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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!
Last edited by meelika; 03/12/18 11:12 AM.
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Super Hero
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Super Hero
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No doubt your professor is right! 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!
If you don't inspect ... don't expect.
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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
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Joined: Feb 2004
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Super Hero
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Super Hero
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Which monitor are you using ... and which simulator? And what settings are being used at both?
If you don't inspect ... don't expect.
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Joined: Jun 2009
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Philosopher
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Philosopher
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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!!
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Super Hero
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Super Hero
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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. 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.
If you don't inspect ... don't expect.
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Philosopher
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Philosopher
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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!!
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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.
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Super Hero
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Super Hero
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The error occured only when the RR and HR were the same value ...
Please give our Best Regards to the professor! 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. 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.
If you don't inspect ... don't expect.
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Joined: Feb 2004
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Super Hero
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Super Hero
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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). Does anyone have any clues? Lastly, here's one that hopefully all can enjoy (I'll have a read of it myself later). * 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)!
If you don't inspect ... don't expect.
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