Long airplane rides can cause blood clots.
I believe long term sitting caused by long airplane rides caused it. The plane he rides are luxury and allow for movement which is the problem when clotting occurs (lack of movement).
I wonder how dangerous air flight is to people with health problems? A good friend of mine, who had a heart transplant, continued to travel heavily afterward - constanting flying long distances. I disapproved but said nothing. My dear friend only lived several years after the heart transplant while others in her support group are still going strong. Has any research been done on this?