AHI hourly index or average over the whole night
Use the SleepyHead Glossary to understand the actual definition to these terms. http://sourceforge.net/apps/mediawiki/s ... r_Glossary A
pneas...Obstructive or Central (Respironics calls them Clear Airway)H
On SleepyHead this is the colored bar section below the pie chart. BTW you can turn off the Pie chart if you wish. Preferences and Appearance tab.
The generally accepted number where therapy is considered to the "acceptable" number in regards to effectiveness of therapy. The medical community likes to have numbers as a standard to go by...so we have AHI and they came up with 5.0.
AHI less than 5.0 is considered "acceptable" in the US. Other parts of the world sometimes go by 10.0.
Obviously lower is often perceived as "better" and perceived as worth going to extraordinary measures to try to obtain less than 1.0 or even 0.0. Let's face it...we all like that perfect test score.
It's just part of human nature.
We often feel like we aren't doing a good job if we don't get "perfect". Some people are very lucky and get perfect or near perfect frequently. Some people just can't get it done no matter how hard they try and they think that there must be SOMETHING they can do to get "perfect".
This is where people tend to start wanting to play with their pressure(s)...dial a wingin.
Human nature again...you see someone on the forum bragging about AHI 0.0 and you look at your 2.2 and wonder what the heck are you doing wrong. Well...likely nothing.
When you start evaluating AHI to decide if you want to go dial a wingin (only if you are comfortable with it and understand what you are doing) make sure what you are trying to fix is fixable with pressure changes.
Centrals or Clear Airway events (index)...we can't do anything about them with just simple pressure tweaks and we shouldn't try unless the numbers are excessive (and increasing the pressure is the wrong way to go anyway). Centrals/Clear Airway events are a whole different animal.
If your AHI is 4.9 and 3.0 of that is Central...that only leaves 1.9 for Obstructive Apneas or Hyponeas.
Obstructive Apneas and Hyponeas are the only things in the AHI that will respond to pressure tweaks.
So make sure what you want to "fix" is "fixable" with pressure tweaks.
Time to explain how the machine reports what it senses. The machine doesn't know if you are awake or asleep. It has no way to know. All it measures is air flow. Often when we spend some time awake on the machine (laying there counting sheep in an effort to get to sleep with the alien plastered on our face) the machine can flag some awake breathing irregularities (awake breathing is often much more irregular than asleep breathing) as some sort of apnea event. Commonly centrals get the flag. Hold your breath for 10 seconds...that's pretty much a "central" but you were awake. The airway is open but no air flow through the airway. We all do it fairly often but we don't realize it. If you do it while the machine is on...well the machine just records what it senses. It doesn't know that you did it on purpose.
Also sometimes people actually have centrals during sleep stage transition..especially during sleep onset. We just do it and it is normal. Now some people do it a lot and can't transition into sleep because of them they repeatedly brought back to an awake state. Then it becomes a problem and that is dealt with by using a different machine. Regular xpap therapy can't fix those.
Open airway cessation of breathing...central/clear airway event...we can't fix with a regular cpap/apap machine even if there are too many of them. In a sleep lab any awake breathing centrals would be discounted because they aren't occurring during a sleep state.
Of course we don't always know if we were awake or not. The machine can't tell us and we don't have EEG brain wave data available at home. So we have to make an educated guess.
Centrals..even if real and occurring during sleep...aren't normally a problem. It's normal to have a few. Even people without any sleep apnea diagnosis can and will have them happen from time to time.
How many is too many? Hard to say but if you are seeing 5 per hour...every hour...every night that you can't explain away by being awake maybe...see your doctor. It may not be anything but whenever in doubt about something you see on your report....go see your doctor.
So...when evaluating your AHI....make sure that what you are wanting to fix is fixable.
Oh..while talking about "centrals" and the "higher pressures can cause centrals" thing.
Well, yes they can but not nearly as frequently as you might think. If it were there wouldn't be all these people using CPAP with a pressure of 18 cm and over 20 and not having any centrals.
There is a small % of people who can have centrals (actually a form of breathing instability) triggered by cpap pressure in general and it doesn't have to be a "high" pressure..it can happen at much lower pressures also like 6 cm. Sometimes there is a pressure where above so and so pressure the centrals will emerge and below it they don't. It isn't nearly as common as people think. Should it happen there are things that can be tried to fix it and there is a special machine for those that can't reduce the centrals to an acceptable level by trying the easy stuff first.
So there's a lot of unnecessary panic about "centrals"....don't get sucked in.
AHI in general will vary from night to night. We simply don't sleep the same every night.
Having an AHI of 1.2 one night and 2.2 the next night is not a significant increase...if you are losing sleep over a slight increase then you are worrying yourself needlessly.
What AHI are you going to find "acceptable" in your eyes? That's up to you and what you may discover when things do their normal nightly variances. Some people swear they feel great only when AHI is below 1.0. Other may not be able to tell any real difference with changes from 0.5 to maybe 4.0...heck the other night I had AHI of 8.33(90% OAs) and felt no different at all the next day. My normal average is between 1 and 2 AHI.
There is no "magic" AHI number that guarantees feeling the miracle. I wish it were that simple but it isn't. There is just so much more to all this sleep stuff than a single little number.
What we do when we don't feel the miracle and we look good on paper...start looking for other factors that affect sleep and believe me...there's a long list to look at.