Hemodynamics

Introduction

hemodynamics refers to science of deformation and flow of blood. Hemodynamics and blood vessels are affecting the flow and deformation of consistency as the object of study, blood and plasma to the body. Hemodynamics, including blood viscosity ratio (ratio of blood viscosity, plasma viscosity, whole blood viscosity), erythrocyte electrophoresis, erythrocyte sedimentation rate, fibrinolysis and the like.

hemodynamics and general hydrodynamic as the basic object of study the relationship between the flow resistance, and pressure. Because blood vessels are elastic and expandable pipe systems, the blood is a liquid instead of the liquid over the various components of blood cells and the like containing colloidal substances, and therefore, in addition to a common hemodynamics and general hydrodynamic addition, there its own characteristics.

SUMMARY

hemodynamics (hemodynamics) refers to the blood flow mechanics in the cardiovascular system, the main blood flow, blood flow resistance, blood pressure, and the relationship between them . Blood is a fluid, so the same basic principles and the principles of the general hemodynamic hydrodynamics. However, since the vascular system is relatively complex elastic piping system, blood is a liquid instead of the liquid over the various components of blood cells and the like containing colloidal substances, and therefore has both common hemodynamic general fluid mechanics, has its own characteristics.

Features

blood flow and blood flow velocity

blood flow (blood flow) refers to a cross-section through a vessel in the blood volume per unit of time, and called volumetric rate. Often expressed as ml / min or liter / min. Blood flow velocity (blood velocity) refers to a blood linear velocity of the particle movement within the tube. When the blood flow within the blood vessel, and blood flow proportional to blood flow velocity, blood vessel cross-sectional area and inversely proportional.

Poiseuille Law

Poiseuille law studied the liquid flowing in the pipe system. The flow rate can be calculated by Poiseuille Law (Poiseuille's law). The Law is expressed as:

may be expressed as:

wherein, Q is the liquid flow rate, ΔP is the pressure across the duct difference, r is the radius of the channel, L is the pipe length, η It is the viscosity of the liquid. K is a constant, and a liquid viscosity η relevant. From this pressure vessel the blood flow to both ends of the unit time difference (P1-P2) and is proportional to the fourth power of the vessel radius, and is inversely proportional to the length of the blood vessel. Under all other factors being the same, if the radius of the blood vessel A vessel acetate twice, then the blood flow of the former is 16 times the latter. So vessel diameter is an important factor in determining how much blood flow.

laminar and turbulent flow

blood flow pattern within the vessel can be divided into laminar flow (laminar flow) and turbulence (turbulence). Laminar flow motion is a rule, in the case of laminar flow, the liquid flow in each same particle direction, parallel to the long axis of the pipe, but different flow rates of each particle, the axis of the duct at the fastest flow velocity, the nearer wall the layer of the slower flow rate axis, each axis of a parabolic velocity vector (Figure 4-16).

Poiseuille Law applicable to laminar flow state. Laminar flow belonging to the body's blood circulation under normal circumstances. However, when the flow velocity is accelerated to a certain extent, laminar flow is destroyed, then the flow direction of each particle in the blood no longer match, swirl, turbulence is called. In turbulent circumstances, Poiseuille's law is no longer applicable. Forming conditions Reynolds number turbulence (Reynolds number, abbreviated as Re) is determined. This parameter is defined as:

wherein Re number without units. V is the average flow rate of blood (in cm / s), D representative of luminal diameter (in cm), ρ is the density of blood (in g / cm3), η representative of blood viscosity (in poise). Usually when Re exceeds 2000, the turbulence can occur. From the above equation, at a blood flow velocity fast, large-diameter vessels, the blood viscosity is low, the turbulence easily occurs. Under normal circumstances, intraventricular there is turbulence, it is generally believed that this is conducive to thorough mixing of blood. Pathological conditions, such as atrioventricular valve stenosis, aortic stenosis, and patent ductus arteriosus, etc., can be formed due to the turbulence generated noise.

flow resistance

flow resistance (blood resistance) refers to the resistance encountered by the blood flow within the blood vessel. The causes blood flow due to friction. Friction energy consumed to heat the general performance of this part of the thermal energy is not converted to potential energy or kinetic energy of blood. Thus the energy consumption of blood flow gradually, the pressure causes the blood flow gradually decreases. Turbulent blood flow in a blood vessel in a direction inconsistent, greater resistance, and therefore consume more energy.

flow resistance generally not measured directly, but rather calculated blood flow through blood vessels and differential pressure measurement ends. Three relations represented by the following formula:

wherein Q represents the blood flow, P1-P2 pressure difference is representative of the blood vessel ends, R representative of flow resistance. This formula shows that the resistance to blood flow across the pressure difference is proportional to the blood vessel, and blood flow is inversely proportional. Binding Poiseuille Law, vascular resistance calculation formula is obtained:

wherein R represents the resistance to blood flow, blood viscosity [eta] Representative, L is the length of the vessel, r is the radius of the blood vessel. 4 is inversely proportional to apparent viscosity and the flow resistance is proportional to the length of the vessel, the vessel radius by the formula vessels. When the vessel length is the same, the greater the viscosity of blood vessel diameter is smaller, the greater the resistance to blood flow. In the same vascular bed, L η with little change over time, the most important factor for the resistance to blood flow vessel radius. Thus each of the vessels in the body section to the maximum resistance at the arterioles. The body's blood flow distribution regulating diameter vascular resistance is performed by controlling each organ.

blood viscosity

Change

blood viscosity (blood viscosity) can also affect the flow resistance. In other factors constant, the higher the viscosity, the greater the vascular resistance. Normal blood viscosity is 4 to 5 times that of water. The main factors that affect blood viscosity are:

1. The percentage of hematocrit blood cells in the total blood volume in the blood is called hematocrit (hematocrit), blood viscosity is the most important factor in the decision. Male average hematocrit of about 42%, about 38% females. The greater hematocrit, blood viscosity higher.

2. Removal rate of blood flow blood removal rate (shear rate) refers to the ratio in the case of two adjacent layers of the laminar flow of the blood flow rate and the difference between the thickness of the liquid layer. Shear rate is the slope of the parabola of FIG. Homogeneous liquid viscosity does not change with shear rate is changed, the liquid is called Newtonian. Instead, the whole blood is non-homogeneous liquids, the viscosity which decreases as shear rate increases, known as non-Newtonian fluid. At higher shear rates, the laminar flow phenomenon is more evident, i.e., red blood cell concentration in the central axis, with its long axis parallel to the longitudinal axis of the vessel, and striking mutual rotation occurs when red blood erythrocytes are rarely moves, so that blood viscosity low. Conversely, when the cut rate is low, red blood cell aggregation, blood viscosity.

3. Large diameter vascular caliber vessels does not affect blood viscosity, but less than the diameter of the blood in the arteriole flow 0.2 ~ 0.3mm, as long as a sufficiently high shear rate, the viscosity of the blood vessel becomes smaller as the diameter decreases . The reason is not clear, but the body has obvious benefits. Otherwise, when the blood flow in small vessels of resistance will be greatly increased.

4. Temperature of the blood viscosity is increased with decreasing temperature. Body surface temperature is lower than the core temperature, blood flow through the body surface portion so that when the viscosity increases. If a finger is immersed in ice water, viscosity may increase local blood twice.

determinants

blood flow

means that blood flow through the blood vessels of a flow cross-section per unit time, but also into the volume velocity. Typically mL / min or L / min units. Blood flow size depends primarily on two factors, i.e. the pressure difference across the blood vessel to blood flow and vascular resistance. Recycling system, the following relationship between the blood flow, blood pressure and blood flow resistance three:

Q = (p2-p1) / R p2-p1 representative of a pressure difference at both ends of the blood vessel, R representative of blood flow resistance, Q represents the blood flow.

is proportional to blood flow with the pressure difference between the ends of the pipe segment, the pipe resistance is inversely proportional to the liquid flow.

flow resistance

blood flow resistance encountered within the vessel. Frictional resistance to blood flow from the blood and the internal friction between the blood and the tube wall, and is closely related to a blood vessel diameter, length, and blood viscosity, the relationship between them can be used Poiseuille Law (Poiseuille "s law ) expressed:

Q = π × r ^ 4 × Δp / (8ηL) η is the viscosity of blood, L is the length of the vessel, r is the radius of the blood vessel (vascular physiological available)

hemodynamics

blood is a fluid having a relatively viscous. under normal circumstances, the coefficient of viscosity of the blood is 3-4 times of water. Since blood is a complex fluids, both liquid (plasma) have a solid phase (blood cells, etc.), factors that affect blood viscosity more.

in most cases, blood viscosity is mainly determined by the number of red blood cells in the blood. red blood cell count per milliliter of blood, the greater the more the viscosity. erythropenia anemia, decrease the blood viscosity, polycythemia patients and disease, increased blood viscosity, blood flow in blood vessels, resistance to blood flow of blood from the internal friction , i.e., viscosity of the blood.

in the whole cardiac cycle, the average velocity of blood flow in the aorta is only half the critical speed, but the speed of ejection during systole begins to exceed the critical speed. strenuous exercise when , 4-5 fold increase in cardiac output, aortic flow velocity have a longer period than the critical velocity, turbulent flow during systole.

lower

normal circumstances, in addition to the vicinity of the heart valve, the circulatory system other sites will not be turbulent laminar flow is calm, there is no sound. there vortex turbulence and vibration, noise occurs. Therefore, heard an unusual noise in the loop should pay attention to is what causes.

in short, the human hemodynamic changes, the internal body due to the emergence and existence of the disease, and therefore there is a problem.

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