RE: Holden versus Ford (ResMed v Philips Respironics)
A short while back on a different board a user pm'd me asking for my opinion about which was the "best" APAP out there on the market. I took the time to copy, paste and edit things I'd written from a whole bunch of different posts into this rather lengthy response, which seems like it is relevant to this particular thread.
What's the best APAP out there---the Resmed S9 AutoSet or the PR System One Auto?
This question is rather like asking, Which tastes better---Coke or Pepsi? There are dedicated Coke and Pepsi fans who have a very strong preference and really dislike the other drink, but for the average consumer? The difference in taste is marginal and either one will do when the person is wanting a cold cola-based soft drink.
It's a similar situation with the APAPs. Both the Resmed S9 AutoSet and the PR Series 60 System One Auto CPAP are top notch machine and both are capable of delivering high quality therapy. But there are some real differences between the S9 AutoSet and the System One Auto and for a small minority of PAPers, these differences are quite important. But it's not like everyone prefers the S9 over the System One---just like there are people who prefer Pepsi to Coke, there are people who prefer the System One to the S9. But for the average new CPAPer? The average new CPAPer probably can't tell any real difference between the two machines and will adjust just fine regardless of which one they choose.
That said, if you've been recently diagnosed with OSA and you're trying to make a decision between which CPAP/APAP to get, it is still worth trying to make an informed, intelligent decision on what you think is going to work best for you. So here are some things to keep in mind about the two most common APAPs on the American market:
On-line prices for the PR System One APAP are quite a bit cheaper than on-line prices for the S9. That may be a consideration if this is an OOP purchase.
Humidifier and heated hose
Both machines come with integrated heated humidifiers and optional heated hoses. The System One's humidifier has two kinds of settings (a "smart" kind of setting and a "classic" kind of setting) when you are using the humidifier without a heated hose. The "smart" setting, the humidifier takes into account the ambient room temperature and humidity and adjusts the heat provided under the tank to minimize rainout. (This system works well in my very cold bedroom). The "classic" setting allows for much more humidity to be added, but at the risk of creating rainout problems.
The S9's humidifier kind of splits the difference between the two types of settings on the System One if you don't use a heated hose.
On the S9, the heated hose's default setting allows you to pick a temperature and the humidity is supposed to be set to 80% relative humidity. Some people find that's not enough humidity and others find it's too much. On the System One, in the default mode for the heated hose you've got a choice of "temp" and "humidity" settings where the humidity settings (1, 2, 3) seem to correspond to 70%, 80%, and 90% relative humidity respectively.
On both machines you can change the heated hose setting from the default mode to a completely manual mode, and this allows you to control the hose temperature and the humidity separately. (On the System One, the is accomplished by using the "Classic" settings for the heated humidifier.)
The S9's heated humidifier can be preheated and that's a plus. The older System One humidifiers cannot; but I believe the newer versions of the Series 60 machines that are using the most up-to-date firmware do allow you to pre-heat the humidifier. When I start out the night my nose always feels cold and damp until my (old Series 50) System One humidifier heats up---it only takes about 10 minutes, but it's still a long ten minutes on a cold night. Check that with the DME if the ability to pre-heat the humidifier is important to you.
Exhalation relief systems
The Resmed S9 system is easier to understand. With EPR there is a straight reduction in pressure that starts with the beginning of the exhalation and it lasts most of the way through the exhalation. The pressure is raised back up to the therapeutic setting just before (or just as) the inhalation starts. When I was using an S9, it seemed as though EPR kicked in before my inhalations started, but most people say that doesn't happen. The EPR setting equals the reduction in pressure. Hence if EPR = 3, there is a 3cm drop in pressure on every exhalation. This is sort of like a poor man's bi-level, but not really. (Or so says my airway---the switch to a real bi-level was important in conquering several of my adjustment problems.)
The PR Flex system is more complex to understand. It provides a variable amount of pressure relief with each exhalation. How much relief and how that relief is delivered depends on which type of flex (A-Flex, C-Flex+, or C-Flex), what the flex setting is, and how forceful the exhalation is. With A-Flex and C-Flex+, there is an initial drop in pressure right at the start of the exhalation, and about half way through the exhalation, the pressure is brought part way back up towards the therapeutic setting; when the inhalation starts, the pressure is further increased all the way back up to the full therapeutic setting. Some people swear by A-Flex or C-Flex and say that it makes breathing with the machine feel very natural. Others dislike it. (I'm one who turned Bi-Flex, the BiPAP version, off as soon as I got my BiPAP because it bugged me.)
Some notes on both exhalation systems: These are supposed to be patient comfort features and they are not supposed to affect the efficacy of the therapy. In practice? A small minority of patients find that they do need to increase their pressure setting to compensate if they are using EPR or Flex, particularly if they're using EPR = 3. Another thing peculiar to Flex is that many people are very sensitive to which Flex setting they use: They may find A-Flex wonderful, but C-Flex awful. They may find A-Flex = 2 very natural, but when A-Flex = 3 it feels as though the machine is rushing them to inhale. PR seems to understand this sensitivity and they make it easy to play with the Flex settings in real time with the mask on your face and that's a very useful feature.
Mask fit, mask alarm, and leak data
PR has a "Mask off alarm" that's not loud enough to actually wake most of us up. It's pretty much useless; Resmed doesn't have a "Mask off alarm"
Resmed has Mr. Green Smiley and Mr. Red Frowny to let you know if the mask fit was "good enough." But Mr. Red Frowny only shows up if you are in Large Leaks for at least 30% of the night.
The leak data on the LCD of the System One is pathetic. You have to have SleepyHead or Encore to track your leaks with a System One.
Both machines offer these things. On the PR System One, they can be controlled separately. On the Resmed S9, you have to turn them on (or off) together. From what I've seen, they can be a bit touchy----particularly for people using low pressures and nasal pillows. Me? I turn my machine on and off manually---it's just not that hard to hit a very large button.
Both machines record full efficacy data, including the wave form, events, and leak data. The S9 shows an incredible amount of detailed summary data right on the LCD; the System One does not. Both machines work well with SleepyHead. It is possible to get your hands on the "official" software from Resmed and PR if you want it.
There are some differences in how the two machines record the efficacy data however.
First: The Resmed S9 overwrites the wave flow data on the SD card every seven days and the other "detailed" daily data every 30 days. If you want all the data, you must download it at least weekly. The PR does not ever seem to overwrite the detailed data, so when you download to SleepyHead you'll see everything that's been written to the card. (But Encore will only download the last night's wave form for some silly reason.)
If you forget to put the SD card back into the S9, the machine will write the summary data to the card when you insert it, but all the detailed data will be lost. If you forget to put the SD card back into the System One, the machine will write all the data except the wave flow to the SD card when you put it back in to the machine. (Both machines write the wave flow data directly to the SD card.)
The Resmed S9 is very picky if anything is written to the SD card by the computer system---this is a problem if you use a Mac or a Windows 8.1 machine and you forget to "lock" the card before inserting it into the computer. The PR System One doesn't seem to care much about things the computer might write to the card. I routinely forget to lock my System One's SD card when inserting it to my Mac and I know the mac writes some hidden .files when I do that. The System One doesn't care.
The snore data and the flow limitation data are recorded as continuous functions on the S9; they are discrete tick marks on the System One. (SleepyHead's version of the snore data is very different than Encore's version of the snore data from a System One machine.)
Both machines flag apneas (and classify them as OAs or CAs) and hypopneas. The System One also flag RERAs (respiratory effort related arousals) using a proprietary algorithm and periodic breathing. The RERA flagging is a bit controversial since a RERA requires an EEG arousal to be scored in the lab and the System One obviously does not have any EEG data to work with.
Finally, you can change the clock in the clinical menu of the S9 and nobody can change the clock on the System One. Both machine's have some problems with clock drift over time. There are some bugs in ResScan where clock drift was apparent back when I was still using an S9.
Finally, when most people are asking "which is better---the S9 AutoSet or the System One Auto?" they really are asking about the auto algorithms the machines use to respond to events during the night.
And it is important to realize that the Auto algorithms of the S9 and System One do differ. But they are both fine machines with auto algorithms that have been thoroughly tested. And both machines can provide top-notch therapy to a patient. But, while the algorithms are not the same, it's impossible to say one is somehow better than the other. It's rather like debating whether Coke or Pepsi tastes better: It all depends on who you ask. And rather like Coke vs. Pepsi, some folks have very, very strong preferences, but for the most part, most people can't really tell enough of a difference to for it to matter.
As for the S9 vs System One APAP choice: It's the same thing---for a handful of people with very sensitive bodies, the differences between how the S9 AutoSet and the System One Auto feel in use matter a great deal, and one of the two machines will feel substantially more comfortable; but which one feels better is largely a matter of how the highly sensitive individual person's body reacts. For the average new PAPer? There's usually not enough of a difference in how the two machines feel for the new PAPer to tell any difference.
Still there are some real differences in the algorithms and for a small minority of patients, the subjective way the two machines feel will make a difference in their comfort while using the machines. So here's the run down on how the two machine's Auto algorithms work so that you can factor that into your choice of machine.
Both machines will respond to snoring, flow limitations, and clusters of OAs and Hs by increasing the pressure. Both machines will attempt to determine whether a given apnea is a clear airway apnea or an obstructive apnea. Both machines will lower the pressure back down after the algorithm is satisfied that your breathing is now stable.
Both machines use proprietary algorithms to determine the patency of the airway when the airflow has dropped to 0 L/min for at least 6 seconds or so. The S9 uses FOT, which is a series of rapid small oscillations in pressures, and the System One uses PP, which is a short "pressure pulse" of a rapid, short lived increase in pressure by about 2cm. In both cases, the machine analyzes what happens to the back pressure when the change in pressure is applied. Most people don't notice either the FOTs or the PPs, but some people are bothered by them. A few people are bothered by them enough to be woken up by them (at least occasionally), although the usual problem is when the machine decides to send some FOTs or PPs out while you are still barely awake, but in the transition to sleep your breathing is just a bit ragged. Some people are more bugged by the FOTs than the PPs since they last longer; others are more bugged by the PPs than the FOTs because they're bigger changes in pressure.
The S9 algorithm tends to respond to events by rapidly increasing pressure and then, once it is happy with the shape of the wave flow, it immediately starts to slowly decrease the pressure back down. And it will keep decreasing the pressure until the machine detects snoring, flow limitations, OAs, or Hs. If more events occur, the machine once again will rapidly increase the pressure. This gives the S9's pressure curve a characteristic "wave" appearance where the fronts of the waves are steep and the back sides of the waves are much more gently sloped.
The System One algorithm is slower to respond to events and is slower to start decreasing the pressure back down once it is happy with your breathing. The System One also uses a "hunt-and-peck" algorithm for determining the optimal pressure: About every ten minutes or so, the System One will increase the pressure by 2cm over something like a two minute period while checking for improvements in the wave flow pattern. If improvements are found, the baseline pressure is reset to the pressure that gave the optimal wave flow. If no improvements are found, the pressure is then dropped back to the baseline setting over the course of a minute or so. And the machine waits for about 5-6 more minutes before starting the new hunt-and-peck cycle. To decrease the pressure, the System One does a reverse "hunt-and-peck": It temporarily decreases the pressure slightly looking for any deterioration in the shape of the wave flow. If it sees any deterioration, no matter how minor, it bumps the pressure back up to the current setting. But if no deterioration is seen, then the baseline pressure setting is reset at the lower level. And the machine then waits for about 5-6 minutes before testing whether the pressure can be decreased again. The "hunt-and-peck" algorithm used on the Respironics machines gives the pressure curve a characteristic saw tooth appearance.
The net result is that both the ResMed and PR Auto algorithms allow the machine to gracefully respond to a need for a modest increase in pressure and hence improve patient comfort by reducing the overall pressure needed to splint the airway open. Both the S9 and the System One have some problems providing high quality therapy if the minimum pressure setting is way, way below what the person needs. (Hence running the machine wide open with a pressure range of 4--20cm usually does not improve patient comfort.)
But each has its own strengths and weaknesses in terms of therapy:
The S9 can respond very quickly to a nasty cluster of events (in an effort to "bust the cluster up" as it's often put around here). And that quick response to events is a real strength of the S9 algorithm. But it can be very slow to lower the pressure back down. And if the min pressure is set far too low, it can lower the pressure back down to a pressure level that is clearly not high enough, which can then trigger another cluster of events. The fact that the S9 increases pressure only in response to snoring, flow limitations, OAs, and Hs also means that it always waits until something happens to increase the pressure and it always tries to lower the pressure all the way back down the minimum pressure setting.
The System One is much slower to respond to clusters of events. Judging from the pressure curves I've seen it appears that the System One will raise the pressure in 1-2 cm increments once a minute in response to snoring, flow limitations, OAs, and Hs. And then it waits to see if things clear up before it increases the pressure again by a 1--2 cm increase. So that can make it less effective at "busting up" clusters of events. But the System One is less likely to lower the pressure too much after the events are over. And theoretically that "hunt-and-peck" algorithm proactively raises the pressure before the flow wave deteriorates to the point of where snoring, flow limitations, OAs, and Hs can take place. In other words, the "hunt-and-peck" algorithm is supposed to help the machine figure out the appropriate pressure level even in the absence of event clusters.
As for comfort? Again there are strengths and weaknesses of both algorithms:
The S9's rapid pressure increases disturb some folks and wakes them up. Those rapid pressure increases can also trigger leaks. But except for when the machine is actively increasing the pressure in response to clear events (including snores and flow limitations as well as OAs and Hs), the machine is running at a stable or slowly decreasing pressure. And if the min pressure is pretty much set to what you need for at least 50%-60% of the night, you'll have nice long periods where the pressure is not changing at all.
The System One's pressure increases are not dramatically fast. And that means they are less likely to wake you up. And they're less likely to trigger a leak. But that hunt-and-peck algorithm is constantly kicking in. And so every 10 minutes or so there is a pressure increase. And that's enough to bother some people. But that hunt-and-peck algorithm is also going to help keep the machine from decreasing the pressure below a therapeutic level when the min pressure setting is set too low: Once the pressure is suboptimal, the subtle differences in the wave flow combined with the hunt-and-peck algorithm will prevent the machine from further decreasing the pressure much of the time.
Overall, there is some evidence that the System One's algorithm provides less overall variation in pressure and a quicker return to the baseline pressure after a series of "events" and attempts to locate a meaningful baseline pressure through the hunt-and-peck algorithm. The S9's algorithm provides a quicker response to clusters of events, a gentler decrease in pressure going back down to baseline, and a stronger effort to use the min pressure setting as the target baseline pressure.
Finally, Robert McCoy and Ryan Diesem have written a scholarly paper that discusses the Resmed and Respironics auto algorithms, along with auto algorithms from several other manufacturers. The paper is a bit dated: The machines being looked at are the Resmed S8 and the Repironics M-Series. This generation of machine was not capable of distinguishing between CAs and OAs. But the two companies overall choices in the design of their auto algorithm have not changed and so the stuff in the paper about how and when pressure is increased and decreased pretty much applies to the current S9 AutoSet and the PR System One Auto. The biblographic information for this paper is:
A Bench Comparison of Five Auto-Adjusting Positive Airway Pressure Devices, Response to Apnea, Hypopnea and Flow Limitation, by Robert McCoy BS RRT FAARC, Ryan Diesem BA, Valley Inspired Products Inc. (December 1, 2008)
But the link I used to have to this paper no longer seems to work.