Blood pressure is typically not measured in a very thorough way. It is measured at the arm, with a cuff and a stethoscope, not inside the head. It is measured by listening to the sound. Because venous pressure is so low by comparison with arterial, I am thinking (possibly wrongly) that venous pressure is not measured at all with the cuff on the arm. The BBB is subject to arterial pressure on the arterial side, and venous pressure (much lower in every case) on the outflow side.
Ohm's law with fluids says that pressure = flow * flow resistance. That results in a pressure drop across the stenosis or narrowing. So if that is in the neck, then venous pressure, even if it were measured by an arm cuff, or some kind of plethysmographic method, would be higher on the brain side of the obstruction. I doubt that is what is referred to by the IR.
Would low blood pressure affect sheer stress?
It seems to me that low blood pressure would indicate slower flow and according to one of the IRs many of his patients have low blood pressure.
Pressure (not rate) should be lower post-obstruction, due to its resistance to flow. A flow measurement on either side of the stenosis should show that only pressure is affected, not flow rate; on either side of the stenosis, flow rate should be the same.
There are only two sources of cerebral blood pressure: muscles (heart and others) and gravity. Gravity is a major factor in drainage of areas which are physically above the heart, because the pressure due to other muscles pumping is low in comparison, due to pressure losses in the capillary beds and venules.
The spinal veins drain upward, when you are upright and they are below the heart. That may be why the azygus figures in CCSVI. You are in double jeopardy if the jugulars are blocked (brain drains sideways when prone) and the azygus
is also blocked (spine and ribcage drain upward -- via azygus -- when upright. Parts are below heart).
That said, venous pressure lowered more than normal by a stenosis, would affect the laminar-ness (not the rate, except globally).