Acclimitisation for non pressurised planes.

[peeush]

Hi
This is about high altitude acclimatisation requirement for flight crew. Consider a crew taking off from sea level (where they don't have to use supplementary oxygen) in a non pressurised cockpit and landing at 15000 ft for a work schedule of 5 days.

The crew would have used supplementary oxygen during the flight above 10000 ft, but after landing at destination at 15000 ft they are without it and breathing out of a rarefied oxygen atmosphere.

So, do they need an acclimatisation program of two-three days before they fly again or it would be fine to fly the very next day since they would be using supplementary oxygen during the flight?

Thanks

[homonculus]

If you live at altitude, the amount of haemaglobin in your blood will increase to compensate for the lower partial pressure of oxygen in the air. This takes weeks not days.

Our ability to work at altitude varies. The military have a strict rule about oxygen at 10000 feet but many people can fly above this with little evidence of diminished performance. However many people will find physical exercise more strenuous. Younger people may also get altitude sickness where fluid enters the lungs before older people. This can be controlled to an extent with a drug called acetazolmide but the two issues are separate.

So after a couple of days at altitude the physiological need for oxygen will be unaltered. At this sort of altitude mental performance may not seriously compromise the ability to fly an aircraft let alone be a passenger but there may be a regulatory requirement as long as the aircraft is above a certain altitude. I can't see that the period at altitude would make a flight back to sea level any more of a problem provided the period at altitude has not itself caused harm.

One issue is that hypoxia has similar symptoms to being drunk. Higher centres in the brain are more sensitive and people behave in a perverse way. If I was flying a patient who had had hypoxia I might be cautious in case they became disorientated or rarely aggressive.

[Pace]

Peeush

10000 feet is only a European thing! In the USA where Americans have bigger lungs than us :) the rules are unlimited to 12500 feet, 30 minutes without sup oxygen 12500 to 14000 feet.
Sup Oxygen continuous above 14000 feet for crew.
Pax do not need to go on oxygen till 15000 feet.

There are breathing exercises which will help one used by the RAF years back called power breathing.
Tolerance varies from person to person and their fitness levels as well how well acclimatized you are to higher altitudes

Homonculous
I was told that when there is more haemaglobin in your blood the blood becomes stickier and advised to take an aspirin to help with high altitude flight! Old wives tale or some truth to that ???

[homonculus]

High altitude flight wont make your blood thicker - you are not up long enough. You have to LIVE at altitude. It takes weeks. But if you do have a raised haemaglobin you are correct in stating you have an increased risk of deep vein thrombosis etc so low dose aspirin, if not contraindicated, is a good idea

Not sure I understand how any exercises can make any difference - must work on the same principle as carrots allowing you to see in the dark!!!

[Pace]

Power Breathing (http://www.yosemitewilderness.com/wilderness_experiences/powerbreathing.html)

Just a quick google on power breathing.

Pace

[gingernut]

It may be useful to look at the Oxygen–haemoglobin dissociation curve.

Never got to the full grips me'self, :confused:

[homonculus]

Thanks for this

When we use a ventilator, we can add a modality called PREP or positive end expiratory pressure. Instead of allowing the positive pressure forcing the gases into the lungs to fall to zero (expiration then occurs passively because the chest wall is elastic) the machine keeps a positive pressure on

PEEP will increase the amount of oxygen in the blood for a given oxygen concentration.

BUT you have to maintain this positive pressure every breath for many hours to get the effect. Of course it is impossible to maintain this pressure throughout expiration without sophisticated electronics.

Simply expiring against a closed glottis as described here is no more than a valsalva. We use it in medicine to check for leaks in the brain. It reduces cardiac output and in the conscious patient can cause loss of consciousness. Back in the 1960s it was a common wheeze in UK prep schools where you could make yourself lose consciousness. There were reports of deaths - not sure if they were true but this is certainly dangerous. It also reduces the oxygen in the blood

So at face value I don't buy it, although it may make you feel a bit high

[Pace]

Homonculus

I stand to be corrected but I believe it was used as a method for high altitude flight by the RAF years back?
I have used the method of breathing which basically means you pressurize the air in your lungs using the diaphram and chest muscles with each in breath before expelling.
It appears to be beneficial and would make some sense although I appreciate the benefits could be psychological :)

See below this U tube demo which I admit is a fairly crude demonstartion

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


Pace

[homonculus]

Thanks Pace

What is demonstrated isn't even a Valsalva. It is merely deep breathing. The amount of pressure and the duration is not going to do diddly.

Maximum breaths may increase marginal levels of low oxygen by recruiting or bringing into play additional parts of the lungs but when your oxygen levels get down to the stage where you need oxygen and are feeling exhausted I don't see it will help. After all most climbers are in effect doing this when climbing. If it really was effective they could dispense with oxygen. A colleague of mine Charles Clark is a neurologist who went with several of the Everest expeditions and he assured me there was no way round taking oxygen.

Of course as you have pointed out most flying doesn't really need oxygen nor does it involve hard physical work so deep breathing or these exercises may bring up your oxygen saturation but the level isn't a problem in the first place