The prevalence of internal jugular vein (IJV) valve incompetence, as assessed by ultrasound, was found to be more prevalent in patients with TGA [transient global amnesia] than in controls. In all of these studies, IJV valve incompetence was detected in 97 of 131 [TGA] patients (74%) and in 65 of 191 controls (34%).
So 1/3 of the general population may have internal jugular valve incompetence and the resulting reflux.
I know that Zamboni focuses more on stenosis than on valve incompetence, and that Zamboni also usually found problems with the azygous veins, but it seems problematic that the research on transient global amnesia has found so much reflux in controls, while Zamboni found almost no blood flow problems with controls.
I'm hoping that there's a good explanation in support of CCSVI, but the research on controls in the transient global amnesia studies seems problematic, especially considering the problems that so many doctors and sonographers around the world apparently have had in detecting CCSVI.