Uses of Pulse Oximeter in Rhythm Monitoring

[Jerry_NJ]

Most (all?) of you have seen the small clip-on-the-finger over a finger nail used in doctor offices to measure the Oxygen Saturation level in your blood (target 95% or better I believe).  These doctors don't have a pulse display on their units or simply prefer the manual method to measure pulse rate, which both the nurse and doctor do, the doctor of course also listens to my heart with a stethoscope.

It is difficult for me to feel my pulse (a blessing in many respects) and I have for years used a stethoscope to count my pulses, heart rate.  The only indication I have of the blood oxygen saturation is if I am dizzy or breathless more than what I recall as normal.  I have thought that it would be helpful to be able to measure the O2 level at those times and even to run a DIY sleep test (this in general would require a recording meter).

When I saw this type instrument with a combined HR and O2 plus a pulse intensity readout for under $25 delivered I ordered one.

Here's what I learned for my profile and what I have concluded about a number of aspects of my AFib condition on my physical being.  I compared/checked the device HR by counting my HR while using the clip on, good agreement.  I checked my wife who does not have any diagnosed heart conditions and found reaso6 nable readings and a smoother more uniform heart intensity readout than I got for myself with AFib.. as expected.  I take the intensity differences between her and me indicative, not quantitative even though it is provided via a 6 bar readout scale.  

I found my O2 consistently obove 95% even when I was feeling O2 starved, like when standing up quickly.  I also found my HR reasonable and in the 70s when resting and typically around 100 when in light physical activity.  

Now for sleeping, or really maximum rested times.  

I did not get a recording meter for $25, but as I wake up often during the night it is easy for me to clip the device on with minimum physical effort when I wake up.  Some interesting findings (to me) - I am on a normal release Metoprolol (BB) and Calcium CB which is taken at about 10:30 PM, so by 1:30 AM I am still in the fully medicated area of the BB concentration (half life of 4 hours assumed).  

Early in the morning (around 2 AM) I found my fully relaxed in bed HR as low as upper 50s and O2 levels as low as 90%.  Later in the morning (around 5 or 6 AM) I found my HR around 70, suggesting the BB had lost a considerable % of its strength (now in its 2nd half live, about 75% metabolized) and the O2 levels over 95%.  This seems reasonable and in fact during the day my seated and fully resting HR runs in the 70s to 80s.    The lower O2 level of 90%, which is the threshold of trouble as I understand, at 2 AM is a minor concern to me.  This many not be a trouble indicator under the condition of being under BB and CCB near full strength and just in/out of sleep resting state.  I continue to check and see if my results are consistent/repeated.

In any case I find having this testing device affordable and quick way to check my HR, and also get the O2 saturation  -  the value of the heart intensity readout is not clear, but does give me some concern... guess it is the variations I hear with the stethoscope.

[Jerry_NJ]

The reading I've done says "yes" to your question... the bone and finger do make a difference, and "stuff" like nail polish may prevent the device from working.  

I did the one calibration check I could make, the HR, I counted my pulse and over a period of time, 15 seconds minimum, and the count method gave a HR within a count or two f what the monitor displayed.  Here I assume the device "sees" the movement in the vein (artery - whatever its called) and counts each expansion as a pulse.  Just a guess, but continuing it seems to me an older person, for example, would on average have harder/stiffer veins/arteries and thus less expansion, which is reflected by the number of bars displayed - if this is true it the number of bars has nothing to due with the blood flow beyond the variations it displays on an individual - and that variation may be due to movement of the hand/finger or other external causes. I have decided to accept the HR and O2 are good-enough and the number of bars a curiosity of the device. .

[ireneo]

This is confusing, isn't it?  So the oxygen level is shown by a digital readout (97 for example) and pulse rate is shown by number as well. The big mystery is the purpose of the bars. Funny the instructions don't clearly explain what that's for.

I like the other response about how things can change due to circulation: being cold, hot, position of arm. Another question: is there a difference between a skinny finger and a chubby finger? LOL Seriously. Can the LED and infra red read as easily on a chubby finger? Will a hand swollen by fluid retention make a difference in readings?

Ah well. Sweet mysteries of life.

[Jerry_NJ]

Thanks for sharing your experience, I find it helpful as I am sure others who have or are considering such a device find your reply helpful.

The "Intensity" may have come out of my "head"... a Jerry-creation.  I can not find that term used in my brief search of the "literature".  Clearly, it is more than a pulse indicator, a simple single bar flashing would accomplish that.

I have struggled to determine the number of bars in the pulse "indicator" (I'll now call it).  I rarely hit the top and when I do it is a very brief flash, but I am sure it is at least six, and I see much of my indication being up;down between bar 2 and bar 4.  I have AFib, and am in AFib all the time.

I did look a little deeper into the technical details and learned that the device uses to (high intensity - my term again) LED light sources (top over finger nail) one is visible Red the other invisible Infra-Red.  With these light sources passing through the finger and picked up by detectors on the bottom of the device. a read-out of the color of the arterial blood is determined. then with the wonders of a micro processor with data base and firmware it can computer the O2 saturation, which is indicated by the color of the hemoglobin carrying oxygen, or not carrying.  I believe through this detection the device also "sees" the pulsing and thus can display the HR.  As for intensity, not sure that is a good term for the bar readout.

[helyanna]

I have used a pulse oximeter for many years. I use it when I have some blood circulatory problems. I think that the intensity may be affected by many things. When I go out and there is a cold weather, the blood circulation  to my fingers decreases. Then the intensity may be low. It can sometimes be low (two bars) even in the room temperature, and on the other hand, sometimes can show all the bars (I cannot count them). One reason for low bars could be the position of the arm (the artery can be compressed). But often I cannot find any cause. The variation can result form the normal autonomous regulation.

[Jerry_NJ]

I'm not sure the "intensity" is a measure of efficiency.  My echo measured EF is over 60% which is considered good, yet the intensity readout goes most of the time to only 4 bars.  

The device itself appears to get its data by shinning a very bright LED through the finger to a receiver on the opposite side of the finger.  I have no idea how that can determine the % saturation but it seems possible to me that the light signal is modulated by the pulsating pressure/blood in the finger.  The height (number of bars) may be more affected by the blood pressure and the difference between the upper/lower values. If that is the case the high bar reading would suggest high BP, maybe too hight.  I looked briefly at the instructions that came with the device to learn more about the intensity reading, and understanding what it tells.  The instructions were silent - I'll see if I can find some explanation on the web.

[ireneo]

Thanks for the explanation on "intensity." So more bars is higher intensity which is a good thing. Palpitations which feel like a pounding heart seem like a bad thing. I wonder if they register on the meter.

Then lower bars mean the heart isn't beating as effectively as it should.

Interesting.