the truth about AHI

if your spo2 is too low but you survive then there is a bigger chance of damage than a high AHI can cause.
For sure a high AHI is bad, but a low spo2 for too long is far worse.

LSAT wrote:Quit going to doctors at the free clinics for your information.

xxyzx wrote:What does AHI measure anyway?

AHI measures apneas and hypopneas that are arbitrarily declared after ten seconds and ignoring all shorter ones no matter how frequent
and AHI also ignores how long they are.
Thus this metric ignores the significance of frequent sleep disturbances as well as damage due to low oxygen.

this is bad statistics and a mostly meaningless metric that is handy for bureaucrats to have an objective number to say you get a cpap.
A better statistic would include all apnea/hypops along with their duration and also their effect on spo2 as well as disturbances and weight all the data.

AHI that is high is bad for sure.
But a low AHI does not mean you wont have serious sleep problems. Only that your apnea/hypops arent as bad as with a higher number.

RDI includes all the respiratory sleep problems no matter how high or low your AHI is.
a low RDI is meaningful , while a low AHI is not very meaningful.

If your spo2 is too low for too long then you die. AHI does not relate to spo2 issues at all.
if your spo2 is too low but you survive then there is a bigger chance of damage than a high AHI can cause.
For sure a high AHI is bad, but a low spo2 for too long is far worse.

The AASM guidelines include having a desat of 4% in addition to restricted breathing for ten seconds.
The xpaps dont know about the desats (in most cases) and declare hypops based only on time duration.
This distorts an already questionable metric based on bad statistics.

References
AASM Standards
Getty and Downey - Symptomatic and Undiagnosed
Medicrap rules by region


Indices for sleep-disordered breathing
The indices commonly used to assess sleep disordered breathing (SDB) are the apnea-hypopnea index (AHI) and the respiratory disturbance index (RDI).

The AHI is defined as the average number of episodes of apnea and hypopnea per hour.

The RDI is defined as the average number of respiratory disturbances (obstructive apneas, hypopneas, and respiratory event–related arousals [RERAs]) per hour. If the AHI or RDI is calculated based on less than 2 hours of continuous recorded sleep, the total number of recorded events to calculate the AHI or RDI during sleep testing is at least the number of events that would have been required in a 2-hour period.

No universal consensus exists on whether the AHI or the RDI should be the standard index used to determine treatment by specialists and insurance carriers, with Medicare being the most confusing as it varies by region as to whether AHI and RDI can be used.

In the view of Getty and Downey, the RDI is preferable to the AHI because it includes flow-limitation events that end with arousals.

The RDI is better suited to meet the new American Academy of Sleep Medicine (AASM) diagnostic criteria for OSA ).

RDI = (RERAs + Hypopneas + apneas) X 60 / TST (in minutes)




“There is not much association between the AHI and anything else—sleepiness, muscle dysfunction,” or other markers for SDB, claimed Dr. Sullivan, who heads the Sleep Disorders Unit at the University of Sydney in Australia. The management of SDB should hinge on the history, examination, and clinical judgment, he asserted.

LIMITATIONS OF THE AHI

The lack of a standard definition for hypopnea is another limitation of the AHI. Furthermore, measuring hypopnea is difficult because of the inaccuracy of the devices currently available to monitor airflow during sleep.

For example, thermistors do not actually detect airflow but the passage of hot air, Dr. Sullivan explained. Even pressure transducers, which do measure airflow, have only limited ability to detect changes in breathing, he noted.

The AHI can mislead physicians about the severity of SDB, Dr. Sullivan added. At certain points in the menstrual cycle, for example, women with SDB may respond to apnea with a large rise in blood pressure (BP) rather than in the AHI. Catastrophic BP elevations with no change in the AHI were even observed during sleep apnea in a woman with preeclampsia.

In infants and children, apnea usually manifests as partial upper airway obstruction; breathing is loaded even though the AHI is very low. In these groups, the AHI is “unequivocally the wrong metric” of SDB, Dr. Sullivan stated.

What alternatives are there to the AHI? “Hypertension is a good start,” said Dr. Sullivan. It has long been known that BP rises in obstructive sleep apnea, he related. [other doctors say RDI]

Researchers are also evaluating the usefulness of measuring fibrinogen concentrations, which are often elevated in the morning in patients with SDB. Others are looking at sleep apnea–induced changes in the levels of circulating and cellular mediators and in cellular adhesion molecules.


viewtopic/t3983/posting.php?mode=quote&f=1&p=31703

snork1 wrote:Just to complicate it even further....
According to my pulmonologist sleep doc, Hypopneas only count when they result in a drop in oxygen levels. According to my sleep study (specifically, an oximeter) my blood oxygen doesn't drop during my hypopneas, so the doc told me to ignore the hypopneas on my Encore Pro read out and just look at the Apnea events. My personal OPINION is that I am leary of this doc's advice and still try to optimize my setup to at least minimize hypopneas, figuring they could still be DISTURBING my sleep, even if they aren't dropping my oxygen level.

another thread said
O2 saturation (or lack of) will effect your physical health more, so people with low O2 saturations are more likely to have high blood pressure and heart, blood sugar and vascular problems/symptoms. However, hypopneas absolutely can DISTURB your sleep and cause you to have sleep disordered breathing without causing desaturations below 92%. In my experience you can be exhausted without desaturating because your body is not allowed to experience adequate sleep cycles if you have enough breathing disturbances, limb movement, etc, throughout the night.

there is more out there if you care to google for the truth

xxyzx wrote:

TedVPAP wrote:
I read your post.
I can't easily determine what you think versus the perspective that you are merely posted.

The perspective that there is no perfect metric is not new. No metric is perfect. It doesn't need to be perfect, but simply serves as a sign to dig deeper.
Which metric is better can only be answered in context. You provided no context so I can't respond.
For example, a friend of mine was tested and had a lower AHI but had a similar RDI. Whose OSA is worse ???? is not relevant. Both patients need treatment.

A high AHI indicates some problem
A low AHI does not mean there is no problem

A high RDI indicates some problem
a low RDI does indicate that there is no SDB problem although there may be other sleep problems

and as i noted low spo2 can kill you or cause damage short term
but a high AHI is only a problem long term

xxyzx wrote:

TedVPAP wrote:

xxyzx wrote:

TedVPAP wrote:
I read your post.
I can't easily determine what you think versus the perspective that you are merely posted.

The perspective that there is no perfect metric is not new. No metric is perfect. It doesn't need to be perfect, but simply serves as a sign to dig deeper.
Which metric is better can only be answered in context. You provided no context so I can't respond.
For example, a friend of mine was tested and had a lower AHI but had a similar RDI. Whose OSA is worse ???? is not relevant. Both patients need treatment.

A high AHI indicates some problem
A low AHI does not mean there is no problem

A high RDI indicates some problem
a low RDI does indicate that there is no SDB problem although there may be other sleep problems

and as i noted low spo2 can kill you or cause damage short term
but a high AHI is only a problem long term

Thanks for boiling it down.
I agree with some of your points.
The sleep reports I have seen report AHI and RHI so clearly they are not entirely synonymous.
Even if AHI does not cause a spo2 problem, don't you think that sleep deprivation determined via AHI is still a serious problem worth treating?
What exactly is the difference between AHI and RDI and can a data machine distinguish?

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ahi has nothing to do with sleep deprivation or even disturbance
it totally ignores that

that is the problem
you really need a PSG to get RDIs
although an IHT can do it too
but xpaps dont have the data channels to do more than AHI
which is why AHI is not a useful metric for anything except OA

and that is why RDI is the meaningful metric as it does include RERAs and disturbances not just flow limitations

xxyzx wrote:

Oltremare wrote:Why this boring debate between AHI and RDI?
It's a matter of goat's wool!

When we have a sleep study, the doctor does not connect our body to an AHI counter or even to an RDI counter!
Our body is analyzed at 360 ° until all apnea, hypopnea, flow limitations, awakenings, SPO2 lowering, REM sleep etc. are found. etc. etc. etc. etc. Then, the test results are evaluated and a final diagnosis is made.
Sometimes the diagnosis is OSAS, sometimes it is pneumonia, sometimes it is more serious.
No doctor has ever diagnosed OSAS with AHI test alone!
No doctor ever did a diagnosis of OSAS with RDI tests only!
Thanks for boring me ... so I sleep better
You now can, you can insult me, it is right but, I hope you find irony and, i don't badness in my comment.
Hello

=========
not everybody has a sleep study
nobody has them constantly to know how their treatment is working

some people worship AHI
yet they get low AHI and still feel bad

the point is that RDI and spo2 are meaningful and we can measure those without a lab study

actually doctors have diagnosed OA without even AHI
AHI over 5 will result in a diagnosis but not necessarily treatment

xxyzx wrote:the problem is that most xpaps focus on AHI and not on all the SDB issues because they cant measure the other things some do try to show RERAs

Arlene1963 wrote:My original sleep study used 30% as their definition for hypopnea and Resmed uses 50% in their definition, so for that reason it is of interest to me. Please feel free to correct me if I am wrong here...?