Hi Green1960 and thanks for this post. We cannot provide medical advice or diagnostics over the internet (for your own safety), but your very real concern certainly warrants a reply. There are a variety of reasons as to why oxygen levels drop in the course of the day - your doctor is the best one to advise you. However, oxygen saturation levels of 82-86% would be considered as low for any patient. This is especially true since you did say the levels do return to 90% at some point. Since you have a pulmonary surgical history, I would suggest you contact your medical doctor, who manages your COPD, and/or the surgical doctor, who performed the surgery. There may be something else going on that requires medical intervention at this point. Please be sure to check back and let us know how you're doing. Wishing you well, Leon (site moderator)