6. Cardiac Physiology II Flashcards
Circuits in Series
Flow must be equal
CO of R and L heart are inter dependent bc series arrangement
Hemodynamics
Blood flows in closed system
Blood
- noncompressible fluid
- heterogeneous (plasma, cells, proteins)
Vessels are compliant (flexible), not rigid
-size depends on internal pressure and vascular smooth muscle contractile state
Pressure Profile
BP changes throughout CV system
Heart spends more time in diastole than systole
MAP
Mean arterial pressure
Delta P
change in pressure
largest change in arterioles
Large Artery Properties
Thick walled
Under high pressure
Lots of smooth muscle
Large Vein Properties
Thin walled
Under low pressure
Capillaries
Not a lot of anything (smooth muscle, elastic tissue, fibrous tissue)
Transport processes!
Area and Volume Contained in Systemic Blood Vessels
Biggest cross sectional area: capillaries
(beds not individuals)
Greatest amount of blood: veins
(stretch easily, hold a lot of blood)
Q=delta P/R
Q: flow (how much travels)
- turbulent
- laminar
- velocity (how fast it travels)
delta P: change in pressure
R: resistance
- fluid viscosity
- vessel diameter
- vessel length
v=Q/A
Q: flow
v: velocity
A: total cross sectional area
Tube: pi r squared
If flow through a tube is constant then …
velocity increases as total cross sectional area decreases
Capillaries
Smallest diameter (individually)
Velocity is the least
Total cross sectional area is huge (beds)
Laminar Flow
Ideal
Streamline
Concentric lamina slide past one another
Parabolic effect to flow (highest velocity at center, not much moving on ends)
Predictable
Viscous forces dominate
Turbulent Flow
Eddy currents
Noisy
Larger pressure require to maintain constant flow
Going in all different directions
Large fluctuations in velocity causing swirling effect
Inertial forces dominate
Reynold’s Number
Re=vpD/n
inertial forces: vpD
viscous forces: n
v: velocity
p: fluid density
D: tube diameter
n: viscosity
Re < 2000 –> laminar flow
Depends more on velocity than diameter
Anemia
Decreased hematocrit –> decreased mass of RBCs –> decreased viscosity
Dec viscosity –> inc Re
Causes turbulent flow and functional murmurs
Also associated with inc velocity
Thrombi
Blood clots in the lumen of vessels
Diameter narrows –> inc blood velocity at site –> Re inc –> turbulent flow
Flow is directly related to pressure
Q=deltaP/R
Flow is dependent upon pressure difference
P1-P2 = deltaP = pressure gradient
Flow is inversely related to resistance
inc resistance –> dec flow
R=deltaP/Q
Major mechanism for changing resistance in CV system is by …
changing resistance of blood vessels (smooth muscles in arterioles)
Resistance
Directly proportional to viscosity
Directly proportional to length
Inversely proportional to fourth power of radius !!!
Poiseuille Equation
Resistance=8nL/piR^4
L: length
R: radius
Vascular Beds: Series
Blood flows from one vessel to another in sequence
Vascular Beds: Parallel
Blood flow is distributed simultaneously among parallel vessels
Series Resistance
Sequential arrangement
- total flow through each level of system is the same
- pressure dec progressively
Total resistance = sum of individual resistances
In Series
All tubes have the same flow in and flow out
Rin>Pout (delta P inc)
Total R has to increase
Parallel Resistance
Simultaneous arrangement
- mean pressure in each artery will be close to mean pressure in aorta
- adding new resistance to this circuit decreases total resistance
Total resistance is less than any of the individual resistances
In Parallel
Qin=Qout (Q varies in each tube)
Pin=Pout for all tubes
R varies as well
P is constant
Q and R are changing
