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The Apnea-Hypopnea Index: Useful or Useless ?
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zonk Offline

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Post: #1
The Apnea-Hypopnea Index: Useful or Useless ?
The Apnea-Hypopnea Index: Useful or Useless ?

[parts of this thread were copied from our old forum]

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. 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 amount of positive pressure.

IMPERFECT BUT USEFUL

The AHI may not be perfect, but it is useful, argued Dr. Rapoport. No one has devised anything better for distinguishing people with and without obstructive sleep apnea, pointed out Dr. Rapoport, Medical Director of the Sleep Disorders Center at New York University School of Medicine in New York City.

Furthermore, efforts have been made to improve the AHI. The American Academy of Sleep Medicine has recently attempted to standardize the index, for example, and work has begun to define its normal range.

Also, AHI values correlate with symptoms of SDB. "[The correlation] is mediocre perhaps, but it is not absent," stated Dr. Rapoport, countering Dr. Sullivan's earlier assertion. Because the AHI is imperfect, Dr. Rapoport views it as a marker for the apnea-hypopnea syndrome and not as a definitive metric. He has found the AHI most useful for detecting severe apnea-hypopnea syndrome.

He defines severe cases as those with an AHI of 30 to 50 events per hour or greater. "This is definitely bad .. and I want to treat it," he stressed. Obstructive sleep apnea symptoms are also likely to be severe enough to warrant treatment in patients with an AHI of about 20 per hour; SDB can probably be ruled out at an AHI of about 10 per hour.

Dr. Rapoport cautioned against over-interpreting the "gray zone" between AHIs of 10 and 20 per hour. "I do not quite know what that means," he acknowledged.

Reference
1. Sullivan CE, Rapoport DM. The apnea hypopnea index is a useless metric of sleep disordered breathing: pro-con. Presented at: Annual Meeting of the American Thoracic Society; May 21, 2002; Atlanta, Ga.
02-26-2012 12:56 AM
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zonk Offline

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Post: #2
RE: The Apnea-Hypopnea Index: Useful or Useless ?
Ltmedic66 wrote:

Thanks zonk. This is a very good article and it kind of touched on what I think are one of the problems with modern medicine. We tend to always want to find "the" indicator" for a given medical condition. There are probably a number of reasons for this: The increased reliance on diagnostic tools, advanced imaging, reduced reliance on subjective clues, a requirement to fit everthing into a neat insurance code for reimbursement, ect.

I support a more holistic approach. In many conditions, and I think sleep apnea is one of them, symptoms can be vague and vary from person to person. There probably is not a single "magic" diagnostic indicator for OSA. Rather, a more "whole body" view is more appropriate. OSA can manifest with a variety of symptoms and physiological responses, and they need to be considered in total when evaluating OSA and its treatment.

AHI is just one of many factors that should be looked at. It should not be viewed as the end all, be all indicator of OSA.
02-26-2012 12:58 AM
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zonk Offline

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Post: #3
RE: The Apnea-Hypopnea Index: Useful or Useless?
JudgeMental wrote:
Good find Zonk
The Lt's last sentence is what I was trying to quote... Good statement, LT

zimlich wrote:
Enlightening article zonk. Thanks.

zonk wrote:
Dr. Sullivan is the inventor of CPAP

Katie wrote:
I didn't know that. Maybe that's why ResMed has a CPAP called the "Sullivan V"?
Thinking-about

Steven wrote:
Sullivan was indeed the inventor of CPAP.
And my very 1st CPAP only 12 1/2 years ago was the Sullivan V.
CPAP therapy is not that old !

archangle wrote:
Using AHI to evaluate sleep apnea is sort of like using blood pressure and pulse rate to evaluate heart health.
Checking BP and pulse rate is a really good idea. It's useful info. It isn't the end all and be all of heart health checks.
Even though BP and pulse rate don't tell you everything, a doctor who doesn't bother to check BP and pulse rate is an idiot.
The same would be true for a doctor who ignores AHI. Or for one who ignores the apnea numbers or other data recorded by a CPAP machine.

HeadGear wrote:
Absolutely! AHI is an important index for monitoring treatment. I think even Mr. Sullivan would have to agree that something may be amiss with a high AHI and investigate further.

zonk wrote:
When Dr Colin Sullivan began work at the University of Sydney's sleep clinic as a young medical researcher, his friends ribbed him for choosing such an unglamorous area of research.

In 1979, he studied some patients who were heavy snorers. He noticed that they had apnea and he guessed that other snorers could also have this condition. As his father was an inventor, he had grown up with the attitude that problems can be solved. He had the idea of supplying pressurised air via the nose (nasal continuous positive airway pressure, or nasal CPAP ) to keep his patients ' airways open during sleep.

To test the idea, he glued tubes into a patient's nostrils and connected them to a vacuum cleaner (no that's not a joke !) set up to blow air into the tubes. This worked for some patients, although others could not get to sleep while hooked up to the experimental machine.

So Dr Sullivan had developed and tested a treatment for sleep apnea and he had realised that the condition might be fairly common. He had seen an opportunity to improve many people's quality of life - and to create an industry.

His next step was to develop a device to supply the positive air pressure via a mask, rather than through uncomfortable tubes. He patented his first nasal CPAP device in 1981, but further development and design work would be needed to make it suitable for mass production and everyday use.

http://www.powerhousemuseum.com/australia_innovates/idea.php
(This post was last modified: 02-26-2012 01:26 AM by zonk.)
02-26-2012 01:13 AM
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Post: #4
RE: The Apnea-Hypopnea Index: Useful or Useless ?
I so see red when I encounter these "sleep specialists" who totally pooh-pooh and ignore CPAP data!!!!! Or those who rely on it despite the patient's self-reporting of continued exhaustion, disrupted sleep, etc.

They are IDIOTS!

One thing I learned fairly early on in over 30 years of raising dogs and interacting w/the veterinary profession: the GOOD vets were those who ran the necessary tests, took the results in consideration of the patient symptoms and followed their common sense and instincts when deciding on treatment, NOT just on the test results to the exclusion of patient symptoms.

I've found that holds true in human medicine as well - the tests, even the best of tests, are just the best they have at the time and not 100% accurate or to be totally relied on. AND the TOTAL patient HAS to be taken into considertion, NOT JUST the digestive system, or cardiac system, or reproductive system or whatever. The patient is an ENTIRE HUMAN BEING and must be evaluated as such INCLUDING their symptoms and how they feel!!!

HuhsignSleep-well
02-26-2012 03:27 PM
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