I've just been reading a report which seems to conclude there is really no difference between left/right lying positions with regards to breathing or blood flow. However, if there is one diseased lung, there seems to be benefits with this lung being the lower of the 2. Pregnant women are often recommended to lay on the left, to keep the weight of the uterus off the liver. Open heart surgery patients are recommended to lay on the left, as I was. I don't know why.
There is a much bigger difference between sitting in a chair and laying, the circulation/breathing is better in a chair.
I'd be interested in hearing more about this. I've never heard of it being a problem in just elderly patients. I know many people with arrhythmias find that laying on the left side seems to trigger more PVC's and such. Easy fix - don't lay on that side. But as a general practice, I'm not sure how laying on just that side would impede circulation. I'll be watching for answers too.