That's a good question! Every time my husband is doing something that seems to leave him breathing hard I get out the oximeter & measure his sat levels. They have never dropped below 98%?? I don't get it either :>))

It's because of the carbon dioxide buiding up.

I think we are like a one legged man trying to run a foot race. If the other leg is not there,it kinda prevents the race. Our lung damage only gives us part of what we need to 'compete' with healthier lungs.

CO2 build up makes sense.

I think that altitude plays a part in what our readings will be. I live at an altitude of 2,000 feet, and my readings will always be lower than when I'm at sea level where they are higher. If I go up the mountains more, to say 4,000 ft. they'll drop accordingly - actually I have trouble at much over that.

Something else, too...heavier people can sound just like us, when it comes to SOB, and their lungs are fine...but everything works harder because of the extra weight.

I think Jack has it right as far as why not do so much more oxygen. Also, retaining a lot of CO2 in your blood will make your pulse ox read higher.

I worry sometimes that even the 2L that I use makes the carbon dioxide much worse. I am a serious retainer when it comes to getting rid of the C02.

And as Joni said, I don't feel that I am getting an accurate reading on the oximeter because of it.

I am more aware that my pulse rate shoots up before my SATS drop to below 90 so that tells me that I need to stop whatever I am doing and allow the pulse to return to "normal" My base pulse is 90 but it can go to 140+ amazingly quick. Doesn't seem to alarm the docs so I just deal with it.

It sounds reasonable that the CO2 is part of the problem. I have been told I am not a retainer but my diffusion is low (40%) so it does not take too much exertion to make my sats drop. I'm not bad if I go slow, but if I speed up or carry stuff,,, boom, sats drop and pulse goes up.

My pulse rate shoots up first also before my sats drop. My regular pulse wqas at 110 for about 1 1/2 years and then they put me on cartizem to lower it and now it.s at 88 when I first wake up but shoots up to 98pretty fast. On exertyion it goes pretty high pretty fast and then SOB and then sats drop into the 80s pretty fast. I'm on 2 LPM.

I find when ever I excert myself no matter what the task is my heart rate shoots up to at least 100. Normally at rest it will go back to high 70's or low 80's. which is good.
I am a co2 retainer but was told by the resp therapist to exhale by blowing out hard and fast like blowing up a balloon. They said this would help get rid of any excess.
When I had my heart surgery and was on a ventilator for 8 days after the surgery/once I came off the vent the lung Doc told me he would like to see my stats around 92/93. Not sure why as some things are still foggy to me about that time frame. How ever my stats are true to being around 94-97 on 1.5 liter of 02. I went in hosp on 3 liters and came out on 1.5 and have remained on that almost 2 yrs later.
I am blessed.