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What has been your experience when sleeping at altitude? I went from sea level to an elevation of 6850 feet and my AHI and central jumped 700%. Did not make any changes to my Airsense10 autoset device. Reported pressure was below my upper setting and leak was not a factor as one night I even had zero leak. Room temp same. Humidifier normal water consumption.
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I go from around sea level to 5800 feet 3 or 4 times a year. Sometimes my AHI is lower and sometimes higher. Same settings-same equipment.

Best Regards,

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The only issue with measuring efficacy by AHI is that it only tells you how many events you had, and does not tell you how severe these events were. You have to dig deeper and parse the info to determine that, and each and every event will be more serious at altitude where 02 is less available.

At altitude, or if you have any condition that lowers the efficiency of using available oxygen, that matters. IOW, if you are either at altitude or you have such an issue, or both, your desats will be worse, regardless whether the AHI stays the same or not. Altitude will not automatically count more events, because there will be essentially the same amount of events. But each event will be more significant because there is less 02 delivered. A 12-second CA at sea level is one thing, but a 12-second CA at altitude may be more equivalent to a 42-second CA in how desatted you become.

And of course, that is the whole goal of xPAP, is to get the normal amount of AVAILABLE 02 to you. At altitude, there is less 02 available, and less that can be delivered. Folks without breathing issues have a surplus at sea level, but may have very little surplus at altitude. They are still OK, and over the Mendoza line. Those with breathing issues have less of a surplus available at sea level, and may have less 02 than they need at altitude, and a simple xPAP by itself might not be enough for them, because a simple xPAP is there to keep the airway open, and not to otherwise deliver higher concentrations of 02.

If you are concerned about 02 levels, use an oximeter and determine if you need supplemental 02. If your readings court 92% or below at sea level, they will probably be a lot lower, alarmingly lower, at altitude, while your AHI may stay about the same. Bottom line, if there is any suspicion of a breathing issue or an 02 issue, at altitude do not be lulled into a sense of false security simply because your AHI stays about the same. If you are just above the borderline of needing supp 02 at sea level, you will need supp 02 at altitude to stay above that borderline.
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The Airsense automatically compensates for altitude changes up to approximately 8,500 feet, so theoretically from a pressure standpoint it should make no difference whether you are using your machine at sea level or up to 8,500 feet above sea level.

I am located at about 6,000 feet at home and I make no adjustments in my settings when I travel to lower altitudes and I see no statistically significant changes in my reported AHI.

I think something may be amiss if you have such wild swings in your AHI with the altitude change..........if everything is working correctly and all other things are the same, the altitude change should not make any difference in terms of therapeutic airway pressure.
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You were around 2000 metres, which is a relatively low mountain, a ski resort or some such - at those levels, altitude compensation by the machine is pretty straightforward. You may have had a day or so to adjust to the lowered air pressure, but after that you should have been fine - there is no reason for you to have had a massive increase in apnoea events based on such a low altitude, except that you might have needed a pressure adjustment to compensate against the lowered air pressure. Your machine might have interpreted a skipped breath or a held breath, common at altitude for those not used to it, for a CA.
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(05-19-2015, 06:27 AM)DocWils Wrote: ........Your machine might have interpreted a skipped breath or a held breath, common at altitude for those not used to it, for a CA.

Solely out of my curiosity, what makes a skipped or held breath common at altitude?

Best Regards,

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I live in Switzerland - every doctor gets basic training in this problem here, so the science of it has been gone into a lot - mountains, mountains everywhere, so here goes......

For those not used to it, there is an involuntary reflex to either breath faster or to hold or skip breaths, usually the latter when at rest and the former when active. Survival instinct when encountering a lowered oxygen pressure, in order to ensure sufficient oxygen saturation. Our ancestors never moved from one extreme of air pressure to another at such a pace as we do today, so they had time to adapt as they went up or down, but we don't give our bodies that chance, so our brains interpret it as a threat of less oxygen, even though there is not sufficiently less oxygen to make a real difference at those altitudes - in fact there is the same available oxygen as at sea level, but at lowered pressures. If you had hiked it the whole way over a day or two, as our ancestors would have, they would have adapted to the lowered blood volumes caused by the change in the pressure gradient. Because our lungs exchange oxygen based on the pressure gradient, the involuntary skip or hold breathing is the body's attempt to raise the pressure gradient to what it is accustomed to.

Okay a bit of medical science in lay man's terms: After we inhale, oxygen in the alveoli (tiny air sacs in the lungs) passes to the blood to be transported to the tissues. This gas exchange between the alveoli and blood takes place due to a pressure difference called a pressure gradient. The pressure oxygen exerts in the alveoli is greater than the pressure of oxygen in the blood surrounding the lungs. This drives oxygen from the lungs into the blood. Any reduction in the pressure of oxygen entering the lungs will reduce the pressure difference or gradient. The result is less oxygen being driven from the lungs into the blood. At high altitudes that is exactly what happens. The weight of air and the barometric pressure it exerts has an effect on the partial pressure of oxygen. At sea level, oxygen has a partial pressure of 159mmHg. At the top of Everest, it drops to 48mmHg, which is nearly equal to the blood surrounding the lungs. With very little pressure difference at this level oxygen exchange is severely impaired and that is why you need supplemental oxygen - it is not the amount of oxygen that you need, that is already there, more or less, in terms of the make-up of it in normal air, it is the pressure of it. You can breath as fast and as heavily as you want, you cannot get more oxygen into your blood stream because of the pressure gradient problem, not the lack of oxygen availability. If it was simply a matter of oxygen availability, then a more rapid breath would be sufficient, even in the thin air of Everest. Still plenty of air up there, and tons of oxygen, but the pressure isn't, and that is the problem.

So, when you go rapidly from the accustomed pressure to a less accustomed one, your body does what it needs to adapt, and interprets the lack of pressure as a problem, finding ways to raise the pressure for exchange. It ignores the fact that holding the breath means there is a less rapid exchange of oxygen in favour of the raising of the pressure so that what oxygen there is can be exchanged as normal (it doesn't really work, btw, but the body doesn't know that - it interprets the problem the same way it would if you were submerged). After a day to two (or three or four) the body adapts by changing the blood volumes and the pressures needed for the exchange.

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....... I get a nosebleed when I watch the "Sound of Music."
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(05-19-2015, 06:27 AM)DocWils Wrote: ........Your machine might have interpreted a skipped breath or a held breath, common at altitude for those not used to it, for a CA.
I definitely do this when I go up to the cabin (around 5,800ft). Heck I do it even at home due to CHF and occasional pain. At the cabin after a day's exposure I acclimate and never have to change my CPAP settings. I have no real difference in AHI when on the machine at night there. Most likely not high enough though if I went much higher I would have issues during the day.
Current Settings PS 4.0 over 10.6-18.0 (cmH2O) BiLevel Auto
TNET Sleep Resource Pages
CPAP Machine Database
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(05-18-2015, 07:48 PM)ROSIE Wrote: my AHI and central jumped 700%

CA (clear airway) can occur during sleep/wake transition.
If you slept restlessly in the new location, that could account for some of the increase in CA's logged by your machine.

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