Just FYI. @A MyCOPDTeam Member, a spirometry or Pulmonary Function Test won't tell you or the doc anything at all about the need for O2. You're right that he needs to see a pulmonologist, but not for a PFT or spirometry; he needs someone to talk with him about the dangers of not using his O2 when it's been prescribed. @ Newby, if you're asking is it normal for O2 saturation levels to fall as soon as you take the O2 off, the answer is yes. There's no cumulative benefit from O2; you either have it or you don't. So it doesn't last.

To answer your original question about can O2 hurt you, the answer is no, not with the equipment you have. You can't do any damage to yourself.

O2 saturation level lower than 88 can cause damage, both right heart failure and brain damage. The damage can be because of long periods of low saturation or for a whole bunch of short periods. The number of people with COPD whom I know who have brain damage is frightening. Don't become one of them.

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A MyCOPDT...

Smithy, you sure can have brain damage from lows in the 60s. Use your O2 when you get up and move. Turn it off when you're sitting. Don't let it go that low!!!

Been at this for almost 5 years now .. right now i am on 6 liters after hospital visit but plans are to get need below 5 so can use portable tanks again .. when i get up first thing mh o2 iz zround 79 tom82 .. i do not see any difference but am not very active .. during thd day, sitting mostly, my o2 will come up to,91 to 93.. yesterday one of the o2 concentrators went off an my o2 dropped to 69 .. now that i felt .. got it back up almodt immddiately to 88 so came out ok ..
Below 88 might be medically bad but my actual run does not seem to affect me at that ldvel .. dr did, however, said i should shoot for 90 and over .. so once i can keep it above 91 i will cut back on my o2 liters ..
Ok that putsme up to,date go by how you feel and get some exercise ..

I was very foolish by not using oxygen at night when my pulmonary doctor ordered it. Two years ago I had to be rushed to the hospital I could not breath, it was my heart. I was not getting enough oxygen while I was sleeping, thank God I am fine now. I now have to wear oxygen 24/7 but my heart is back to normal. Listen to your doctor regarding oxygen use.

@judge69, I assumed that it was prescribed because of the way the question was stated, but possibly it hasn't been. If not, then what @newbie needs is a 6 minute walk test to determine if he needs O2. A pulmonologist is definitely needed, but neither a spirometry nor a pulmonary function test will give any information leading to an O2 prescription.