RDI vs. AHI which one is more important

There seems to be more talking about RDI lately and I'm wondering if RDI is a better indicator of OSA than AHI. I looked into CPAPopedia and it sounds as if AHI is a subset of RDI...am I correct?
I was looking at my sleep study results and my AHI (during titration study) was <2 (it was 5.5 during the 1st study) and my RDI (during titration) was an "index" of 9.8 (I don't understand what index means). My total arousals (during titration) were 67. Can somebody help me understand this.
Thanks! Amy

I did a little research so hopefully my answer is close to correct.

AHI is the total apneas and hypopneas that you have in one hour.

RDI is the total number of disturbances in your sleep due to ALL respiratory conditions: including apneas and hypopneas, snoring arousals, hypoventilation episodes, desaturation events, etc. They are often identical, but depending upon what is scored, the RDI may be larger than the AHI.

So, one is not more important than the other. The insurance companies have switched from wanting a specific RDI number to wanting AHI, so it's scored that way now.

Your sleep study may also show "total arousals". Which can include your breathing disturbances as well as other disturbances such as periodic limb movements. My AHI is only 15.8, but my total arousals per hour is around 30 due to my additional leg movements. My leg movements went away after my apnea was treated.

Ask your doctor about your total arousals. It sounds like you may be questioning your low AHI. Don't, we have many people with mild sleep apnea that benefit a great deal from CPAP because of the TOTAL arousals that sleep disordered breathing can cause (such as limb/leg movements). You'll know if the CPAP helps your sleep apnea if you feel a lot better.

Hope this helps,
Joyce

And this further confuses things for me Colin Sullivan was the "inventor" of the original CPAP, if I remember right....

http://www.respiratoryreviews.com/sep02 ... Index.html


THE APNEA-HYPOPNEA INDEX: USEFUL OR USELESS?
ATLANTA—The apnea-hypopnea index (AHI) is useless for measuring the severity of sleep-disordered breathing (SDB), says Colin E. Sullivan, MD, PhD. He presented arguments in support of that statement in a pro/con debate at the recent annual meeting of the American Thoracic Society in Atlanta.[1] Offering the opposing view was David M. Rapoport, MD, who maintains that the AHI does have its place in clinical practice.

“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.

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.

Probably the best indicator of SDB, however, is simply the response to continuous positive airway pressure (CPAP) treatment. “It really is a no-brainer,” Dr. Sullivan remarked, pointing out that CPAP administration is especially easy with the newer devices that automatically set the appropriate

Probably the best indicator of SDB, however, is simply the response to continuous positive airway pressure (CPAP) treatment. “It really is a no-brainer,” Dr. Sullivan remarked, pointing out that CPAP administration is especially easy with the newer devices that automatically set the appropriate

That's exactly what I did. I didn't have a sleep study, so I have no idea what my AHI or RDI is without treatment. No insurance.

I felt 100% sure I had plain vanilla OSA, based on drowsy driving and grogginess after naps symptoms, plus lifelong heavy snoring. I borrowed a cpap from a friend and had immediate good response to it - felt more "awake" and ready to get up that next morning than ever before in my life. Soon after, I got a good old family G.P. to write me an Rx and I bought myself one of the "newer devices" -- autopap and heated humidifier -- online.

Took awhile to get comfortable with all that "stuff" and new way of sleeping, of course. Lots of wasted dollars on various masks before finding the ones I liked best. Added accessories to make it nicer, like the Aussie heated hose. Learned from the message boards tricks like mouth taping, hanging the hose out of the way, modifying headgear. Using a narrow pressure range (raised the lower pressure considerably) that suits me better, got advice about using software to monitor and tweak my own treatment, got help with a borrowed recording pulse oximeter to see what my untreated and treated SPO2 levels were (dips without/very good with.)

I've had good treatment and great results for almost two years now. I couldn't have done it at all without the message boards.

If I ever see a sleep clinic offering "free PSG" maybe I'll bother to find out what my untreated AHI/RDI is.

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.

Speaking of complicating things My oxygen never dropped below 92% the whole test. I remember it only dropping to 89% during my first test 8 years ago. so technically, I don't even really need to worry about apneas either *shrug* I have great blood pressure too - it's usually 110/65

"pulmonologist-sleep doctor" you wouldn't happen to have BonVallet, would you?

yawn wrote:...my AHI (during titration study) was <2 (it was 5.5 during the 1st study)...

wow, your initial sleep study numbers are better than my numbers on cpap. Some nights my AHI is as good as 4.0, but typically i range up to 10. Before CPAP my AHI was 45.


ron

Those were my numbers while being titrated. They were worse on the 1st sleep study. I had lots of hypopneas and my O2 levels dropped into the 80s most of the time...that's why they wanted me on CPAP (plus I can't keep my eyes open during the day time)

Barb (Seattle) wrote:"pulmonologist-sleep doctor" you wouldn't happen to have BonVallet, would you?

Nope, its Dr Henry Su. A very high tech and friendly clinic in Kirkland just a couple miles from my home. But I sometimes wonder if all that high tech stuff and fancy facility REALLY makes that much difference.

He also found my RLS numbers to be "inconsistent" from study to study, and so left it up to me whether I wanted to give the RLS meds a "try".

At some point it seems like it would be easier and certainly a whole lot cheaper to give it ALL a "try" and figure it out on our own, just by whatever makes us feel better....if only insurance would agree with that tact.

All doctor practice medicine different, I think what many people don't realize is that the reason we suddenly have a talk room with ALL of these people comparing All of their different symtoms and numbers, is because western medicine is just now (last 3 years) starting to understand how many people really have sleep apnea and how it effects our mental, emotional and physical health.
So, Lets be careful about throwing out doctors names and comparing how they do medicine. Remember, most of our certified sleep doctors are dealing with a very different disease than they originally thought it was 25 years ago when they first started testing for it and treating it. The population of patients that they now know has it, has changed dramatically in just the last 3 years. Equipment has just started to advance to allow medicine to collect really get good information about breathing and sleep and that means that the medical world is just starting to collect numbers, compare it to symtpoms and really try to understand it themselves......

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.

Hopefully that helps,
Joyce.

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I was "throwing out my doctor's name" because I REAALLY like him! I really agree with your post. I think your last sentence really applies to me...even though I might have adequate oxygen, there are other things going on in my case too...

Got it now Barb, thanks for clarifying, I see a lot of people here frustrated with their doctors, so I definitely didn't mean to single you out. I'm glad you've found a doctor that you like and that is getting you the treatment you need.

For others: if you you're not happy with your doctor, definitely get a second oppinion.

Joyce

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.

Excellent point, Joyce.

I am so glad I found this thread before I started another one just like it. I was wondering the same question about the AHI vs RDI. During my sleep study my AHI was 6 and were mostly respiratory effort related hypopneas, my RDI was 18. My SP02 was 95% except for a total of 2 min. during the entire night at 88%. So what I am understanding from this thread is that even though my SPO2 was relatively good my sleep is still being interrupted based on my RDI enough to cause my fatigue? I guess I feel like I won't really benefit from CPAP because of how low my indexes are. I guess my other question is that if my sleep is being interrupted due to arousals more than from lack of oxygen, am I at less risk for other health problems?

I have been on APAP for about 5 weeks now and cannot tell a big difference in how I feel. Last week my AHI was 4 with cpap, 3.8 of those were hypopneas.