Measuring CPAP pressure

Sleeping Disorder » Sleep Disorder » Measuring CPAP pressure

Question:

Joe, when they did the sleep study, where did they measure the pressure? My guess is that it was at the source, so your actual delivered pressure was lower during the test as well as later. All of which means that the pressure-drop from the blower to the interface is already factored out. Paul R "Joe" <j…@nowhere.com> wrote in message

news:tIoWa.1256$qp5.1056@news.cpqcorp.net… – Hide quoted text — Show quoted text -> The place where I got my CPAP machine measures the pressure, rather than > simply relying on the readout on the CPAP machine itself. I’ve noticed > however that the pressure I measure at home, at the mask, is lower than my > prescription. For example, the unit was set for a readout of 10.5cm, my > prescription is for 11cm, and I measured only about 10cm at the mask. To get > a measured pressure of 11, I had to adjust it such that the readout was > about 11.5. (the readout only has a precision of 0.5cm). The method I use to > measure the pressure is to attach a tube to the oxygen port of my mask, seal > the main nose opening, leave the exhale exhaust open, and dunk the tube > (fixed to a ruler) into a tall container of water, and note the point at > which the bubbles just stop > I raised this issue with them, and they showed me how they do the > measurement. They have this simple water based manometer which fixes to the > outlet of a humidifer chamber. There is a little hole on the manometer, > right at the point at which it connects to the chamber, which simulates the > exhaust of the mask (presumably). There is one tube which sticks up – the > water rises up this tube and a reading is taken. Interestingly, I noticed > that when they sealed the exhaust on the manometer, the pressure went *down* > about 0.5cm. (and returned to it’s original level when the seal was removed > again). > I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & > Paykel HC221 – I now have the next model which is quieter). The readout > shows 10.0 this time. I just bet that when I get home and measure it, it’ll > be at least a cm less than my prescription again. > Any ideas why this discrepancy is occurring? Is there something wrong with > the way I am measuring the pressure? They said they didn’t have the > equipment to measure the pressure at my mask. > If it makes any difference, I am in Australia. > Joe.

Response:

On Sun, 03 Aug 2003 18:34:34 -0400, Lurker1023 <Lurkwe1…@hotmail.com> wrote: >Aparently there is a good reason we never have a consensus. There >does not seem to be any real hard data on this available. Is there >any standard practice for setting up machines? or is it left up to the >individal RT ?

I know ResMed specifies exactly how to do it: connect the gauge at the oxygen ports, with a blind cushion (or a hand over the cushion). >IMHO you are making a mountain out of a mole hill. Just because >cpap’s have nice digital displays and sleep studies are done with >computers does not imply that the results are actually that acurate. >As evidenced by responses here many have required adjustments in >pressure shortly after their titration and mant doctors allow small >changes without retitrating.

Also, titration is a one-night stand.

Response:

Charles Perrin wrote: > On Sun, 03 Aug 2003 18:34:34 -0400, Lurker1023 > <Lurkwe1…@hotmail.com> wrote: >>Aparently there is a good reason we never have a consensus. There >>does not seem to be any real hard data on this available. Is there >>any standard practice for setting up machines? or is it left up to the >>individal RT ? > I know ResMed specifies exactly how to do it: connect the gauge at the > oxygen ports, with a blind cushion (or a hand over the cushion).

Good to know. Have you indicated this in the past? If so I missed it. You do mean at only one of the oxygen ports, right? I think some masks have 2. Using myself as an example. If my titration pressure showed 12cm, I was receiving less than 12 by virtue of the drop (however slight) through tube,mask and airway(s). When the tech set up my machine for 10, as you described above, it had an implicit assumption that my tube, mask, and airway would not cause any kind of drop. In reality, the pressure then would be slightly less than 12 at my mask. Right? – Hide quoted text — Show quoted text ->>IMHO you are making a mountain out of a mole hill. Just because >>cpap’s have nice digital displays and sleep studies are done with >>computers does not imply that the results are actually that acurate. >>As evidenced by responses here many have required adjustments in >>pressure shortly after their titration and mant doctors allow small >>changes without retitrating. > Also, titration is a one-night stand.

Response:

- Hide quoted text — Show quoted text -Lurker1023 wrote: > On Sun, 03 Aug 2003 05:58:41 GMT, NormC <no…@socal.rr.com> wrote: >>eric wrote: >>>Many mfgrs >>Of what? Blowers? In the User’s Manual? >>>advise that you check the pressure at the point of delivery >>>via a ‘blind mask’. >>What is a blind mask? >>>Measurements which do not factor in the hoses and >>>the CO2 venting of the mask are inadequately accurate. >>So I’ve thought. >>>regards, >>>eric pearson >>>db2e…@nospammindspring.com > Aparently there is a good reason we never have a consensus. There > does not seem to be any real hard data on this available.

Never been a concensus attempted for the very reason you state. > Is there > any standard practice for setting up machines? or is it left up to the > individal RT ?

I don’t think we know at this point. > IMHO you are making a mountain out of a mole hill.

Not sure who you are referring to; you have responded to a couple of people. Evidently you have had a successful experience with your CPAP, right? My only interest is because so many people come here, having had one test or another, even a "gold standard" PSG and titration in a fully equipped lab, having their CPAP, and still feel like crap months later. I understand enough about PSGs and titrations to be satisfied, at the moment, in the assumption that the problem is occuring between the testing and titrating and using the CPAP, and that’s the setting of the pressure. > Just because > cpap’s have nice digital displays and sleep studies are done with > computers does not imply that the results are actually that acurate.

Very true. With respect to Joe, he’s finding a 0.5 cm difference. Possibly a measuring error. Probably insignificant. > As evidenced by responses here many have required adjustments in > pressure shortly after their titration and mant doctors allow small > changes without retitrating.

That my point. Why? Because it was measured wrong when setting up, or the setup was wrong, to me, pretty much the same problem. > When I had my titration I do not recall seeing any pressure measuring > device attached to me! I believe they rely on the pressure reported > by the CPAP. All they are using is a remote control CPAP so they do > not have to come into the room to change the pressure, no magic. They > look at your responce to the pressure indicated by the CPAP and that > is your titration pressure, measured at the machine.

You may have come with the right set of words to provide the key here. (BTW, that’s why YOU should do more than just lurk <g>). I never thought it through before, but, given that the pressure at the titrating blower reads, and is, 12, when other instrumentation shows that I no longer have any apneas, the pressure at the mask is a little less than 12 by virtue of the drop through the hose, mask design, and my airway resistance. So my prescription should be written for 12. Now, by rights, the tech should set MY blower to 12 when it is seeing the same air resistance ‘circuit’ the titrating blower saw. This is exactly what you say below. > If your machine > was set up properly and you use a similar length hose and a similar > style mask your pressure should be correct.

That’s exactly what I’ve been digging for. I wasn’t paying enough attention either time my blower was checked/set. I don’t recall taking any of my stuff along. I don’t even remember if they used anything but a manometer, which I do remember. Do you remember how they set yours up? – Hide quoted text — Show quoted text -> If not who knows? But > Norm’s standard question how do you feel in the morning is the best > gauge of whether you are receiving adequate treatement. > IMHO the > readout is no more important that a room thermometer. They are all a > little different and only a guide, if you feel hot, you feel hot > regardless of what the thermoter is reading.

Response:

Eric – I’ve never gotten into this before, but isn’t there a mask spec that has to do with the handling /dispersing of carbon dioxide/exhaled air? I’ve gotten the impression that they vary from mask to mask, and has to do with mask design, in particular with the exhaust port. If so, wouldn’t they have to have many blind masks, one for each spec? We, all, oughta start asking a lot of questions of our HME/DME providers. See comment below eric wrote: > A blind mask is one that the DME uses for adjustments. It is like a > regular mask except that the part which normally touches your face is > sealed shut.

This would assume that when you put your own mask on your face, your airways look like an infinite resistance to the blower. Everyone happy with that assumption? Not sure I am. – Hide quoted text — Show quoted text -> This allows them to measure the pressure including any > effects of vent ports, hose resistance, etc. > regards, > eric pearson > db2e…@nospammindspring.com > On Sun, 03 Aug 2003 05:58:41 GMT, NormC <no…@socal.rr.com> wrote: >>eric wrote: >>>Many mfgrs >>Of what? Blowers? In the User’s Manual? >>>advise that you check the pressure at the point of delivery >>>via a ‘blind mask’. >>What is a blind mask? >>>Measurements which do not factor in the hoses and >>>the CO2 venting of the mask are inadequately accurate. >>So I’ve thought. >>>regards, >>>eric pearson >>>db2e…@nospammindspring.com >>>On Fri, 01 Aug 2003 07:32:41 GMT, "Joe" <j…@nowhere.com> wrote: >>>>The place where I got my CPAP machine measures the pressure, rather than >>>>simply relying on the readout on the CPAP machine itself. I’ve noticed >>>>however that the pressure I measure at home, at the mask, is lower than my >>>>prescription. For example, the unit was set for a readout of 10.5cm, my >>>>prescription is for 11cm, and I measured only about 10cm at the mask. To get >>>>a measured pressure of 11, I had to adjust it such that the readout was >>>>about 11.5. (the readout only has a precision of 0.5cm). The method I use to >>>>measure the pressure is to attach a tube to the oxygen port of my mask, seal >>>>the main nose opening, leave the exhale exhaust open, and dunk the tube >>>>(fixed to a ruler) into a tall container of water, and note the point at >>>>which the bubbles just stop >>>>I raised this issue with them, and they showed me how they do the >>>>measurement. They have this simple water based manometer which fixes to the >>>>outlet of a humidifer chamber. There is a little hole on the manometer, >>>>right at the point at which it connects to the chamber, which simulates the >>>>exhaust of the mask (presumably). There is one tube which sticks up – the >>>>water rises up this tube and a reading is taken. Interestingly, I noticed >>>>that when they sealed the exhaust on the manometer, the pressure went *down* >>>>about 0.5cm. (and returned to it’s original level when the seal was removed >>>>again). >>>>I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & >>>>Paykel HC221 – I now have the next model which is quieter). The readout >>>>shows 10.0 this time. I just bet that when I get home and measure it, it’ll >>>>be at least a cm less than my prescription again. >>>>Any ideas why this discrepancy is occurring? Is there something wrong with >>>>the way I am measuring the pressure? They said they didn’t have the >>>>equipment to measure the pressure at my mask. >>>>If it makes any difference, I am in Australia. >>>>Joe.

Response:

- Hide quoted text — Show quoted text -On Sun, 03 Aug 2003 05:58:41 GMT, NormC <no…@socal.rr.com> wrote: >eric wrote: >> Many mfgrs >Of what? Blowers? In the User’s Manual? >> advise that you check the pressure at the point of delivery >> via a ‘blind mask’. >What is a blind mask? >> Measurements which do not factor in the hoses and >> the CO2 venting of the mask are inadequately accurate. >So I’ve thought. >> regards, >> eric pearson >> db2e…@nospammindspring.com

Aparently there is a good reason we never have a consensus. There does not seem to be any real hard data on this available. Is there any standard practice for setting up machines? or is it left up to the individal RT ? IMHO you are making a mountain out of a mole hill. Just because cpap’s have nice digital displays and sleep studies are done with computers does not imply that the results are actually that acurate. As evidenced by responses here many have required adjustments in pressure shortly after their titration and mant doctors allow small changes without retitrating. When I had my titration I do not recall seeing any pressure measuring device attached to me! I believe they rely on the pressure reported by the CPAP. All they are using is a remote control CPAP so they do not have to come into the room to change the pressure, no magic. They look at your responce to the pressure indicated by the CPAP and that is your titration pressure, measured at the machine. If your machine was set up properly and you use a similar length hose and a similar style mask your pressure should be correct. If not who knows? But Norm’s standard question how do you feel in the morning is the best gauge of whether you are receiving adequate treatement. IMHO the readout is no more important that a room thermometer. They are all a little different and only a guide, if you feel hot, you feel hot regardless of what the thermoter is reading.

Response:

A blind mask is one that the DME uses for adjustments. It is like a regular mask except that the part which normally touches your face is sealed shut. This allows them to measure the pressure including any effects of vent ports, hose resistance, etc. regards, eric pearson db2e…@nospammindspring.com – Hide quoted text — Show quoted text -On Sun, 03 Aug 2003 05:58:41 GMT, NormC <no…@socal.rr.com> wrote: >eric wrote: >> Many mfgrs >Of what? Blowers? In the User’s Manual? >> advise that you check the pressure at the point of delivery >> via a ‘blind mask’. >What is a blind mask? >> Measurements which do not factor in the hoses and >> the CO2 venting of the mask are inadequately accurate. >So I’ve thought. >> regards, >> eric pearson >> db2e…@nospammindspring.com >> On Fri, 01 Aug 2003 07:32:41 GMT, "Joe" <j…@nowhere.com> wrote: >>>The place where I got my CPAP machine measures the pressure, rather than >>>simply relying on the readout on the CPAP machine itself. I’ve noticed >>>however that the pressure I measure at home, at the mask, is lower than my >>>prescription. For example, the unit was set for a readout of 10.5cm, my >>>prescription is for 11cm, and I measured only about 10cm at the mask. To get >>>a measured pressure of 11, I had to adjust it such that the readout was >>>about 11.5. (the readout only has a precision of 0.5cm). The method I use to >>>measure the pressure is to attach a tube to the oxygen port of my mask, seal >>>the main nose opening, leave the exhale exhaust open, and dunk the tube >>>(fixed to a ruler) into a tall container of water, and note the point at >>>which the bubbles just stop >>>I raised this issue with them, and they showed me how they do the >>>measurement. They have this simple water based manometer which fixes to the >>>outlet of a humidifer chamber. There is a little hole on the manometer, >>>right at the point at which it connects to the chamber, which simulates the >>>exhaust of the mask (presumably). There is one tube which sticks up – the >>>water rises up this tube and a reading is taken. Interestingly, I noticed >>>that when they sealed the exhaust on the manometer, the pressure went *down* >>>about 0.5cm. (and returned to it’s original level when the seal was removed >>>again). >>>I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & >>>Paykel HC221 – I now have the next model which is quieter). The readout >>>shows 10.0 this time. I just bet that when I get home and measure it, it’ll >>>be at least a cm less than my prescription again. >>>Any ideas why this discrepancy is occurring? Is there something wrong with >>>the way I am measuring the pressure? They said they didn’t have the >>>equipment to measure the pressure at my mask. >>>If it makes any difference, I am in Australia. >>>Joe.

Response:

Norm, I will try various search arguments. One of the terms Terry used (I’d not heard it before) was ‘deadhead’ (meaning to measure directly at the pap rather than after hoses, masks, etc. regards, eric pearson db2e…@nospammindspring.com – Hide quoted text — Show quoted text -On Sun, 03 Aug 2003 05:56:15 GMT, NormC <no…@socal.rr.com> wrote: >One entry came up, showing 50 posts, some of which were yours and >some of which were mine, and none of which were from Terry Bliss. >I think the only reason anything came up at all was because you >mentioned his name in that thread. Now what? >eric wrote: >> Norm, Joe: >> Please search the Google archives for postings from Terry Bliss on >> exactly this subject. There is some good info in those threads. >> regards, >> eric pearson >> db2e…@nospammindspring.com >> On Sun, 3 Aug 2003 09:25:47 +1000, "Joe" <j…@nowhere.com> wrote: >>>"NormC" <no…@socal.rr.com> wrote in message >>>news:3F2C184C.4020206@socal.rr.com… >>>>How do you seal the main nose opening? >>>By pressing the mask down on a flat surface. I have also tried measuring the >>>pressure with the mask on my face, while I am holding my breath – same >>>result. >>>>>leave the exhale exhaust open, and dunk the tube >>>>>(fixed to a ruler) into a tall container of water, and note the point at >>>>>which the bubbles just stop >>>>Are you an engineer? <g> >>>Yes However, I didn’t devise this myself – I learnt about this by >>>searching the archives of this forum. >>>>>They have this simple water based manometer which fixes to the >>>>>outlet of a humidifer chamber. There is a little hole on the manometer, >>>>>right at the point at which it connects to the chamber, which simulates >>>the >>>>>exhaust of the mask (presumably). There is one tube which sticks up – >>>the >>>>>water rises up this tube and a reading is taken. >>>>So neither the tube/hose, you, or your mask were in the >>>>’circuit’, right? >>>Correct. However they did try connecting a hose between the CPAP machine and >>>the humidifer, but that didn’t change the result. (their manometer always >>>connects directly to the outlet of the humidifier, which is a Fisher & >>>Paykel) >>>The manometer they use is this shown here: >>>http://www.cpap-pro.net/mano.htm >>>>>Interestingly, I noticed >>>>>that when they sealed the exhaust on the manometer, the pressure went >>>*down* >>>>>about 0.5cm. (and returned to it’s original level when the seal was >>>removed >>>>>again). >>>>That’s more than interesting. Seems to defy the laws of physics, >>>>let alone the laws of fluid dynamics. Do you have any >>>>explanation for this? >>>No, I don’t. It’s puzzling. >>>>>I’ve exchanged my CPAP machine today for a newer model. (I had the >>>Fisher & >>>>>Paykel HC221 – I now have the next model which is quieter). The readout >>>>>shows 10.0 this time. I just bet that when I get home and measure it, >>>it’ll >>>>>be at least a cm less than my prescription again. >>>>>Any ideas why this discrepancy is occurring? >>>>My first guess would be that the resistance to flow, from the >>>>tube/hose and mask results in a .5 cm drop. >>>Even if that is the case, 0.5cm is only half of the difference. They are >>>setting it to more than a 1cm less than my prescription. (if I’m measuring >>>properly) >>>>>Is there something wrong with >>>>>the way I am measuring the pressure? >>>>Looks great to me. >>>Thanks. >>>I think my next step will be to take it to my hospital and ask them "what >>>prescription is this unit currently set to?". Should be interesting. (I know >>>they have manometers which can be connected to the mask, if required). I’ll >>>offer to let them measure it with my tube and mask, but they may say they >>>don’t need any of that to measure the prescription. >>>Joe.

Response:

eric wrote: > Many mfgrs

Of what? Blowers? In the User’s Manual? > advise that you check the pressure at the point of delivery > via a ‘blind mask’.

What is a blind mask? > Measurements which do not factor in the hoses and > the CO2 venting of the mask are inadequately accurate.

So I’ve thought. – Hide quoted text — Show quoted text -> regards, > eric pearson > db2e…@nospammindspring.com > On Fri, 01 Aug 2003 07:32:41 GMT, "Joe" <j…@nowhere.com> wrote: >>The place where I got my CPAP machine measures the pressure, rather than >>simply relying on the readout on the CPAP machine itself. I’ve noticed >>however that the pressure I measure at home, at the mask, is lower than my >>prescription. For example, the unit was set for a readout of 10.5cm, my >>prescription is for 11cm, and I measured only about 10cm at the mask. To get >>a measured pressure of 11, I had to adjust it such that the readout was >>about 11.5. (the readout only has a precision of 0.5cm). The method I use to >>measure the pressure is to attach a tube to the oxygen port of my mask, seal >>the main nose opening, leave the exhale exhaust open, and dunk the tube >>(fixed to a ruler) into a tall container of water, and note the point at >>which the bubbles just stop >>I raised this issue with them, and they showed me how they do the >>measurement. They have this simple water based manometer which fixes to the >>outlet of a humidifer chamber. There is a little hole on the manometer, >>right at the point at which it connects to the chamber, which simulates the >>exhaust of the mask (presumably). There is one tube which sticks up – the >>water rises up this tube and a reading is taken. Interestingly, I noticed >>that when they sealed the exhaust on the manometer, the pressure went *down* >>about 0.5cm. (and returned to it’s original level when the seal was removed >>again). >>I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & >>Paykel HC221 – I now have the next model which is quieter). The readout >>shows 10.0 this time. I just bet that when I get home and measure it, it’ll >>be at least a cm less than my prescription again. >>Any ideas why this discrepancy is occurring? Is there something wrong with >>the way I am measuring the pressure? They said they didn’t have the >>equipment to measure the pressure at my mask. >>If it makes any difference, I am in Australia. >>Joe.

Response:

One entry came up, showing 50 posts, some of which were yours and some of which were mine, and none of which were from Terry Bliss. I think the only reason anything came up at all was because you mentioned his name in that thread. Now what? – Hide quoted text — Show quoted text -eric wrote: > Norm, Joe: > Please search the Google archives for postings from Terry Bliss on > exactly this subject. There is some good info in those threads. > regards, > eric pearson > db2e…@nospammindspring.com > On Sun, 3 Aug 2003 09:25:47 +1000, "Joe" <j…@nowhere.com> wrote: >>"NormC" <no…@socal.rr.com> wrote in message >>news:3F2C184C.4020206@socal.rr.com… >>>How do you seal the main nose opening? >>By pressing the mask down on a flat surface. I have also tried measuring the >>pressure with the mask on my face, while I am holding my breath – same >>result. >>>>leave the exhale exhaust open, and dunk the tube >>>>(fixed to a ruler) into a tall container of water, and note the point at >>>>which the bubbles just stop >>>Are you an engineer? <g> >>Yes However, I didn’t devise this myself – I learnt about this by >>searching the archives of this forum. >>>>They have this simple water based manometer which fixes to the >>>>outlet of a humidifer chamber. There is a little hole on the manometer, >>>>right at the point at which it connects to the chamber, which simulates >>the >>>>exhaust of the mask (presumably). There is one tube which sticks up – >>the >>>>water rises up this tube and a reading is taken. >>>So neither the tube/hose, you, or your mask were in the >>>’circuit’, right? >>Correct. However they did try connecting a hose between the CPAP machine and >>the humidifer, but that didn’t change the result. (their manometer always >>connects directly to the outlet of the humidifier, which is a Fisher & >>Paykel) >>The manometer they use is this shown here: >>http://www.cpap-pro.net/mano.htm >>>>Interestingly, I noticed >>>>that when they sealed the exhaust on the manometer, the pressure went >>*down* >>>>about 0.5cm. (and returned to it’s original level when the seal was >>removed >>>>again). >>>That’s more than interesting. Seems to defy the laws of physics, >>>let alone the laws of fluid dynamics. Do you have any >>>explanation for this? >>No, I don’t. It’s puzzling. >>>>I’ve exchanged my CPAP machine today for a newer model. (I had the >>Fisher & >>>>Paykel HC221 – I now have the next model which is quieter). The readout >>>>shows 10.0 this time. I just bet that when I get home and measure it, >>it’ll >>>>be at least a cm less than my prescription again. >>>>Any ideas why this discrepancy is occurring? >>>My first guess would be that the resistance to flow, from the >>>tube/hose and mask results in a .5 cm drop. >>Even if that is the case, 0.5cm is only half of the difference. They are >>setting it to more than a 1cm less than my prescription. (if I’m measuring >>properly) >>>>Is there something wrong with >>>>the way I am measuring the pressure? >>>Looks great to me. >>Thanks. >>I think my next step will be to take it to my hospital and ask them "what >>prescription is this unit currently set to?". Should be interesting. (I know >>they have manometers which can be connected to the mask, if required). I’ll >>offer to let them measure it with my tube and mask, but they may say they >>don’t need any of that to measure the prescription. >>Joe.

Response:

Many mfgrs advise that you check the pressure at the point of delivery via a ‘blind mask’. Measurements which do not factor in the hoses and the CO2 venting of the mask are inadequately accurate. regards, eric pearson db2e…@nospammindspring.com – Hide quoted text — Show quoted text -On Fri, 01 Aug 2003 07:32:41 GMT, "Joe" <j…@nowhere.com> wrote: >The place where I got my CPAP machine measures the pressure, rather than >simply relying on the readout on the CPAP machine itself. I’ve noticed >however that the pressure I measure at home, at the mask, is lower than my >prescription. For example, the unit was set for a readout of 10.5cm, my >prescription is for 11cm, and I measured only about 10cm at the mask. To get >a measured pressure of 11, I had to adjust it such that the readout was >about 11.5. (the readout only has a precision of 0.5cm). The method I use to >measure the pressure is to attach a tube to the oxygen port of my mask, seal >the main nose opening, leave the exhale exhaust open, and dunk the tube >(fixed to a ruler) into a tall container of water, and note the point at >which the bubbles just stop >I raised this issue with them, and they showed me how they do the >measurement. They have this simple water based manometer which fixes to the >outlet of a humidifer chamber. There is a little hole on the manometer, >right at the point at which it connects to the chamber, which simulates the >exhaust of the mask (presumably). There is one tube which sticks up – the >water rises up this tube and a reading is taken. Interestingly, I noticed >that when they sealed the exhaust on the manometer, the pressure went *down* >about 0.5cm. (and returned to it’s original level when the seal was removed >again). >I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & >Paykel HC221 – I now have the next model which is quieter). The readout >shows 10.0 this time. I just bet that when I get home and measure it, it’ll >be at least a cm less than my prescription again. >Any ideas why this discrepancy is occurring? Is there something wrong with >the way I am measuring the pressure? They said they didn’t have the >equipment to measure the pressure at my mask. >If it makes any difference, I am in Australia. >Joe.

Response:

Norm, Joe: Please search the Google archives for postings from Terry Bliss on exactly this subject. There is some good info in those threads. regards, eric pearson db2e…@nospammindspring.com – Hide quoted text — Show quoted text -On Sun, 3 Aug 2003 09:25:47 +1000, "Joe" <j…@nowhere.com> wrote: >"NormC" <no…@socal.rr.com> wrote in message >news:3F2C184C.4020206@socal.rr.com… >> How do you seal the main nose opening? >By pressing the mask down on a flat surface. I have also tried measuring the >pressure with the mask on my face, while I am holding my breath – same >result. >> > leave the exhale exhaust open, and dunk the tube >> > (fixed to a ruler) into a tall container of water, and note the point at >> > which the bubbles just stop >> Are you an engineer? <g> >Yes However, I didn’t devise this myself – I learnt about this by >searching the archives of this forum. >> > They have this simple water based manometer which fixes to the >> > outlet of a humidifer chamber. There is a little hole on the manometer, >> > right at the point at which it connects to the chamber, which simulates >the >> > exhaust of the mask (presumably). There is one tube which sticks up – >the >> > water rises up this tube and a reading is taken. >> So neither the tube/hose, you, or your mask were in the >> ‘circuit’, right? >Correct. However they did try connecting a hose between the CPAP machine and >the humidifer, but that didn’t change the result. (their manometer always >connects directly to the outlet of the humidifier, which is a Fisher & >Paykel) >The manometer they use is this shown here: >http://www.cpap-pro.net/mano.htm >> > Interestingly, I noticed >> > that when they sealed the exhaust on the manometer, the pressure went >*down* >> > about 0.5cm. (and returned to it’s original level when the seal was >removed >> > again). >> That’s more than interesting. Seems to defy the laws of physics, >> let alone the laws of fluid dynamics. Do you have any >> explanation for this? >No, I don’t. It’s puzzling. >> > I’ve exchanged my CPAP machine today for a newer model. (I had the >Fisher & >> > Paykel HC221 – I now have the next model which is quieter). The readout >> > shows 10.0 this time. I just bet that when I get home and measure it, >it’ll >> > be at least a cm less than my prescription again. >> > Any ideas why this discrepancy is occurring? >> My first guess would be that the resistance to flow, from the >> tube/hose and mask results in a .5 cm drop. >Even if that is the case, 0.5cm is only half of the difference. They are >setting it to more than a 1cm less than my prescription. (if I’m measuring >properly) >> > Is there something wrong with >> > the way I am measuring the pressure? >> Looks great to me. >Thanks. >I think my next step will be to take it to my hospital and ask them "what >prescription is this unit currently set to?". Should be interesting. (I know >they have manometers which can be connected to the mask, if required). I’ll >offer to let them measure it with my tube and mask, but they may say they >don’t need any of that to measure the prescription. >Joe.

Response:

Tal wrote: >>If you happened to catch all of the stuff in the archives on >>setting pressures, we never did reach any conclusions as to >>EXACTLY how the prescribed pressure should be set. > seems to me that the BEST way to set the pressure is to use the machine you > will haev when you go to your titration……then it doesn’t matter what the > number is…..all that matters is that that was what best suited your > needs……..of course, i realise this isn’t at all practical LOL

My concern has always been that it be tested under the most realistic operation possible, particularly the first time. My pressure requirement from sleep center titration is 12 cm H20. I have no idea if putting a manometer on my blower and setting it to 12 will provide me with 12 cm when I put on the hose and mask and put it on my face. It has to be a lower pressure, but we still don’t know how much lower. It may be a very small difference, but, then again, until we know, we don’t know.

Response:

- Hide quoted text — Show quoted text -NormC wrote: > Tal wrote: >>> If you happened to catch all of the stuff in the archives on >>> setting pressures, we never did reach any conclusions as to >>> EXACTLY how the prescribed pressure should be set. >> seems to me that the BEST way to set the pressure is to use the >> machine you >> will haev when you go to your titration……then it doesn’t matter >> what the >> number is…..all that matters is that that was what best suited your >> needs……..of course, i realise this isn’t at all practical LOL > My concern has always been that it be tested

"tested" should be "set" – Hide quoted text — Show quoted text -> under the most realistic > operation possible, particularly the first time. > My pressure requirement from sleep center titration is 12 cm H20. I have > no idea if putting a manometer on my blower and setting it to 12 will > provide me with 12 cm when I put on the hose and mask and put it on my > face. It has to be a lower pressure, but we still don’t know how much > lower. It may be a very small difference, but, then again, until we > know, we don’t know.

Response:

"Kit" <ksm…@nospam.com> wrote in message

news:3f2c6afa$0$15132$afc38c87@news.optusnet.com.au… > Are you in Sydney BAC? > The F&P rep who services this area is terrific. He gave me a F&P manometer & > showed me how to set the pressure on my machine as part of my battle with > wind.

Yes, I am. I might try to get one of those Fisher & Paykel manometers myself. Even if I have to buy one they don’t appear to be very expensive. (I’ve seen a price on the web for about US$21.00) Thanks, Joe.

Response:

"NormC" <no…@socal.rr.com> wrote in message

news:3F2C4F56.3010906@socal.rr.com… > > By pressing the mask down on a flat surface. I have also tried measuring the > > pressure with the mask on my face, while I am holding my breath – same > > result. > You mean the pressure change, right? What did the pressure > measure with the mask on your face when you were breathing.

Not sure what you mean by "pressure change". I just meant "pressure". I.e, the static pressure that results when I am holding my breath, with the mask on my face. I haven’t done any careful testing when I am breathing, but it seems that the pressure drops a bit when inhaling (about 0.5cm or so I think), and rises a bit when exhaling. This seems logical. (I found a post in the archive which suggests that this is normal, too) Joe. > I remember reading something similar, but it sure sounded more > complicated than your description. Oh well, I had cognition > problems before sleep apnea <g>.

No, you may be thinking of the "U" type water manometer, which is more complicated. I haven’t bothered making one of them yet. > So, in this case only you and your mask were not in the circuit, > right?

Correct. > > The manometer they use is this shown here: > > http://www.cpap-pro.net/mano.htm > Why no price?

I have no idea. I merely found that web page with a search. Here’s a price: http://www.etrode.com/moreinfo.cfm/Product_ID/19865&CFID=1598325&CFTO… > There seems to be a little bit of a rule-of-thumb for a newbie > who doesn’t seem to be feeling better, to up the pressure 2 cm. > I’ve always wondered if it was a matter of not setting the > pressure correctly in the first place. > Please keep us posted. This could be a very important matter.

Yes, they all do seem to think that it’s common to increase the pressure a bit for a newbie. I mentioned that I was waking up after a few hours (between 2 and 3am) for no apparent reason, and they said I might need a pressure increase. (this is despite the fact that I never used to wake up during the night, without CPAP). This waking up has almost disappeared now, and it doesn’t seem to make any difference what my pressure is. I’ll be sure to keep you posted, yes. One idea I have is that they are not positioning the manometer tube properly, relative to the water height, before they turn the CPAP machine on. Seems unlikely though, unless the technician is *very* inexperienced, which didn’t seem to be the case. Joe.

Response:

"Joe" <j…@nowhere.com> wrote in message

news:3f2c74fc$1@duster.adelaide.on.net… – Hide quoted text — Show quoted text -> "Kit" <ksm…@nospam.com> wrote in message > news:3f2c6afa$0$15132$afc38c87@news.optusnet.com.au… > > Are you in Sydney BAC? > > The F&P rep who services this area is terrific. He gave me a F&P manometer > & > > showed me how to set the pressure on my machine as part of my battle with > > wind. > Yes, I am. I might try to get one of those Fisher & Paykel manometers > myself. Even if I have to buy one they don’t appear to be very expensive. > (I’ve seen a price on the web for about US$21.00) > Thanks, > Joe.

Well, if you’d like to give me a clue to your real email address <bg> I’ll send you the contact details. Or send me an email… Kit <off to chilly Melbourne soon – brrrr) — To reply replace nospam with kamuzz

Response:

"Joe" <j…@nowhere.com> wrote in message

Joe Are you in Sydney BAC? The F&P rep who services this area is terrific. He gave me a F&P manometer & showed me how to set the pressure on my machine as part of my battle with wind. Cheers Kit — To reply replace nospam with kamuzz

Response:

Joe wrote: > "NormC" <no…@socal.rr.com> wrote in message > news:3F2C184C.4020206@socal.rr.com… >>How do you seal the main nose opening? > By pressing the mask down on a flat surface. I have also tried measuring the > pressure with the mask on my face, while I am holding my breath – same > result.

You mean the pressure change, right? What did the pressure measure with the mask on your face when you were breathing. >>>leave the exhale exhaust open, and dunk the tube >>>(fixed to a ruler) into a tall container of water, and note the point at >>>which the bubbles just stop >>Are you an engineer? <g> > Yes However, I didn’t devise this myself – I learnt about this by > searching the archives of this forum.

I remember reading something similar, but it sure sounded more complicated than your description. Oh well, I had cognition problems before sleep apnea <g>. – Hide quoted text — Show quoted text ->>>They have this simple water based manometer which fixes to the >>>outlet of a humidifer chamber. There is a little hole on the manometer, >>>right at the point at which it connects to the chamber, which simulates > the >>>exhaust of the mask (presumably). There is one tube which sticks up – > the >>>water rises up this tube and a reading is taken. >>So neither the tube/hose, you, or your mask were in the >>’circuit’, right? > Correct. However they did try connecting a hose between the CPAP machine and > the humidifer, but that didn’t change the result.

So, in this case only you and your mask were not in the circuit, right? > (their manometer always > connects directly to the outlet of the humidifier, which is a Fisher & > Paykel) > The manometer they use is this shown here: > http://www.cpap-pro.net/mano.htm

Why no price? – Hide quoted text — Show quoted text ->>>Interestingly, I noticed >>>that when they sealed the exhaust on the manometer, the pressure went > *down* >>>about 0.5cm. (and returned to it’s original level when the seal was > removed >>>again). >>That’s more than interesting. Seems to defy the laws of physics, >>let alone the laws of fluid dynamics. Do you have any >>explanation for this? > No, I don’t. It’s puzzling. >>>I’ve exchanged my CPAP machine today for a newer model. (I had the > Fisher & >>>Paykel HC221 – I now have the next model which is quieter). The readout >>>shows 10.0 this time. I just bet that when I get home and measure it, > it’ll >>>be at least a cm less than my prescription again. >>>Any ideas why this discrepancy is occurring? >>My first guess would be that the resistance to flow, from the >>tube/hose and mask results in a .5 cm drop. > Even if that is the case, 0.5cm is only half of the difference. They are > setting it to more than a 1cm less than my prescription. (if I’m measuring > properly) >>>Is there something wrong with >>>the way I am measuring the pressure? >>Looks great to me. > Thanks. > I think my next step will be to take it to my hospital and ask them "what > prescription is this unit currently set to?". Should be interesting. (I know > they have manometers which can be connected to the mask, if required).

If you happened to catch all of the stuff in the archives on setting pressures, we never did reach any conclusions as to EXACTLY how the prescribed pressure should be set. There seems to be a little bit of a rule-of-thumb for a newbie who doesn’t seem to be feeling better, to up the pressure 2 cm. I’ve always wondered if it was a matter of not setting the pressure correctly in the first place. Please keep us posted. This could be a very important matter. TIA – Hide quoted text — Show quoted text -> I’ll > offer to let them measure it with my tube and mask, but they may say they > don’t need any of that to measure the prescription. > Joe.

Response:

> If you happened to catch all of the stuff in the archives on > setting pressures, we never did reach any conclusions as to > EXACTLY how the prescribed pressure should be set.

seems to me that the BEST way to set the pressure is to use the machine you will haev when you go to your titration……then it doesn’t matter what the number is…..all that matters is that that was what best suited your needs……..of course, i realise this isn’t at all practical LOL — Beth in Australia =================== FAQ for alt.support.sleep-disorder can be found here http://talhost.net/sleep Newsgroup Archives http://talhost.net/sleep/archives.htm this site is a work in progress – feel free to submit info/articles Remove my name to reply

Response:

"NormC" <no…@socal.rr.com> wrote in message

news:3F2C184C.4020206@socal.rr.com… > How do you seal the main nose opening?

By pressing the mask down on a flat surface. I have also tried measuring the pressure with the mask on my face, while I am holding my breath – same result. > > leave the exhale exhaust open, and dunk the tube > > (fixed to a ruler) into a tall container of water, and note the point at > > which the bubbles just stop > Are you an engineer? <g>

Yes However, I didn’t devise this myself – I learnt about this by searching the archives of this forum. > > They have this simple water based manometer which fixes to the > > outlet of a humidifer chamber. There is a little hole on the manometer, > > right at the point at which it connects to the chamber, which simulates the > > exhaust of the mask (presumably). There is one tube which sticks up – the > > water rises up this tube and a reading is taken. > So neither the tube/hose, you, or your mask were in the > ‘circuit’, right?

Correct. However they did try connecting a hose between the CPAP machine and the humidifer, but that didn’t change the result. (their manometer always connects directly to the outlet of the humidifier, which is a Fisher & Paykel) The manometer they use is this shown here: http://www.cpap-pro.net/mano.htm > > Interestingly, I noticed > > that when they sealed the exhaust on the manometer, the pressure went *down* > > about 0.5cm. (and returned to it’s original level when the seal was removed > > again). > That’s more than interesting. Seems to defy the laws of physics, > let alone the laws of fluid dynamics. Do you have any > explanation for this?

No, I don’t. It’s puzzling. > > I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & > > Paykel HC221 – I now have the next model which is quieter). The readout > > shows 10.0 this time. I just bet that when I get home and measure it, it’ll > > be at least a cm less than my prescription again. > > Any ideas why this discrepancy is occurring? > My first guess would be that the resistance to flow, from the > tube/hose and mask results in a .5 cm drop.

Even if that is the case, 0.5cm is only half of the difference. They are setting it to more than a 1cm less than my prescription. (if I’m measuring properly) > > Is there something wrong with > > the way I am measuring the pressure? > Looks great to me.

Thanks. I think my next step will be to take it to my hospital and ask them "what prescription is this unit currently set to?". Should be interesting. (I know they have manometers which can be connected to the mask, if required). I’ll offer to let them measure it with my tube and mask, but they may say they don’t need any of that to measure the prescription. Joe.

Response:

Sure enough, I measured about 9.8cm when I got the unit home! Also, I note that when I create a leak, the pressure goes *down*, not up. I’m confused as to why the pressure went down when they covered the exhaust port on their manometer. I got them to try using a hose between the CPAP unit and the humidifier chamber, but the pressure was the same. Perplexed…. I’ve again adjusted my pressure – the readout on the CPAP machine is now 11.5, with a measured pressure of 11cm. (I can probably only measure to about 0.3cm accuracy with my setup I suppose) Joe.

Response:

Joe wrote: > The place where I got my CPAP machine measures the pressure, rather than > simply relying on the readout on the CPAP machine itself.

That’s good news. > I’ve noticed > however that the pressure I measure at home, at the mask, is lower than my > prescription. For example, the unit was set for a readout of 10.5cm, my > prescription is for 11cm, and I measured only about 10cm at the mask. To get > a measured pressure of 11, I had to adjust it such that the readout was > about 11.5. (the readout only has a precision of 0.5cm). The method I use to > measure the pressure is to attach a tube to the oxygen port of my mask, seal > the main nose opening,

How do you seal the main nose opening? > leave the exhale exhaust open, and dunk the tube > (fixed to a ruler) into a tall container of water, and note the point at > which the bubbles just stop

Are you an engineer? <g> > I raised this issue with them, and they showed me how they do the > measurement. They have this simple water based manometer which fixes to the > outlet of a humidifer chamber. There is a little hole on the manometer, > right at the point at which it connects to the chamber, which simulates the > exhaust of the mask (presumably). There is one tube which sticks up – the > water rises up this tube and a reading is taken.

So neither the tube/hose, you, or your mask were in the ‘circuit’, right? > Interestingly, I noticed > that when they sealed the exhaust on the manometer, the pressure went *down* > about 0.5cm. (and returned to it’s original level when the seal was removed > again).

That’s more than interesting. Seems to defy the laws of physics, let alone the laws of fluid dynamics. Do you have any explanation for this? > I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & > Paykel HC221 – I now have the next model which is quieter). The readout > shows 10.0 this time. I just bet that when I get home and measure it, it’ll > be at least a cm less than my prescription again. > Any ideas why this discrepancy is occurring?

My first guess would be that the resistance to flow, from the tube/hose and mask results in a .5 cm drop. > Is there something wrong with > the way I am measuring the pressure?

Looks great to me. > They said they didn’t have the > equipment to measure the pressure at my mask.

Does this mean such equipment exists and they just don’t have it? > If it makes any difference, I am in Australia.

Joe – You might want to take a look in the archives. Every-once-in-a-while we get into a discussion about how pressures ARE set up and how they SHOULD BE set up.

Response:

Joe wrote: > Sure enough, I measured about 9.8cm when I got the unit home! Also, I note > that when I create a leak, the pressure goes *down*, not up. I’m confused as > to why the pressure went down when they covered the exhaust port on their > manometer.

So, it goes down when they cover the exhaust port. It goes down when you create an opening/leak. At least what happens to you makes sense. <g> > I got them to try using a hose between the CPAP unit and the humidifier > chamber, but the pressure was the same.

My first guess regarding this is that all hoses are not identical. It would be of great value if you could take your hose in next time and see what you can determine. > Perplexed…. > I’ve again adjusted my pressure – the readout on the CPAP machine is now > 11.5, with a measured pressure of 11cm. > (I can probably only measure to about 0.3cm accuracy with my setup I > suppose)

Thanks for the additional info related to pressure and pressure setting.

Response:

The place where I got my CPAP machine measures the pressure, rather than simply relying on the readout on the CPAP machine itself. I’ve noticed however that the pressure I measure at home, at the mask, is lower than my prescription. For example, the unit was set for a readout of 10.5cm, my prescription is for 11cm, and I measured only about 10cm at the mask. To get a measured pressure of 11, I had to adjust it such that the readout was about 11.5. (the readout only has a precision of 0.5cm). The method I use to measure the pressure is to attach a tube to the oxygen port of my mask, seal the main nose opening, leave the exhale exhaust open, and dunk the tube (fixed to a ruler) into a tall container of water, and note the point at which the bubbles just stop I raised this issue with them, and they showed me how they do the measurement. They have this simple water based manometer which fixes to the outlet of a humidifer chamber. There is a little hole on the manometer, right at the point at which it connects to the chamber, which simulates the exhaust of the mask (presumably). There is one tube which sticks up – the water rises up this tube and a reading is taken. Interestingly, I noticed that when they sealed the exhaust on the manometer, the pressure went *down* about 0.5cm. (and returned to it’s original level when the seal was removed again). I’ve exchanged my CPAP machine today for a newer model. (I had the Fisher & Paykel HC221 – I now have the next model which is quieter). The readout shows 10.0 this time. I just bet that when I get home and measure it, it’ll be at least a cm less than my prescription again. Any ideas why this discrepancy is occurring? Is there something wrong with the way I am measuring the pressure? They said they didn’t have the equipment to measure the pressure at my mask. If it makes any difference, I am in Australia. Joe.