.

[edspurrier]

Right, explanation needed. Bear with me chaps.

The object of pushing blood in to the brain is to supply the whole caboodle with oxygen and other goodies. This is achieved by pumping blood in via two carotid arteries at the front end and two vertebral arteries from the spine at the back which meet in the middle (quadruply redundant, yet).

The brain, which is somewhat jellylike, floats in a fluid known as CSF. The function of this is largely irrelevant except that is soaks the brain and spinal cord which sit in a closed box made of the skull and spinal column. The hole at the bottom of the skull through which the spinal cord goes is pretty teeny and hence can be ignored, so the brain is sitting in a box made of skull. As fluids tend te be, CSF is incompressible and has a pressure of about 10mmHg.

In order for blood to supply relevant bits to brain, there had to be a difference between blood pressure and CSF pressure. This is cerebral perfusion pressure (CPP):
CPP = Mean blood pressure - CSF pressure
.

Now, here the tricky bit. G force increase the weight of blood in the circulation, therefore pushing blood towards feet. It also pushes the heart down, stretching the arteries supplying the head. This means that the column being held up by the heart is longer and there's a greater difference in static pressure between heart and head, so blood pressure at the top falls. The volume of blood in the head also falls as it collects in one's flying boots, further dropping the pressure.

As we said before, the skull is a closed box, so CSF can't go anywhere and CSF pressure remains constant.

So as G force rises, cerebral perfusion pressure falls and the brain starts to run out of fuel. Hence loss of consciousness.

Hence short fat people with high blood pressure have good G tolerance - more blood pressure equals better CPP.

Hence people who are very very fit, take lots of long runs etc, tend not to have great tolerance. Weight training is best.

Ed