hemodynamics Flashcards
pressure
- highest in aorta
- Pressure decreases through system, especially in resistance vessels (sm arteries & arterioles)
- low in capillaries and venous system
volume
- Total blood volume ~ 5 L
2. Largest volume in veins (“capacitance vessels”)
flow equation
Q= ΔP/ R
Q: blood flow
P: pressure
R: resistance
flow in must equal
flow out
the total flow is constant throughout the CV system
Flow (Q)
volume per unit time (ml/min)
CONSTANT through system (since closed loop)
cardiac output (CO) =
(Pa - Pv) / TPR
Pa= mean arterial blood pressure Pv= venous blood pressure TPR = total peripheral resitance
V (Velocity) =
Q/A
velocity is highest in the
aorta (lowest total cross sectional area
velocity is lowest in the
capillaries (greatest cross sectional area)
what is the cardiac output?
the volume of blood pumped per minute by the heart
5L/min at rest
Cardiac output corresponds to the
total flow in the cardiovascular system
poiseuelle’s Equation
Q = ΔP x (π r^4)/8nl
R is the radius
n is the viscosity
l is the length
if you increase radius?
decrease R and increase Q
if you increase viscosity?
increase R and thus decrease Q
if you increase length?
increase R and thus decrease Q
what is the biggest determinant of flow?
Radius because flow is proprotional to the 4th power of the radius
Resistance in parallel
decreases the total resistance
Rf of a parallel network is ____ than the resistance of a single vessel
lower
changing the R of a single vessel effect the system how?
little effect on the whole system
the total resistance in the capillary beds is
low and independent of the individual capillaries because there are many parallel vessels.
resistance in a series is
additive
Rf= R1 + R2 + R3 + …
total resistance of a series is ___ than the resistance of any individual vessel
higher
blood flow through a series is
constant, but the pressure drops
laminar flow
- most efficient
- velocity fastest in the center, zero at the edge
- flow equation assumes laminar flow. Not true in the CV system
turbulent flow
- irregular with eddies and vortices
- less efficient–requires more pressure to achieve same velocity
3
what promotes turbulent flow?
- large diameter
- high velocity
- low viscosity
- changes in diameter
- irregularities on walls
turbulent flow produces
shearing forces that can damage vascular endothelium
Heartbeat produces:
pulsatile flow in aorta, but pulsatile flow requires more work.
Pulse pressure is dampened in arterial system.
in the capillaries, flow is
continuous
