Author Topic: Blood oxygen.  (Read 276 times)

Blood oxygen.
« on: June 30, 2020, 05:32:57 pm »
Didn't want to hijack Wowbaggers thread, so here goes.
Since Covid 19 appears to affect some individuals blood oxygen level my wife has bought two blood oxygen readers that are different makes. One clips it over a finger and it reads both heart rate and blood oxygen.
She's concerned that my blood oxygen is consistently between 93 and 95%, low side of normal apparently. Resting heart rate is 50 beats per minute. What confuses me is that at 59 years old I can still run half marathon in 1 hour 40 minutes and although not race fit for cycling I still did very well on a Wattbike threshold test. I can't remember the figures but was told it was very good, especially for a man of my age (cheek).
So, if I'm otherwise fit, why would I produce relatively low blood oxygen readings. We've been tested for covid 19 and we don't have it and haven't had it.
Is it just the variability in human physiology? I ask because my wife who doesn't exercise has readings of 98%, she's concerned for me. I'm not at all though

Re: Blood oxygen.
« Reply #1 on: June 30, 2020, 05:34:53 pm »
Oops I meant to add, all the best Wowbaggers. Read your threads and comments with great interest. Good luck

hellymedic

  • Just do it!
Re: Blood oxygen.
« Reply #2 on: June 30, 2020, 06:41:34 pm »
Nail varnish?

Re: Blood oxygen.
« Reply #3 on: June 30, 2020, 07:00:26 pm »
It varies over time anyway. Here's mine for the last 7 days (I think this graphs hourly averages, the Garmin Forerunner 945 takes a reading every 10-15 minutes, although more often when asleep).



Usually it's 98%+ for me but this last week it's slightly lower and has even dipped down to 90% at points. (I feel fine and run times are no different than the usual variation.)

I think the week before it barely dipped below 96%.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: Blood oxygen.
« Reply #4 on: June 30, 2020, 07:09:35 pm »
Poor circulation end of hand aka Reynaulds, or was your hand cold when you checked? The accuracy is only about 2% (Above 90%) anyway so add plus minus 2% to any figure you see.

So given accuracy you may be 95-97% and your wife 96%. Overlapping!

Re: Blood oxygen.
« Reply #5 on: Yesterday at 06:04:13 am »
No nail varnish. My hands were warn as far as I remember, although I do frequently have cold hands and feet and have had since I was a child.
Thanks for the replies

IJL

Re: Blood oxygen.
« Reply #6 on: Yesterday at 08:49:00 am »
There's a whole range of thing that can affect pulse oximeter reading, cold, poor circulation, bright lights, heart rate, (very fast or slow and peripheral circulation may be affected)
They're an interesting test in that if you see someone and expect their sa02 to be normal but find its low you tend to explain it away with one of the above reasons
If they're breathless or unwell you take low Sao2 seriously but only as part of the bigger picture, as if they are breathless and unwell with a normal Sa02 you still need to keep looking for the cause
Many people with chest disease such as COPD will not have had normal sa02 in years.
Other observations are needed to understand what going on as Sa02 falls you would expect respiratory rate to rise, fever would come with infection
Every now and again our local nursing home re-discovers their pulse oximeter, this is followed by calls about Fred and his low Sa02, Fred is 96 years old and knackered, his Sa02 hasn't topped 94 in 20 years.  (most nursing homes have 20 Fred's or Freda's)
I discovered that night shifts have a marked affect on my SA02, not sure why.
Sao2 is a bit like temperature, a child with a temp of 38 may be very unwell, but less likely if they're tearing around the waiting room.  You need to use the numbers as part of the bigger picture

Re: Blood oxygen.
« Reply #7 on: Yesterday at 11:25:58 am »
I would agree with IJL. Pulse oximetry should be seen as a trend not a single reading in the fit healthy population.  i am sure somebody will be along to tell us about the statistics of testing in fir versus ill people and the relative sensitivity (or look at some of the early coronavirus threads).  Basically if you are fit and healthy then the test is wrong not you.

Re: Blood oxygen.
« Reply #8 on: Yesterday at 11:41:01 am »
My Garmin watch supposedly measures this but to be honest I am not convinced of it's accuracy having read up about the "proper" kit and how to test, and how even using that can give spurious and inconsistent results if not done absolutely properly.

According to Garmin my level varies between 87 and 98 over the last week.  Always seems higher when I am out for a run.

Re: Blood oxygen.
« Reply #9 on: Yesterday at 12:05:35 pm »
My Garmin watch supposedly measures this but to be honest I am not convinced of it's accuracy having read up about the "proper" kit and how to test, and how even using that can give spurious and inconsistent results if not done absolutely properly.

The Garmin watches uses a dual wavelength sensor (visible red and infra-red light) which is similar to the technology in the "proper" kit. (The main difference is that it doesn't have a sensor through, only through part of the skin (the finger sensors do shine the light through the entire finger tip).

My Garmin 945 gives me the same readings (within 1%) as the Contec CMS50D pulse ox meter I bought a few weeks ago.

The sensors that aren't very accurate are the single wavelength (usually visible red light) sensors such as some phones have.
"Yes please" said Squirrel "biscuits are our favourite things."

Kim

  • Timelord
Re: Blood oxygen.
« Reply #10 on: Yesterday at 02:31:56 pm »
as if they are breathless and unwell with a normal Sa02 you still need to keep looking for the cause

Nahh, you can just write it off as a 'panic attack'.  (DAHIKT)
Careful, Kim. Your sarcasm's showing...