Hi dannyboy and thanks for your post. While we cannot provide medical advice over the internet (for your own safety), your inquiry certainly warrants a comment. Many in our community have opinions about how inhaling steam or salt water-steam seems to help them. Remember that most of our bronchodilator medications are administered via aerosols and so, you may be experiencing the 'placebo' effects you mentioned based on those experiences, but without medication. There is an article here on our site that references "salt lamps' that I thought you might be interested in. You can find it here: https://copd.net/answers/himalayan-salt-lamps . If inhaling the steam helps you to feel better, I would suggest making certain your physician doesn't have any other issues with you utilizing it and then follow his suggestions.
Many years ago, we (as therapists) administered 'normal saline' via aerosol to treat all kinds of conditions. There was no evidence to support that common practice and so it's been largely discontinued. However, there are still patients today who claim they feel much better after using that type of 'saline therapy'.
Please check back with us and let us know how you're doing.
All the best,
Leon (site moderator)