Natty,
Here is a bit more information to start.
Velocity of greater than 50 are considered abnormal. Diameter readings are usually compared from the jugular foramen, C1, and a few points below to the omohyoid muscle looking for stenosis. There is little evidence describing normal active data.
Keep in mind that this testing is very limited for a few reasons:
- it can vary greatly depending on the sonographer’s technique and pressure applied to the probe
- more importantly the readings are taken in supine which does not correlate to the functional position of being upright. Gravity influences the IJV greatly.
While it does have value it is not usually the primary form of imaging but a backup. CTV, MRA/MRV, and venogram are more reliable sources of IJV information but again are all done in supine.
Hope this is helpful!