what is the driving force for blood flow
Bernoulli’s principle and dynamics of blood flow Since blood flows have mass and velocity, blood has kinetic energy (KE). This KE corresponds to the square of the mean velocity (V2; since KE = ½ mV2). Furthermore, as blood flows inside the vessel, pressure is exerted on the vessel wall horizontally; This pressure represents potential energy or pressure energy (PE). Thus, the total energy (E) of the blood flowing in the vessel is the sum of the kinetic and potential energies (assuming no gravitational effect) as shown below. E = KE + PE (where KE ∝ V2) Hence, E ∝ V2 + PEReading: blood flow booster Read more: what is stray in minecraft | Top Q&A There are two important concepts that follow this relationship.
- Blood flow is driven by the difference in total energy between the two points. Although pressure is often thought of as the driving force for the flow of blood, it is in fact the sum of the energy that drives flow between two points (e.g., along the length of a blood vessel or across a heart valve). In most cardiovascular systems, KE is relatively low, so for practical purposes it is said that differential pressure energy (PE) promotes flow. However, when KE is high, adding KE to PE significantly increases total energy, E. To illustrate this, consider the flow through the aortic valve during cardiac ejection. At the end of ejection, intraventricular pressure (PE) falls slightly below aortic pressure (PE), however, outflow continues to push into the aorta. The reason for this is that the KE of the blood as it moves through the valve at a very high velocity ensures that the total energy (E) in the blood through the valve is higher than the total energy of the blood further down in the aorta. .
- Kinetic energy and pressure energy can be reversed so that the total energy remains constant. This is the basis of the Bernoulli Principle. This principle can be illustrated by a blood vessel that narrows suddenly then returns to its normal diameter. In the constricted (narrow) region, the velocity increases as the diameter decreases. Quantitatively, V 1 / D2 because the flow (F) is the product of the mean velocity (V) and the cross-sectional area of the vessel (A) (F = V x A), and A is directly related then the diameter (D) (or radius, r) squared (from A = π r2). If the diameter is halved in the narrow region, the speed increases by 4 times. Since KE ∝ V2, KE increases 16 times. Assuming that total energy is conserved in the narrowing (E actually decreases because of drag as shown in the figure), then a 16-fold increase in KE must lead to a decrease in the magnitude of PE. A decreased PE represents a decrease in lateral pressure on the vessel wall. Thus, an increase in velocity leads to a decrease in lateral pressure, which is the basis for The Venturi Effect. After passing the narrow passage, KE will return to its pre-narrow value because the diameter after the narrowing is the same as the diameter before the narrowing and the flow (and hence, velocity) is conserved. Due to the resistance of the stenosis and the potential for turbulence, the PE and E after the stenosis will both drop. To summarize this concept, the greater the velocity of the blood flowing, the greater the ratio of kinetic energy to potential energy (pressure).
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An interesting but practical application of Bernoulli’s Principle is found when blood pressure measurements are taken from within the ascending aorta. As described above, during ventricular ejection the velocity and hence kinetic energy of the blood flow is very high. The instantaneous blood pressure measured in the aorta will vary considerably depending on how the pressure is measured. As illustrated on the right, if the catheter with the termination port sensor (E) is facing flowing blood, it will measure a pressure significantly higher than that measured by the side port sensor (S ) on the same catheter. The reason for the difference in measured pressure is that the end port measures the total energy of the blood flowing. When the flow “hits” the end of the catheter, kinetic (high) energy is converted to potential (or pressure) energy and added to the potential to equal the total energy. The side gate will not be “hit” by the current, so kinetic energy will not be converted into potential energy. Therefore, the lateral port sensor measures only potential energy, which is the lateral pressure exerted on the aortic wall. The difference between the two types of manometry can range from a few mmHg to more than 20 mmHg depending on the peak velocity of blood flowing in the aorta. | Top Q&A
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