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Altitude
#1
I started CPAP last July and my AHI has been slowly improving since. I also full time RV, meaning that I am constantly traveling around the US. When I first started I was in Illinois at about 600 feet above sea level. I then traveled west crossing the US toward Oregon. On the trip across my AHI numbers skyrocketed while at altitudes of 3-4000 feet. I spent three months on the Oregon coast at sea level then most of the winter near Yuma, AZ under 1000 feet and my numbers slowly came down from an average of 10 per hour in Aug. to just over 5 by the end of January, dropping approx. 1 per month. In February I spent a couple of weeks recrossing the US eastward going through higher elevations in AZ, NM and Texas (in the 3-4000 ft range) where my numbers again went up. I am now in the Rio Grande Valley, well under 1000 feet and my numbers are returning to the just over 5 range.

I am assuming that altitude causes this increase. Most of my Apneas are CAs. I am on straight CPAP at 16 lbs pressure. Is there something I can do to improve AHIs while at altitude? I would love to spend more time over 3000 feet.
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#2
(02-27-2016, 12:49 PM)dzwiss Wrote: I am on straight CPAP at 16 lbs pressure.

First of all I doubt the 16 lbs.
16 lbs is equal to 1124 cmH20.

My Resmed S9 ASV can go up to 30 cmH2O.
Even with a Binfort 4000 CPAP you won´t get that big amount of pressure.

And I believe that your CA´s come because the cpap pressure is still the same as at sealevel.

When you are at sealevel, the pressure inside your body is sealevel also wich is 1013 HPA or 1013 cmH2O in normal athmosphere.

The pressure of your CPAP is 16 HPA or 16 cmH2O
So the pressureratio is 16:1013 at sealevel.

At 3000 ft the atmospheric pressure is 100 HPA less than sealevel = 913 HPA.
The CPAP pressure is still the same.
So the pressure ratio is 16:913 now. Thats 10% less.

The relative CPAPpressure is higher than normal and brings you CA´s.

You must adjust the CPAP pressure for a sleep at 3000 ft to:
16/1013*913= 14,4 HPA

So with 14,4 HPA the ca´s will get back to normal.

Hermann
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#3
These machines are supposed to be self compensating up to about 7500 feet above mean sea level.
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#4
(02-27-2016, 05:45 PM)justMongo Wrote: These machines are supposed to be self compensating up to about 7500 feet above mean sea level.

Quote:The amount of pressure generated by the CPAP fan decreases with altitude due to lower gas density. For this reason, an increase in fan speed is needed to compensate for the modest drop in pressure at altitude. Older machines have adjustable "altitude" settings in them. Newer machines have internal correction for altitude so that no adjustments are necessary.

They compensate to keep the pressure constant.
But one doesn´t need the same pressure at altitude.
If they would compensate to a lower pressure, dzwiss,
wouldn´t have any differences in his/her AHI.

Hermann
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#5
(02-27-2016, 12:49 PM)dzwiss Wrote: I am assuming that altitude causes this increase. Most of my Apneas are CAs. I am on straight CPAP at 16 lbs pressure. Is there something I can do to improve AHIs while at altitude? I would love to spend more time over 3000 feet.

There doesn't seem to be much that you can do at higher elevations other than switch over to ASV. This is impractical for most people.

I suspect you have your CPAP set at 16 cmH2O a common measurement of pressure in ventilation, not 16 lbs pressure. First pounds is not a pressure unit. S condly, if you meant 16 pounds per square inch (psi) you would not have any lungs left as they would have exploded!

Walt
Walter W. Olson, Ph.D., P.E.
Professor Emeritus
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#6
(02-27-2016, 12:49 PM)dzwiss Wrote: I am assuming that altitude causes this increase. Most of my Apneas are CAs. I am on straight CPAP at 16 lbs pressure. Is there something I can do to improve AHIs while at altitude? I would love to spend more time over 3000 feet.

Yes, this is a common effect of higher elevation for those of us who are susceptible to CA events.

Usually, higher pressure tends to raise CAs, and lower pressures tend to raise Obstructive events.

Personally, I am usually more concerned about having obstructive events, because I think obstructive events often stress our body worse than central events.

Also, obstructive sleep apnea is usually strongly positional, with flat on our back usually being the worst position.

If we can totally prevent rolling onto our back while asleep, we can usually get by with significantly less pressure.
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#7
Thank you all for your replies. I feel silly referring to my pressure lbs and will do a little more to educate myself as to the proper terms. I gather that the things I should try to solve this problem are to lower my pressure when traveling at altitude and/or sleep on my side. I will try those on my next trip. I would like to get my centrals down and will be seeing my doctor in a few months and bring this up.
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#8
(02-28-2016, 02:52 PM)dzwiss Wrote: Thank you all for your replies. I feel silly referring to my pressure lbs and will do a little more to educate myself as to the proper terms. I gather that the things I should try to solve this problem are to lower my pressure when traveling at altitude and/or sleep on my side. I will try those on my next trip. I would like to get my centrals down and will be seeing my doctor in a few months and bring this up.
Have you tried changing your machine ipressures? you could experiment with different high and lows and keep a record of exactly what you need at altitudes.

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#9
Quote:Have you tried changing your machine ipressures? you could experiment with different high and lows and keep a record of exactly what you need at altitudes.

I think that is exactly what I will try on my next cross country venture.
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