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Hemodynamics

Cardiology Hemodynamics

QuestionAnswer
What are the components of blood? Plasma (liquid component); cellular components (RBCs, WBCs, and platelets)
Hematocrit volume of RBCs in blood (bottom 45% usually in centrifuged blood)
Plasma Liquid component; contains variety of proteins (albumin, globulin), electrolytes, hormones, enzymes, blood gases
What is the mathematical formulation for Ohm's law (or an extension of) in fluid mechanical terms? Q = (P2-P1)/R , where Q is the volumetric flow rate, P2-P1 is the pressure drop, and R is the resistance provided by the vessels. IMPORTANT: flow is a function of pressure CHANGE, not absolute pressure!
What assumptions does Ohm's law for fluid flow assume about the cardiovascular system (that is, why does not approximate it perfectly)? Assumes blood vessels rigid tubs and blood is a perfect Newtonian fluid
What is the mathematical formulation of Poiseuille's law? Q = (pi * (P2-P1) * r^4) / (8 * n * l) where P2-P1 is the pressure drop across the two ends of the pipe (blood vessel), r is the radius of the tube, n is the viscosity of the fluid, and l is the length of the vessel
What assumptions does Poiseullie's law assume? Assumes that there is laminar flow: the maximum velocity is in the middle, and the velocity towards the edges of the tube is near 0 (due to drag), creating semi-parabolic flow.
What are murmurs? Result of localized turbulence, where some energy is lost due to noise (usually due to structural defect); normal blood flow is laminar and NOT TURBULENT, thus, NORMAL BLOOD FLOW IS SILENT
What is the mathematical formulation for the Reynold's number? Re = (d*v*D)/n , where d is the density of the fluid, v is the velocity of the fluid, D is the diameter of the tube, and n is the viscosity of the fluid.
What is the critical value for the Re in blood (that is, at what Reynold's number will you get turbulent flow?) ~1000; at values >1000, you will have turbulent flow, while at values <<1000, you will have laminar flow
By what factor can arterioles change their radius? Thus, what is the change in the possible flow that passes through? By a factor of 4 (constrict up to 1/4 of their diameter); Can decrease flow by a factor of 4^4 = 256 times
If hematocrit increases, what does that do to viscosity? To flow? Viscosity increases --> flow decreases
Compare the blood flow rate of patients suffering from anemia to those suffering from polycythemia Anemic patients have LESS hematocrit --> faster blood flow, while patients with polycythemia have MORE hematocrit --> slower blood flow
Distole time during which cardiac muscles relax
Systole time during which cardiac muscles contract
How long does a distole last relative to a systole? Distole lasts ~2x long as systol (e.g. if heart rate is 67 bpms, cardiac cycle is 900 msec --> distole = 600 msecs, systole = 300 msecs)
How is energy transferred from the heart to the arteries (i.e. where does the energy of the pressure wave go?) High pressure blood from the contraction of the ventricles transfers 95% of energy to artery walls (fibrous and elastic); that energy gets turned into kinetic energy via elastic recoil
What is the advantage of storing energy from ventricles into the elastic (potential) energy of the arteries? Limits the drop in arterial blood pressure during diastole; further down, arterial tree can function as elastic reservoir for blood flow from arteries to capillaries (allowing for blood flow to be continuous) even if flow is pulsatile
Compliance Tendency of a hollow organ to resist recoil toward its original dimensions. C = (V2-V1)/(P2-P1), where V2-V1 is the stroke volume and P2-P1 is the pulse pressure
Mean arterial pressure (MAP) Driving force for fluid entering arterial circulation
How would you estimate mean arterial blood pressure (MAP) based on diastolic and systolic pressure? MAP = 2/3 (diastolic P) + 1/3 (systolic P); based on the fact that diastole lasts twice as long as systole, though this is inaccurate for high heart rates for this reason
What is the formulation of Ohm's law for flow in terms of the Mean arterial pressure and the total peripheral resistance? MAP = CO * TPR , where MAP is the mean arterial pressure, CO is the cardiac output, and TPR is the total peripheral resistance
Created by: karkis77 on 2011-08-22



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