I use an oximeter frequently, but have very cold hands, and often don’t get a correct reading. I recently had a PFT test, and walk test. My levels drop down to 90 with the walk test, and even below that at times. My doctor said that if my oxygen drops to below 88, and does not come back within 15 minutes I should stop walking. He also said to stop if I’m not able to speak a logical sentence. For some reason that sounds strange. I do use oxygen at night. Any comments?