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Oh what a night......
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diamaunt Offline

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Location: texas

Post: #21
RE: Oh what a night......
I'm trying to find more information, but I have come across this quote by someone that sounds like they know a lot more than I do about it Smile

Quote:The mask type setting is for pressure drop compensation for varying mask geometries. Respironics has a similar setting on their home use machines. In short, things like small and petite sized nasal pillows have higher pressure drops than things like full face masks and regular sized nasal masks. All of these machines compensate for pressure drop at flows through a 6ft length of 22mm tubing, but by knowing some information about the mask it can add an additional compensation to achieve more accurate proximal pressure estimates.

so, I was wrong about 'dead space'...

there was also:

Quote:As to the leak rate calculation:
In short , you typically have an orifice plate type flow sensor or bypass flow meter on the outlet to the blower that can measure flows in the range of approx. -240 to +240 SLPM and a pressure sensor that can measure maybe -20 to +75 cmH2O. This gives two points of data: Total flow and distal pressure. For the sake of argument consider a bi-level device that raises patient pressure during inspiration. The DSP analyzes the waveform from the pressure and flow sensor giving an I/E signal telling an algorithm simply whether the patient is inhaling or exhaling. The machine makes some assumptions about these cycles, mostly that inspiration doesn't' exceed a set time period to detect disconnects and that expiration is negative exponential in shape. When inspiration is triggered (You typically have a flow threshold , pressure, or volume threshold. More advanced features like Auto-Trak affect multiple systems), the CPU starts integrating flow rate to give an inspiration volume. As you start to exhale, the I/E signal switches to exhale and this integration ends. Knowing both the peak flow and total volume of the inspiration phase, a model of the expiration waveform can be accurately created. By comparing this modeled waveform with the measured expiration waveform as it's actually happening, the software can continuously subtract difference between the two: this offset is your leak rate. The real tidal volume and peak patient flows are computed after the expiration phase ends. Over a couple breaths, the system can create a zero-crossing value for the volume rate and determine other values like minute volume and breath rate. Differences from this zero baseline can be treated as unintentional leak flows.

Even Shorter: Leak rate is calculated by the machines, not from a lookup table. The latter is seriously lazy engineering.
07-14-2014 01:35 PM
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PaytonA Offline
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Machine: ResMed S9 VPAP Auto
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CPAP Software: ResScan SleepyHead

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Location: Orange County,California

Post: #22
RE: Oh what a night......
(07-14-2014 01:35 PM)diamaunt Wrote:  I'm trying to find more information, but I have come across this quote by someone that sounds like they know a lot more than I do about it Smile

Quote:The mask type setting is for pressure drop compensation for varying mask geometries. Respironics has a similar setting on their home use machines. In short, things like small and petite sized nasal pillows have higher pressure drops than things like full face masks and regular sized nasal masks. All of these machines compensate for pressure drop at flows through a 6ft length of 22mm tubing, but by knowing some information about the mask it can add an additional compensation to achieve more accurate proximal pressure estimates.

so, I was wrong about 'dead space'...

there was also:

Quote:As to the leak rate calculation:
In short , you typically have an orifice plate type flow sensor or bypass flow meter on the outlet to the blower that can measure flows in the range of approx. -240 to +240 SLPM and a pressure sensor that can measure maybe -20 to +75 cmH2O. This gives two points of data: Total flow and distal pressure. For the sake of argument consider a bi-level device that raises patient pressure during inspiration. The DSP analyzes the waveform from the pressure and flow sensor giving an I/E signal telling an algorithm simply whether the patient is inhaling or exhaling. The machine makes some assumptions about these cycles, mostly that inspiration doesn't' exceed a set time period to detect disconnects and that expiration is negative exponential in shape. When inspiration is triggered (You typically have a flow threshold , pressure, or volume threshold. More advanced features like Auto-Trak affect multiple systems), the CPU starts integrating flow rate to give an inspiration volume. As you start to exhale, the I/E signal switches to exhale and this integration ends. Knowing both the peak flow and total volume of the inspiration phase, a model of the expiration waveform can be accurately created. By comparing this modeled waveform with the measured expiration waveform as it's actually happening, the software can continuously subtract difference between the two: this offset is your leak rate. The real tidal volume and peak patient flows are computed after the expiration phase ends. Over a couple breaths, the system can create a zero-crossing value for the volume rate and determine other values like minute volume and breath rate. Differences from this zero baseline can be treated as unintentional leak flows.

Even Shorter: Leak rate is calculated by the machines, not from a lookup table. The latter is seriously lazy engineering.

Pressure drop from the mask must come from the connector from the hose to the mask.

The leak rate calculation is very interesting but I do not see anything that ensures that the zero baseline is itself free from unintentional leaks which I think would make the calculation less than stellar. Very interesting though.
07-14-2014 11:20 PM
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Sleepster Offline
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Post: #23
RE: Oh what a night......
PRS1 machines use the System One Resistance to compensate for the pressure drop across the mask. You have to set this yourself, the values are X1 through X4. Respironics masks are marked accordingly. This is the "System One" scheme. If you use a mask made by another manufacturer it won't be labeled with the System One Resistance setting. This means you'll deprive Respironics of a sale!

As you dial up the System One Resistance setting you are reducing the pressure by a small amount, probably a fraction of a centimeter when going from zero to the maximum of X4. I used it for awhile and then stopped when I learned it was just lowering the pressure. Why bother with doing that when you can just lower the pressure if you want it lower? I suppose it might be useful for people who regularly switch mask types, like from a nasal mask to a FFM when they have a cold.

With ResMed machines I suppose a similar thing is done when you tell it what type of mask you have, and I think it also uses that information to calculate the unintentional leak rate.

Sleepster
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
07-15-2014 01:21 AM
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Sleepster Offline
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Machine: ResMed AirCurve10 VAuto
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Post: #24
RE: Oh what a night......
(07-14-2014 11:20 PM)PaytonA Wrote:  Pressure drop from the mask must come from the connector from the hose to the mask.

It happens as the air passes from the mask to your body. The smaller the passageway the greater the pressure drop.

Sleepster
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
07-15-2014 01:33 AM
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zonk Offline

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Post: #25
RE: Oh what a night......
(07-15-2014 01:21 AM)Sleepster Wrote:  PRS1 machines use the System One Resistance to compensate for the pressure drop across the mask. You have to set this yourself, the values are X1 through X4. Respironics masks are marked accordingly. This is the "System One" scheme. If you use a mask made by another manufacturer it won't be labeled with the System One Resistance setting.
I recall been said, "0" for non-Respironics masks
[Image: MaskSettingsforSystemOneResistanceC.jpg]
07-15-2014 02:10 AM
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Sleepster Offline
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Machine: ResMed AirCurve10 VAuto
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CPAP Pressure: MaxI 13.6 | MinE 5.2 | PS 4.4
CPAP Software: ResScan SleepyHead

Other Comments: Diagnosed Nov 2011. Conquered aerophagia.

Sex: Male
Location: Houston, Texas

Post: #26
RE: Oh what a night......
(07-15-2014 02:10 AM)zonk Wrote:  I recall been said, "0" for non-Respironics masks

If you want to use the PRS1 Resistance settings you don't need to use a Respironics mask. Just use the setting for the Respironics mask that's the closest match.

It's just a small reduction in the pressure, anyway. If you're using a machine that automatically adjusts the pressure I see no need for the whole silly thing.

Sleepster
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
07-15-2014 09:17 AM
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diamaunt Offline

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Posts: 436
Joined: May 2012

Machine: S9 VPAP Auto 36006
Mask Type: Full face mask
Mask Make & Model: mirage quattro/pilairo q
Humidifier: none
CPAP Pressure: 9-20ish
CPAP Software: SleepyHead

Other Comments:

Sex: Male
Location: texas

Post: #27
RE: Oh what a night......
Quote:It's just a small reduction in the pressure, anyway. If you're using a machine that automatically adjusts the pressure I see no need for the whole silly thing.

the machine adjusts the pressure *at the machine*.

to get the pressure *at your face* right, it has to throw in added calculations about the hose, and mask type.

older resmed vpap machines actually had a separate sensing tube that ran alongside the main hose so it could sense pressure at the mask and be more accurate.

with better cpu's and math, they can factor in what the pressure drop in the hose and mask is, and *raise* pressure at the machine to compensate.

if you look at the chart again, you'll see that the higher x numbers correspond to the more restrictive masks, so the machine would actually have a *higher* pressure for a higher x number, not a lower pressure Smile
07-15-2014 10:23 AM
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PaytonA Offline
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Machine: ResMed S9 VPAP Auto
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Mask Make & Model: Resmed Mirage Quattro
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CPAP Pressure: VAuto MinE14.0 MaxI 20.6 PS4.0
CPAP Software: ResScan SleepyHead

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Post: #28
RE: Oh what a night......
(07-15-2014 01:33 AM)Sleepster Wrote:  
(07-14-2014 11:20 PM)PaytonA Wrote:  Pressure drop from the mask must come from the connector from the hose to the mask.

It happens as the air passes from the mask to your body. The smaller the passageway the greater the pressure drop.

I believe that the pressure drop at the mask is in the attachment to the mask or maybe in the case of nasal pillows it may have to do with the pillow attachment also but that is just my opinion.

Best Regards,

PaytonA
07-15-2014 10:45 AM
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