Pressure Breathing

[Pace]

There is a discussion in the Medical section re high altitude flight in un pressurized aircraft.

I believe there was a practice of breathing called pressure breathing which partially pressurized the air in your lungs using the muscles and Diaphram.
I also believe the RAF from years past used this method.
Does anyone have any knowledge of pressure breathing?
See U tube demo below.

http://www.youtube.com/watch?v=U-ZPjlWK0jc



Pace

[Torque Tonight]

In very simple terms:

The pressure of a mixture of gases is equal to the sum of the (partial) pressures of the constituent gases. Thus air exerts about 15psi at sea level and consists of 80% nitrogen and 20% oxygen. Therefore the partial pressure of oxygen at sea level (which is what matters for breathing) is about 3psi and nitrogen about 12psi.

As you increase altitude the air pressure decreases. To breath as at ground level in an unpressurised aircraft you need to maintain the 3psi of oxygen. By adding oxygen to rarefied air in increasing proportions as altitude increase the 3 psi of oxygen can be maintained - this is known as airmix.

This reaches a limit at 30-something thousand feet where the air pressure is about 3 psi. At this level 100% oxygen is required to continue breathing at 3psi O2. Bear in mind that up to this altitude, the airmix breathed in has been at the ambient pressure but with a partial pressure of oxygen equivalent to sea level.

Above this altitude 100% oxygen at about 3psi must still be breathed even though the ambient pressure is less than 3 psi. This is 'pressure breathing' and feels rather unnatural as you relax the muscles to breathe in and work the diaphragm to breathe out, the reverse of breathing at ambient pressures.

[Whopity]

A bit like someone putting a funnel in your mouth and pouring water in. You have to physically stop it and then force it out again.

[Torque Tonight]

Incidentally, what the woman in the video is doing is not pressure breathing as generally understood by military pilots and aviation medics. She's doing what might be referred to as taking deep breaths and holding it down. If you're not wearing an oxygen mask, you're not pressure breathing.

[Fuji Abound]

In a rather different way in reminds me of an emergency ascent when diving.

Before you start the ascent the air is at the same pressure as the surrounding water, but as you ascend the surrounding pressure falls but, of course the air in your lungs expands. Strangely (perhaps) you are largely unaware that the air is expanding and have little natural desire to exhale. Of course if you don't your lungs will "burst".

So just like pressure breathing it feels incredibly unnatural to breathe out throughout the ascent even though this is precisely what you must do.

I suppose we are simply asking our bodies to do something Darwin never intended.

[Pace]

What I am getting at here is that say at 15000 feet you control your breathing so that in a strange way you are compressing the air in your lungs are you infact acting as if you are at a lower altitude.

I am not talking about pressure breathing using supplementary oxygen!
If you google it there ar references to high altitude walking and climbing!

Ie are you infact in a minor way increasing the pressure within your chest cavity compared to the outside pressure and in a minor way treating your body as a pressurized aircraft?

Fuji we are both divers and hence probably more trained at controlling our breathing to extend bottom time!
For me using these techniques could improve our tolerance of high altitude non pressurised flying without supplementary oxygen.

Pace

[Torque Tonight]

High altitude walking and climbing is a red herring. That is achieved by acclimatisation over weeks. Anything less results in altitude sickness, incapacitation, unconciousness and death.

The video shows a small increase in blood oxygen levels by a very laboured breathing technique that seems not too dissimilar to hyperventilation. I don't really think that is a viable or safe way to operate an aircraft above the usual oxygen limits. I wouldn't fancy keeping up that technique for 5 minutes sitting in a chair at ground level, let alone an hour, piloting an aircraft at high altitude.

In answer to the point in your first post, this is not pressure breathing as the RAF would know it.

[Fuji Abound]

I thought (but havent looked back at the research I possibly read) that people vary greatly in their susceptibility to altitude sickness and their ability to cope with it - regardless of recent acclimatisation. From a genetic point of view that would seem to make sense, albeit how that might account for variation in say the Caucasian population I am not certain.

We also know that fitness has a very significant impact. Embarrassingly I use to be dreadfully over weight and unfit. I am now just a little over weight and pretty fit (but could be fitter ;)). In consequence my blood pressure has fallen from a struggle to meet the certification standard to around 114/76 and my resting heart beat has fallen dramatically to around 50 from the high 70 / low 80s. From a skiing point of view my tolerance to "high" altitude has improved immeasurably and while I cant prove the point because I havent kept a record of blood saturation levels after flights in the FLs without oxygen I feel much fresher than I use to.

.. and this is possibly relevant because I would have thought fitness levels, weight (about which you can do a lot), acclimatisation (which you can only do if you are regularly flying in the FLs) and genetics (about which you can do absolutely nothing) are likely to be far more effective means of increasing tolerance.

[Whopity]

I totally agree that is not pressure breathing. When a whole load of people went into the chamber, the altitude tolerance of different individuals varied considerably, but the reason we did it was to prove that you cannot recognise the condition yourself and to learn to recognise the symptoms of hypoxia in others.

[Lightning Mate]

I have done lots of this.

It's unnatural at the first attempt, but easy with correct training.

[abgd]

At sea level, when I was younger and more foolish, I found I could blow into a sphygmomanometer and make it go up to 200mm Hg. I ended up giving myself surgical emphysaema - somewhere near my ear, the Eustacian tubes burst and the skin near my ear began to feel like bubble wrap making little crackly noises if you massaged it.

200mmHg is 3.9 psi above atmospheric, so I can imagine that at high altitude it may buy you a little more conscious time with which to make an emergency descent. It's not a pleasant thing to do and I can't comment on other aspects such as whether it would work at high altitude, and whether it would be a good idea to breathe out whilst descending.

[Pace]

I do a reasonable amount of scuba diving and I know Fuji does too.
We are both used to controlled breathing and minimal exertion and body movement.
The controlled breathing comes down to a fine art and requires staying relaxed and slowly exhaling.
The more you do the less compressed air you use and you can extend the time a cylinder of air lasts considerably. Sometimes at the end of a dive I will have a 1/3 rd more air remaining compared to others.
It makes sense that by using your chest and diaphram muscles you can pressurize the contents of air in your lungs forming a pressurized cabin in your chest cavity.
Obviously only to a fraction of what riding in a pressurized cabin would do but equally maybe improving matters for some in the legal no supplementary oxygen levels.
We know in the UK that is 10K
FAA is unlimited to 12500 feet
12500 to 14000 feet 30 minutes
Above 14000 feet continuous oxygen
Pax oxygen above 15000 feet
Very different spread to the 10000 feet in the uk.

Pace

[India Four Two]

I have done lots of this.

It's unnatural at the first attempt, but easy with correct training.

I agree. The one time I tried it in the chamber at North Luffenham, the initial breath took me by surprise. I felt I was being inflated like a balloon. It takes a conscious effort to overcome the pressure and exhale.

[thing]

Maybe the air is thicker in the US.




































:}

[24Carrot]

Unfortunately, if you breathe pure Oxygen at 3psi ambient pressure,
you only get about 1.5 psi in your lungs - approx 1.5psi is "occupied"
by water vapour and carbon-dioxide produced by the body.

[abgd]

The video shows a small increase in blood oxygen levels by a very laboured breathing technique

I'd have to differ on that. Sustained Oxygen saturations of 83% will cause hypoxic brain-damage in the medium-long term, and certainly impair cognition and decision-making. Levels in the mid 90s are perfectly acceptable though.

[dublinpilot]

Obviously only to a fraction of what riding in a pressurized cabin would do but equally maybe improving matters for some in the legal no supplementary oxygen levels.
We know in the UK that is 10K
FAA is unlimited to 12500 feet
12500 to 14000 feet 30 minutes
Above 14000 feet continuous oxygen
Pax oxygen above 15000 feet
Very different spread to the 10000 feet in the uk.


Only true in the UK for public transport flights.

For aerial work and private flights it's only required between FL100 and FL130 if flying there for more than 30 minutes.
Only compulsory immediately above FL130.

ANO section 93.

[Pace]

For aerial work and private flights it's only required between FL100 and FL130 if flying there for more than 30 minutes.
Only compulsory immediately above FL130

DublinPilot

The FAA always talk altitude as FLs can vary substantially to the pressure of the day.
I am surprised they quote FLs with limitations for using or not using supplementary oxygen?

Pace

[24Carrot]

The temperature in your lungs is always body temperature :), so pressure is all that varies, and so FL is appropriate.

[BackPacker]

As the whole problem of hypoxia is air pressure related, and FLs are defined using a constant pressure, it makes a lot more sense to define the oxygen requirements as FL than as altitudes.

Unfortunately in the US the transition altitude is well above the altitude (or FL, whatever you prefer) so it makes sense for the US to express the oxygen requirements as altitudes.

[Fuji Abound]

I must remember to keep one altimeter on 1013 and one on barometric so I can switch on the oxygen at the appropriate moment ;).

[Pilotage]

As the whole problem of hypoxia is air pressure related, and FLs are defined using a constant pressure, it makes a lot more sense to define the oxygen requirements as FL than as altitudes.

Unfortunately in the US the transition altitude is well above the altitude (or FL, whatever you prefer) so it makes sense for the US to express the oxygen requirements as altitudes.

It is however the human body which has the casting vote.

It defines the oxygen requirements in terms of density altitude.

P

[dublinpilot]

DublinPilot

The FAA always talk altitude as FLs can vary substantially to the pressure of the day.
I am surprised they quote FLs with limitations for using or not using supplementary oxygen?

Pace

Pace,

I was correcting your post in relation to UK requirements, not FAA requirements.

The details that I posted are from the UK ANO. Nothing to do with FAA.

dp

[24Carrot]

It defines the oxygen requirements in terms of density altitude.

Not really. The body only works at body temperature, so the air temperature in the lungs is body temperature, so pressure is proportional to density in the lungs. Not in the atmosphere, standard or otherwise.

It makes much more sense to work in pressures. The Saturated Vapour Pressure of water is a pressure. The partial pressure of CO2 in the blood is a pressure. The "A-a" gradient is a pressure.

Google "Alveolar Gas Equation".

[Pace]

DublinPilot

That was not pointed at you ;) and maybe its me that is being totally stupid :E

Standard pressure is just that an artificial figure which if your lucky may coincide with an actual presssure of 1013 but is very likely to NOT!

It is the actual pressure which is relevant to Hypoxia.

There can be a huge variation from Standard high or low meaning the aircraft can be higher or lower than the standard pressure setting level showing on the altimeter.

Hence I find it hard to see how a flight level can be used with accuracy without reference to the actual pressure or at worst regional pressure setting

Pace

[Pilotage]

Not really. The body only works at body temperature, so the air temperature in the lungs is body temperature, so pressure is proportional to density in the lungs. Not in the atmosphere, standard or otherwise.

It makes much more sense to work in pressures. The Saturated Vapour Pressure of water is a pressure. The partial pressure of CO2 in the blood is a pressure. The "A-a" gradient is a pressure.

Google "Alveolar Gas Equation".

Fair point - my error. Partial pressure of oxygen is the critical player. Brain fade!

Although it's still the human body, not the regulations, that have the casting vote.

P

[24Carrot]

Pace wrote:
Hence I find it hard to see how a flight level can be used with accuracy without reference to the actual pressure or at worst regional pressure setting

Pace, I know you know this:), but FL measures atmospheric pressure (albeit in units of feet), so it is exactly what the regs should specify.

It is the altitude which is less accurate, though as Backpacker said, altitude may be more practical if the TA is high.

Pilotage: agreed, the body can even over-rule the equations!

[Pace]

Carrot

Its Ok I am having brain fade too :eek: I think?

Pace

[dublinpilot]

Pace, I know you know this, but FL measures atmospheric pressure (albeit in units of feet), so it is exactly what the regs should specify.

It is the altitude which is less accurate, though as Backpacker said, altitude may be more practical if the TA is high.

Don't you have that backwards?

If I'm standing on the shoreline, at the time exactly halfway between high tide and low tide, then I'm at mean sea level. If the pressure at that point (at MSL) is 1000hpa and I set my altimeter subscale to 1000hpa then my altimeter would accurately read 0ft.

If I set it to flight levels (1013hpa) then it would read 390ft (13*30) which is FL003.9 (Not that you'd ever replort FL003.9 to anyone!). While using a standard scale is convenient for aircraft seperation, it is less accurate than altitude.

I'm standing at MSL (shore line half way betwen low and high tide) and altitude is reading 0, and FL is reading 390ft. So altitude is more accurate. In terms of the effect on the body using 0ft in your calculations must be more accurate than 390ft at that point.

I think that is the point that Pace was trying to make.

But of course in the UK an aircraft at that level will have their altimeter set to 1013 and the differences in effect on the body are likely to be small. The change is risk of hypoxia is probably considered to be far smaller than the risk of someone having a miss-set altimeter due to changing it to check the pressure altitude and back to FL.

dp

[Pace]

DP

That is my point and I am still trying to get my head around how an artificial setting of 1013 which bares no relationship to the actual pressure of the day can be used as a level limitation for avoiding hypoxia.
Forget 1013 lets make an artificial setting of 1040 or one of 980 why not use those? They would be as accurate as 1013? everyone could fly around in teh airways using 1040 or 980 with the push of a regulation pen.
You could be talking about a difference of 1000 feet from your flight level to your actual altitude.
Am I missing something here or being stupid?


Pace, I know you know this, but FL measures atmospheric pressure (albeit in units of feet), so it is exactly what the regs should specify

A flight level doesnt measure anything and altimeter with 1013 set will show an altitude if the QNH happens to be 1013 but will show a FL which bares no relationship to an altitude if the pressure of the day is not 1013

Pace

[abgd]

Well, if standard pressure was changed, the flight-level-limit would have to be changed to match. e.g. if standard pressure was 980mb rather than 1013, then the limiting flight level would be set at FL 120 rather than 130.

If a cosmic storm whisked away the earth's atmosphere, we'd still die at sea level because our lungs knew they were at flight level 10000, and this is the more valid metric to use for this purpose.

Or am I misunderstanding something too?

[24Carrot]

I hope it's not me that's missing something!
I think a FL limit is appropriate for hypoxia because:

An altimeter is a barometer. It measures pressure plus how much you turned the sub-scale knob. If you always use the same sub-scale setting, you are only measuring pressure.

If everybody agrees on sub-scale setting to use, (which is 1013 by convention, but could be any agreed number), then everybody's altimeter measures the pressure in the same units. (feet, on a non-linear scale).

That means everybody can agree on an altimeter reading which was the limit for hypoxia, and it would correspond to an atmospheric pressure limit for hypoxia. Pressure is all that matters for hypoxia.

If the regulators specify a FL, they have specified an atmospheric pressure. It truly does not matter what the altitude is. The lungs do not care.

As an example, let us say we are at FL100, which is approx 700hPa if memory serves. That 700hPa is all our lungs care about.

Very roughly, 100hPa in the lungs will be CO2 and water vapour, 120hPa will be O2 and 480hPa will be N2. That adds up to 700hPa. The 120hPa partial pressure of oxygen is all that matters for hypoxia.

You will notice I have not mentioned the altitude yet, and that is because it doesn't matter, except as a rough indication of what the pressure might be at that altitude.

If the air below us is very cold, and QNH is very low, we could be at 8,000 ft. What do our lungs care? They are breathing in air at 700hPa. The O2 partial pressure is still 120hPa.

[cumulusrider]

Back to the original topic- pressure breathing

Sufferers of sleep aponea use a CPAP machine which provides air to a mask at a raised pressure. The effect to the user is the same as described. ie you relax to breath in and have to use the diaphram to force air out. It feels most unatural at first as if the machine is trying to blow you up like a balloon.

[BackPacker]

An altimeter is a barometer. It measures pressure plus how much you turned the sub-scale knob.

That's exactly the point I was trying to make.

If you define the hypoxia air pressure (assuming there is one) as a flight level, you can simply set the subscale to 1013, read the flight level and see if you're in the danger zone or not. Whereas if you define the hypoxia danger zone as an altitude, you need to correct for the subscale setting, but backwards from what we're used to. So it makes a lot more sense to define the hypoxia/oxygen limits as flight levels instead of altitudes.

Going along with Carrots example. Suppose for a moment that 700 hPa is the start of the danger zone. If the air pressure is 700.0 hPa or lower you run an hypoxia risk, if the air pressure is 700.0 hPa or higher you're fine. (I know it's not such a black and white issue, but let's go along with that for now.)

We have no way of knowing the actual air pressure in the aircraft unless we bring an actual barometer. But, hey, our altimeter is a barometer too, just with a scale that works the other way round (increasing air pressure leads to a reduction of the readout) and its datum is adjustable.

Flight Levels are defined against a "QNH" of 1013. In other words, FL000 = 1013 hPa, FL001 = 1010 hPa, FL002 = 1007 hPa and so forth. And since that relation is not entirely linear and since I don't have the ISA atmosphere definitions to hand, let's assume FL100 = 700 hPa. This means I can use my altimeter to find out whether I'm in the danger zone or not: Set the subscale to 1013, see if I'm above 10.000' on the dial and I'm in the danger zone.

But as soon as you start setting a different subscale, because you insist on flying altitudes rather than flight levels, 700 hPa air pressure no longer corresponds to a reading of 10.000' on the altimeter. It corresponds to something that may be a few 100s of feet lower or higher. So you need to correct for that correction again.

As an example, suppose the QNH is 1007 and you have that set on the dial. This means that zero feet on the dial now corresponds to a barometric pressure of 1007 hPa. 100 feet corresponds to 1004 hPa, 200 feet corresponds to 1001 hPa and so forth. And the 700 hPa level no longer corresponds to the readout of 10.000'. Instead, the 700 hPa hypoxia danger level is now found where the altimeter reads 9.800 feet.

So on a low pressure day you may be in danger of hypoxia even below 10.000 feet altitude. Conversely, a high pressure day will give you a few hundred feet above 10.000 feet where you will not suffer from hypoxia. (Again, assuming it's black and white, which it isn't.)

Now try calculating that when you're already suffering from hypoxia.:ok:

[Pace]

BackPacker

You took the words right out of my mouth
:----)

Pace

[mad_jock]

Pace you could see what it feels like by getting a fat burd to sit on your chest.

Opps got the pressures the wrong way round but you can try it anyway :p

[Pace]

MJ

I do not want a fat burd sitting on anything only go for slim ones :E

So getting this right? If you have a fat Burd sitting on you you will know at what level hypoxia will set in? Does that work in a Cessna 150? ;)

Pace

[mad_jock]

well it will be breathing under pressure :D

Oh and my take on this is...

you have two things.

1. the required partial pressure to allow oxygen transfer across the cellular wall in the lungs. Its not binary but a none linear curve.

2. The up take of oxygen in the blood and transfer to the organs.


Pressure breathing only increases the partial pressure and puts you up the curve for number 1. Smokers etc will require higher to get the same transfer.

[dublinpilot]

I think a FL limit is appropriate for hypoxia because:

An altimeter is a barometer. It measures pressure plus how much you turned the sub-scale knob. If you always use the same sub-scale setting, you are only measuring pressure.

Thanks 24C. Very clearly and polietly explained. Thank you. :ok:

dp

[Lightning Mate]

Look guys, pressure breathing is based upon cabin/cockpit pressure - everything else is irrelevant.

The aeroplane I flew was officially cleared to 60,000ft, but has been higher.

In the event of pressurisation failure the oxygen regulator would automatically feed pressurised oxygen to the mask - all that was required was to pull down the mask toggle which would pull the mask very tightly to the face.

Now, the pressure suit and helmet and suit were something else.

Try this little lot.......

http://i636.photobucket.com/albums/uu82/Lightning_29/altitude_zps475d0efd.jpg

[Pace]

Lightning Mate

Fantastic shot especially in black and white as they add atmosphere! Was the shot of you with the lightning?

Pace

[Lightning Mate]

No mate - not me, or I would have airbrushed out the name below the cockpit.

One little word - PERFORMANCE

[BackPacker]

Going back to the original question, about pressure breathing manually. In other words the objective is to raise the air pressure in your lungs significantly higher than ambient (and thus helping the transfer of O2 to your blood) by blocking your throat somehow and using your rib cage and diaphragm to pressurize your lungs. Hold this for a few seconds, exhale and inhale quickly and hold again.

I have never tried this to increase ppO2, but I have been taught this, combined with applying muscle tension strategically, as part of the straining technique to combat high Gs in aerobatics. All I can tell is that it is extremely tiring, and very bad things may happen if you get it wrong. (G-LOC for instance.) In aerobatics you only need this for a few seconds at a time. For a prolonged high-altitude flight without oxygen/pressure suit/pressure hull I would be very, very careful.

[Lightning Mate]

....and there I was thinking this thread was about pressure breathing.

[Pace]

It is a technique used by high altitude climbers probably confused over another type of pressure breathing you mention.
Maybe controlled breathing to maximize oxygen intake maybe a better description.
There is nothing wrong with controlled breathing uncontrolled breathing as in hyperventilating is far worse.
Scuba Diving we use controlled breathing to maximize bottom time and to use as little air as possible.
Yes this would be different again where you are maximizing oxygen intake in high altitude situations but I cannot see why it cannot improve matters.

Pace

[Fuji Abound]

It is a common technique in diving however I wonder if there are different reasons why it is so effective.

Diving often involves a degree of excitement, panic or a combination of both! Perhaps just like flying! So the diver breathes more rapidly (and even hyper ventilates). Breathing more rapidly simply means the air is gulped from the demand valve and not used efficiently. Hyper ventilation is a great deal more serious because it suppresses the normal level of C02 in the blood and counter intuitively constricts the blood vessels interfering with the transport of oxygen - all bad. (Pace I know you know this)

As we have rehearsed and in contrast at altitude the lungs gradually diminish in their ability to transfer oxygen; I dont see by holding the air in the lungs this will change anything. It is not that the pilot is trying to conserve air, after all it is not that it is in short supply, rather there is not enough oxygen in the air relative to the ambient pressure. Breathing rapidly clearly will make matters worse, and I would guess holding each breath a little longer might mean the oxygen available is better absorbed, but I would guess the difference is negligible. Pressurising the air clearly is beneficial but as the discussion has flowed it would seem this is very difficult to do in a controllable and meaningful way.

I still reckon fitness is the simplest way of improving matters. There is no doubt the fitter you are the more effective your lungs are at absorbing what oxygen is available and the better the body is at transporting the gases around the body (with the caveat as we have discussed that fittness and altitude resilience dont necessarily go hand in hand). I reckon if you want to operate at higher altitudes without oxygen get your weight down to recommended levels, do lots of aerobic exercise and of course quit smoking (if you do).

[Pace]

Altitude.org | Why do low oxygen levels cause altitude sickness? (http://www.altitude.org/)

This is an excellent site for explaining things as well as having a calculator which is interesting for us flying types

Pace

[mad_jock]

You could breath in. Hold it, then get a fat burd to sit on your chest. That would increase the partial pressure but slightly not pratical in flight.

I think you used to get elsticated chest straps years ago didn't you for high altituded?