Strange readings on pulse oximeter

Pulse-oximeter readings aren't always reliable

by crustyg - 2021-09-18 03:20:56

Pulse-oximeters work by detecting the difference in absorption of light between beats - the light absorption allows it to calculate your percentage oxygenation (and there are several things that can make this number incorrect, but not for you).

The detection-of-difference depends on each beat being about the same intensity, and this is probably what's going on here.  If your heart is beating too fast, or some of the beats are of reduced strength (as often happens in AFib, Aflut and many other episodes of some arrhythmia or run of ectopics) then the pulse-ox may not detect them all and give a worryingly low HR.

You're going to have to learn to feel your own pulse.  In the privacy of your home, the big pulse in the groin (a little to the outside of the crease between thigh and crotch) is the most reliable.  If that's no good for you, try to feel the big pulse in the neck (the carotid), whilst looking straight forward.  It's not always as easy to feel as people imagine and if you turn your head to one side there's a big muscle that gets in the way - and if you feel around in your neck too much you end up massaging the carotid sinus which can also affect your HR.

Or just practice feeling your pulse at the wrist - the radial artery.  Count for at least 15s (ideally 30s) and use a watch with a sweep second hand. 

Once you've proved to yourself that a pulse-rate by feeling is something that you can reliably do, it will become second nature and you can ignore incorrect readings from the pulseox.

Sounds as though you had an episode of some form which is why you felt so terrible - it's not always easy to stay calm and start counting your own pulse when it feels as though you're nearing the end!

Best wishes.

Home monitors in the presence of irregular arrhythmias

by Gemita - 2021-09-18 07:56:12

Sasha, yes I would agree with crustyg, in the presence of an “irregular” arrhythmia, our home monitors cannot always be relied upon.  I have a quality BP monitor which can cope well with a fast, regular arrhythmia like say, atrial tachycardia, but it can give an “error” reading or a false reading in the presence of an irregular arrhythmia, like atrial fibrillation or benign ectopics. 

Benign ectopics frequently cause pausing, thumping, slowing of my pulse and these delayed, inefficient beats can be very difficult to accurately assess with home monitors.  They can affect my blood flow and make me feel absolutely awful.  I often get readings of low 40 bpm with my home blood pressure monitor, whereas my doctors tell me that my pacemaker is accurately sensing my pulse and keeping my heart rate set at my base rate of 70 bpm.  They have categorically told me that my pacemaker will not allow my heart rate to fall below my base rate, even though it can feel like it.

From my symptoms alone, I usually know what my heart rate and heart rhythm is doing.  However, I always feel my neck pulse to confirm whether rate is fast, slow, irregular or regular.  You will soon get to know from the feel of your pulse what is happening.

In your shoes, I would continue to seek help if you have worrying symptoms like sudden breathlessness, chest pain, dizziness/faintness or any other concerning symptoms, although I see you have an ICD so I presume you are being closely monitored for signs of any new arrhythmia?   I wish you well

Heart rate

by AgentX86 - 2021-09-18 13:08:28

What exactly does "heart rate" mean?  If your pulse is irregular, what defines the rate?  Minimum time between beats?  Maximum?  Average?  We'd all likely answer "average".  OK, average over what period?  There's the (or one of the) rub.  A puls-ox meter can only measure the time between pulses.  It's not smart enough to do any averaging.  This is in addition Crusty's point about the pulse-ox not being able to see the pulse reliably because of adjacent beats being "seen" as differing in amplitude. IOW, pulse-ox sorts of meters are useless for those of us with arrythmias.  The PM can "see" every heartbeat and can do averaging.  It knows when its pacing, obviously. 

When you manually count your rate, you're averaging, too.  If you count for a minute, you're averaging over that minute.  If you count for 30-seconds, you're averaging over that 30-seconds and multiplying by two.  You're also multiplying the error by two.  You can see the problem with the pulse-ox.  It's "averaging" over one heartbeat.  At 60bps, multiply the error by 60.  In reality, most just give up and either display an error or worse, some random number.  Never trust pulse-ox meters. Count manually, for as long as you need (30-seconds is a good compromise).

Strange readings on pulse oximeter- rsponses

by Sashafout - 2021-09-18 14:18:25

I'm still learning my way around this site, but I want to thank those of you who took the time to respond to my question about weird pulse-ox readings.

It was curiosity about how a pulse-ox would come up with readings like that. It made me anxious the first time it happened but I realize that the pulse-ox is the least precise device involved in the process and the most affected by variables. I have a Merlin home monitor and my EP checks my readings remotely between visits to the device clinic, but I had an A-V node ablation so depend 100% on my pacemaker and sometimes feel at its mercy, so to speak. As I said, I have a complex cardiac history and try to keep things in perspective. I've had 3 aortic valve replacements, 3 heart attacks from clots forming on the first replacement mechanical valve and getting into coronary arteries, a Mitraclip on a leaky mitral valve to avoid yet another open-heart, several cardioversions and ablations for highly symptomatic Afib and finally the A-V node ablation and pacemaker/ICD.  Thanks again for taking the time to explain the factors involved that could result in the symptoms I experienced.

Sasha

Strange

by AgentX86 - 2021-09-18 17:09:22

Sasha,  You're not alone here.  I've had my share of what you describe.  No valve problems or heart attacks but I've come way too close. I also have a long history of very symptomatic Afib, bypass surgery (with Maze and AtriClip), causing Aflutter.  To stop the flutter, I had three ablations and finall, like you, an AV ablation. 

I look at it slightly differently. I'm not at the mercy of my pacemaker, rather it was what released me from being at the mercy of Aflutter.  The pacemaker is easy to live with.  Aflutter, not so much.