Resmed S9 Autoset question

[projman65]

I woke up at 4:45 AM this morning and couldn't fall back asleep. 10-15 minutes later, I noticed the air pressure being pretty high on my face. I looked over to the screen on the machine, and it showed the pressure at 15.4 (my settings are 10-16).

I am a little puzzled why the pressure was so high, even 10-15 minutes after being awake and breezing normally without having any apneas. Shouldn't it have been 10? the lower end? I was under the impression that the S9 provides pressure as needed, breath by breath. Am I missing something here?

I then decide to use the bathroom...I turn the machine off, unplug myself, use the bathroom, plug myself back, turn the machine on...now the pressure start as normal at 10.

Any ideas?

[CHanlon]

It doesn't drop instantly back down to the lowest setting, sort of maintains what it thinks you need. If you pull up last night in ResScan, and look at the detailed info, pressure graph, you'll see how it moves up and down throughout the night, and tails off gradually after each rise.


Since you turned off in between, you should even be able to see that exact point in the graph, you'll see the "session break" in the data.

[PaulaO2]

Your breathing changed when you woke up. The autoset was trying to figure out why. It cannot tell if you are awake or asleep, only that the air pressure is blocked or not.

[projman65]

It doesn't drop instantly back down to the lowest setting, sort of maintains what it thinks you need. If you pull up last night in ResScan, and look at the detailed info, pressure graph, you'll see how it moves up and down throughout the night, and tails off gradually after each rise.


Since you turned off in between, you should even be able to see that exact point in the graph, you'll see the "session break" in the data.

Your explanation makes sense...so I guess it doesn't really adjust the pressure breath to breath.

[greatunclebill]

It doesn't drop instantly back down to the lowest setting, sort of maintains what it thinks you need. If you pull up last night in ResScan, and look at the detailed info, pressure graph, you'll see how it moves up and down throughout the night, and tails off gradually after each rise.


Since you turned off in between, you should even be able to see that exact point in the graph, you'll see the "session break" in the data.

Your explanation makes sense...so I guess it doesn't really adjust the pressure breath to breath.

BINGO!!!! this is why setting a machine, any auto cpap, at 4 - 20 and letting it self adjust is just plain wrong. now you see why people say to go a couple points above and below the cpap number and see where it takes you.

[zonk]

so I guess it doesn't really adjust the pressure breath to breath.

AutoSet devices adjust pressure on a breath-by-breath basis to suit patient needs as they change throughout the night.
Source: ResMed

[JumpStart]

[...so I guess it doesn't really adjust the pressure breath to breath.

From ResMed site:

AutoSet devices evaluate flow limitation on a breath-by-breath basis and adjust pressure according to a five-breath average. (emphasis added)

[CHanlon]

[...so I guess it doesn't really adjust the pressure breath to breath.

From ResMed site:

AutoSet devices evaluate flow limitation on a breath-by-breath basis and adjust pressure according to a five-breath average. (emphasis added)

I *knew* I'd seen that somewhere when I was researching them, but of course I couldn't find it when this question came up. That's the detail that explains the entire operation.

[JumpStart]

I *knew* I'd seen that somewhere when I was researching them, but of course I couldn't find it when this question came up. That's the detail that explains the entire operation.

From the duration of this thread to the time of my posting, I guess you noted that this info was not exactly on the tip of my tongue, either! :grin:

[zonk]

Sleep Review: How does your product respond once a sleep-disordered breathing event is detected?

ResMed:
The AutoSet algorithm is truly a predictive approach allowing proactive treatment of sleep apnea rather than simply reacting with a pressure change after an event has occurred; this is achieved by detailed analysis of the inspiratory flow versus time curve. Flow limitation analysis in the AutoSet algorithm is a complex blend of clinical sleep science and engineering; it provides very small adjustments in pressure, sometimes as little as 0.2 cm H2O at a time to ensure that the patient is not aroused from sleep (as measured by EEG) with such pressure changes. This approach allows AutoSet to preemptively treat many obstructive sleep apnea events before they even occur. When an event does occur that is not possible to prevent by the flow limitation approach, AutoSet will respond reactively as well. ResMed's AutoSet algorithm assesses the severity of the event using a blend of the inputs such as duration of the event severity and frequency of the event over time. The AutoSet algorithm then determines the optimal pressure change solution to treat the event and prevent future events and applies it comfortably with minimal disturbance to the patient's sleep.
AutoSet responds to events based on a five-breath moving average of the inspiratory flow-time curve in order to prevent the device from responding to sporadic breathing events, such as sighs or coughs. Inspiratory flow limitation, or partial airway closure, usually precedes snoring and obstructive hypopnea and apnea events; it is also most often associated with obstructive hypopneas as they occur. AutoSet adjusts in increments as small as 0.2 cm H2O to ensure that pressure increases only as much as is necessary.
For flow limitation, AutoSet calculates the shape of the inspiratory flow-time curve and the value for every breath (using a metric known as the flattening index); however, it responds based on the average value of the most recent five breaths, as described above. Detection of flow limitation enables the device to increase the pressure before obstruction occurs, making treatment preemptive, and thus reducing the number of respiratory events and arousals. The apnea response is determined by the severity of the event and current therapy pressure. Apnea pressure changes are delivered after the event such that the pressure change will not arouse the patient. Snore response is measured using the severity of the vibrations of the snore. A more severe snore will give a larger pressure response, but this proportional response is delivered over the next series of breaths such that the pressure change does not disturb the sleeping patient.
If no further flow limitation, snore, or apneas are detected, therapy is reduced over time toward the minimum pressure prescribed by the physician with a 20-minute time constant. This approach allows the pressure from ResMed's AutoSet algorithm to return to lower pressures for increased patient comfort in the absence of any respiratory events.
http://www.apneaboard.com/forums/Thread-...y-Pressure