Blood Flow in the Body – An Application of Fluid Engineering
image source The flow of blood within the human body is an http://davidbjelland.com/epilepsy interesting application for these principles of fluids engineering. The circulatory system is regulated in part by muscles in the arterial walls that contract and expand to control how much blood will flow through different parts of the body. Blood pressure is determined by the output of the heart and by the extent of contraction and resistance in the capillary system.
Application of Fluid Engineering in Determining the Blood Flow of the Body
The diameter of a blood vessel can be an important factor in determining pressure, since Δp in Equation (below) scales with the fourth power of diameter. If the diameter of a blood vessel decreases by a factor of 2 and all other factors remain the same, the pressure must increase by a factor of 16 to maintain the same volumetric flow rate. Some medications for hypertension are designed around this principle, and they lower blood pressure by limiting the contraction of blood vessel walls.
Of course, a number of caveats and limitations are associated with applying Poiseuille’s equation to describe blood flow in the human body. First of all, blood does not flow in a steady manner because it pulses with every beat of the heart. In addition, the analysis behind Poiseuille’s law stipulates that the pipe is rigid, but blood vessels are flexible and compliant tissue. Blood is also not a homogeneous liquid. At very small scales, the diameter of a capillary is actually smaller than the blood cells themselves, and those cells must bend and fold in order to pass through the tiniest capillaries. While Poiseuille’s equation may not be directly applicable, it nevertheless does provide a qualitative indication that bloodvessel diameter and the partial blockage of bloodvessels are important factors in influencing blood pressure.