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Lower max pressure affecting pressure increases
#1
Last nightI lowered my max pressure from 16 to 14. My max pressure has never risen above 10 or 11.

The question is: Does the degree of change in pressure depend on the available max limit.

My pressure would not raise above 10 or 11 with the 90 % being in the 9 range. Last night my pressure MAX was 8.88 with a 90% pressure of 8.16.
AHI of 1.1, zero OAs, and split between CAs and HAs.

I am not sure if I am explaining this right but does the pressure change algorithm look the available change allowed.

I am thinking that my pressure change was not as severe as before which is allowed me to sleep better.
CPAP is a journey like “The Wizard of Oz”. It’s a long slow journey. You will face many problems and pick up many friends along the way. Just because you reach the poppies, it doesn’t mean you are in Kansas. 
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#2
I don't think changing the maximum setting will cause the machine to operate in a lower pressure band generally. It will go as high as it needs to and you can sometimes see the pressure graph bumping along the maximum. This indicates that it wants to go higher.

On the other hand, there has been some discussion that Resmed machines respond aggressively and can overshoot or "run away" when raising pressure in response to events.

As always with apnea, one night does not constitute a trend. It would be interesting to look at a week's worth of SleepyHead graphs before and after the change to see what's happening over a longer period, and in a bit more detail.
DeepBreathing
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#3
If that were the case, there would be no reason to lower the max pressure. Unless the purpose would be solely to stop runaway pressure increases.
CPAP is a journey like “The Wizard of Oz”. It’s a long slow journey. You will face many problems and pick up many friends along the way. Just because you reach the poppies, it doesn’t mean you are in Kansas. 
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#4
(07-16-2016, 07:21 PM)Rcgop Wrote: If that were the case, there would be no reason to lower the max pressure. Unless the purpose would be solely to stop runaway pressure increases.

That's one reason. An Autoset machine should not go higher than the clinical demand but we know anecdotally that sometimes they do. Reasons to set a maximum are: 1) prevent pressure runaway; 2) prevent the pressure going higher than you can tolerate (even if there might be a clinical demand for a higher pressure).
DeepBreathing
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www.ApneaBoard.com


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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#5
That makes sense to me.

Thanks
CPAP is a journey like “The Wizard of Oz”. It’s a long slow journey. You will face many problems and pick up many friends along the way. Just because you reach the poppies, it doesn’t mean you are in Kansas. 
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#6
It's hard to find information on exactly what the pressure response algorithm does in detail. This table from an article on auto CPAP algorithms has some information about it. Based on what it says, the pressure algorithm does not take the maximum pressure setting into account in calculating its response. (aside from not increasing the pressure above the maximum, of course) With ResMed machines, pressure increases are smaller at higher pressures, though. (The same apnea might cause a 2 cm pressure increase at 7 cm but only a 0.5 cm increase at 18 cm.)

I agree with Deep Breathing's suggestion to look at more than one day's data. I have had the same impression as you from looking at my daily graph after changing the max pressure limit.

(07-16-2016, 07:21 PM)Rcgop Wrote: If that were the case, there would be no reason to lower the max pressure. Unless the purpose would be solely to stop runaway pressure increases.

As far as I know, the only reasons to set a maximum pressure value are to keep the pressure from going higher because a) it's not comfortable, b) it has historically caused mask leaks or mouth leaks or c) it's in our nature to want to put on upper limit on something that's happening while we're asleep.

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#7
Some people have a high pressure threshold, above which they suddenly get severe central sleep apnea. Lowering the Max Pressure below this threshold avoids the central problem, at the cost of possibly getting higher number of obstructive events.

At least a few patients have seen increased intraoccular presssure from CPAP therapy and have limited their Max Pressure for that reason.

In addition, high CPAP treatment pressures have been known to cause dizziness or hearing problems, especially if patients had taken in recent months one of the very many ototoxic (poisonous to the inner ear) prescription or non-prescription meds.
Medicines which are Ototoxic are thoroughly covered in Neil Bauman's third edition of his book Ototoxic Drugs Exposed. An old article on the subject:
http://www.hearnet.com/features/articles...xposed.pdf


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#8
(07-16-2016, 07:21 PM)Rcgop Wrote: If that were the case, there would be no reason to lower the max pressure. Unless the purpose would be solely to stop runaway pressure increases.

I have the same machine, and have had the similar results. The 90% tracks upward when I raise the upper limit. The lower also seems too have the same effect on the average pressure.

14 day averages
Average Pressure 13.61 13.52 13.37 12.88 12.65 11.26
Min Pressure 13.00 12.80 12.00 11.00 10.00 5.00
Max Pressure 15.40 15.60 15.80 15.60 16.00 15.00
90% Pressure 14.32 14.54 14.88 14.68 15.02 13.92

I have found I have less events when if I keep the 90% bellow 14.60 and the average above 13.50

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#9
(07-17-2016, 12:09 PM)green wings Wrote: I agree with Deep Breathing's suggestion to look at more than one day's data. I have had the same impression as you from looking at my daily graph after changing the max pressure limit.

I do think it's valuable to look at each day's data, but not to draw conclusions based on a small sample. After awhile you begin to see the patterns and understand how they affect you.


Ed Seedhouse
VA7SDH

Part cow since February 2018.

Trust your mind less and your brain more.


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#10
Okay, some more good reasons to use the max pressure setting. I did not know about any of those except for the central apnea problem.

(07-17-2016, 01:00 PM)vsheline Wrote: Some people have a high pressure threshold, above which they suddenly get severe central sleep apnea. Lowering the Max Pressure below this threshold avoids the central problem, at the cost of possibly getting higher number of obstructive events.

At least a few patients have seen increased intraoccular presssure from CPAP therapy and have limited their Max Pressure for that reason.

In addition, high CPAP treatment pressures have been known to cause dizziness or hearing problems, especially if patients had taken in recent months one of the very many ototoxic (poisonous to the inner ear) prescription or non-prescription meds.
Medicines which are Ototoxic are thoroughly covered in Neil Bauman's third edition of his book Ototoxic Drugs Exposed. An old article on the subject:
http://www.hearnet.com/features/articles...xposed.pdf

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