Term
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Definition
| hemodynamics is consideration of the physical forces responsible for moving blood through the CV system; it is involved in both the heart's job of moving blood and the factors which alter distribution of blood flow to various organs |
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Term
| what are the functions of the circulatory system? what is the principle method of exchange in the CV? |
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Definition
| the CV is responsible for nutrient delivery, waste removal, and hormone/messenger transport. blood is a "liquid tissue" that exchanges material via diffusion |
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Term
| what does force in a liquid system manifest itself as? what are the 2 major observable effects of this? |
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Definition
| pressure; which can be hydrostatic, or pressure at rest and hydrodynamic, which is pressure generated from a pump |
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Term
| what is the principle force in hydrostatic pressure? how is it measured? what is the equation used in determination of hydrostatic pressure? |
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Definition
| gravity. hydrostatic pressure is measured in mmHg and determined by the equation P=HPG, where H = height, P = density of the fluid and G is gravity. PSI is the technical measure of pressure, from this equation, but mmHg is the standard medical unit even though it lacks the area component |
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Term
| why was mercury chosen to measure arterial pressure? |
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Definition
| it has a relatively high density, making it possible to meaasure pressure using a relatively short tube |
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Term
| what is hydrodynamic pressure? |
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Definition
| pressure generated by a pump, the energy of which eventually dissipates though the CV system as the blood moves due to resistance from smaller blood vessels and its own viscosity |
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Term
| does hydrostatic blood pressure change according to location in the body? |
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Definition
| if a person lies down, their blood pressure should be relatively globally equal, but if a person stands up, pressure will change according to where the measurement is taken in the body due to gravitational differences |
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Term
| what did stephen hales first do? |
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Definition
| measure hydrodynamic blood pressure in a horse |
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Term
| what pressures determine when a blood vessel will be open? |
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Definition
| if intraluminal pressure is higher than extraluminal, the blood vessel will remain open. if intraluminal is less than extraluminal, the blood vessel will collapse |
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Term
| what is transmural pressure |
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Definition
| the pressure difference across the wall of a vessel |
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Term
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Definition
| the relationship between the change in volume and change in pressure (C= change volume/change transmural pressure) in a vessel. the more compliant a vessel, the greater the (diameter) change in volume for a given change in transmural pressure. |
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Term
| what is laplace's law? what does it tell us? |
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Definition
| T= P x r. in a hollow cylinder, the tension (T) equals the product of the pressure across the wall (P) and the radius (r). this tells us that with a larger radius comes more tension, and therefore a thicker arterial/vein wall is necessary |
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Term
| is the pressure the same on every part of a vessel that has separate dilated and constricted areas? what is different? |
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Definition
| the pressure is the same on all points due to pascal's principle, but the tension will be greater on dialated areas due to the greater radius |
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Term
| what is darcy's equation? |
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Definition
| Q or flow = change in pressure gradient/resistance to flow. (same as I=V/R, ohm's law) a greater difference in pressure = greater flow and a smaller vessel diameter = higher resistance (directly proportional) and a higher flow (indirectly proportional) |
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Term
| if cardiac output is the same (~5 L/min), how does that affect the flow? |
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Definition
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Term
| how would the fact that flow is constant affect the velocity of blood vessels that get progressively smaller? why is blood flow in our capillaries not exponentially faster? |
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Definition
| because Flow or Q = velocity x area, if area decreases, but flow remains the same, then velocity would have to increase. in our bodies, the multiplication of many capillaries allows the total cross-sectional area to be high enough to keep capillary velocity from over-increasing |
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Term
| where does the biggest change in cross-sectional area occur? |
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Definition
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Term
| what is the relationship between velocity and cross-sectional area in a system with a set total volume? |
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Definition
| it is an inverse relationship |
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Term
| where is the maximal cross-sectional area and most minimal flow velocity in the bodie? |
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Definition
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Term
| how can darcy's equation be applied to the CV? |
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Definition
| F = change in pressure/R can also be expressed as R = change in pressure/F. change in pressure in the CV is calculated: MAP-CVP, flow is CO (cardiac output), and R is TPR (total peripheral resistance). normal values are MAP: 95 mm Hg, CVP: 5 mm Hg, CO: 5L and TPR: 18 mm Hg/L/min. [R (TPR) = MAP – CVP/CO] |
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Term
| what factors influence fluid flow through tubes? |
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Definition
| change in pressure (Pi - Po), tube length, tube radius, and fluid viscosity |
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Term
| what is flow proportional to when fluid is moving from a full to empty container? |
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Definition
| the pressure in the first container. (flow is proportional to change in pressure) |
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Term
| what is flow proportional to when fluid is moving from a container 2x the volume of the second container that it is arriving at? |
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Definition
| flow increases proportionally to the pressure difference (Pi-Po), so if the first container is double the pressure, the flow will also be doubled. (flow is proportional to change in pressure) |
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Term
| how does the length of tube traveled between two containers affect the flow of the fluid? |
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Definition
| tube length is inversely proportional, (if L is 2x more, the flow is 2x less and vica versa) |
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Term
| how is flow through a tube affected by radius? |
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Definition
| if the radius is doubled, flow increases 16-fold and vica versa (flow is proportional to radius ^4, so if vessel radius drops 50%, the flow will be dropped to a 16th) |
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Term
| how does blood viscosity affect flow? |
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Definition
| flow is inversely proportional to viscosity, so doubling viscosity decreases flow by half |
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Term
| how are the effects of change in pressure (Pi - Po), tube length, tube radius, and fluid viscosity on flow expressed in pouiselle's law? |
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Definition
| F = pi x change in pressure x r^4/8 x L x viscosity (pi and 8 are fudge factors) |
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Term
| if pouiselle's equation is manipulated to where R = 8 x L x viscosity/ pi x r^4, what does this tell us about resistance (R)? |
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Definition
| resistance has a geometric component, (radius & length) and a viscous component |
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Term
| if tubes are increased in series, (or total length of a tube is increased), how does this affect resistance? |
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Definition
| R= R1 + R2 + R3....increase in series = directly proportional increase in resistance |
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Term
| how does addition of tubes in parallel affect total resistance? |
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Definition
| 1/R total = 1/R1 + 1/R2 + 1/R3...addition of tubes in parallel decreases resistance |
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Term
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Definition
| the ability of the system to conduct. C = 1/R, or the resistance for individual vessels in parallel vascular arrangements. C total = C1 + C2 + C3....etc, (the addition of another conduit increases flow and decreases the total resistance, which is why resistance is lower in capillaries evn though they have smaller diameter) |
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Term
| how is MAP in the modified darcy's equation: [R (TPR) = MAP – CVP/CO] calculated? |
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Definition
| MAP = P diastole + (P systole - P diastole)/3 which is about 95 mmHg. it is divided by 3 to account for more time spent in diastole. |
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Term
| where does the highest velocity of flow usually occur in a vessel? |
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Definition
| in the center, because they are farthest from the stationary wall (concentric lamina of blow flood layers project in towards the center that progressively become faster) |
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Term
| what does it mean to say that blood flow can become nonlaminar or non-newtonian? |
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Definition
| usually blood is laminar/newtonian, meaning its viscosity is constant and independent of flow rate/tube size. BUT with blood, its viscosity can change according to vessel diameter and decrease with smaller vessels by lining up differently |
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Term
| what is reynold's number? |
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Definition
| a non-dimensional number that results from an equation that has had high velocity, large vessel diameter, and low blood viscosity are plugged in. in values in excess of 2000, reynold's number indicates a high likelihood of turbulent flow |
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Term
| what is the viscosity of water? normal blood? plasma? |
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Definition
| water is 1, blood is 3.5, (most viscosity of which is due to RBCs - hematocrit: 45%), plasma is 1.5. therefore blood viscosity increases with hematocrit (though not directly) |
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Term
| why is the effect of pressure on blood flow usually greater than expected? |
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Definition
| increase in arterial pressure not only increases the force pushing blood through the vessels, but it also distends the arteries, decreasing the resistance. therefore blood flow at 100 Hg is 4-6x greater than that at 50 mm Hg. |
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Term
| how does stimulation/inhibition of sympathetics affect vessels? |
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Definition
| stimulation of sympathetics can constrict vessels to the point of zero flow for a few seconds despite high arterial pressure, while inhibition greatly dialates them |
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