Remember you cannot totally take what an oximeter says as the truth of your oxigen status only blood gases are reliable if taken properly.smokers and people with known lung problems should never think they are accurate,just take it as a rough reading.
Exercise is the ONLY WAY to improve your lungs.also eat well,good proteins and avoid milk and all milk products they are known to effect the lungs with allergys and mucus.drink almond milk or soya milk.