S9 broken?

[Roemere]

Is there any place that sells just that half of the unit (not the humidifier) as a replacement? Even a used or remanufactured unit?

[justMongo]

Check Supplier #2 on the list. See Supplier List at top of page.

[PaytonA]

Since the blower is an impeller type, it does indeed speed up when one inhales. Has to speed up to keep constant pressure with the higher outflow. I can hear it speed and slow on my S9.

I am not sure it would matter whether it is an impeller or not. Also, we are talking about a small volume of air in an otherwise partly-closed (vented) system. If it were speeding up and slowing down to maintain precise total pressure (a function of static pressure combined with velocity pressure), a change in fan speed would probably be imperceptible in that small volume at these relatively weak pressures, because the change in static (and therefore in the total) pressure as you inhale and exhale is very minimal. But it probably is not maintaining precise total pressure anyway, because there is no therapeutic reason for it to do that.

Would you please educate me. I would like to know what velocity pressure is and how it is that we have 2 kinds of pressure in our PAP air system. I also do not know of any static pressure in the system.

The pump must have an impeller in order to maintain even pressure. A reciprocating pump can not do that.

The pressure is based on cm of H20 (how far a column of water will rise when static pressure combined with velocity pressure is applied to a pressure tap in the airflow), so these are tiny differential pressures compared to atmospheric pressure or an increase of a couple of PSI in a tire.

The CPAP bases pressure settings on velocity pressure, which is set to be constant, even though the total pressure in the system might vary slightly through the respiration cycle due to slight changes in static pressure when you breathe in and out. Compare the airflow of a normal exhale to the airflow of a xPAP putting out 10-15 cm, and the difference is pretty great.

The static pressure varies slightly as you breathe in and out, so the total pressure does vary slightly, but not enough that the velocity pressure must be modulated by the xPAP to keep the total pressure constant. There is no real therapeutic advantage to having the tiny change in static pressure variance compensated for by modulating the velocity pressure.

Also, the pressure of CPAP is therapeutic only during inhalation; there is no need to have that pressure maintained all that precisely during exhalation, and for the few patients where significant EPAP control is necessary, a CPAP is not prescribed anyway.

OSA is a problem with airway collapse on inhale. The airway does not generally collapse on exhale. So whether the total pressure in the system goes up during exhale is not relevant to the therapy, and compensating for that change in total pressure during exhalation is not needed.

EPAP pressure *IS* is what controls obstructive apnea otherwise the airway might start to close during exhale and be harder to maintain open for the inhale.

IOW, the total pressure does not need to be maintained that precisely, only the velocity pressure to assist inhalation. The therapeutic difference between a pressure of 10 and a pressure of 10.1 is probably not even discernable medically, which is probably why the granularity is not any greater than that.

That applies to CPAP fixed-brick pressure. If you have an auto machine, or an ASV, VPAP, or a Bi-PAP, or if you are using pressure relief for inhale, certainly velocity pressure and therefore total pressure will vary, and you might be able to notice that. But a properly functioning S9 AutoSet should be absolutely silent regardless what velocity pressure it is putting out or how much it may be varying.

Best Regards,

PaytonA

[vsheline]

S9 Autoset. ... Still under warranty so they will replace machine, but they no longer sell the S9 so they gave me a System One to try but I can't get that machine to humidify adequately (started another thread on this issue).

I really like the S9 and am hoping I can find a fix.

Roemere,

Please call ResMed Customer Service immediately and report the DME provider for unethical business practice.

The ResMed standard operating procedure has been to cover warranty returns for 26 or 27 months (actually a little more than the "two years" people commonly describe it as being) after date of manufacture. ResMed would completely replace the unit for free with a new S9 AutoSet (if available) or a new AirSense 10 AutoSet unit.

That new A10 AutoSet should go to you as current owner of the warranty return machine. The replacement machine would be shipped under warranty to any DME provider who calls in, gets an Return Material Authorization number (RMA number) and returns the bad unit to ResMed. (Machine owners are required to return the unit using a DME provider, but any helpful DME provider can be used - it does not have to be the DME provider which originally sold the machine).

It would be unethical and illegal for a DME provider to sell the brand new warranty replacement unit to someone else and give you a used or different machine.

A greedy DME provider can get in a lot of legal trouble for trying to substitute a lesser machine, in trouble from ResMed and in trouble from his/her state licensing agency.

Please call up ResMed customer service immediately. The first questions ResMed Customer Service will ask are what was the REF number and Serial Number of the malfunctioning blower unit, or what is the RMA number. If you don't have this information the DME who sent in the unit is legally required to give you this information. If he/she refuses, please call ResMed Customer Service immediately and tell them the situation and the name and address of the DME provider.

Take care,
--- Vaughn

[TyroneShoes]

Would you please educate me. I would like to know what velocity pressure is and how it is that we have 2 kinds of pressure in our PAP air system. I also do not know of any static pressure in the system.

I have a lot of trouble just educating myself (which may be evident). The pressure from a xPAP is velocity pressure. Total pressure is velocity pressure plus static pressure. Static pressure is somewhat like atmospheric pressure. A blown up balloon has static pressure inside it, for instance. Wikipedia can probably explain this better than I ever could, but neither velocity pressure nor static pressure exist in a vacuum (no pun) in an xPAP-aided breathing system; respiration is always a function of total pressure.

And the reason I got so deep as to make the distinction is because of the system we have, which is partially closed. It is a closed system if you ignore the CO2 venting (and of course the fact that we have an airway to the outside), so for all intents and purposes you can then consider a simplified version of human breathing with xPAP a closed system, at least for this explanation.

In normal breathing, the diaphragm changes the volume of the cavity where the lungs exist, essentially changing the volume of the lungs themselves. When you breath in, the static pressure inside your lungs decreases differentially as opposed to the atmospheric pressure outside your lungs, and the greater static pressure outside is what pushes the air into your lungs. Actually, I said that wrong; the change in differential pressure is what causes you to breathe in. When you exhale, the diaphragm attempts to reduce the size of the volume of the cavity, and the static pressure inside your lungs is then greater than the atmospheric pressure, and the internal, higher pressure is what pushes the air back out of your lungs. Static pressure always attempts to equalize via flow when there is no barrier, and those changes in pressure caused by the diaphragm are what causes airflow in and out.

So that static pressure oscillates mildly, with or without the presence of the CPAP velocity pressure introduced into the system, and only due to the diaphragm modulating the internal static pressure in comparison to the external static pressure. Since total pressure is V pressure plus S pressure, total pressure also changes slightly depending upon whether you are inhaling or exhaling. But the V pressure from the CPAP does not change, and does not need to change (once set properly, of course).

The pump must have an impeller in order to maintain even pressure. A reciprocating pump can not do that.

The only thing unique about an impeller is that it is the "fan blade" part of a centrifugal pump. But any fan can blow air, and will work just the same as an impeller-driven centrifugal pump, and could theoretically power an xPAP. Modern xPAPs might indeed all use impellers, but that is not critical to blowing air. Either a centrifugal pump or a simple fan can blow air, and all either needs to modulate pressure is a servo feedback system to accelerate or retard the speed of the fan blade or the impeller. Certainly a reciprocating pump would never be appropriate, exactly for the reason you state. But whether an xPAP uses an impeller or not is not relevant to being able to modulate pressure or maintain even pressure, because a simple fan can do this as well.
...

EPAP pressure *IS* is what controls obstructive apnea otherwise the airway might start to close during exhale and be harder to maintain open for the inhale.

"OSA is a problem with airway collapse on inhale. The airway does not generally collapse on exhale. So whether the total pressure in the system goes up during exhale is not relevant to the therapy, and compensating for that change in total pressure during exhalation is not needed."

I restated that here because I believe it to be true and to be the very central to how xPAP therapy works. And how physics works. Blowing air into (increasing the differential pressure) into any cavity results in a stenting effect which is due to the difference between the total pressure outside the cavity as compared to inside the cavity. When that pressure is greater inside the cavity, this helps prevent the walls of the cavity from collapsing. When the pressure outside the cavity is greater than inside the cavity, this instead contributes to the tendency for the walls of the cavity to collapse.

Since the differential pressure is greater on the outside of your lungs when you inhale, this is when the airway is in danger of collapse. When you exhale and the pressure is greater inside your airway, there is no danger of the airway collapsing, barring any highly-unusual exceptional cases, due to the stenting effect. In fact, the higher pressure "balloons" out your airway during exhale. That's Fluid Dynamics 101.

And what xPAP does is eliminate the negative differential pressure by adding positive velocity pressure, which stents your airway even during inhale. Theoretically, you could turn the blower off during exhale altogether (other than the danger of CO2 rebreathing) and the airway would never collapse, although that is not practical because it would be hella annoying. But bottom line, exhaling is never the problem with OSA, only inhaling. The CPAP blows air as a therapeutic aid to inhalation, not exhalation.

Back in the day I sold Electrolux solid tank vacuums door to door to work through college. One of the tricks we used was to turn on the customer's old bag vacuum, then turn on the Electrolux vacuum, and then connect the two hoses together. It was like a suction (pressure) tug-of-war. Since the Electrolux solid tank vacuum had more structure and suction than the customers' old garden-variety bag vacuum, all you had to do was wait about 5 seconds, and the bag on their old vacuum would shrivel into a pitiful little noodle. The look on house-mom's face alone was worth it. I sold a lot of vacuums that way, and if ever there was an illustration of how differential pressure worked, I think this might have been it.

[me50]

S9 Autoset. Data doesn't show any pressure change, only that I wake up after four hours and therapy is interrupted as I try to get it to work.

I took it to my provider and they ran it for about 40 mins and pressure gauge showed 17, and no issues. Still under warranty so they will replace machine, but they no longer sell the S9 so they gave me a System One to try but I can't get that machine to humidify adequately (started another thread on this issue).

I really like the S9 and am hoping I can find a fix.

So they don't want to give you the newest model of Resmed's? As suggested, if they are going to replace the machine, maybe you should talk with your doc and see if they will give you a script for a vpap but you will have to pay some toward it...how much depends on whether you have insurance or not and what the coverage is for that under your policy.

[PaytonA]

Would you please educate me. I would like to know what velocity pressure is and how it is that we have 2 kinds of pressure in our PAP air system. I also do not know of any static pressure in the system.

I have a lot of trouble just educating myself (which may be evident). The pressure from a xPAP is velocity pressure. Total pressure is velocity pressure plus static pressure. Static pressure is somewhat like atmospheric pressure. A blown up balloon has static pressure inside it, for instance. Wikipedia can probably explain this better than I ever could, but neither velocity pressure nor static pressure exist in a vacuum (no pun) in an xPAP-aided breathing system; respiration is always a function of total pressure.

I am still having a problem wrapping my head around this. To me, pressure is simple and is caused by compressing the gas. I can understand that the pressure you feel when a strong wind blows on you is velocity pressure but it is very localized to near the surface of your skin.

The pump must have an impeller in order to maintain even pressure. A reciprocating pump can not do that.

The only thing unique about an impeller is that it is the "fan blade" part of a centrifugal pump. But any fan can blow air, and will work just the same as an impeller-driven centrifugal pump, and could theoretically power an xPAP. Modern xPAPs might indeed all use impellers, but that is not critical to blowing air. Either a centrifugal pump or a simple fan can blow air, and all either needs to modulate pressure is a servo feedback system to accelerate or retard the speed of the fan blade or the impeller. Certainly a reciprocating pump would never be appropriate, exactly for the reason you state. But whether an xPAP uses an impeller or not is not relevant to being able to modulate pressure or maintain even pressure, because a simple fan can do this as well.
...

Sorry, this was just me considering a fan just another type of impeller.

EPAP pressure *IS* is what controls obstructive apnea otherwise the airway might start to close during exhale and be harder to maintain open for the inhale.

"OSA is a problem with airway collapse on inhale. The airway does not generally collapse on exhale. So whether the total pressure in the system goes up during exhale is not relevant to the therapy, and compensating for that change in total pressure during exhalation is not needed."

This I believe to be true to a certain extent. If EPAP is set too low it can allow the airway to begin to or completely collapse at the end of exhale and/or at the normal pause between exhale and inhale. This is why I consider that EPAP is what controls obstructive apneas.


Best Regards,

PaytonA

[Sleeprider]

This thread got a bit off topic, and unnecessarily complicated.

Velocity is not very relevant to CPAP. Velocity is speed, so the volume of air flowing through a length of tube over a period of time has velocity (V=velocity/time). The same volume of air will travel faster in a smaller diameter tube than a larger diameter tube, and it can do this without changing absolute or differential pressure.

Pressure is the force applied by the flow of air. In the case of CPAP the force (pressure) of air can displace column of water to a certain height in a tube against atmospheric pressure. It is the amount of pressure (force) greater than atmospheric pressure measured in cm-H2O. Pressure is what keeps the airway open (not velocity or volume). Pressure can be present even when flow is blocked or static.

A good article here, but it's kind of advanced: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3297530/

[eseedhouse]

Pressure is what keeps the airway open (not velocity or volume). Pressure can be present even when flow is blocked or static.

Forgive me for being perhaps overly picky here, because your explanation is quite well done and easy to understand. But to succumb to my stickler gene, I believe it is strictly accurate to say that it is difference in pressure, not pressure alone. Your airway is opened by pressure that is elevated with respect to the ambient air pressure in the room. Should for some odd reason the ambient pressure go up by the same amount as the xpap machine is pushing up the pressure in your airway it would have no effect. Mind you I can't imagine how this could happen but I warned you I was going to be picky!

[pholynyk]

Quote: "Your airway is opened by pressure that is elevated with respect to the ambient air pressure in the room."
and
"I warned you I was going to be picky!"


Right on both counts!