Author Topic: Blood oxygen.  (Read 1571 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: July 01, 2020, 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: July 01, 2020, 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: July 01, 2020, 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: July 01, 2020, 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: July 01, 2020, 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: July 01, 2020, 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...

Re: Blood oxygen.
« Reply #11 on: July 03, 2020, 01:45:58 pm »
Back to the coronavirus origin of this thread, I’ve read a couple of times of people with Covid having significantly lowered oxygen saturation and showing signs. What I haven’t seen is any commentary on whether theybwerwbshowing no signs under sedentary conditions or if they could still go out and do an hours hard run or cycle at normal pace. To me, this seem unlikely.

Anyone have any info on this?

Mike

Re: Blood oxygen.
« Reply #12 on: July 03, 2020, 02:42:57 pm »
I’d be interested to know what SpO2 monitors you are using. There is a lot of rubbish out there and I spend an inordinate amount of time keeping that stuff out of the NHS.

hellymedic

  • Just do it!
Re: Blood oxygen.
« Reply #13 on: July 03, 2020, 02:58:53 pm »
One of the scary features of COVID is that patients can have very low blood oxygen without being breathless.

This silent lack of oxygen has been associated with death, especially outside hospital.

IJL

Re: Blood oxygen.
« Reply #14 on: July 03, 2020, 03:11:53 pm »
Quote
Back to the coronavirus origin of this thread, I’ve read a couple of times of people with Covid having significantly lowered oxygen saturation and showing signs. What I haven’t seen is any commentary on whether theybwerwbshowing no signs under sedentary conditions or if they could still go out and do an hours hard run or cycle at normal pace. To me, this seem unlikely.

Anyone have any info on this?

Mike
not sure if you have missed a "not" out but a quick google reveals the following from some LMC guidance


Quote
Anecdotally we are being told by clinicians that they are detecting people with symptoms of Covid19 infection but not experiencing shortness of breath, who then on performing pulse oximetry are
found to be hypoxic.

I would be very dubious about low SA02 in people who are well, not short of breath, have a normal respiratory and heart rate and don't have chronic chest disease.  Its more likely due to the vagaries of pulse oximeters than genuine hypoxia.  In hospital such people would have their blood gases measured (not a pleasant experience).

As discussed earlier Sa02 needs to be seen as part of the bigger picture, in isolation its not very useful

This is the guidance ( this is aimed at those in the trade)

https://www.lmc.org.uk/visageimages/Covid-19/Guide%20to%20using%20pulse%20oximeters%20during%20Covid-19%20pandemic.pdf





Re: Blood oxygen.
« Reply #15 on: July 03, 2020, 03:29:41 pm »
I have a friend who has switched his company to making bits for the NHS. He is a scuba diver, well versed on blood oxygen measurements.

The 'low oxy without breathless' is a real thing. I can't say anything about whether it is accompanied by no changes in heart rate.

If they have cv-19, isn't that an acute respiratory disease?
<i>Marmite slave</i>

Re: Blood oxygen.
« Reply #16 on: July 03, 2020, 03:32:06 pm »
I would be As discussed earlier Sa02 needs to be seen as part of the bigger picture, in isolation its not very useful
To avoid confusion SaO2 in measured via analysis of blood. SpO2 is measured using a pulse oximeter of the type described above (absorption of red and infrared light).

Correlation between the two varies depending on where the SpO2 sensor is sighted, whether the test subject smokes and test subject’s skin pigmentation with a only a few of the possible reasons.

IJL

Re: Blood oxygen.
« Reply #17 on: July 03, 2020, 04:25:45 pm »
Quote
I have a friend who has switched his company to making bits for the NHS. He is a scuba diver, well versed on blood oxygen measurements.

The 'low oxy without breathless' is a real thing. I can't say anything about whether it is accompanied by no changes in heart rate.

If they have cv-19, isn't that an acute respiratory disease

The issue in chronic rather than acute resp' disease is that often in chronic disease there is physiological adaptation to relative hypoxia.


T42

  • Old fool in a hurry
Re: Blood oxygen.
« Reply #18 on: July 03, 2020, 04:43:10 pm »
Pulse oximeters can also be fooled by badly controlled diabetes. Glycated haemoglobin combines happily with oxygen, but unlike normal haemoglobin it doesn't like to let go of it again, so that the O2 it's carrying is useless but will still be measured by an oximeter.  In normal people around 5.5% of haemoglobin will be glycated, but in diabetics with control problems it can be a few percent higher.  When I was first diagnosed, 30+ years ago, my glycated haemoglobin was 11.5%.

The 'low oxy without breathless' is a real thing. I can't say anything about whether it is accompanied by no changes in heart rate.

Breathing rate is controlled by blood CO2 concentration.  In happy hypoxics, SARS-CoV-2 has reduced O2 uptake by the blood but CO2 can still diffuse outward, so that there's no effect on breathing rate.  Dunno about heart rate, but I'd be surprised if it didn't accelerate.
I've dusted all those old bottles and set them up straight.

Re: Blood oxygen.
« Reply #19 on: July 03, 2020, 05:02:16 pm »
I’d be interested to know what SpO2 monitors you are using. There is a lot of rubbish out there and I spend an inordinate amount of time keeping that stuff out of the NHS.

My sensor is built in to my Garmin Fenix 6 Sapphire watch and uses Garmin's most up-to-date technigy.  Like I said up thread though, I doubt the accuracy of it given how I read about the kit used in the NHS and even how that needs to be carefully and properly used for accurate results.

I am sure too that my albinism resulting in no pigment is a factor in what the sensor reads as I suspect that calibration for skin pigmentation is set at an "average".

I tend to look at trends on these devices rather than absolutes as I just don't see how a small wrist device can be nearly as accurate as pro kit in the same way that a smartphone can never match image and video quality of pro cameras, etc.

hellymedic

  • Just do it!
Re: Blood oxygen.
« Reply #20 on: July 03, 2020, 05:09:28 pm »
Hospital pulse oximeters usually shine their red light through fingertips (earlobes and toes are used occasionally).

There's not much pigment in my fingertips.

My SpO2 was 98-100% (on air) when I had a hospital procedure in 2018.

Re: Blood oxygen.
« Reply #21 on: July 03, 2020, 05:21:20 pm »
I’d be interested to know what SpO2 monitors you are using. There is a lot of rubbish out there and I spend an inordinate amount of time keeping that stuff out of the NHS.

My sensor is built in to my Garmin Fenix 6 Sapphire watch and uses Garmin's most up-to-date technigy.  Like I said up thread though, I doubt the accuracy of it given how I read about the kit used in the NHS and even how that needs to be carefully and properly used for accurate results.

I am sure too that my albinism resulting in no pigment is a factor in what the sensor reads as I suspect that calibration for skin pigmentation is set at an "average".

I tend to look at trends on these devices rather than absolutes as I just don't see how a small wrist device can be nearly as accurate as pro kit in the same way that a smartphone can never match image and video quality of pro cameras, etc.
I have the same watch and can confirm, whilst it is good, it isn’t as good as one used in healthcare.

In saying that you don’t have to spend a fortune* to get something accurate for the majority of people.

E.g. https://www.wms.co.uk/wms/en/GBP/Pulse-Oximetry/Nonin-9590-Onyx-Vantage-Finger-Oximeter/p/W9590BK

*thought prices have crept up a little due to supply and demand in times of Covid.

Re: Blood oxygen.
« Reply #22 on: July 03, 2020, 08:06:07 pm »
Very helpful folks, thanks. T42 mentions diabetes, as it happens by Mum(81)has late onset diabetes (60), and so did her five siblings. None on my Fathers side. I've been checked at doctors and bloods are normal. We have blood sugar strips which one urinates on(weekly), no sugar detected in urine.
Its quite possible that at 59 and having worked in construction since 1977 I'm a little worn. That's acceptable to me. When this pandemic calms down I may pay for a thorough all in body check. That may seem a bit extreme, but let's face it how much does the average Joe spend on car servicing. Only analogy I could think of.

T42

  • Old fool in a hurry
Re: Blood oxygen.
« Reply #23 on: July 04, 2020, 01:44:55 pm »
Very helpful folks, thanks. T42 mentions diabetes, as it happens by Mum(81)has late onset diabetes (60), and so did her five siblings. None on my Fathers side. I've been checked at doctors and bloods are normal. We have blood sugar strips which one urinates on(weekly), no sugar detected in urine.
Its quite possible that at 59 and having worked in construction since 1977 I'm a little worn. That's acceptable to me. When this pandemic calms down I may pay for a thorough all in body check. That may seem a bit extreme, but let's face it how much does the average Joe spend on car servicing. Only analogy I could think of.

IIRC urine strips aren't all that accurate, but I haven't been tested that way since the 80s.  Doc then remarked that they don't usually show a result when you're blood sugar's below 180 mg/dL (normal range 80/120 mg/dL). They're probably more accurate these days, though.

I've dusted all those old bottles and set them up straight.

hellymedic

  • Just do it!
Re: Blood oxygen.
« Reply #24 on: July 04, 2020, 03:28:53 pm »
Glucose will only spill into the urine at levels above the 'renal threshold', which is higher than acceptable. This is why blood glucose is measured.

Brits measure blood glucose in mmol/litre while Americans quote mg/dl. 180mg/dl = 10mmol/l.