Flow Flashcards
What determines the flow for a given pressure gradient?
Amount of resistance: viscosity, vessel length/cross-sectional area
What is the relationship between velocity and cross-sectional area at a constant flow? Apply this principle to capillaries
Velocity is inversely proportional to cross-sectional area
Capillaries individually have small CSAs and high velocities, but together the largest CSA which lowers their velocity to match the aorta’s
What is laminar flow?
Velocity gradient from middle (fastest) outwards (slowest)
What generates turbulent flow and what can be heard?
Mean velocity increases - gradient of laminar flow breaks down - turbulence “bruit”
Now, with constant pressure what is the relationship between mean velocity and cross-sectional area
Mean velocity is proportional to the cross-sectional area
What does Poiseuille’s law state?
Resistance increases as viscosity and length increases, resistance decreases with the 4th power of the radius
What is the relationship between resistance and pressure drop?
Resistance and pressure drop are proportional
*pressure drops occur when fixed flow meets area with higher resistance (i.e arterioles)
Why do arteries need high pressure?
To drive CO and overcome arteriole resistance
What is transmural pressure?
The pressure in the tube compared to outside of it
Explain pulsatile flow/systolic and diastolic pressure, what affects both?
Systole: blood flows into arteries, arteries stretch and pressure rises to max = systolic pressure
FOC, TPR, artery stretchiness
Diastole: arteries recoil to push blood into arterioles, pressure falls but never hits 0, veins fill
Systolic pressure, TPR
What determines total peripheral resistance?
TPR = resistance of all arterioles
How would you calculate average pressure?
Diastolic + 1/3 pulse pressure
