AlmostClever wrote:Where can you get this percentage?
All I was told was "mild" and "moderate" - no percentages.
Taking measurements from my venogram images, I can determine my vein narrowed down to 5.5 mm from 9 mm so is this about a 50% blockage based on diameter or 70% based on cross section area?
Just wondering what the official ruling on this is...
Vessel length does not change appreciably in vivo and, therefore, can generally be considered as a constant. Blood viscosity normally does not change very much; however, it can be significantly altered by changes in hematocrit, temperature, and by low flow states.
If the above expression for resistance is combined with the equation describing the relationship between flow, pressure and resistance (F=ΔP/R), then
This relationship (Poiseuille's equation) was first described by the 19th century French physician Poiseuille. It is a description of how flow is related to perfusion pressure, radius, length, and viscosity. The full equation contains a constant of integration and pi, which are not included in the above proportionality.
In the body, however, flow does not conform exactly to this relationship because this relationship assumes long, straight tubes (blood vessels), a Newtonian fluid (e.g., water, not blood which is non-Newtonian), and steady, laminar flow conditions. Nevertheless, the relationship clearly shows the dominant influence of vessel radius on resistance and flow and therefore serves as an important concept to understand how physiological (e.g., vascular tone) and pathological (e.g., vascular stenosis) changes in vessel radius affect pressure and flow, and how changes in heart valve orifice size (e.g., in valvular stenosis) affect flow and pressure gradients across heart valves.
Although the above discussion is directed toward blood vessels, the factors that determine resistance across a heart valve are the same as described above except that length becomes insignificant because path of blood flow across a valve is extremely short compared to a blood vessel. Therefore, when resistance to flow is described for heart valves, the primary factors considered are radius and blood viscosity.
What if an upper jugular stenosis causes a greater pressure rise in the venous sinuses than a lower jugular stenosis: would that mean that a 50% upper jugular stenosis is more severe than a 50% lower jugular stenosis? How big is the vein and how flexible is the vein? A 80% stenosis of a large vein allows more flow past than an 80% stenosis of a small vein because of the differences in size of the vein. A more elastic vein might compensate better for the effects of the stenosed area. We need a physicist with equations and access to a flow quantification database and the drive to figure this all out mathematically.
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