Here is an interesting article about the differences in cardiovascular benefits from APAP verses CPAP and the possible mechanisms for the differences. It is a seminal article published last month and by no means the final word, but a subject to watch for future studies which are planned. Chest is a highly regarded peer reviewed medical journal among physicians and researchers. The full-length article can be downloaded for $9.00 and I strongly suggest you read it.

Fixed and autoadjusting continuous positive airway pressure treatments are not similar in reducing cardiovascular risk factors in patients with obstructive sleep apnea.

The conclusion also states this:

""We would like to underline that our results do not imply that APAP should be disregarded as a treatment option for OSA, based on its high potential in terms of cost-effectiveness," Dr. Montano said. "On the contrary, we believe that these devices should be tested not only in terms of efficacy on sleep and respiratory indexes, but also in reducing cardiovascular risk factors."

Abbreviations:
Abbreviations: AHI = apnea-hypopnea index; APAP = autoadjusting continuous positive airway pressure; BMI = body mass index; CPAP = continuous positive airway pressure; CRP = C-reactive protein; CT90 = cutoff time 90; DBP = diastolic BP; ESS = Epworth sleepiness scale; HOMA-IR = homeostasis model assessment index; HR = heart rate; ns = not significant; ODI = oxyhemoglobin desaturation index; OSA = obstructive sleep apnea; SaO2 = arterial oxygen saturation; SBP = systolic BP

Vicki

Am I reading this correctly?? CPAP was superior to APAP in reducing systolic and diastolic blood pressure after 3 months of use?

You read my post before I finished editing it Crohnie .

Vicki

And why are we both awake at this hour?

Vicki,

I wouldn't put too much faith in this study. I have read the study and it has problems. The results actually strengthen the argument for using APAPs, especially in cases of excessive oxygenation indicated by CPAP therapy-induced central apnea from too much pressure, excessive swallowing of air and mask leaks, all of which impact compliance, but the APAP MUST be set correctly for the patient to benefit.

APAPs are new enough (10+ years old) that few doctors and/or therapists have a great deal of experience in using the machines or haven't been trained in their use and with the latest systems any study using equipment over a year old is outdated. It's unwise to take the study results as gospel without reviewing the actual data. I will be happy to send copies of this study and the other two I reference to anyone who wants them. Just PM me your email address.

This study was aimed at comparing APAPs and CPAPs in improving cardiovascular risk factors and it showed some interesting results. After three months, compliance to therapy and OSA indexes were greatly reduced and comparable in both groups, (meaning the APAPs were just as effective for controlling sleep apnea as the CPAPs). However, in the standard CPAP group significant differences in lowering blood pressure and insulin resistance were also observed but NOT in the APAP group. Why? These cardiovascular risk factors improve with improved blood oxygenation which is the only factor xPAPs can influence. In this study CPAP therapy increased oxygenation more than APAP therapy with an ODI of 1.1 ± 1.3/h (CPAP) vs. 4.8 ± 2.1/h (APAP). (ODI is oxygen de-saturation index - the number of times per hour oxygen saturation goes down a certain percentage (≥ 3 % in this study) below the baseline level which was 41.6 ± 14.4/h in this study. The lower the ODI the better.) Other studies have shown minor blood oxygenation differences with xPAP systems, but not to the extent shown in this study.

In a crossover study done in 2006 but to different ends, "Equivalence of Autoadjusted and Constant Continuous Positive Airway Pressure in Home Treatment of Sleep Apnea," Chest 2006; 129; 638-643, Respironics APAPs were set to a pressure band of 5 to 15 in the first part of the study, then to CPAP mode at the titrated pressure in the crossover, yet had an ODI of 4.1 ± 0.7/h (CPAP) vs. 4.2 ± 0.7/h (APAP) for a 0.1 ± 0.7/h ODI difference. The low pressure (5) was only one cm H2O higher than the first study's pressure (4) but made a significant difference! In another crossover study, "Evaluation of an auto-CPAP device for treatment of obstructive sleep apnoea," Thorax 1998;53;643-648, using Respironics Remstar+Auto first in APAP and then CPAP mode with the pressure band set 4 mbar (1 mbar = 1.022 cm H2O) below and 2 mbar above the titrated pressure, the APAP actually did better with an ODI of 2.5 vs. 3.1 for CPAP mode. Most other studies have results similar to these, always very close easily within the margin of error.

This study had several skewing factors that should be considered when contemplating relying on the study results:

1.The pressure range was set for 4 to 15 cm H2O, an 11 point spread, which is greater than should normally be used for actual therapy. This factor alone skews the whole study because the APAP was not set to therapy pressures. For therapy, the pressure MUST be set for only a few cm H2O below and above the titrated pressure. Proper APAP settings would eliminate the differences found in this study.

2.No crossover study, i.e., switching users, was done to validate the data.

3.The APAP and CPAP systems were from different makers and were different types. The APAP was a ResMed Autoset T flow based system and the CPAP was a Somnocomfort vibratory-based system. Both are older systems that I believe have been discontinued. I understand the APAP model was discontinued about 4 1/2 years ago I guess when the Spirit was released. This study was funded in 2003 but only submitted for publishing in 2006. Was it done when the machines were new or recently with outdated machines? The APAP also apparently used an outdated algorithm (A-10).

4.The study had only 31 subjects and lasted for only 3 months.

5.This was an exploratory study meant only to set additional study direction.

6.No allowance was made for the CO2 capacity of the mask or whether all subjects used the same mask or different masks. This problem would have been reduced by a crossover study.

7.This study's results are not confirmed by any other studies with current xPAPs.

The reason cardio doctors latch onto this study is not obvious, but here it is from the horse's mouth: they believe CPAPs prevent sleep disturbances, but APAPs respond to disturbances after the fact. This may have been true in the early days of APAPs, but is no longer a valid argument. Today's APAPs can predict and prevent disturbances in a single breath, they don't just respond to them after the fact. This by itself should be sufficient to allay the critics, but these doctors feel this delay in responding is what causes the differences shown in this study and it is harmful to the cardiopulmonary system. In reality the time difference is there but measured in the time it takes to take a single breath. The latest APAPs algorithms can sense the difference or deviation in a single breath and apply the appropriate pressure during that breath.

The real culprit here is oxygenation, the goal of all xPAPs and the only thing they can provide whether before or after the fact. When an APAP pressure band is set too broad, and the lower end is set too low it doesn't oxygenate the blood enough. This is not good for the cardiopulmonary system. That's why the bottom pressure on an APAP is so important for actual therapy. It must be set high enough to adequately oxygenate the blood to a minimum level while set low enough to prevent the side effects of too much pressure. Too little oxygenation shows up as morning headaches, high blood pressure and insulin resistance. Too much pressure causes swallowed air (bloating), initiation of central apneas which causes awakening gasping for breath or just waking up, or mask leaks. It can also show up as 'APAP runaway' This happens when the upper limit is too high. Patients who are sensitive to the pressure may be pushed into central apnea (CA) by a slightly high pressure. Since the APAP only sees an apnea, it raises the pressure to suppress it. When the CA doesn't respond to a higher pressure, which it won't, the APAP raises the pressure more. If the upper band is too high, the pressure keeps going up until it hits the top bound. This is different than a large leak because it has back pressure. A large leak does not. APAP runaway is cured by lowering the upper pressure limit. It can be temporarily stopped by simply restarting the APAP. This is not much of a problem in the lastest APAPs. CPAPs/APAPs cannot control central apnea. I believe one of the ResMed VPAPs is currently the only system that claims to control central apnea.

Runningbare

runningbare wrote:For therapy, the pressure MUST be set for only a few cm H2O below and above the titrated pressure...When an APAP pressure band is set too broad, and the lower end is set too low it doesn’t oxygenate the blood enough.

Please provide a reference for this. I'd like to look into it.

runningbare wrote:APAP runaway is cured by lowering the upper pressure limit.

If apaps only function properly using narrow limits what's the sense of using them? With this logic the best solution for "runaway" pressure would be using a straight cpap machine.

Here we go again. I addressed this in another post. I don't believe the study is flawed. This is the very first study, of course it has a low n number, that is how preliminary studies are done. That any equipment over a year old is outdated may be false. I called ResMed technical service a few months ago and their algorithm had not changed since the first AutoSet T. I haven't checked with ResMed and Respironics since then and don't have time to so someone else feel free to call technical service for me and ask if and when the algorithms have changed.

I also have the study. It is the first study ever looking at the cardiovascular effects so of course there are no other studies. They can't cover all the variables at once. This study is called "Proof of Principle" a seminal study to suggest further study which the researchers say, even in the abstract, they will be doing.

A quote from my previous post:
"I would find it more interesting if they find that only one APAP shows decreased cardiovascular benefit. Wouldn’t it be interesting to learn why the algorithm of that one brand of APAP doesn’t function as well to prevent cardiovascular effects of OSA if indeed that is the case? Finding that all APAPs do not decrease cardiovascular risk would be boring and a serious blow to APAPs. Then again, maybe their results will not be repeatable. That is the basis of scientific inquiry, results must stand up to scrutiny and they must be reproducible."

Just because a paper is the first paper ever published on a subject does not mean it should be discounted. I didn't say this is the final word, please reread my post. I, in fact, said it wasn't the final word but a subject to watch. Scientists have to keep an open mind. As a scientist, far to often I see people discounting good theories and hypothesis just because they do not fit conventional wisdom and/or it isn't what they want to hear.

I do like your theory, it makes sense, and I will be interested to hear if, when and how algorithms have changed.

Vicki

Vicki,

Let me say first that I mostly agree with what you say, but, this study leaves many unanswered questions and even though the researchers say they meant this as an exploratory study it's being used by anti-APAP doctors as the golden rule for how APAPs DO NOT reduce cardio and diabetes risk factors and therefore should not be used for therapy. This is important because it's prevented many people from getting therapy that can help them. My case in point. I am stuck with sleep doctors (military hospital) who are using this study just for this purpose. As a result, they want me to use a CPAP that has proven itself to be inadequate to the task for over three years with daily use. When I wake up gasping for breath, they want me to use relaxation techniques to get back to sleep rather than use an APAP that will help me sleep through the night in the first place. I have an APAP that is helping me sleep through the night. My blood pressure is also remaining at the same level, with some minor downward trend, as when I was on straight CPAP. This is important because of my history of hemoragic stroke caused by high blood pressure from sleep deprivation.

I don't believe the study is flawed.

If it's looked at as an exploratory study, the magnitude of the flaws are diminished. Even so, the researchers should have followed standard procedures for setting APAPs for therapy rather than titration. This is not an uncommon error is seems. This is the major flaw in their study as with many other evaluating APAPs. The funny thing is even when APAP pressures are left open, they still provide the breathing therapy just as well as fixed pressure xPAPs. When an APAP has a lower bound set near the titrated pressure, it's acting as a fixed pressure machine at that pressure. The only difference with an APAP is that the upper pressure can change with differences in user needs. From reviewing many studies, the minimum lower bound for APAPs to achieve adequate oxygenation is at least 5 cm H2O. This seems to be the magic pressure for most people. This study had the lower bound set to 4. Why? This is the machine default and the lowest pressure it can be set for. The upper bound was lowered to 15 from its default value of 20. Why was the lower bound not raised to a pressure that provided some therapy? The researchers should have had at least some knowledge of what setting the lower bound so low would do, that's why they were doing this study in the first place! Why was no crossover done to verify the results?

This is the very first study, of course it has a low n number, that is how preliminary studies are done....I also have the study. It is the first study ever looking at the cardiovascular effects so of course there are no other studies. They can't cover all the variables at once. This study is called "Proof of Principle" a seminal study to suggest further study which the researchers say, even in the abstract, they will be doing.

If this is study's results are so earth-shattering, why has another verifiying study not been done? This study was funded in 2003. Was it completed in 2003? If so, why did it take so long for it to be published? What is different about this study that orients it toward cardio pulmonary and diabetes factors? (The patient blood pressure and insulin resistance were measured.) What in the xPAP therapy would affect this factors? (Blood oxygenation.) What is used to measure the critical blood osygenation level? (ODI, oxygen desaturation index, or the number of times per hour the blood oxygenation falls a specified % below a certain level.) Why is that level 3 % in this study, but in all other studies at least 4 % and normally more? Normally blood oxygenation doesn't become a problem until the blood oxygenation falls below 90 %. Oxygenation runs from 95 to 99 percent in someone who is conscious and breathing normally. What are the ODIs involved in the study? (CPAP - 38.4 untreated, 1.1 treated for an average decrease of 37.3; APAP - 41.6 untreated, 4.8 treated for an average decrease of 36.8. The decrease differences are only 0.5 times per hour. Not much of a difference for such a significant difference in blood pressure and insulin resistance.) Why so little difference? Why was the ODI for the Somnocomfort so low? Was it because it is a vibratory rather than flow based system? All other studies show a very close ODIs of between 4 and 5 for both APAPs and CPAPs regardless of whether or not they are flow based or vibratory based systems, especially when the minimum APAP pressure is set to at least 5.

That any equipment over a year old is outdated may be false. I called ResMed technical service a few months ago and their algorithm had not changed since the first AutoSet T. I haven't checked with ResMed and Respironics since then and don't have time to so someone else feel free to call technical service for me and ask if and when the algorithms have changed.

These companies are in business and if their products don't improve they will not be able to sell more product. These companies are NOT out there to provide us with xPAPs, they are out there to make money. Period! If they don't change for the better, the company will not increase the bottom line. Both ResMed and Respironics have new algorithms for their systems because if their programs to run the machines don't change, new features, such as ResMed's new VPAP Adapt SV and Respironics new APAP A-Flex would not work. Some definitions: An algorithm is the outline of program. A program is the actual code that runs the machine. There may be no difference in the machine's goal (algorithm) but the implementation of the algorithm (the program code that makes the machine work) does change. If it doesn't change, the machine it not improving and would not be purchased. All this is really fairly moot because the machines do what they were intended to do, aid breathing to increase oxygenation. The algorithms just determine how they do that job. The big thing here is does the APAP prevent, or respond to sleep disturbances after the fact. This is the critical part of this study the anti-APAP forces use to deny use of APAPs for therapy.

A quote from my previous post:
"I would find it more interesting if they find that only one APAP shows decreased cardiovascular benefit. Wouldn’t it be interesting to learn why the algorithm of that one brand of APAP doesn’t function as well to prevent cardiovascular effects of OSA if indeed that is the case? Finding that all APAPs do not decrease cardiovascular risk would be boring and a serious blow to APAPs. Then again, maybe their results will not be repeatable. That is the basis of scientific inquiry, results must stand up to scrutiny and they must be reproducible."

Just because a paper is the first paper ever published on a subject does not mean it should be discounted. I didn't say this is the final word, please reread my post. I, in fact, said it wasn't the final word but a subject to watch. Scientists have to keep an open mind. As a scientist, far to often I see people discounting good theories and hypothesis just because they do not fit conventional wisdom and/or it isn't what they want to hear.

Yes. I agree wholeheartedly. The fact is this study is being used as the basis for denying APAPs to people who could use their features, some of whom will die as a result. A doctor should not publish a document that is unverified and that causes harm. As far as I'm concerned this a violation of the doctor's hypocratic oath.

I do like your theory, it makes sense, and I will be interested to hear if, when and how algorithms have changed.

Yea. Me too. I try to review these studies without any bias or as little as I can muster. In my job I critically review and evaluate studies and systems to find the best we can with as little bias as possible. It makes me angry when researchers who should know better interpret study results to justify their actions or agendas.

Ron

runningbare wrote:The fact is this study is being used as the basis for denying APAPs to people who could use their features, some of whom will die as a result. A doctor should not publish a document that is unverified and that causes harm. As far as I'm concerned this a violation of the doctor's hypocratic oath.

Agreed, physicians should not be making a decision based on this preliminary paper. It is the physicians that are making this call, not the researchers who published this paper. In fact, the researchers said this:

"We would like to underline that our results do not imply that APAP should be disregarded as a treatment option for OSA, based on its high potential in terms of cost-effectiveness," Dr. Montano said. "On the contrary, we believe that these devices should be tested not only in terms of efficacy on sleep and respiratory indexes, but also in reducing cardiovascular risk factors."

I agree with them. I think the reduction in cardiovascular risk factors should be assessed.

This is exactly why papers undergo a peer review before publication in reputable journals and why they are published, so they undergo scrutiny.

runningbare wrote:If this is study's results are so earth-shattering, why has another verifiying study not been done? This study was funded in 2003. Was it completed in 2003? If so, why did it take so long for it to be published?

It hasn't been verified because the study was just published (therefore the research and study became public information) just last month. Three years is very standard for granting of funding to publication. Especially if you have to organize and set up clinical trials. It also takes awhile once a paper is submitted for it to go through the acceptance and then publication process. My first paper took 3 1/2 years of research and writing and then 7 months to go through the publication process. Once you have a research course, then you can crank out papers more quickly. But it will still be quite awhile before we see the next paper or independent verification.

You have valid points and I think you should email them to the P.I (Montano, N). It would be interesting to hear her/his response and rational for the way they set their study up.

runningbare wrote:It makes me angry when researchers who should know better interpret study results to justify their actions or agendas.

Me too.

Vicki

Viki wrote:I called ResMed technical service a few months ago and their algorithm had not changed since the first AutoSet T.

This is not true. The AutoSet T does not have the same functionality as the AutoSet S8 Vantage. ResMed may have an algorithm (US patent 5245995, 1993) which all their auto cpap technology is based on. However, Resmed has continued to expand its apap technology over the years with patented revisions as late as 2004. The S8 AutoSet Vantage utilizes technology addressing central apneas not available on Autoset T:

Resmed wrote:US Patent # 6817361 (2004)

The present invention will correctly increase the CPAP pressure for most closed airway apneas, and correctly leave the CPAP pressure unchanged for most open airway apneas.

This is just one example. If you search through all the patents listed for the S8 AutoSet Vantage you will notice a timeline of constant revisions to their auto cpap algorithm:

4944310
5199424
5245995
5522382
5704345
6029665
6138675
6240921
6363933
6367474
6398739
6425395
6502572
6591834
6635021
6705315
6745768
6817361

Viki wrote:That any equipment over a year old is outdated may be false.

My best guess is the AutoSet T was marketed around 2001 since there is mention of "initial testing" in 1999 and its description as "commercially available" in a 2002 study. Why would a 2007 study use equipment so old when later ResMed models were commercially available? Runningbare's mention of the study being funded in 2003 helps explain that question. Runningbare makes a great argument.

References:

Lofaso F, Leroux K, Quera-Salva MA, Mroue G, D'Ortho MP, Isabey D, & Louis B. (2002). Snoring detection during auto-nasal continuous positive airway pressure. The European Respiratory Journal : Official Journal of the European Society for Clinical Respiratory Physiology. 19(1), 108-12.

Manuel, thank you so very much for providing me with the infomation to prove my point. You should at least read the abstracts. Runningbare's arguements make so more rational and objective sense. However, I wasn't talking about an APAP designed to correct central apneas. Of course it is going to be different. That is not what this study was about. Instead of looking up all the non-applicable patents and Sullivan's first one (how very cool) all you needed to do was call ResMed, they will actually tell you.

I am not a patent attorney and am not going to read the patents, but I imagine when you eliminate the patents which are not applicable to what we are talking about, the remaining patents are for each particular feature of the mechanism of detection (snore, etc.). It is moot anyway since none are newer than 2002.

4944310 Sullivan/Somad Filed 12/29/1988
5199424 Sullivan et al. Filed 12/12/1991
5245995 Sullivan/ResCare Filed 05/27/1992
5522382 Sullivan/ResMed Filed 01/10/1995 For delay/ramp feature
5704345 Berthon-Jones et. al./ResMed Filed 11/04/1994
6029665 Berthon-Jones/ResMed Filed 10/14/1997
6138675 Berthon-Jones/ResMed Filed 09/16/1997
6240921 Brydon et. al./ResMed Filed 04/22/1997 For AutoStart
6363933 Berthon-Jones/ResMed Filed 12/16/1999
6367474 Berthon-Jones et. al./ResMed Filed 01/19/1998
6398739 Sullivan et al. Filed 08/02/1999
6425395 Brewer et al. Filed 12/21/1999 For Mask Leaks
6502572 Berthon-Jones et. al./ResMed Filed 04/21/2000
6591834 Colla et. at. Filed 06/05/2001 For fault diagnosis
6635021 Sullivan et. al./ResMed Filed 09/19/1997
6705315 Sullivan et. al./ResMed Filed 06/06/2001
6745768 Colla et. al/ResMed Filed 04/08/2003 For fault diagnosis
6817361 Berthon-Jones et. al. Filed 10/29/2002

Vicki

manuel wrote: The S8 AutoSet Vantage utilizes technology addressing central apneas not available on Autoset T:

I have the S8 AutoSet Vantage. Is it supposed to treat central apenas? I have mostly (85%) obstructive hypopneas, obstructive apneas, but only 1 central event over two full night sleep studies.

Thanks in advance for any info.

Yes MJ. You can read about it at the ResMed website:

www.ResMed.com

Vicki

Vicki wrote:Manuel, thank you so very much for providing me with the infomation to prove my point. You should at least read the abstracts.

I provided all the patents for the S8 Vantage. The following patents are revisions/additions of the device's basic algorithm:

5704345 Algorithm
6029665 Algorithm
6138675 Algorithm
6363933 Algorithm
6367474 Algorithm
6398739 Algorithm
6502572 Algorithm
6705315 Algorithm
6817361 Algorithm

There is debate whether the Vantage actually has a central apnea feature but I believe it to be true--it's patented as so. This feature is not mentioned in the clinician's manual expect for the following excerpt:

Vantage Clinician's Manual wrote:The pressure will not rise above 10cm H2O when an apnea is detected, to prevent an inappropriate response to central apneas.

However, when reading the patent description in detail, the central apnea function is followed by:

Patent 6,817,361 wrote:
In the above implementation, apneas can only cause the CPAP pressure to rise as far as 10 cmH.sub.2 O, but subsequently, indicators of partial obstruction can increase the CPAP pressure to 20 cmH.sub.2 O, which is sufficient to treat the vast majority of subjects.

Of course, I will call Resmed as Vicki suggested.

To my understanding CPAPs, APAPs and standard BiPAPs/VPAPs do not have the ability to detect and suppress central apneas.

The ResMed VPAP Adapt SV is the only system (so ResMed says) capable of handling central apneas.

In reality, the other machines can detect central apneas but cannot distinguish them from obstructive apneas. The problem is central apneas are handled differently than obstructive apneas. Obstructive apneas are suppressed by additional pressure/air flow volume. Central apneas are handled not by an increase in pressure, but by stimulating a rythmic breath much like a mechanical ventilator. The VPAP is not intended to actually breathe for the patient like a ventilator, but just start a breath.

Runningbare