Hemodynamics Flashcards
Mechanism of blood flow through vessels
- pressure differences drive blood flow through vessels
- difference between arterial and venous pressure drives blood flow through organ
Location of highest pressure and highest resistence
- high pressure @ aorta
- largest drop in pressure/highest resistance @ arterioles
Total blood volume
~ 5L
Location of greatest blood volume
-venous system = “capacitance vessels”
Flow definition w/in context of CV system
- (Q)=volume per unit time (ml/min)
- constant throughout closed system
Cardiac output definition
-total flow in CV system
Velocity definition w/in context of CV system
- (v)=distance per unit time (cm/sec)
- inversely related to cross-section area (A)
- velocity high w/small A (i.e. aorta) & velocity low w/high A (i.e. capillaries)
Flow equation
- Q=P/R
- Q=flow
- P=pressure difference
- R=resistance
- aka CO=(mean arterial pressure - mean venous pressure)/total peripheral resistance (TPR)
Poiseuille’s Equation
- Q=P x (pi*r^4)/(8nl)
- Q=flow
- P=pressure difference
- r=radius
- l=length
- n=viscosity of blood
Resistance of vessels in series vs. parallel
- total resistance of vessels in series is higher than any individual vessel
- total resistance of vessels in parallel is less than the vessel with the smallest resistance
Laminar flow definition
- smooth, streamlined, most efficient
- velocity slowest at edge, fastest at center
Turbulent flow definition
- irregular
- requires more pressure for same average velocity (vs. laminar)
Factors that increase turbulent flow
- large diameter
- high velocity
- low viscosity
- abrupt diameter change
- irregularities on tube walls
Pulsatile flow
-heart pumps intermittently–pulsing flow through aorta; pressure is not constant
Systolic vs. Diastolic pressure
-peak aortic (~arterial) pressure vs. minimum aortic pressure
Pulse pressure definition
-pulse pressure=systole - diastole= 120 - 80 = 40mmHg
mean arterial pressure (MAP) definition
MAP ~ diastolic + 1/3(systolic - diastolic)
Compliance definition/equation
- C=(change in V)/(change in pressure)
- represents the elastic properties of a vessel
- determined by proportion of elastin to collagen
Arteriosclerosis
- loss of compliance cause by thickening/hardening of arteries
- some normal comes w/aging
LaPlace Law equation
- T=(P*r)/u
- T=tension
- P=transmural pressure
- r=radius
- u=wall thickness
Pressure/radius impact on Tension (i.e. in LaPlace Law)
-Tension increases w/increasing pressure and radius –> hypertension increases stress on vessel/chamber walls
Transformation of pulsatile flow –> continuous flow
-degree of compliance in main arteries contributes to transformation of pulsatile flow deriving from heart to continuous flow @ capillaries
Major types of transport of CV system
- bulk transport=cargo brought from point A to B
- transcapillary transport=movement of cargo between capillaries and tissues
Fick’s principle definition and equation
- considers how much of a substance is used by a tissue
- x(used)=x(in)-x(out)=Q([x]in - [x]out)
Hydrostatic pressure definition
- ~blood pressure
- net hydrostatic @ capillaries: difference between pressure and interstitial pressure
- promotes filtration
Oncotic pressure definition
- osmotic force created by proteins in blood and interstitial fluid
- alpha globulin and albumin = major determinants of oncotic pressure
- solutes move from high to low concentration vs. solvents move towards high concentration
- promotes reabsorption of fluid
Starling equation
- Flux=k[(Pcap - Pint) - (Ocap - Oint)]
- k=constant
- Pcap=cap hydrostatic pressure
- Pint=interstitial hydrostatic pressure
- Ocap=cap oncotic pressure
- Oint=interstitial oncotic pressure
Net flux fluctuations @ capillary bed
- factors that increase hydrostatic (blood) pressure (hypertension) or reduce oncotic pressure (liver disease) –> excess filtration –> edema
- arterial end=more filtration vs. venous end=more reabsorption
- different net flux at different cap beds
