I had a look around to see if I could get you those dimensions EddieF, but all I could find was one reference that inferred 7mm was within "normal range". I also found a children's study where the diameter of the Jugular vessels was 6.5mm, so I would assume your left vessel measuring 8mm, would fall in the normal range, even if at the upper limit. http://www.ajnr.org/cgi/content/full/24/1/45

It's good to remember that the human body is evenly balanced throughout, and when we have bilateral "anything", then the correlating anatomical part on the other side of the body, will be almost the same size.

With that in mind, it's pretty obvious that your jugular vein measurements are not even close in size, and if the left measures 8mm and is the upper parameter of normal, then 4mm would most likely indicate a stricture.

JMHO .... as I can't find an article to back that up.