blood oxygen content?

[SStell]

When the medical practitioner puts that little sensor on your finger and tells you your oxygen level in a percentage, say 98%, what are they using as the 100% level?

How does this tool know how much oxygen can fit into a particular persons blood?

If you get 98% on a test, you know what the 100% meant.

None of the medical people I have asked have been able to answer that question. Just curious.

[Endy0816]

 

Oxygen saturation is a term referring to the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal blood oxygen levels in humans are considered 95-100 percent.

 

https://en.wikipedia.org/wiki/Oxygen_saturation_%28medicine%29

[BabcockHall]

"A pulse oximeter uses light to measure the oxygen saturation level, the percentage of hemoglobin in your red blood cells carrying oxygen. Normal oxygen saturation levels fall between 95 and 99 percent." From http://www.livestrong.com/article/124374-normal-range-blood-oxygen-level/ This is about what I would have expected. When blood passes through resting muscle, the hemoglobin saturation level drops considerably, but IIUC not to anywhere near zero. This leads to an interesting question, which is how such a device is able to focus on arterial blood, which should be richer in oxygen than venous blood. " Pulse oximetry technology utilizes the light absorptive characteristics of hemoglobin and the pulsating nature of blood flow in the arteries to aid in determining the oxygenation status in the body. First, there is a color difference between arterial hemoglobin saturated with oxygen, which is bright red, and venous hemoglobin without oxygen, which is darker." http://www.hopkinsmedicine.org/healthlibrary/test_procedures/pulmonary/oximetry_92,P07754/

 

So far I have just skimmed this site, but there appears to be some good information: http://www.howequipmentworks.com/pulse_oximeter/

Edited October 15, 2015 by BabcockHall

[fiveworlds]

How does this tool know how much oxygen can fit into a particular persons blood?

 

It doesn't it measures how much light can pass through your finger. This can be affected by nailpolish or lack of nails.

 

Generally it works on the principle that haemoglobin changes the color of your finger and this affects the ability of light to pass through.

Edited October 15, 2015 by fiveworlds

[Xalatan]

Oxygen saturation is how well the haemoglobin in the RBC are holding onto the oxygen. It's dependent on the arterial oxygen tension in the blood. My understanding is the probe shines a light at your finger, and the colour (frequency of light) that your finger glows can be measured as how well your haemoglobin is holding onto the oxygen. 100% would be a shade of red that shows your haemoglobins are being 100% saturated with oxygen.

 

Haemoglobin follows a sigmoid dissociation curve so when your sats dip below 94% or so it corresponds to a significant drop off in arterial oxygen tension.