Pressure Transducer

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Postby Neil » Mon Nov 09, 2009 1:24 pm

Like all these things, best approach is a process of elimination. Swap out one component at a time, just one. In this case it seems to be the PTAF Lite unit itself, although you don't make it clear if that was the only thing you swapped or not.

I guess one thing I don't understand is--although again it's not clear if this is exactly what happened--why this troubleshooting was done at night rather than during the day. To my mind, if you know something is wrong in a system then the time to try and resolve it is during the day when you're not relying on it working to collect data from patients.

Just some thoughts; probably not overly helpful. :)

Neil
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Postby slowdavesleep » Mon Nov 09, 2009 9:54 pm

Remember when you changed that transducer you did several things at once, including reconnecting the cannula to the transducer and unplugging and replugging the pins. Or to put it another way minimize the variables being manipulated at one time in your series of mini-experiments.

Ohh and the ptaf lite has no batteries because it is a piezo-electric (not piezo-resistive) pressure transducer. It also has a gain switch on the side. I've also noticed that the material that the nasol-oral cannulas are made out of varies within the same manufacturer. Sometimes they use a thinner tubing that produces a far worse signal (I forget which company).

Protec has been really good about switching out transducers we suspect are bad for us.
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Postby Rick » Mon Nov 09, 2009 11:39 pm

Hey 'Slim, Did not get whether you are using nasal or nasal oral cannulas.

On a personal note I detest nasal oral cannulas, expensive and now that the AASM has asked for thermal oronasal and nasal pressure, no need to try nasal oral cannulas. The problem is that if the oral prong is not sealed, in some models, the pressure from the nasal prongs will go out that prong and no pressure is read by the transducer.

Changing the unit during a study changes more than just the pressure transducer, one cannot help but rouse the patient, who moves their head, changing the position of the cannula. Just like the transducer with batteries, out of frustration a tech will go in the room and change the bateries, voila, signal improves, next time there is a problem that is the first thing tried.

Okay, off the soapbox now.
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Postby DBradley » Tue Nov 10, 2009 10:48 pm

This is getting to be a very interesting discussion so I thought that I would jump in with my 2 cents.

It looks like we are discussing three separate issues here:

1. How to easily troubleshoot a Pressure/Flow Signal.
2. Piezo electric vs. Piezo resistive(silicon) pressure sensors.
3. Which is better Nasal/Oral or Nasal only cannulae?

1. How to easily troubleshoot a Pressure/Flow Signal.
As Neil previously said breaking down your system and swapping sections is the logical way to deal with effectively troubleshooting. First thing I check is placement of the cannula. This can also include checking inside the nose to see if the prongs of the cannula are being occluded and that the nasal and oral openings are aligned proper. Then check that the pressure sensor is operating properly. You can check the status indicator for low battery power on silicon based pressure sensors. I would then do a simple test with a multi meter or if you trust that you have set your PSG system up properly use that. Place your thumb over the pressure port and squeeze in and out. This is very similar to actual breathing. Lastly ensure that your PSG system is setup correctly. This includes filters, gains, and sampling frequencies.

2. Piezo electric vs, Piezo resistive(silicon) pressure sensors.
This is one of my several pet peeves. Piezo electric material does not have the frequency response that we require in measuring the pressures that are associated with breathing. They are incapable of showing accurate flow limitation, or maintaining a proper baseline. The biggest advantage with a Piezo electric pressure sensor is the fact that they do not require a battery. On the other hand a Silicon pressure sensor has an excellent frequency response. We can accurately see flow limitation, calibrate them to give us accurate pressures and with certain versions use them as for measuring esophageal pressures. They show a proper baseline so inhalation and exhalation look proper.

3. Which is better Nasal/Oral or Nasal only cannulae?
The AASM scoring manual states only use Nasal cannulae. I understand the issues as to why they would opt for this. I do wonder how one deals with oral only flow limitation (oral hypopneas)? Do we not want t know what is going on with our patients. Ideally we want to know that amount of air that is moving in and out of the patient. Braebon has spent many years on this issue. We have looked at how to design a cannula/pressure sensor that can give an accurate signal for both nasal and oral breathing. Most oral/nasal cannulae have a common chamber right under the nose where the nasal and oral inputs merge. This allows the pressure wave to easily migrate out the nasal prongs and not proceed down the tube to the pressure sensor. The addition of using almost the same diameter tubing for nasal and oral openings does not yield a signal that is similarly proportional for both nasal and oral airflows. Braebon has developed our PureFlow cannulae to generate almost similar waveforms for both oral and nasal breathing events.

Getting an accurate total picture of what is actually going on with your patient is paramount. Patient safety is always first.

I trust that I was not too long winded and that this information is of some assistance.

Don
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Postby "Montana Slim" » Wed Nov 11, 2009 12:25 am

zack wrote:What brand and model canula are using?


On an off topic side note, I remember in seventh grade when I or some one would get suspended, the other kids would think it was so cool and would bring up the kids who where kicked out all the time to try to get a rise out of the grown ups. In 7th grade it was called being a 7th grader on the internet its called trolling I think, it dosnt bother me except I'll be happy when it gets old and I don't have to read through silly stuff in non miscellaneous threads to get to interesting stuff :]


Dispomed--this is the type of nasal canulas we are using.
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nasal cannula

Postby stars » Thu Nov 12, 2009 2:00 am

Well Rick I use you cannula many years.But last few months moreand more cannula need replace.Just not pick up signal from start.
I think your company need increase control prodact standart.
Just last week I trash at list 5 cannula.Just no signal flat from start.
open another bag look like same and signal ok????? And this is exactly cannula not protech-devise itself
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Re:

Postby zack » Tue Jul 22, 2014 2:11 am

DBradley wrote:This is getting to be a very interesting discussion so I thought that I would jump in with my 2 cents.

It looks like we are discussing three separate issues here:

1. How to easily troubleshoot a Pressure/Flow Signal.
2. Piezo electric vs. Piezo resistive(silicon) pressure sensors.
3. Which is better Nasal/Oral or Nasal only cannulae?

1. How to easily troubleshoot a Pressure/Flow Signal.
As Neil previously said breaking down your system and swapping sections is the logical way to deal with effectively troubleshooting. First thing I check is placement of the cannula. This can also include checking inside the nose to see if the prongs of the cannula are being occluded and that the nasal and oral openings are aligned proper. Then check that the pressure sensor is operating properly. You can check the status indicator for low battery power on silicon based pressure sensors. I would then do a simple test with a multi meter or if you trust that you have set your PSG system up properly use that. Place your thumb over the pressure port and squeeze in and out. This is very similar to actual breathing. Lastly ensure that your PSG system is setup correctly. This includes filters, gains, and sampling frequencies.

2. Piezo electric vs, Piezo resistive(silicon) pressure sensors.
This is one of my several pet peeves. Piezo electric material does not have the frequency response that we require in measuring the pressures that are associated with breathing. They are incapable of showing accurate flow limitation, or maintaining a proper baseline. The biggest advantage with a Piezo electric pressure sensor is the fact that they do not require a battery. On the other hand a Silicon pressure sensor has an excellent frequency response. We can accurately see flow limitation, calibrate them to give us accurate pressures and with certain versions use them as for measuring esophageal pressures. They show a proper baseline so inhalation and exhalation look proper.

3. Which is better Nasal/Oral or Nasal only cannulae?
The AASM scoring manual states only use Nasal cannulae. I understand the issues as to why they would opt for this. I do wonder how one deals with oral only flow limitation (oral hypopneas)? Do we not want t know what is going on with our patients. Ideally we want to know that amount of air that is moving in and out of the patient. Braebon has spent many years on this issue. We have looked at how to design a cannula/pressure sensor that can give an accurate signal for both nasal and oral breathing. Most oral/nasal cannulae have a common chamber right under the nose where the nasal and oral inputs merge. This allows the pressure wave to easily migrate out the nasal prongs and not proceed down the tube to the pressure sensor. The addition of using almost the same diameter tubing for nasal and oral openings does not yield a signal that is similarly proportional for both nasal and oral airflows. Braebon has developed our PureFlow cannulae to generate almost similar waveforms for both oral and nasal breathing events.

Getting an accurate total picture of what is actually going on with your patient is paramount. Patient safety is always first.

I trust that I was not too long winded and that this information is of some assistance.

Don


Hello, I have been asking around and searching about #3. I see its very common for techs to prefer nasal only cannulas and I know the AASM only requires nasal. But I have the same question...if we use nasal only are we missing out on oral flow limitation? Or...honestly, is it better to pick up oral breathing followed by a desat/ arousal that- using a nasal only canula- can be counted as a hypopnea? Or would that not happen? Seems like it could...
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Re: Pressure Transducer

Postby bduce » Tue Jul 22, 2014 11:01 am

The oral portion of an oronasal cannula does not give you that much of a signal.
The nasal cannula is measuring differential pressure (flow). To get differential pressure you need a pressure drop to occur. This happens between the nares and the atmosphere where the nares has an increased resistance to flow.
At the mouth the resistance to flow is very small small and thus you do not get much differential pressure between the mouth opening and the atmosphere.
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Re: Pressure Transducer

Postby RBonato » Tue Jul 22, 2014 11:18 am

@bduce

"Oral portion doesn't give you much of a signal" will vary by equipment used. In our comparison of the BRAEBON oronasal cannula vs others we found substantially better signal because of (a) larger oral surface area to capture oral flow and (b) no common chamber to lose oral flow pressure into the nares (or vice versa). Ideally, both oronasal thermal & pressure gives the best quality information but I see people doing lots of poor quality lab and home studies using only nasal pressure and then scoring apneas that could actually be hypopneas. But then again they don't care about quality as long as someone pays.
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Re: Pressure Transducer

Postby bduce » Tue Jul 22, 2014 12:45 pm

@rbonato
you are correct. apologies. I forgot about your capture device. I was thinking of the salter cannulae that I trialled some years back which was basically two nasal cannulae piggy backed to each other (one upside to the other). Signals were less than optimal to put it mildly.

As for the remark about the nasal pressure only and apnoeas vs hypopnoeas, I'm a bit less strident in that department. Don't get me wrong we use both nasal cannula and thermal sensor on every study in my lab but I'm not sure how important it is to define perfectly an apnoea and a hypopnoea. Since we do not treat patients differently (at the moment) if they primarily have apnoeas or hypopnoeas, the value of properly differentiating between a hypopnoea and an apnoea is not going affect outcomes. (Of course this logic is tempered by the fcat the AHI method is a rather poor way of determining OSA severity).
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Re: Pressure Transducer

Postby zack » Wed Jul 30, 2014 3:08 am

bduce wrote:...I'm not sure how important it is to define perfectly an apnoea and a hypopnoea. ...


So is this really the only advantage of using nasal vs nasal/oral cannulas?
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