Home Articles Downloads Forum Products Services Seminar Contact
Previous Thread
Next Thread
Print Thread
Rate Thread
Patientmonitor can't show correct respiration rate #73810
Joined: Nov 2018
Posts: 5
Estonia
M
meelika Online content OP
Newbie
meelika  Online Content OP
Newbie
M

Joined: Nov 2018
Posts: 5
Estonia
Hello! I'm new to this forum, also just a student studying BME and MP. We had an assignment where we had to check whether ECG patient monitor works correctly or not. We used a simulator for measurements. Whenever we gave heart rate and respiration rate the same value on the simulator (for example: HR=50 and RR=50) the monitor showed heart rate value but respiration rate value was 0. What could cause such 'bug'? The respiration sine wave was there, but it just didn't show the value. I can't seem to figure out this thing that supposedly should be obvious according to my professor.
Thanks for the answers! smile

Last edited by meelika; .
Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73812
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

No doubt your professor is right! smile

50 is very (way too) high ... whilst a HR of 50 is low. Are you testing the monitor alarms?

How does the monitor you are using measure RR?

Hint: look up "impedance pneumography" versus "respiration thermistor". Also tachypnea!

Re: Patientmonitor can't show correct respiration rate [Re: Geoff Hannis] #73828
Joined: Nov 2018
Posts: 5
Estonia
M
meelika Online content OP
Newbie
meelika  Online Content OP
Newbie
M

Joined: Nov 2018
Posts: 5
Estonia
Hmm, so I'm thinking the monitor has a hard time distinguishing between the voltages that the simulator gives out?

I do understand that the monitor measures impedance change and thermistor measures the temperature of the air we breathe out.

I figure this should be obvious, but I'm confused as hell right now laugh

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73829
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

Which monitor are you using ... and which simulator?

And what settings are being used at both? think

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73830
Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
DaveC in Oz Offline
Philosopher
DaveC in Oz  Offline
Philosopher

Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
What you are seeing here may in fact be the correct function of the monitor.

Measuring respiration using impedance changes is a difficult thing for a machine to do. Some times the measurement can be distorted by the system seeing changes in impedance caused not by the movement of the chest but rather by the volume of blood in the heart. This can cause monitors to read the respiration rate incorrectly (there is a name for this but my mind has gone blank for the moment). Some monitoring systems deal with this by removing the resp rate is the heart rate and resp rate are within 10% of each other. Try setting a more realistic rate for both HR and RR (ie HR=80 and RR=20) and see if it picks it correctly. If so then that is what the issue was.

Dave


Thoughts and information provided on this forum are mine and mine alone and do not necessarily reflect the policy of NSW Health. They may also be complete bollocks!!
Re: Patientmonitor can't show correct respiration rate [Re: DaveC in Oz] #73831
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

I think that the stimulator HR and RR settings being the same was what Meelika's professor was hinting at, Dave. As well as them being outside of normal values, hopefully. smile

Meanwhile, shallow breathing (in real patients, but not a simulator) can confuse a (impedance pneumography) signal - in that cardiac signals can get counted as respiration cycles. And as we know, RR displays can also easily be disturbed - even more than ECG signals - by patients moving about!

Were you thinking of pulsus paradoxus?

Here's a (hopefully useful) thesis* for students of this interesting topic! Also this one.

* A bit old; but never mind.

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73832
Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
DaveC in Oz Offline
Philosopher
DaveC in Oz  Offline
Philosopher

Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
To quote from the manual for the old Marquette Solar 8000 monitors

Cardiac Artifact Alarm
The Cardiac Artifact Alarm alerts you to the fact that the respiration
rate is within 5% of the heart rate (over 30 consecutive breaths). If this
happens, the respiration program may be counting heartbeat artifact as
respiration. The Cardiac Artifact Alarm is an advisory alarm. The
message “ARTIFACT” is displayed in the respiration values window, and
a one-beep tone sounds.
There is no adjustable limit for this alarm, but you can turn it off and on.
WARNING
If the Cardiac Artifact Alarm is turned off, apnea events
may not be detected.
To turn the alarm off and on, select the CARDIAC ARTIFACT ALARM
option from the respiration menu. This is a direct action menu option.


(Ok, 5% not 10% but I was close.........)

So a similar way of dealing with this false reading may occur in other makes of monitors such as removing the RR altogether.


Thoughts and information provided on this forum are mine and mine alone and do not necessarily reflect the policy of NSW Health. They may also be complete bollocks!!
Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73833
Joined: Nov 2018
Posts: 5
Estonia
M
meelika Online content OP
Newbie
meelika  Online Content OP
Newbie
M

Joined: Nov 2018
Posts: 5
Estonia
First of all the equipment we had.
Monitor: HP Omnicare M1204A
Patient simulator: FLUKE Biomedical PS420

We had to test all the respiration rate options available on patient simulator (ranging from 0-120). The error occured only when the RR and HR were the same value, if for example HR=80 and RR=20, then there were no errors.

For me, it seems like the most probable cause is that the monitor can't give out the values when they're in the 5% range within each other. I could check that in theory, but I don't know/don't think the patient simulator had the option to adjust custom HRs and RRs. We were using the manual and it stated only the available RRs: 0, 15, 20, 30, 40, 60, 80, 100, 120 [rpm] (and about the same values for HR).

I am going to defend these labs tomorrow to my professor. If this is not the correct answer, I will find out nevertheless. smile

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73834
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

Originally Posted by meelika

The error occured only when the RR and HR were the same value ...


Please give our Best Regards to the professor! smile

How's it done? You would need to dig into the Service Manual of the monitor. Hopefully there are some circuit diagrams and even an explanation in there. Otherwise, maybe you could figure out a method yourself. Filtering plus some sort of sampling (and) or comparator circuit(s), I wonder. There are plenty of such circuits available on the web.

Also, I notice there are a couple of RESP adjustments on the monitor that you could take a look at.

Lastly, to get back into the professor's good books, perhaps you could interest him in this. He might be interested in this one, as well.

Good luck with your studies. smile

I have just checked the PS-420 manual. Orginally from Metron, this nice piece of test kit has now been discontinued by Fluke. The Respiration settings look comprehensive enough; including Baseline Impedance, also Apnea [sic] - so you might like to have a play with those as well.

Re: Patientmonitor can't show correct respiration rate [Re: DaveC in Oz] #73835
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

Interesting, Dave - not that I would call the Marquette Solar 8000 old myself, of course.

I have had a dig around on line to see if I could find some examples of "how it's done". These days I suspect that the clever stuff is carried out inside custom chips* - using algorithms, Fourier analysis and such boffin-related wizardry.

I guess what we really need is a reference to the first monitor that ever included this feature, then take a look at the circuits it used!

Or failing that, one of the biomed text books (mine have all gone now). frown

Does anyone have any clues? think

Lastly, here's one that hopefully all can enjoy (I'll have a read of it myself later). smile

* Such as AVR. See here ... and here. I am intrigued that this guy (Jim Lynch) was involved with the development of the Mennen Horizon 2000 - the first colour patient monitor (a hefty beast, if ever there was one) - and one that used Motorola 68000 processors (and sometimes spotted these days on eBay)!

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73842
Joined: Nov 2018
Posts: 5
Estonia
M
meelika Online content OP
Newbie
meelika  Online Content OP
Newbie
M

Joined: Nov 2018
Posts: 5
Estonia
So the final answer is - we used only 3 electrodes to measure 2 things at the same time (heart rate and respiration rate). smile If we wanted to avoid that, we would have to connect more electrodes to a simulator (if it is possible).

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73847
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

But ...

Originally Posted by meelika

The error occured only when the RR and HR were the same value, if for example HR=80 and RR=20, then there were no errors.


So something doesn't sound right, there.

Pity I'm not there to have a go myself; I'm not sure exactly how the PS-420 simulator works (whether it can output two - both - signals simultaneously).

But bear in mind that on a Real Patient, three well-positioned electrodes will (should) give both ECG and RR. smile

Where - to which pins - have you got your three leads connected on the simulator? And does the LA/LL slide switch make any difference?

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73848
Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
DaveC in Oz Offline
Philosopher
DaveC in Oz  Offline
Philosopher

Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
Much as I hate to admit it but, I agree with Geoff. eek

There is no reason that having only a RA, LA, LL lead should cause this issue. This lead combination still allows for both leads I and II to be monitored and those are the two leads used for respiration monitoring.


Thoughts and information provided on this forum are mine and mine alone and do not necessarily reflect the policy of NSW Health. They may also be complete bollocks!!
Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73856
Joined: Nov 2018
Posts: 5
Estonia
M
meelika Online content OP
Newbie
meelika  Online Content OP
Newbie
M

Joined: Nov 2018
Posts: 5
Estonia
Sorry for delayed answer! End of the semester and lots of things to do smile Moving on..

Fair points are being made by both of you. I was confused myself when he told me this. I did at first offer him the 5% range possibility, but he shrugged it off.

RA, LA and LL were connected to accordingly (pins that were marked accordingly). I didnt check the LA/LL switch (the lab is now done and I can't really go and check it), but we used LL position. Also, someone did switch the LA/LL switch, but I don't remember why it came up and would it be relevant to this case. I will check with him and let you know later!

However, let's not forget the fact that I'm still a first year student (in masters) and there could be things I myself am missing here and can't deliver. :P

On a site note: the monitor did show both signals (HR waves and RR sinewave), but it just didn't show the RR value, which means that the signal was measured, right?

Edit: The guy who tried switching the LA/LL switch said the respiration wave flatlined after switching to LA.

Last edited by meelika; .
Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73857
Joined: Feb 2004
Posts: 13,604
the path less trodden
Geoff Hannis Offline
Super Hero
Geoff Hannis  Offline
Super Hero

Joined: Feb 2004
Posts: 13,604
the path less trodden

If the ECG and respiration waveforms were being correctly displayed, then the simulator must have been producing them; and your note about the LA/LL switch confirms this.

To be honest, I'm now having doubts about your professor. Has he taught you the lesson (given his explanation) yet? think

Re: Patientmonitor can't show correct respiration rate [Re: meelika] #73859
Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
DaveC in Oz Offline
Philosopher
DaveC in Oz  Offline
Philosopher

Joined: Jun 2009
Posts: 743
Coffs Harbour, NSW, Australia
Originally Posted by meelika


On a site note: the monitor did show both signals (HR waves and RR sinewave), but it just didn't show the RR value, which means that the signal was measured, right?

Edit: The guy who tried switching the LA/LL switch said the respiration wave flatlined after switching to LA.


The fact that the monitor showed the RR waveform means it was seeing it and should have been showing the rate you are correct in that. This makes me think again that it is because the HR and RR were the same but perhaps some investigation into how HP/Agilent/Philips do their resp measurement is worth a look. Are there tech/user manuals available on-line?

As to the second point, this is to be expected. If you switch from Lead II (RA to LL) to lead I (RA to LA) then you need to tell the monitor to look at the different lead as well. Unlike ECG monitoring where multiple leads are checked simultaneously resp monitoring looks at only a single lead at any one time.


Thoughts and information provided on this forum are mine and mine alone and do not necessarily reflect the policy of NSW Health. They may also be complete bollocks!!

Moderated by  DaveC in Oz, KM, RoJo 

Who's Online Now
5 registered members (Roma, Huw, Dustcap, meelika, 1 invisible), 641 guests, and 32 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums25
Topics10,306
Posts69,976
Members9,298
Most Online1,391
Mar 26th, 2018
Powered by UBB.threads™ PHP Forum Software 7.6.2