Oxygen levels on short flights found to be low

[Wirraway]

Fri "Sydney Morning Herald"

Oxygen levels on short flights found to be low
By Julie Robotham and Alexandra Smith
March 19, 2004

Oxygen levels in some commercial aircraft may be too low for people with health problems to travel safely and short-haul flights are of greater concern than longer trips, researchers have found.

Doctors from Concord Hospital measured cabin altitude pressure - which in turn affects oxygen availability - on 79 flights, including international flights and shorter routes within Australia and overseas.

"We found cabin altitude pressure was significantly higher on shorter flights," researcher Leigh Seccombe said.

Ms Seccombe said that at sea level, air breathed in contained about 21 per cent oxygen. At the maximum pressure allowed in an aircraft cabin - equivalent to 2438 metres above sea level - air entering the lungs typically contained only about 15 per cent.

The researchers found long-haul flights in Boeing 747s were well within the standard, offering air containing about 17 per cent oxygen. But while all flights they monitored conformed to cabin pressure regulations, the air pressure in Airbus planes was typically closer to the maximum limit.

"If you're normally healthy you increase your respiratory rate without knowing it," to compensate for the reduced oxygen content, said Ms Seccombe, who will present the results to the Thoracic Society of Australia and New Zealand in Sydney next week. "But people with lung disease could be really struggling."

She said the only previous research into cabin pressure was in the US in the early 1980s. But aircraft had changed significantly since then and older people in particular were flying more.

In a separate study, the same researchers found people with lung disease ran into breathing difficulties at lower air pressures than had previously been realised.

Matthew Peters, the head of respiratory medicine at Concord Hospital, said the results indicated "fitness to fly" guidelines might need revision to take account of rapid falls in blood oxygen levels among some patients who would be deemed healthy enough to travel by current standards.

Associate Professor Peters examined 15 people with interstitial lung disease - in which there is scarring or fibrosis in the lungs - and 10 with chronic obstructive pulmonary disease, in a test that simulated minimum oxygen levels on planes.

He found "profound hypoxia" among several people whose medical condition was otherwise deemed good enough for them to fly. The tests showed it was impossible to anticipate which people with lung disease would have in-flight breathing problems, he said.

Associate Professor Peters said it was possible people might misread their falling oxygen levels as panic attacks or hyperventilation. The most serious potential consequence of inadequate oxygen intake was a heart attack. Although this was rare, he said, if it did occur, people might not connect it to respiratory distress.

Australia's new low cost domestic airline, Qantas-owned Jetstar, will fly Airbus A320 planes from June and will eventually have an all-A320 fleet - the same planes as in the study.

Qantas has seven Airbus A330s in its fleet, which will soon be phased out of domestic routes and used only for international flights - though these planes were not specifically considered by the Concord Hospital team. Virgin Blue has no Airbus planes.

A spokesman for Qantas declined to comment.

===========================================

[Desert Dingo]

"We found cabin altitude pressure was significantly higher on shorter flights
At the maximum pressure allowed in an aircraft cabin - equivalent to 2438 metres above sea level -
Obviously no idea about altitude vs air pressure, or maximum vs minimum.
Journalists. :yuk: (I hope the doctors are being misquoted)

[Hugh Jarse]

The researchers found long-haul flights in Boeing 747s were well within the standard, offering air containing about 17 per cent oxygen. But while all flights they monitored conformed to cabin pressure regulations, the air pressure in Airbus planes was typically closer to the maximum limit.
This research kindly funded by Boeing or associated companies with an interest in seeing Airbuses product fall into disrepute in Australia. :}

[404 Titan]

Ms Seccombe said that at sea level, air breathed in contained about 21 per cent oxygen. At the maximum pressure allowed in an aircraft cabin - equivalent to 2438 metres above sea level - air entering the lungs typically contained only about 15 per cent.
Here we go again with the recycling of air in the cabin. These researchers should get a life and test the air in their own labs or the average office tower. The reality is these places are far worse than any aircraft cabin.

[slamer]

OK, apart from the obvious "Journo dig" how come you people are jumping to the defence a a fairly 5hity work enviroment? ( Cockpit and Cabin) that is savage on ones state of health.

[itchybum]

Well said, slamer. In the fashionable rush to sink the boot into the journos (who usually have it coming, I admit) the guys are ignoring the facts.

Bring on humidifiers and water tanks...... damn the weight.

[Junipa]

Hello everyone.

Im new to this site and it was recommended to me because I am looking for some answers.

I am a well controlled asthmatic on one inhaler only (ventolin)

I have flown a few times and the past two years, I have flown to Australia.

Apart from the usual dry mouth that comes with flying, fixed by drinking water, have never had any problems with my asthma at all.

Recently flew from London to Vancouver with Zoom airlines. Had a full medical before I flew and had the lung capacity of a non asthmatic.

Feeling quite smug, boarded the flight to Canada.

About 3 - 4 hours into the flight, I felt myself getting more tired than normal.

A little later, my asthma was going from no sypmtoms to worrying symptoms.

What was interesting, was when you have gradual worsening of symptoms, you don't realise how bad you are getting.

To cut a long story short, I spent a very uncomfortable flight, slowly becoming very hypoxic.

The whole week in Canada was spent with me having bad asthma and the flight back was even worse.

With the return flight going back completely full, I spent vast amounts of time in the toilet (much cooler in there)

And before anyone suggests that I might have been panicking, well I have never panicked with my asthma, I know how to deal with it.

I have seen my doctor and have been put on nebulisers (breathing machine) and steroids with a view to going in hospital should I not improve.

Now, I could have put this down to coincidence, but I have had an email from a friend reporting the same happened to her,

Please help me someone to explain this.

[justanotheraviator]

Let me see...... constant cabin diff......

on a short flight at higher altitude due to lower aircraft weight due to low fuel load gives higher cabin altitude.

on a long flight at a lower altitude due to a higher aircraft weight due to a higher fuel load gives a lower cabin altitude at least initially.

Can I have a PHD now please

:D

[quim]

Junipa, you should go and see an Aviation Medical specialist in whichever country you are in. Your asthma attacks realy have nothing to do with this thread. Having said that, I hope you find your answer and get well.

The most worrying thing about this study? We probably funded it as taxpayers. 79 flights? Expensive. Results? Pointless...:yuk: :yuk: :yuk:

[MeatHunter]

Twenty one percent O2 in standard atmosphere. As the body only consumes about half that a cabin altitude of 8000 ft should not be too much of a problem. Simple solution is to breath deeper.

[quim]

Just ocurred to me. I'd reckon this study was done exclusively on Virgin aircraft.

Both their staff AND passengers are oxygen theives! :} :} :}

[Jamair]

How strange; when I'm in a cabin altitude of say 10,000 ft pressurised at 5 PSI, I'm still breathing air which comprises 21% oxygen....or even in the mighty piston twin, breathing unpressurised air at 10,000 ft, I'm still breathing air comprising 21% oxygen. I wonder where the other 6% of oxygen has gone in these tests, and what has replaced it?

Of course, the density of the air that I'm breathing at 10,000 ft is considerably lower than the density at sea level, which means the PARTIAL pressures of the gases that comprise air are also correspondingly lower - but the percentage of those gases changes NOT AT ALL. IT IS STILL 21%. Daltons Law: The pressure exerted by any gas in a mixture is the same as the pressure it would exert if it alone occupied the same volume.

Media nongs.:yuk:

[The_Cutest_of_Borg]

Jamair, i thought the same thing. However as pressure decreases, then the partial pressure of the oxygen in the cabin air also decreases. This means that the lungs cannot absorb whatever oxygen there is in the air no matter what the concentration.

At altitude, this can be offset somewhat by pressure breathing, i.e having the oxygen delivered at an overpressure via a mask, but this is something that must be practised, is tiring and is not practical for the average passenger aeroplane

This is by no means new knowledge though. Makes me wonder why it is newsworthy.

[OverRun]

Junipa,

This breathing problem is not new - read more about it, cabin air flows, and how it can be countered by the passenger. Just above the big table on the following page:
http://www.geocities.com/profemery/entertainment/legroom.html

[Sunfish]

Its about money possums.

Cabin air is bleed air, suitably cooled.

Lower cabin altitude needs more bleed air. Higher cabin altitude needs less bleed air.

Air recirculation saves bleed air.

More bleed air = higher fuel consumption.

Fuel consumption = money.

OK all you experts, now come and slaughter me over max pressure differential and programmable pressure controllers. My ears used to get to the runway two thousand feet before the plane did.

Or is it just that the Airbus controller isn't as smart as the Boeing version?

As for Asthma, a simple oil seal leak somewhere can mean contaminated bleed air - that will give you asthma.

Anyone remember the Bae !46 business?

[Milt]

Blood Oxygen Levels

Does anyone know the blood oxygen % when an average person is on the edge of unconsciousness.

I would guess about 60% of normal 100% at sea level.

Relative pressure at 8,000 ft is 0.743 and pressure 10.92 pnds/sq inch or 0.768 Kg/sq cm

[Jamair]

milt: Respiratory failure is usually defined as a blood/oxygen saturation of <90%, but the point at which an individual will loose consciousness will depend on the individuals capacity to tolerate lower oxygen levels. Best I've seen is 73% with person still functional - but not for long and only at rest.

Sunfish: No amount of airborne contaminant can 'give' you asthma; it is a condition which already exists, that may then be exacerbated or triggered by things such as airborne contaminants, pollen, salt etc.

Cutest of Borg (& I love Voyager BTW): Partially correct; the pressure decreases, the percentage does not - it remains as 21%. For example, the standard sea level pressure of air is 760mm Hg, so the partial pressure of oxygen in the mixture is 21% of 760, or 159 mmHg. As the total pressure decreases with altitude, the partial pressure of O2 also decreases; at 10,000ft the atmosperic pressure is 563mm Hg, 21% of this is 110mm Hg.

This becomes important when considered in light of the oxygen cascade, or the dilution of oxygen concentrations and partial pressures as inhaled air is variously routed and absorbed to the point where O2 actually gets into the cells. At sea level, from an initial partial pressure of 159mmHg, the pressure of O2 on reaching the lungs is down to only 104mmHg, further dropping to 40mmHg in the pulmonary blood flow and down to only about 5mmHg at cellular level. Draw this on a rough graph and you can easily see that a reduction in PPO2 from 159mmHg to 110mmHg in inhaled air is going to have a significant effect on the levels of O2 actually reaching the cells. This can be obviated to some degree by increasing the PPO2 of inhaled air by enriching the O2 mix, with supplementary O2 (ie using a mask or nasal cannula to increase the PPO2 to 30%, 40%, etc). Breathing more rapidly will not alter the PPO2 but it will remove CO2 which is undesirable. A reasonably detailed discussion of hyperventilation was in the last Flight Safety magazine. The higher you go, the greater the percentage of O2 must be in the breathed air to acheive adequate cellular oxygenation.

The point? The article discusses percentages, which is inaccurate.

[Bad medicine]

Oh I love a discussion on respiratory physiology. Hyperventilation does actually increase the partial pressure of oxygen in the lung (and is in fact a natural response to hypoxia). It does this by reducing the partial pressure of carbon dioxide, as Jamair said. The effect isn't great, but it is a reflex protective mechanism.

The PO2 at the distal end of the pulmonary capillaries is very close to the PO2 in the alveoli (~100mmHg). The PO2 in the venous blood is about 40mmHg - this is what drives the diffusion of O2 from the alveoli into the blood stream.

At 10000ft, the saturation of haemoglobin with O2 in the arterial blood is still about 90%, which is why a relatively healthy individual can function reasonably well without supplementary O2. After this, though, the saturation falls off rather more rapidly, and supplementary O2 is required. Above about 40000, even 100% O2 at ambient pressure is insufficient, and pressure breathing is required.

So, in summary, O2 requirements are:

MSL - 10000ft Air
10000 - 33700ft Airmix (with increasing % of O2)
33700 - 40000ft 100% O2
>40000 100% O2 under pressure.

Cheers,

BM

[Jamair]

:ok: Well said BM; hyperventilation can have some positive effect on PPO2 at the alveolar level by reducing the normal dilution effect of CO2. You'd be the Moderator of an Aeromedical forum I guess? Cheers ;)