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Why do clinicians set min pressure so low on APAP?
I just upgraded my 10 year old Puritan Bennett GoodKnight 420G travel CPAP to a new HDM Z1 Auto. It was beginning to wear out and I travel three weeks a month for business and really needed a replacement; one that was small and had battery backup was ideal as I often travel to India where losing power every day is the norm. Even though my prescription is for 7.0 pressure, I wanted to try auto with this new unit after over a decade to see if that would help even more.

My new HDM Z1 Auto arrived and I was surprised to find that the MIN pressure setting for auto was 4.0 even though the prescription provided to <Link to Supplier #1 removed by Moderator> was 7.0. I gave it a try anyways. After two miserable nights of feeling like I was a scuba diver trying to draw air out from a regulator on an airtank hitting empty, I had enough. I also saw that the unit really never moved more than .2 up from 4.0 while doing its APAP thing. My AH count, according to their software was also in the mid 40s.

I downloaded the Clinicians Manuals from this site for this new unit (THANK YOU! THANK YOU! THANK YOU!) and set the MIN to my prescription rate of 7.0. Last night was SO MUCH better! I felt refreshed and my AH Count had dropped to 24, almost half of what it was the previous two nights. Not ideal, but way better than before. What I did notice as well as the APAP never deviated from 7.0, even during the one hour where I had the most incidents (yes, it is in APAP vs. CPAP mode).

Two questions: 1) Why do clinicians set the MIN so flipping below your prescription when configuring APAP vs. CPAP? 2) How long does it take for APAPs to "learn" or "react" to what they need to do?

Based on my results last night alone, I feel comfortable taking the HDM Z1 Auto with me on travel, but am curious about my questions above.


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Without seeing the graph or at least seeing a report, I'll be guessing when I say that your AHI index is dominated by CA's. They do not cause the machine to adjust pressure but are scored nonetheless. Sometimes they occur when you are awake and can be ignored. Other times they are a sign that you may need a different type of machine to handle your problem.

Welcome aboard and stick around for other opinions.

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(11-13-2015, 01:02 PM)MarkMaxPayne Wrote: Two questions: 1) Why do clinicians set the MIN so flipping below your prescription when configuring APAP vs. CPAP?

My best guess is "lazy" or "incompetent".
They're supposed to set it as ordered. If your doc said 7-13, you should have received the machine set for 7-13.

(11-13-2015, 01:02 PM)MarkMaxPayne Wrote: 2) How long does it take for APAPs to "learn" or "react" to what they need to do?

Sorry, no idea. It's specific to the machine/manufacturer and I've never seen a Z1

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(11-13-2015, 01:02 PM)MarkMaxPayne Wrote: Two questions:
1) Why do clinicians set the MIN so flipping below your prescription when configuring APAP vs. CPAP?

CPAP is a fixed pressure setting and is typically set to a signgle number between 8 - 14 for most people. The exact pressure is determined by a sleep study where they titrate the pressure until they find the best one to reduce your apneas.

APAP is an auto-adjusting machine that can start out at lower settings and will titrate to higher levels as your apnea events decrease until it reaches a pressure when your apneas start getting worse, then it will lower the pressure back down. By using this type of machine and software like SleepyHead or Encore you can see which pressures your machine is on for most of the night.

One advantage of using a low starting pressure such as 4 is that it sometimes help people to fall asleep while the pressure is low and then after you go to sleep the pressure starts cranking up to keep away your apneas. Some machines even have a Ramp feature that lets you dial in the amount of time you want for the machine to stay on low pressure.

However, your doctor should have written a prescription for a range of pressures if that's what he wanted the clinician to set up. They aren't supposed to deviate from what the doctor writes. So if your doctor set it up to be a static 10, then the clinician should have set yours up so it was always at 10 (which means it would be operating exactly like a CPAP instead of an APAP. If you want a range of pressures, then ask your doctor to prescribe a range.

Quote:2) How long does it take for APAPs to "learn" or "react" to what they need to do?

It depends on your machine, but most of them take measurements constantly and are able to adjust the pressure every two minutes (or so) if it detects you are having certain types of apnea events. If your range is from 4-20 then typically it will only be at the low setting for a short time then it will ramp up until it gets to an "ideal" setting. If your pressure isn't changing at all then it's either the machine is not working or you aren't having any apnea events that the machine is set to correct for.

Another good thing about having a range of settings is that your condition changes over time. Even over night. Alcohol and medications can make your apneas worse and an APAP machine will boost the pressure on those nights to compensate. Also as you age and lose weight or gain weight it will affect your apneas. An APAP can adjust automatically without having to go through another sleep study to determine your proper pressure.
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Hi MarkMaxPayne,
WELCOME! to the forum.!
Much success to you as you continue your CPAP therapy.
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(11-13-2015, 04:47 PM)trish6hundred Wrote: Hi MarkMaxPayne,
WELCOME! to the forum.!
Much success to you as you continue your CPAP therapy.

Just a quick note about "settings" and auto machines.

Most machines reset every day, so it doesn't matter that it took an hour to get up to where it needed to go last night, tonight it will start off at it's minimum setting again.

Ideally, you'll want to set the minimum pressure to be a little lower than what it takes to prevent your events, so it starts off close to where it needs to be. A smaller range = less sleep disturbance from pressure changes, as well as preventing the events it was responding to in the first place.

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DME's may tend to do this for many reasons:
  • Many patients complain about too much pressure.
  • They tend to believe that "auto" means "the machine figures out everything."
  • They haven't figured out that low pressure often leads to a feeling of suffocation.
  • They haven't figured out that the machine doesn't start adjusting up until after you fall asleep.
  • They don't realize that the machine takes a while to find the right pressure once you turn it on.
  • They haven't figured out that the machine forgets what it's "learned" every time you turn the machine off.
Get the free SleepyHead software here.
Useful links.
Click here for information on the main alternative to CPAP.
If it's midnight and a DME tells you it's dark outside, go and check it yourself.
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Fixed CPAP deliver one fixed pressure all night long (except Ramp time), the pressure has to be high enough to deal with all types events in all sleeping positions and stages. You might don't need this pressure all night long but because its fixed, the machine will delivered it even if you don't need it all night long. APAP automatically adjusts pressure in response to events between lower and higher allowable pressures. There is no therapeutic benefit in setting the lower pressure too low as would feel like not getting enough air. For me, 9 or 10 is ideal for lower pressure, feel comfortable enough and the pressure is already at a level where most of the events are been taken care-off and the machine only need to go a bit higher to deal with some stubborn events or/and deeper sleep or supine position
It goes without saying, the higher is the pressure, the higher is the side effects and vice versa

As for " How long does it take for APAPs to "learn" or "react" to what they need to do?"
I think CPAP machine is more like driving a new car for the first time, there is an adjustment period where you get the feel of the car and figure out how the car respond in certain driving condition
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This is where Sleepyhead is vital. Yes, I am new to this, but am not new to the mechanics of it. Get your start pressure close to, but a little lower than the pressure your events respond to. You will get used to the higher pressure while going to sleep. The main reason for doing this is to reduce pressure fluctuations to a minimum. Pressure fluctuations can disrupt sleep.
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Why do DME's set min pressure so low? They are ignorant of sleep apnea, most don't have a clue. If the Rx doesn't prescribe a range, but just prescribes an auto machine, you are going to get one set to wide open. Most on-line suppliers do not set up the machine, unless it is a straight CPAP. You are here, you have access to the clinicians manuals, take charge of your therapy. Our profit driven healthcare system means very few "professionals" really are interested in you getting the best therapy. Close enough for a hand grenade is all they care about.
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