Mooney down in Atlantic

[aviatoreb]

I think it's highly probable that if one goes unconscious due to lack of oxygen it becomes more then a little nap till a lower altitude. I would think the brain shuts down and there's no coming back and that happens fairly quickly. When we practice high-dives from FL430, (simulating loss of pressurization) if the oxygen masks don't deploy or activate by pulling the mask to your face, people will die. That's why in the safety briefings they say put your own mask on before helping others. At those altitudes useful consciousness is about 5 seconds. Even diving at Mach snot takes several minutes to get to thick air.

 

 

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I'm not doubting what you say - I am just really confused.  I can sit here and hold my breath for more than 5 seconds.  I can hold my breath for maybe 2 minutes.  Some people can hold their breath for 5 minutes.  I totally get the 3 minute thing at low FL20's.  That makes sense to me.  What is going on at high altitude to make it 5 seconds?  Is it the explosive decompression aspect of loss of pressure at FL43?

[Deb]

From: http://www.avmed.in/2011/10/cabin-pressurisation-–-hazards-of-rapid-decompression/

"The physiological effect of decompression depends upon the pressure differential, the duration of decompression and the final cabin altitude. The most severe hazards associated with a rapid decompression to high altitude ishypoxia. This hazard is particularly significant for the following three reasons.

• a.  In the case of high differential cabins with a cruising cabin altitude of 1,500 m – 2000 m (6000 to 8,000 ft), the crew is most unlikely to use oxygen equipment at the time of the decompression.
• b.  If the final cabin altitude is very high i.e. above 10,000 m (33,000 ft), the time of useful consciousness (TUC) for various crew members breathing air may be reduced by as much as one third from the figures which would normally be expected for that ambient altitude. This is due to the fact that during the escape of gas from the lungs, the partial pressure of oxygen in the alveoli is reduced to below 40 mm Hg which is the approximate value for the oxygen tension in the venous blood. There is an actual reversal of the oxygen diffusion gradient across the alveolar membranes and oxygen passes back into the lungs from the venous blood. Immediately following a rapid decompression to these very high altitudes, therefore, the arterial blood leaving the heart would be carrying a little or no oxygen and the onset of hypoxia would be very rapid. This shows the advantage of having the pilot or one of the pilots on oxygen the whole time when ambient aircraft altitude exceeds 8.5 Km (30,000 feet)."

[PTK]

   "...The physiological effect of decompression depends upon the pressure differential, the duration of decompression and the final cabin altitude..."

"...This is due to the fact that during the escape of gas from the lungs, the partial pressure of oxygen in the alveoli is reduced to below 40 mm Hg which is the approximate value for the oxygen tension in the venous blood. There is an actual reversal of the oxygen diffusion gradient across the alveolar membranes and oxygen passes back into the lungs from the venous blood..."

This sums it up nicely.

Also important to remember is that this partial pressure of oxygen (PO2) of 40 mm Hg is very low at this point to begin with because this is blood returning to the lungs from systemic circulation having depleted its O2 and loaded up on CO2. This shifts the hemoglobin dissociation curve against us! It's all downhill at this point.

Edited September 14, 2015 by PTK

[charlesual]

I hear you. I found it hard to believe 5 seconds useful consciousness myself until I saw training videos that show what I say to be true. I tried to find them on YouTube to no avail but I saw with my own eyes a video where a guy goes from completely conscious to night night in 5 seconds in an rapid decompression video. Made me a believer. Probably the reason for the FAR that mandates one pilot at the controls be continuously on supplemental oxygen FL410 and above. (FL350 under part 91)

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[Shadrach]

I'm not doubting what you say - I am just really confused.  I can sit here and hold my breath for more than 5 seconds.  I can hold my breath for maybe 2 minutes.  Some people can hold their breath for 5 minutes.  I totally get the 3 minute thing at low FL20's.  That makes sense to me.  What is going on at high altitude to make it 5 seconds?  Is it the explosive decompression aspect of loss of pressure at FL43?

What Is different about holding your breath is that you are focused on taking in as much O2 dense air as possible and counting from there. When breathing normally at sea level, the average person takes a breath about every 3.5 secs. In the flight levels on a nose hose, a pilot is likely to breath even more frequently. It matters not how long you can hold your breath if you just unknowingly exhaled your last breath of O2 rich air.

Edited September 14, 2015 by Shadrach

[EMB]

I hear you. I found it hard to believe 5 seconds useful consciousness myself until I saw training videos that show what I say to be true. I tried to find them on YouTube to no avail but I saw with my own eyes a video where a guy goes from completely conscious to night night in 5 seconds in an rapid decompression video. Made me a believer. Probably the reason for the FAR that mandates one pilot at the controls be continuously on supplemental oxygen FL410 and above. (FL350 under part 91)

 

 

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Wow - I guess that rule is quite well placed then.  5 seconds is surreal.

[carusoam]

Consider a cognitive experiment...

breath out...

hold your breath...

walk down the driveway...

how far would you get?

when you guys are saying you can hold your breath for a minute or two, did you breathe in first?

in real life, I don't think you will get that luxury...

they call that good lung capacity.  When you run out of O2 your lung capacity has been cut to an incredibly small number. Unless something tells you to take a breath and hold it because you have one breath left...

five seconds sounds like a bit of a stretch, because we only breath once every five seconds normally without noticing the immediate need to breathe again.

again this is a mental exercise, don't go try this to see how far you get.  It will probably end up poorly.  

Depending on your skills, You will definitely have the feeling that you need to sit down. Ignoring that feeling will leave you toppling...

A few minutes is way too much to expect.  What is your heart rate going to be during an emergency?

Edited September 14, 2015 by carusoam

[DXB]

Comparing breath holding to altitude-related hypoxia is apples to oranges.  In a breath hold, the discomfort, anxiety, and urge to gasp mainly comes from sensing increased blood CO2 (hypercapnia) and the resulting acidosis, not decreasing O2 availability to tissues (hypoxia), which drops pretty slowly at first and does not immediately alter blood pH (until lactic acidosis occurs- but that's another topic).  Hypercapnia is not a problem when becoming hypoxic during climb to altitude because you are breathing just fine, which gets rid of the CO2. In fact the exact opposite tends to occur - i.e. hyperventilation in response to hypoxia causes hypocapnia thus alkalosis (which contributes to "altitude sickness" in some folks).  In general, the experience of hypoxia is more insidious than hypercapnia because we are more strongly wired to regulate our breathing rate and depth based on blood CO2 levels- this makes sense because CO2 directly impacts blood pH, which must be maintained in a fairly narrow range to support the chemistry of our metabolism. Different tissues can tolerate prolonged hypoxia pretty well, albeit to varying degrees - the brain is the worst given its very high energy demand and minimal capacity for anaerobic metabolism.  

As far as immediate loss of consciousness during decompression at extreme altitudes that Mooneys are incapable of, Deb's post above is on point. This is another animal. 

 

[Deb]

Comparing breath holding to altitude-related hypoxia is apples to oranges.  In a breath hold, the discomfort, anxiety, and urge to gasp mainly comes from sensing increased blood CO2 (hypercapnia) and the resulting acidosis, not decreasing O2 availability to tissues (hypoxia), which drops pretty slowly at first and does not immediately alter blood pH (until lactic acidosis occurs- but that's another topic).  Hypercapnia is not a problem when becoming hypoxic during climb to altitude because you are breathing just fine, which gets rid of the CO2. In fact the exact opposite tends to occur - i.e. hyperventilation in response to hypoxia causes hypocapnia thus alkalosis (which contributes to "altitude sickness" in some folks).  In general, the experience of hypoxia is more insidious than hypercapnia because we are more strongly wired to regulate our breathing rate and depth based on blood CO2 levels- this makes sense because CO2 directly impacts blood pH, which must be maintained in a fairly narrow range to support the chemistry of our metabolism. Different tissues can tolerate prolonged hypoxia pretty well, albeit to varying degrees - the brain is the worst given its very high energy demand and minimal capacity for anaerobic metabolism.  

As far as immediate loss of consciousness during decompression at extreme altitudes that Mooneys are incapable of, Deb's post above is on point. This is another animal. 

 

As DXB has eloquently summarized, the physiology of hypoxia occurring at altitude in our Mooneys is very different from that of either breath holding or decompression.

As one ascends in a non-pressurized Mooney, the body remains at anbient pressure. When supplemental oxygen is decreased (or removed), there is no decompression event. Respiration and gas exchange continues with a diminished amount of oxygen, an amount which may be significantly less than at sea level, depending on altitude.

Experiencing hypoxia in a controlled environment is certainly educational, particularly in the recognition of one's physiologic reaction to hypoxia. It is important to note that one's cognitive function can decrease with even mild hypoxia; studies have shown that volunteers have difficulty performing simple math calculations when mildly hypoxic (calculations they could easily perform at baseline.) As Don Muncy has posted, with the slow and insidious onset of an hypoxic event, the symptoms which occur may not be recognized because cognitive impairment may have already occurred. Thus, hypoxia is unrecognized. Worse, judgement is impaired and even if the hypoxia is recognized, one may not be able to (think to) execute the appropriate corrective measures.

Hopefully the discussion in this forum will promote a better understanding of the physiology and risks of flying at hypoxic altitudes and what best mitigates those risks.

For a comprehensive review of breath holding physiology: http://onlinelibrary.wiley.com/doi/10.1113/expphysiol.2005.031625/full. 

[DonMuncy]

I've done high altitude training. I know the symptoms of hypoxia in myself, and because I've had the chance to do it 3 times, I know they are generally consistent.

Ryan,

Do you feel really comfortable with the knowledge you will recognize the symptoms and know to do something about it. (Unlike the times when we hear the gear warning and say "what the ... is that")

I'm not criticizing. I want to know the answer.

[bradp]

For the pilots who fly in the flight levels unpressurized I have a question about your pulse oximetry setups. Most of those I find on spruce etc seem like simple setups. Do you constantly monitor or just sport check? Does the monitor run of batteries or ships power or both? Do you have an alarm set? If so at what % SpO2? I'm curious to understand the monitoring that is involved If flying the flight levels.

Thanks

Brad

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[DonMuncy]

The only oximeters I have seen are battery operated, and you have to physically hook it on your finger and look at the readings. So with these, you just have to spot check.

[Marauder]

The only oximeters I have seen are battery operated, and you have to physically hook it on your finger and look at the readings. So with these, you just have to spot check.

There is a panel mounted unit from Guardian Avionics that can be purchased. It can be interfaced with certain JPI analyzers.

[Marauder]

http://www.guardianavionics.com/aero455.html

[DonMuncy]

Wow. An AMU for an oximeter to replace one which can be had for under $50. Admittedly, it has some extra stuff, but you still have to stick your finger into it to get a reading.

[aviatoreb]

Thanks David, I am learning a lot here. It is counter intuitive to me how different this is from breath holding, and especially how if we are breathing about every 3 seconds how 5 seconds could be a TUC time, but counterintuitive as it is, then all the more I am happy to learn what is the science.

[Danb]

Brad

i fly with 2 nonan oximeter sand check them every 5 minutes when I wear o2' I generally go on O2 between 8000-9000 ft depending how I feel or tired I am. Also don't forget an extra set of batteries, flying long cross country at 11000 ft. Is boring so adding this to your to do list gives you something else left to do. When my wife is with me she's shoving the oximeter at me in less than my 5 minutes. I just hang it on the co pilots yoke and just reach over and use it.

i used to get headaches at 8000 ft. Prior to the meter and the turbo. Now that's gone.

in addition if you fly at night,I don't ...use O2 at 5000 for your eyes and lower as you age.

 

 

[aviatoreb]

Brad

i fly with 2 nonan oximeter sand check them every 5 minutes when I wear o2' I generally go on O2 between 8000-9000 ft depending how I feel or tired I am. Also don't forget an extra set of batteries, flying long cross country at 11000 ft. Is boring so adding this to your to do list gives you something else left to do. When my wife is with me she's shoving the oximeter at me in less than my 5 minutes. I just hang it on the co pilots yoke and just reach over and use it.

i used to get headaches at 8000 ft. Prior to the meter and the turbo. Now that's gone.

in addition if you fly at night,I don't ...use O2 at 5000 for your eyes and lower as you age.

 

 

I seem to still be in the mid/lower 90s at 8-10k without supplemental.

I don't use O2 at night simply because I don't fly at night.  But I would if I did.

[Marauder]

Wow. An AMU for an oximeter to replace one which can be had for under $50. Admittedly, it has some extra stuff, but you still have to stick your finger into it to get a reading.

The big difference with this panel mounted unit is the reminders that it emits to test yourself. Part of the problem with hypoxia is the sense of wellness. Unless you are Dan's wife who reminds you, if you are becoming hypoxic you may need a reminder...

[DXB]

http://www.guardianavionics.com/aero455.html

 

I like that it comes coupled with a CO detector- yet another relevant topic when thinking generally about pilot incapacitation.  

Pulse oximeters are revolutionary devices that have transformed health care, but they can be fickle too, and their limitations are worth keeping in mind. The biggest one is that they behave erratically with decreased blood flow on a cold finger - this is more a problem for some folks like me who get poor blood flow at extremities at times, even without cold temps.  They typically read too low or won't pick up at all in this condition.  Secondly, they are useless for detecting CO poisoning- your blood's O2 carrying capacity could be wiped out in this circumstance, but the oximeter might still read 99%.  Lastly they tend to read higher than is real with dropping O2 saturation in dark-skinned people.

[DonMuncy]

I agree reminders could be quite valuable.

[carusoam]

You're gonna have to stop wearing fingernail polish too...

best regards,

-a-

[Marauder]

I wonder if there are other styles of these oximeters rather than the finger end version. Anyone research this? I often wonder if it can be obtained through some other method (like your earlobe with an extension cable). If so, I suspect pilots might be likely to wear it through the flight.

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[Houman]

Well I bought the CSM-50E and they work great, alarm and also extension for kids, also it can keep history of your numbers.

The battery usually last several hours and you can use it while plugged into the usp cigarette connection. Well worth it. I find the pharmacy ones a bit on the cheep side and this is one thing I don't want to go cheep on...

 

Here is the model.

http://www.amazon.com/dp/B00IWOKTC0/ref=asc_df_B00IWOKTC03897028?smid=A1PZW27L88W9HW&tag=nextagmp-20&linkCode=df0&creative=395129&creativeASIN=B00IWOKTC0&ascsubtag=-8790307373345049463

P.S. Over 14000, I wear it continusoly without ever removing it and position my finger on yoke in a way I can always see the numbers...

[LANCECASPER]

This one looks kinda cool. No batteries needed:

http://www.amazon.com/Safe-Heart-iOximeter-Smartphone-Oximeter/dp/B0039N7HAQ/ref=pd_sim_121_3?ie=UTF8&refRID=0DM1EKXVWDEY1D1B6JMV