Oxygen levels low. Meter show occasional low reading for pulse

My oxygen levels have been low with allergies and when I test with meter  it shows occasional pulse readings in the 50s and 40s. I had a sinking feeling when this happened.

I've had a two wire pacemaker 5 years. This happened  before and was put on a monitor which did not find low readings in hospital over night. Pacemaker Tech said that happens occasionally and not to worry, Pacemaker works more reliable thann tester. I've haad that sinking feeling again. My Cardio Doc agreed with tech. I have 6 month checkup in one month. Any concerns?


Home monitors

by Gemita - 2022-01-05 11:57:59

Dear FisherGuy,

May I ask “how are you feeling”?  What symptoms do you have apart from “that sinking feeling” which I know well?  If you are measuring your oxygen and pulse with a home monitor these may not be entirely accurate in the presence of any heart rhythm disturbances (arrhythmias).

I frequently get “that sinking feeling” in my stomach before an arrhythmia, like an ectopic beat and this can cause weakness and a feeling of anxiety.  If these strange, irregular beats continue for any length of time, I can become slightly breathless and faint.

I used to use my home blood pressure monitor to measure my heart rate when this occurred and like you I often got a reading in the 50s or even lower in the 40s.  My doctors said the same thing, that a pacemaker will not allow my heart rate to drop below the minimum set level.  What is probably happening is that your home monitors are not picking up ectopic beats which can be very faint and inefficient and can easily be missed by our home monitors.  Our pacemaker instead correctly senses these inefficient, faint beats and continues to regularly pace us at the Base Rate set.

I wouldn’t be concerned unless you are getting symptoms like breathlessness, dizziness, chest pain.  What might be a good idea is to go to your GP taking your home monitors with you and let them check your pulse and oxygen levels just to be sure and for them to confirm whether your home monitor is working correctly.  We often get a message like yours here.  I hope you are reassured, but go by your symptoms.  Obviously with low oxygen levels you can expect symptoms, so please check with your doctor.

Why the pulse/ox and other measures can disagree

by Gotrhythm - 2022-01-05 12:40:02

Occasionally when I am having lots of PVCs, my pulse/ox meter will seem to report a heart rate in the 50's and a lower than nomal O2 saturation.

It doesn't mean anything is wrong with my pacemaker. What happens is that PVCs are counted as heartbeats by your pacemaker--because that's what they are. PVCs are real heartbeats but they are inefficient beats, not as strong as they should be because the contraction is happening in the ventricle a little before it should, before the atria have had time to fill completely. (For a complete explanation of PVCS,  there is a really good youtube video "Dr Joshua Brown PVCs in Plain English" that you might want to view.)

Because the PVC is an inefficient beat, the pulse in your finger might not be strong enough to be picked up by your pulse/ox meter.

The pacemaker is tracking contractions of the heart. Something like a Holter monitor will also be recording what's happening at the heart. The pulse/ox is recording pulses in your finger. Two different things. Ususally, they match but, as you have seen, sometimes they don't.

PVCs are not the only reason you could see a discrepancy between the pulse/ox and other measures of heart rate. Other arrythmias can cause it too, but PVCs are so common they are considered "normal."

Re your question "Any concerns?" here is my strictly lay person's opinion. You feel a "sinking feeling." The pulse/ox gives objective confirmation that something measurable is happening, so you are not imagining it or making something out of nothing.

No, there's no reason to be concerned about your pacemaker. And if the problem is PVCs, most of the time doctors feel they are "nothing to worry about." 

But ultimately what matters is how do you feel? How much are the "sinking feelings" bothering you or interfering with your life? Is this something you can live with or is your quality of life being seriously undermined?

You've been told your pacemaker is working fine, but something is making you have sinking spells. It's time to have a talk with your doctor and ask, "It's not my pacemaker but what is it? and what can be done to help me feel better?"


by AgentX86 - 2022-01-05 13:26:24

As others have indicated, pulse-ox meters including BP cuffs are terrible pulse rate meters. However, even if the count is way off, the blood oxygen measurement should be quite accurate to a couple of percent. 

Pulse-ox meters measure the oxygen saturation in the blood by using two LEDs (red and infrared).  The transmission properties of these two sources is different for oxygenated blood than it is for deoxygenated blood.  The pulse-ox meter calculates the oxygen saturation from the ratio of these two values.  The pulse rate doesn't figure into this equation but it is measured by the values (not the ratios) changing.  This may be off but it's information that isn't used in the blood saturation calculation.

Forget about what it's telling you about your heart rate (count that yourself) but if your blood oxygen saturation numbers are going down, something is wrong.  Below 95% is low.  Below 90% worrisome.  Below 85% it becomes critical; the brain isn't getting enough oxygen.

Tell your doctor

by Gotrhythm - 2022-01-07 14:27:50

I'm glad AgentX86 chimed in with his explanations about the oxygen saturation function of the pulse/ox, what it is measuring, and how.

You didn't say that you are seeing low saturation numbers at the same time that the pulse rate is below what should be your resting HR. Is that what's happening? Is it happening at the same time you are having the sinking feeling? If so, I would say it is definitely something you should mention to your cardio when you see him next and let him figure out how concerning it is.

Here's how I reason it out. If the pulse number is low, and at the same time the O2 number is low, and at the same time, I have a sinking feeling, is is reasonable to assume that it's not a coincidence. I don't feel well. Something is happening that is causing all three. Therefore I need to consult a doctor.

I wouldn't try to diagnose you, but speaking for myself, when I see low pulse numbers, lowish oxygen sat numbers, and feel tired, faint, week etc., the cause is arrythmias. In my case PVCs and lately PSVT. 




Machine tolerances are accepted

by Stache - 2022-01-08 15:55:27

Like yourself, I have a dual-chamber pacer beating at 60 bpm 100% of the time.  My pulse used to be 32 and lower at night.  I have always exercised a lot and my O2 reading was 98% to 100% and still is every day.  Of course, my heart chamber pumps a lot of blood per beat due to the size as to why my doctor was not concerned about my slow heartbeat until I went into cardiac arrest and vapor locked this past February 8th.  I now have two stents plus the dual-chamber pacer.  I have been tracking my blood pressure, O2, weight, and temperature two to three times a day on a spreadsheet for the past 11-months.  I have noticed my blood pressure has dropped to normal and my O2 has remained the same.  After my 1-hour walk, every morning or bicycle ride my O2 reading is always 100%.

I am told the key is exercise walking or riding the bike in my case.  Have to say the exercise has kept the weight off as well I weigh the same now as when I went into the Marines.  Pain is weakness leaving the body.

NOTE:  My blood pressure machine will read differently than my O2 monitor often.  I have checked them against what the doctor uses in the hospital even their machines have a wide tolerance. As to why I check several times a day, it’s always different.

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