3 - Properties of the Vasculature Flashcards
What type of system is the cardiovascular system?
One way, closed system
Layers of Vessels:
Intima
Media
Adventitia
Intima - Innermost, single layer of endothelial cells
Media - Smooth muscle cells, in matrix of collagen, elastin, glycoproteins*
Adventitia - Outermost, collagen, fibroblasts, blood vessels, autonomic nerves (sympathetic adrenergic)
*Ratio of smooth muscle/collagen/elastin determines mechanical characteriistics (e.g. Aorta = more elastin, arterioles = smooth muscles, etc)
What is unique about the layers within capillaries?
Only single endothelial layer, Intima
How does the Aorta damped pulsatile pressure?
Acts as temporary storage vessel during each heartbeat to accommodate the ejected blood
What is the primary vascular regulator of blood pressure?
Arterioles provide primary resistance to flow
What vessels have the greatest cross sectional area?
What is unique about these?
Capillaries
Have no smooth muscle
Where is most blood volume within the body at any given time?
Venules and veins
What allows veins the ability to expand and store blood?
Thin walls provide mechanism to stretch and provide capacitance (blood storage)
Where does the largest pressure drop occur within the vascular network?
What causes this drop?
Where does pulsatility disappear?
Through arteriolies
Energy is consumes overcoming resistance
Pulsatility disappears at the level of the capillaries
What is the equation for Cross-Sectional Area and Velocities of Blood Flow?
What is the rough trend for velocity?
v = Q / A
v: Velocity of flow (cm/sec)
Q: Flow (mL/sec)
A: Cross-Sectional area (cm2)
Smaller cross sectional area = faster velocity (flow is unchanged)
What two factors determine the flow of blood through vessels?
Equation?
- Pressure Difference (gradient, perfusion pressure)
- Resistance
F = ΔP / R
F: Flow (or Q)
ΔP: Pressure difference
R: Resistance
*How do you determine Resistance (R) ?
What are general trends regarding this?
R = 8nL / πr4
Longer = Increase resistance (direct)
Smaller radius = Increase resistance (inverse)
Poiseuille’s Equation
General trend to know?
Rate of blood Flow is directly proportional to radius4
What is the major mechanism for changing blood flow in the CV system?
Changing resistance in blood vessels via radius changes
Autonomic Effects:
Sympathetic Stimulation
Stimulation: Constrict vessels, blood flow decrease
Inhibition: Dilates vessels, blood flow increase
What is an approximation we make regarding increase to arterial pressure and increase in flow?
Non linear, curved increase due to distanetion of vessels (not rigid tubes)
What is the effect of Blood Hematocrit and Blood Viscosity on Vascular Resistance and Blood Flow?
Anemia?
Temperature?
Greater Viscosity = Less Flow
Hematocrit Increases Viscosity
Anemia Decreases Viscosity
Temperature Increases Viscosity
Laminare vs Turbulent Flow in Blood Vessels?
Laminar - Orderly, streamlined flow, max velocity at center
Turbulent - Irregular flow, can be caused by obstructions, sharp turns, rough surfaces, high flow
Relation of Reynolds Number to Laminar and Turbulent Flow?
(Re > 2000 = Turbulent Flow)
Clinical Representation?
Method to predict when turbulence will occur
Common in Aorta
Small vessels, Re not usually high enough to cause turbulence
Clinical: Turbulent flow is often accompanies by audible vibrations
Murmur = Turbulence in Heart
Bruits = Turbulence in a Vessel
How is resistance calculated to vessels within a series?
Total blood flow?
Total resistance = sum of resistance of each vessel
Assume total flow through each blood vessel is the same
How do you calculate resistance for blood vessels in parallel?
What type of vessel is this important for?
How is this important for organ arrangement?
Reciprocal of the total resistance is equal to sum of reciprocals of the individual resistances
Parallel Vessels greatly reduce resistance
- - -
Capillaries are arranged in this method; greatly reduces resistance
Parallel arrangment allows independent tissue regulation (vs other areas of body)
How do you apply the basic flow equation to series of vessels?
Remember: Q = ΔP / R
Calculate Resistance for Series: 1/Rtotal=1/R1 + 1/R2 + …
ΔP = Pi - Po
You can apply the equation just as a single vessel
Vascular Compliance
Compliance = How much volume changes (ΔV) w/change in pressure (ΔP)
C = ΔV / ΔP
Venous System > Arterial System (Compliance)
*The venous system can greatly change its volume with some changes in pressure compared to arteries–i.e. they stretch*
Why is some distensibility important for arteries (compliance)?
Reduces pressure of pulsations; greadually decreasing until none at capillaries
Prevents all flow of blood at once during systole, and none during diastole; this ensures constant supply of blood
Systolic Pressure
Diastolic Pressure
Pulse Pressure
Systolic Pressure: Pressure at top of each pulse
Diastolic Pressure: Pressure at trough of each pulse
Pulse Pressure: Systolic - Diastolic
Mean Arterial Pressure (MAP)
Equation?
What factors determine it biologically?
Average of the arterial pressures throughout the cardiac cycle, measured over t ime
MAP = Pdiastolic + 1/3 (Psystolic - Pdiastolic)
Cardiac Output (CO): Overall blood flow in total circulation
Systemic Vascular Resistance (SVR): Resistance to blood flow offered by all of systemic valculature (exclude pulmonary vasculature)
Central Venous Pressure: Blood pressure in throacic vena cava near right atrium (~ “0”)
MAP = (CO x SVR) + CVP
How do we change local blood flow and central arterial pressure?
(think in terms of what affects MAP)
Arteriole Radius
Whole Body: This changes Total Peripheral Resistance (TPR), raising Arterial Blood Pressure at given cardiac output.
Constriction = Raise BP
Dilation = Lower BP
Single Organ/Tissue: Local blood flow altered, w/little effect on TPR or BP (think about salivary gland release, doesn’t change BP on a large scale)
What factors affect Arterial Pulse Pressure (Pp)?
Stroke Volume (SV) and Compliance (C)
Pp = SV / C
Application of : ΔP = ΔV / C
- -
Pp tends to increase with age because reduced compliance (hardening of the arteries).
Clinical: Measuring Systolic and Diastolic Pressures
Direct: Needles or Catheters into peripheral arteries
Indirect: Blood pressure cuff (auscultatory) (brachial artery pressure)
Systolic = Beginning of Sounds (turbulent)
Diastolic = No Sound (laminar)
Venous Pressure and Volume regulation
Due to thin walls, veins are more susceptible to physical influence than arterioles
Increase of tone, decrease compliance as walls become stretched
Centra Venous Pressure (CVP)
Approximation for what chamber of the heart?
What factors influence CVP?
Approximation of right atrial pressure
- - -
Clinical: If Right Ventricle fails, CVP may be high enough for jugular impulse to be visible when patient upright
*Anything causing venous return elevates CVP:
- Increased blood volume (I.V. injection)
- Increased large vessel tone (decreased compliance)
- Dilation of the Arterioles, which decreases peripheral resistance and allows rapid flow of blood from arteries into veins
How does gravity affect Venous Pressure?
How does blood not just pool below the heart in the lower extremities due to gravity?
Orthostasis (standing) distend veins below heart level;
pressure increases in all vessels below heart level, and falls in all above heart level (gravitational impact)
Veins have one-way valves that permit blood flow toward heart
What is the Skeletal Muscle Pump?
Method veins use to facilitate blood flow back to the heart.
Veins surrounded by skeletal muscle are squeezed, pushing blood back to heart (valves prevent back flow)
Clinical: Varicose Veins
Venous valves become incompetent, muscle pumping becomes ineffective.
Blood volume and pressure increase in the veins of dependent limbs–increase capillary pressure, may cause edema
What is the Respiratory Pump?
Inspiration facilitates venous return, leads to increase in atrial and ventricular preloads
Expiration, venous return falls
We can force expiration: Valsalva, Coughing
Net effect: Increase Venous Return / Cardiac Output
