What must remain constant proximal to, at, and distal to a stenosis?

In the context of fluid dynamics and the principles of blood flow in vessels, the volumetric flow rate must remain constant proximal to, at, and distal to a stenosis. This concept is rooted in the principle of conservation of mass, often articulated as the continuity equation in fluid mechanics.

Within a closed system, such as the circulatory system, the amount of blood that enters a segment of the vessel must equal the amount that exits it over time, assuming no blood is being added or removed. Therefore, even though there may be changes in velocity and pressure due to the narrowing (stenosis) of the vessel, the total volume of fluid passing a given cross-section per unit time—volumetric flow rate—remains consistent.

As the stenosis reduces the diameter of the vessel, the velocity of the blood may increase at the point of stenosis in accordance with the principle of continuity, which states that an increase in the speed of a fluid occurs as it is forced to flow through a narrowed section. However, despite these changes in velocity and the potential drop in pressure across the stenosis, the total volumetric flow rate remains constant. This understanding is essential in the assessment of vascular conditions and aids in the prognosis and treatment planning for patients