palerider wrote:while others don't agree with me, I believe that this commonly held idea is wrong.RogerSC wrote:There is a setting for mask type in the S9 menus. That is supposed to help correct for a mask's normal venting. The setting that I'm using is "nasal pillows" and works fine for me, but since nasal pillows don't vent as much as a full face mask, not setting this one appropriately could be your problem. If you haven't set this already *smile*.
if you look at a chart of resmed mask vent rates, and add in others from other manufacturers. you'll find that they all vent at approximately the same rate. around 20lpm @4cm to around 50lpm@20cm, there are minor differences, but they are minor.
however, if you look in the manuals for the masks and look at their RESISTANCE specs, they all pretty much line up with full face having the lowest resistance, nasal having slightly higher, and pillow masks having the greatest resistance.
this data leads to the conclusion that the mask type setting in the resmeds is so that the machine can adjust it's pressures to compensate for the resistance that the different masks provide, in much the same way that the hose type setting allows it to compensate for the different types of hoses.less, yes, but not enough to trigger a leak alert.Code: Select all
pressure p10 f10 4 20 22 8 29 32 12 37 41 16 43 48 20 49 54
contrast that with the resistance, with the p10, @50lpm, .4cm @100lpm, 1.4cm f10: @50, .2cm @100 1.0cm.
knowing the pressure you've set, and the type of hose and mask, the machine can raise the pressure where it's measured (by the air outlet) to compensate for the pressure drops at the mask, and thus give you the desired pressure.
Jay Aitchsee wrote:Interesting theory, but those pressure drops stats are given at fairly high flow rates (50 and 100lpm) which would generally correspond to static vent rates at pressures of 20cmH2O and higher. But even at 50lpm the difference in resistance for the two masks is only .2cm. Since, I think, resistance is a function of the square of flow, the absolute difference in the two at more typical values of use would be even less.palerider wrote:this data leads to the conclusion that the mask type setting in the resmeds is so that the machine can adjust it's pressures to compensate for the resistance that the different masks provide, in much the same way that the hose type setting allows it to compensate for the different types of hoses.
...contrast that with the resistance, with the p10, @50lpm, .4cm @100lpm, 1.4cm f10: @50, .2cm @100 1.0cm.
I'm just sayin'
Edit: In thinking about this a little more, it may not make any sense to talk about static vent flow rates in conjunction with Resistance. Maybe Minute Ventilation would be more appropriate? Mine is about 30Lpm max and 8 average with FFM and 15lpm max and 7 average w/ pillows. Don't know, it is interesting.
What if it does both; i.e., set the flow rate and the resistance value? From using different masks, with different settings, I'm pretty sure the setting determines the base leak/vent threshold. For example, my Simplus, which has a slightly lower static vent rate, always shows a lower base leak line than my F10. I'm pretty sure, though not positive, that the base line shifts slightly if a different setting is used with the same mask.palerider wrote:it sounds to me like you're onto something there...Jay Aitchsee wrote:Edit: In thinking about this a little more, it may not make any sense to talk about static vent flow rates in conjunction with Resistance. Maybe Minute Ventilation would be more appropriate? Mine is about 30Lpm max and 8 average with FFM and 15lpm max and 7 average w/ pillows. Don't know, it is interesting.
to get the applicable flow rate, you'd have to look at the expected flow @presssure, say, 35lpm@10ish cm. then add in the varying flow from breathing, looking at one night of my data, I see breathing flows up to 120lpm, though usually more like 30-60.
that gives a wide range of flow from 65-155lpm on the plus side.
without the mask type compensation, your actual delivered pressure would vary more, I think that respironics resistance control is their way of copying the idea in the 60 series, but they got more specific. it makes perfect sense to me,
without the added compensation for the flow resistance of the masks, the final end pressure isn't nearly as accurate.
Your point was the static vent rates were practically the same for all types of ResMed masks, so the vent rate wouldn't need differentiation. However, I differ with that view. From the latest ResMed Flow Rate chart: FFM @8 = 32, @20 = 54, while pillows @ 8 = 29, @20 = 49. For differences of 3 and 5 cmH2O. Those differences are great enough to shift the computed leak base line if the wrong value is used.
Now, if the setting is used to set the resistance, then the resistance for each class of mask should be the same, or quite close. I haven't looked at that. It might be interesting to do so. I agree that the Resistance of the mask will affect the pressure delivered and at 100lpm a 1.4cmH2O pressure drop could exceed ResMed's claim of a pressure tolerance within a nominal +/- 0.5 cmH2o +/- 4% of the measured pressure. Though I think, under normal circumstances, 100lpm is quite high.
So, maybe both?
