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LOW AHI vs actual REAL quality sleep
08-25-2015, 05:43 PM
AHI is based on sound science when you can trust the data such as during a sleep study. The problem lies in an xPAP machine trying to guess at an event based upon a human programmed algorithm. That's what makes a bit "fuzzy". As I said, it's a good place to start if you are not feeling rested.
08-25-2015, 06:51 PM
(08-25-2015, 05:43 PM)sonicboom Wrote: AHI is based on sound science when you can trust the data such as during a sleep study. The problem lies in an xPAP machine trying to guess at an event based upon a human programmed algorithm. That's what makes a bit "fuzzy". As I said, it's a good place to start if you are not feeling rested.
Algorithms by definition are "precise", not "fuzzy". It's the real world that fuzzy, thus algorithms often get slightly out of sync with it.
We are really just disagreeing about the meaning of words, of course.
The above is my opinion. It is just possible that I may, occasionally, be mistaken.
I am neither a Doctor, nor any other kind of medical professional.
Everything put together sooner or later falls apart.
Your brain is not the boss.
Granted, the xpap method of detecting apnea uses fuzzy logic designed by a human making a guess about the real world. It does a reasonably good job but isn't perfect. I'd say it's good enough for most cases.
Anatomically restricted breathing is only one cause of apnea and apnea is only one cause of sleep disturbance. One thing you can be sure of is that sleep disturbance is unhealthy in the long run. Stopping breathing for 10 seconds intervals for more than 5 times or even 10 or 20 times per hour isn't really all that harmful but being disturbed 5, 10 or 20 times per hour is where the most harm comes from. You need to get into deep sleep mode if possible or else you won't get properly rested and you can't do that if something is periodically disturbing you.
In some cases the xpap machine substitutes its own sleep disturbance so that the treatment isn't a cure but merely an exchange of disturbance types. It takes a very long time for some users to get over the invasion of this equipment.
If your xpap therapy isn't working, in spite of low AHI's, and you have been at it for more than three months, I'd suggest seeing your doctor for further diagnosis.
08-25-2015, 07:22 PM
SD2 wrote: If your xpap therapy isn't working, in spite of low AHI's, and you have been at it for more than three months, I'd suggest seeing your doctor for further diagnosis.
that is where I am heading 4 months in and I feel terrible...
08-25-2015, 09:07 PM
I think that some of the misunderstanding here is the "feeling" that events can not be sensed and measured indirectly with good accuracy. The fact of the matter is that we do this all of the time. Range finding with radar or sonar is an indirect measurement. We can not use a yardstick to measure the distance from the airport to an airplane. We do it with radar. Is it accurate? We had better hope so.
The PAP machines are perfectly capable of determining when you stop breathing and for how long. This determination is very straight forward. Determining if your airway is open with the PAP machine has been shown to be quite reliable. Does that meet the exact definition of a central apnea? No but it is a pretty good bet.
The AHI is an exact number as is the RDI. Do these numbers explain all sleep problems? They do not.
There is a problem that us humans fall prey to and that is trying to read too much into the data. Then when the data does not support our hypothesis, we blame the data. Must be unreliable (fuzzy?) data.
08-25-2015, 09:33 PM
(08-25-2015, 09:07 PM)PaytonA Wrote: I think that some of the misunderstanding here is the "feeling" that events can not be sensed and measured indirectly with good accuracy. The fact of the matter is that we do this all of the time. Range finding with radar or sonar is an indirect measurement. We can not use a yardstick to measure the distance from the airport to an airplane. We do it with radar. Is it accurate? We had better hope so.
08-26-2015, 01:04 AM
Dedicated to QALity sleep.
You'll note I am listed as an Advisory Member. I am honored to be listed as such. See the fine print - Advisory Members as a group provide advice and suggestions to Apnea Board administrators and staff concerning Apnea Board operation and administrative policies. Membership in the Advisory Member group should not be understood as in any way implying medical expertise or qualification for advising Sleep Apnea patients concerning their treatment.
08-28-2015, 02:48 PM
In follow up to my post (#21 above) and all of the great comments that followed I thought I'd do a quick internet search (by no means intended to be exhaustive) on what research has been done on the question of the accuracy of APAP AHI scoring versus sleep study (PSG). I found two studies that seem to be on point.
Accuracy of Auto-Titrating CPAP to Estimate the Residual Apnea-Hypopnea Index in Patients
with Obstructive Sleep Apnea on Treatment with Auto-Titrating CPAP.
Himanshu Desai M.D.1, Anil Patel M.D.2, Pinal Patel M.B.B.S.1, Brydon J.B. Grant M.D.1 and M. Jeffery Mador M.D.1, 3.
"Bland and Altman plots demonstrate that the difference between auto-CPAP AHI and PSG AHI was not uniform with auto-CPAP overestimating the AHI at lower values of AHI and underestimating the AHI at higher values of AHI." (My quotes added)
The second study: (I have excerpted a few paragraphs. You should read the whole thing when you have time.)
Volume 2013 (2013), Article ID 314589, 6 pages
Accuracy of Positive Airway Pressure Device—Measured Apneas and Hypopneas: Role in Treatment Followup
Carl Stepnowsky,1,2 Tania Zamora,1 Robert Barker,3 Lin Liu,4 and Kathleen Sarmiento2,3
1Health Services Research & Development Unit, Veterans Affairs San Diego Healthcare System, San Diego, CA 92161, USA
2Department of Medicine, University of California, San Diego, CA 92037, USA
3Pulmonary Service, Veterans Affairs San Diego Healthcare System, San Diego, CA 92161, USA
4Department of Family and Preventive Medicine, University of California, San Diego, CA 92037, USA
Received 30 April 2013; Revised 16 July 2013; Accepted 19 July 2013
Academic Editor: Giora Pillar
Copyright © 2013 Carl Stepnowsky et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Improved data transmission technologies have facilitated data collected from positive airway pressure (PAP) devices in the home environment. Although clinicians’ treatment decisions increasingly rely on autoscoring of respiratory events by the PAP device, few studies have specifically examined the accuracy of autoscored respiratory events in the home environment in ongoing PAP use. “PAP efficacy” studies were conducted in which participants wore PAP simultaneously with an Embletta sleep system (Embla, Inc., Broomfield, CO), which was directly connected to the ResMed AutoSet S8 (ResMed, Inc., San Diego, CA) via a specialized cable. Mean PAP-scored Apnea-Hypopnea Index (AHI) was 14.2 ± 11.8 (median: 11.7; range: 3.9–46.3) and mean manual-scored AHI was 9.4 ± 10.2 (median: 7.7; range: 1.2–39.3). Ratios between the mean indices were calculated. PAP-scored HI was 2.0 times higher than the manual-scored HI. PAP-scored AHI was 1.5 times higher than the manual-scored AHI, and PAP-scored AI was 1.04 of manual-scored AI. In this sample, PAP-scored HI was on average double the manual-scored HI. Given the importance of PAP efficacy data in tracking treatment progress, it is important to recognize the possible bias of PAP algorithms in overreporting hypopneas. The most likely cause of this discrepancy is the use of desaturations in manual hypopnea scoring.
Given the improved PAP data transmission technologies and resultant increased use of these data, we sought to investigate the accuracy of the PAP-measured AHI. We had the opportunity to conduct “PAP efficacy” studies in which participants wore PAP devices simultaneously with Type III cardiopulmonary recording equipment. Therefore, the goal of the present study was to specifically examine the accuracy of the identification of apneas and hypopneas by the PAP device.
2.2. Equipment Used
The Embletta (Embla, Inc., Broomfield, CO) was directly connected to the ResMed AutoSet S8 (ResMed, Inc., San Diego, CA) via a specialized cable that allowed for the direct recording of S8 data. Signals recorded include oximetry, chest effort, and body position. Airflow from the PAP device was used for scoring. RemLogic software was used for manual respiratory scoring. Apneas and hypopneas were manually scored according to the 2007 American Academy of Sleep Medicine guidelines, which included defining a hypopnea as being associated with a ≥4% oxygen desaturation . AutoSet respiratory events were autoscored by the device, and summary statistics were obtained within RemLogic. Manual scoring was blind to the AutoSet-scored respiratory events.
In this study of home-based PAP efficacy, as measured by the S8 APAP device, the PAP-scored HI was on average more than double the manual-scored HI. Given the importance of PAP efficacy data in tracking treatment progress, it is important to recognize that this particular APAP device may overscore hypopneas. The most likely causes of this discrepancy are (a) the use of a proprietary algorithm and (b) the use of desaturations in manual hypopnea scoring. Because the number of apneas was underscored relative to manual scoring, the overall AHI does not appear to be different from manual scoring. This study and the evolving literature in this area suggest that it is important to understand how a specific PAP device identifies both apneas and hypopneas.
In summary, PAP devices have automated, proprietary algorithms for respiratory event detection. When event detection scoring is combined with PAP use duration in the denominator, a proxy AHI value is derived. Given the increased reliance on the PAP-scored events by both providers and patients, it is important to better understand the nuances of specific algorithms and how the PAP-scored AHI, HI, and AI values compare to those same values from manual scoring. Doing so is an important step toward making more informed treatment decisions.
08-28-2015, 03:37 PM
Thanks for the research sonicboom. Very interesting.
The differences in hypopnea scoring are understandable since the PAP machine can not measure desats which is part of the definition that I was not aware of or had forgotten. Interesting enough the comparative study was done with an S8 machine and when the S9 came out it reported significantly less in the way of hypopneas. I am sure that Resmed did not add oxygen sat sensors to the PAP machines. I have also seen in the literature a range of respiration reduction in defining a hypopnea. Just FYI, oxygen saturation sensors are a secondary measurement of the amount of oxygen in the blood. Does that make it inaccurate?
When it comes to apnea determination the measurement in the PAP machine is quite straightforward. The instrumentation may not be of the same caliber as what is used in the clinical machines as there will be some variations but is it inaccurate? The manual method of scoring is based on human observation of data and human judgement. The PAP method is based on data and rules. My opinion is that, within the limitations of measurement accuracy, the PAP machine is more consistent over time and therefore is good for identifying significant changes.
One other thing to consider is that, at least the second study, uses a PAP machine that is 2 generations back.
(08-28-2015, 03:37 PM)PaytonA Wrote: One other thing to consider is that, at least the second study, uses a PAP machine that is 2 generations back.
For this reason, the study should be considered obsolete. The S9 came out at least 7 years ago and we know that the algorithm is quite different. (same thing with the Respironics machines). No different from other medical technologies. Xrays in a digitized form were kindof a novelty item for a brief period - then an improvement and films completely disappeared. I honestly have more confidence in what my machine is telling me over a month period than a two nighter at the sleep study lab.
What I'd really like to know is how the OP is doing NOW that he has a new mask! Improvements? Same issues? what?
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