Long Term Review: ResMed S9

My first impressions of the ResMed S9 were nothing short of impressive. I felt better in the morning, and the numbers from the charts are nothing short of amazing. My AHI dropped from an average of 1.28 to about 0.45, with occasional dips down to 0. That's right, 0 apnea/hypopnea events. This never happened with the system one. I was surprised by the huge difference, and so I had a conversation with my doctor about it. Her response:

I checked w the sleep clinic doctors. 
While u think it may be quieter or lighter, it should not make any difference in clinical response in terms of treatment w the exception of FP. Both resmed and respironics are equal in terms of efficacy.

So I collected more data. After a month,  you don't even need the detailed numbers to see that the ResMed S9 performs better. Just look at the above chart. The red-circled portion is the ResMed S9 transition, and it's very obvious that it's just doing way better than the Respironics System One was doing.

Now, it's very possible that the numbers recorded on the ResMed S9 are "doctor'd" somehow, and that the ResMed records hypopnea events differently or on a different basis, hence the numbers are skewed. But the fact that I was sleeping better and sleeping longer couldn't be ignored. (I had also switched partially to the Nasal Pillow mask over the full face mask --- let me know if you want a separate review of that) I did a bit of searching to find out why the ResMed could be better for me. It turns out, that the ResMed runs a very different algorithm from the Respironics on this forum post:

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.

It's quite clear from looking at my graphs what's been happening. Basically, my apnea pattern comes in clusters. My family has an incredibly unpredictable snoring pattern, which is one reason why it's hard for others to get used to our snoring. Because of this clustering effect, the S9's algorithm stamps out the apnea/hypopnea events right away with a sudden ramp in pressure, and then the back off is very comfortable. The System One's slower response allows for more apnea/hypopnea events, which leads to worse sleep for me.

I pointed my doctor to this web-page and her response:

Thanks for this. It is v helpful as it explains why the S9 gives people the burst of aerophagia. I think the S9 are really better for floppy airways. I do think PR is better for the patient with bad allergies as the S9's quick response can - the rush of air can trigger nasal congestion.

 I think I am going to take the recommendation of the lady then that they should try both machines lying down. That's a good idea.

So what's the takeaway? Well, if you have a snoring pattern like mine, or what my doctor calls "floppy airways", then you want the ResMed S9. Otherwise, you want  the Respironics System One with its built in hysteresis. The way to tell is to try both machines if you can get a chance to do so. Otherwise, basically every time you switch machines, you should try the other brand once just to see whether it works for you. I used to think the machines were all alike, and now I realize that's not so. Medicine is extremely personalized. My doctor focused on and prescribed the Respironics because her patients usually also came with bad allergies. My allergies are largely controlled, and so her experience did not apply to me. Caveat Patient!

I've also tested the S9 DC Power Converter Plug for one night of camping (works great), and acquired the lighter power supply. In any case, that the machine is quieter just by itself is a huge win for both me and my wife. Highly Recommended.