Pressure Breathing
 

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.




Pace

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.

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.

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.

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.

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

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.

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.

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.

I have done lots of this.

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

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.

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

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.

Maybe the air is thicker in the US.




































:}

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.

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.

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.

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

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

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.