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18 Cards in this Set
- Front
- Back
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Poiseuille's Equation: Definition, Variables, and Significance for Hemodynamics
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Q = ΔP x πR^4 / 8 L η
Q = flow, ΔP = driving pressure, R = radius, L = length, η = viscosity This only applies for laminar flow. note: doubling R has a 16 fold increase in flow. |
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Reynold's number: definition, and applications
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Reynold's number = velocity x diameter x density / viscosity
When R > 2000, laminar flow deteriorates into turbulent flow. Thus innocent (or "functional", "hemic") murmurs can be heard that are caused by an increase in Reynold's number, e.g. in anemia because of the decrease in viscosity. |
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Viscosity of blood changes as a function of...
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Viscosity of blood changes as a function of the hematocrit, the velocity of flow, and the geometry of the vessel.
At high V, RBC's streamline into bullet shapes and accumulate in the center of the vessel forming an axial core flow-- greatly diminishing resistance. When blood flows through arterioles less than 0.5mm in diameter, blood behaves as if it were less viscous and flows faster than expected. In the venules, flow becomes sluggish and the apparent viscosity of the blood increases. |
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What is the Fahraeus-Linddquist effect?
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When blood flows through arterioles less than 0.5mm in diameter, blood behaves as if it were less viscous and flows faster than expected. This is the Farhaeus-Lindquist effect.
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normal CVP value
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less than 10mmHg
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What percentage of the cardiac output do different organs receive in a person at rest?
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Of the 5L/min total cardiac output: 15% goes to the brain, 25% to the GI tract, 20% to the kidneys,4% the coronary arteries, and the remaining ~40% goes to the musculoskeletal system and skin.
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What percentage of total blood volume do different compartments in the body hold at rest?
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A normal body contains 5L of blood split up as follows: 65% in the venous circulation (peripheral veins, and venous reservoirs in the spleen, liver), 15% in the arteries and arterioles, and 15% is in the heart and pulmonary vessels. Only 5% is in the capillaries because they are very short.
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How to measure total peripheral resistance?
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TPR = MAP - CVP / CO
Total peripheral resistance is equal to the difference in the mean arterial pressure (MAP) and the central venous pressure (CVP) divided by the cardiac output (CO). TPR = MAP - CVP / CO |
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The linear velocity of blood is inversely related to....
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The linear velocity of blood is inversely related to the mean cross-sectional area of the vessels through which blood is moving.
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Explain how aneurysms form, using LaPlace's equation
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T = P x R
When the wall of a large vessel becomes weak (e.g. atherosclerosis), it bulges out under pressure, increasing the effective radius of that part of the vessel. Assuming the BP is the same, this will result in an increase wall tension, which will lead to further bulging, creating a positive feedback loop that eventually bursts the vessel. |
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Pulsus parvus
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A weak and thready pulse, which one may encounter in a patient who is in circulatory shock.
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Bifid pulse
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A sluggish, biphasic pulse of low velocity, which one may encounter in left ventricular outflow obstruction.
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Corrigan pulse
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AKA water hammer - A bounding, strong pulse seen with high pulse pressures in anemia or in aortic insufficiency.
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Pulsus paradoxus
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When the pulse pressure decreases more than 10% upon inspiration. This is because of cardiac tamponade/pericardial effusion, where the right ventricular (which would otherwise bulge into the pericardial space) bulges into the AV septum and into the LV, reducing LV stroke volume.
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Pulsus alternans
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When the intensity of the pulse may vary from one beat to the next. It is a sign that the LV is unable to eject similar stroke volumes from one beat to the next, and usually signifies severe left ventricular failure.
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Why is maintaining a minimum pressure important in arteriolar blood flow?
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Arterioles will collapse at less than 20mmHg, and thus need blood pressure to keep the vessels distended.
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How would a blood volume over blood pressure curve look like for a young person's arteries? For a middle-aged? For an old person?
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Each of these curves will be a gradually plateauing compliance curve. The older the person, the more the volume will plateau at a given pressure (less volume change at any given pressure = less compliance).
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Why does blood pressure rise in large arteries?
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Because the compliance of large arteries is relatively constant, the pressure depends on the volume of blood in that compartment. When either stroke volume/CO (in-flow) or total peripheral resistance (1/outflow) increases, the blood pressure will rise.
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