TURBULENT OR LINEAR
The dynamics of blood flow can differ within a blood vessel according to changing circumstances such as blood vessel health, mechanical pressure, blood vessel length, blood viscosity, and especially blood vessel radius. There are healthy dynamics and unhealthy dynamics; There is normal and abnormal blood flow.
Normal and health promoting blood flow occurs parallel to the blood vessel walls, and is made of several sub-currents of blood flow, as opposed to the perception of one current (similar to a river). The blood flow sub-currents in the middle are faster moving than those closer to the blood vessel walls. In other words, blood flows faster in the middle of the blood vessel, than in its outer aspects.
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Parallel blood flow is more efficient since less energy is invested in the advancement of blood per unit of distance or volume. It is very much similar to the road, where we expect cars to advance in straight lanes (for the most part), and any deviation from the lane has the potential of causing problems. In a blood vessel, any sideways flow will result in turbulent flow, which is messy, inefficient, and promotes abnormal function and possibly unhealthy function.
Turbulent blood flow increases the chances of molecules colliding, breaking up, and more blood flowing sideways or barely advancing. In all cases, this reduces oxygen and nutrients supply, required for optimal function, and livelihood. Turbulent blood flow is most likely the result of the inability of blood to flow normally (in straight currents).
Thus, anything that reduces the blood vessel walls' smoothness, will increase the chances of turbulent blood flow. Such is the case with extensive cholesterol and other types of fat sedimentation. As the blood vessel's wall tears even a bit, it promotes the binding of cholesterol and other sediments to it at the location of the tear. Over time, an obstacle increases in size, disrupting normal blood flow.
The idea of flow in general is described and defined as relationship between a drive force and resistance to flow. In blood vessels, blood pressure acts as the mechanical driving force that propels blood forward, while the resistance is the natural resistance to flow that resistive blood vessels such as arteries display naturally. According to the Poiseuille equation, flow = (P2 - P1)/R or ΔP/R. P2 and P1 represent two different measurements of pressure creating a pressure gradient within the blood vessel causing forward flow of blood, while R represents the blood vessel's resistance to flow (known as vascular peripheral resistance to blood flow).
Resistance to flow is influenced by the length of the blood vessel, blood viscosity, and evermore so the radius of the blood vessel. Poiseuille applied Darcy’s Law of Flow to blood vessels, resulting in an equation for vascular peripheral resistance to blood flow. According to the equation, the longer the blood vessel and more viscous the blood, the greater its resistance to flow. On the other hand, the greater the blood vessel's radius, the lesser the resistance to flow.
Since the radius of a blood vessel influences resistance to blood flow to the forth power (mathematically), it is of the greatest influence of all factors. This bears the meaning that even the slightest change to a blood vessel's radius, has enormous influence on resistance to blood flow. The greater the radius of the blood vessel, the lower the resistance to blood flow gets. The equation is: R = 8Lη/π(r)(r)(r)(r).
R = vascular resistance to blood flow; L = the length of the blood vessel; η = blood viscosity; r = blood vessel radius (to the forth power (mathematically). The equation allows us to understand the relationship between blood pressure and the width of the blood vessel, as represented by the its radius. A more narrow blood vessel decreases its radius, causing an enormous increase in resistance to blood flow, also increasing blood pressure, and vice versa.
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This would be the perfect place and time to remind ourselves of the advantages and disadvantages of high blood pressure. High blood pressure accelerates the supply of oxygen and nutrients to the needy cells and tissue, yet at the same time, increases the risk of wear and tear of the walls of the blood vessels, and the chances of sediment accumulation.
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