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# Phys Exam 2: Ch 14

### Physics of Circulation

How is blood flow measured? Flow = change in pressure/resistance --> measured in mL/min or L/min
What is laminar flow? Flow pattern marked by smooth changes in pressure & velocity (SMOOTH!)
What is turbulent flow? Flow pattern that includes irregular variations in pressure & velocity (NOT SMOOTH!)
What is Reynolds Number (Re)? A measure of turbulence
What causes Re to increase? Velocity of flow, vessel diameter increases, decreased viscosity
What causes Re to decrease? Increased viscosity
What does a high (~200-4000+) Re value indicate? A low (0-~100) Re value? Turbulence; laminar flow
Define BP Force of blood against the blood vessel wall, measured in mmHg
How do you calculate Reynolds Number (Re)? Re = (velocity of flow x diameter of vessel) / kinematic viscosity [n/p]
Define Resistance The force that must be overcome for the blood to flow
How do you calculate Resistance? R = change in pressure/flow
If you have Arterial-venous pressure difference = 100mmHg and Cardiac output 100mL/sec, what is the Peripheral Resistance Unit? 100mmHg/100mL/sec = 1 PRU
How do you calculate PRU? PRU = (AV pressure difference)/Cardiac output
What is the typical range of PRU? 0.2 (extreme vasodilation) to 4 (vasoconstriction)
If you have a pulmonary pressure differential is 14mmHg, what is PRU? 14mmHg/100mL/sec = 0.14 PRU
What is the resistance of the entire systemic circulation? 100mmHg/100mL/sec
What is conductance? The measure of blood flow for a given pressure distance (i.e. the inverse of resistance)
GHow do you calculate conductance? Conductance = 1/Resistance
What is the take away message from Poiseuille's Law? As the radius of the blood vessel increases, the flow of blood quadruples
What is the effect of blood vessel diameter on blood flow? Flow increases as the 4th power of the radius of the vessel (i.e. increases 4-fold)
What is hematocrit? The % of blood that is RBCs
What happens if the hematocrit increases? Blood viscosity increases
How does blood doping lead to heart attacks? Increasing the % of RBCs (hematocrit) increases blood viscosity
What happens as the % of blood cells in a volume of blood increases? The viscosity increases, resistance to flow increases
How many circulatory systems exist in the body? 2 - pulmonary circulation and systemic circulation
What are the 3 principles of control of the circulation? 1. the rate of blood flow to a tissue is based on the need of that tissue; 2. Cardiac output is based on venous return; 3. Arterial pressure is controlled independently of either local flow or cardiac output
Why is it important that rate of blood flow to a tissue is based on that tissue's needs? Because not all of the tissues need the same blood flow supply at one time
Created by: hclark86