Flow Flashcards
What is flow?)
The volume of blood that passes a certain point per unit time (ml/min
F = velocity x cross sectional area
F = change in P/ R
What is the driving force of blood?
Pressure gradient
What is a pressure gradient and what is it proportional to?
The difference in pressure between 2 points
Proportional to flow (F)
Where does the greatest resistance to flow occur?
Pre-capillary resistance vessels
-Arterioles, metarterioles, precapillary sphincters
What is the equation for resistance?
R = 8nI/pi r^4 n = viscosity l = length of vessel r = radius
What is a parallel circuit?
1/RT = 1/R1 + 1/R2 + 1/R3……. or RT = 1/ ((1/R1) + (1/R2) + (1/R3))
RT
What is a series circuit?
RT = R1 + R2 + R3 RT = sum of individual Rs
What kind of circuit is systemic circulation?
Predominantly parallel
What are 3 advantages of parallel circulation?
- Independence of local flow control
- Minimizes total peripheral resistance
- Oxygen rich blood supply to every tissue
What is total vascular resistance (TVR) equal to?
the sum of total pulmonic resistance + total peripheral resistance
because pulmonic and systemic circulations are in series with one another
What is viscosity?
Internal friction of a fluid associated with the intermolecular attraction
What is the viscosity of blood?
3 (most due to RBCs)
What is the viscosity of plasma?
1.5
What is the viscosity of water?
1
With blood, is viscosity proportional to velocity?
No, inversely proportional
What are the 3 viscosity considerations at microcirculation?
- Velocity decreases which increases viscosity
- Cells can get stuck at constriction points which increases viscosity
- Cells line up which decreases viscosity and offsets 1 and 2
What is hematocrit?
Percentage of packed cell volume (primarily RBCs)
normal = 38-45%
What are characteristics of laminar flow?
Streamline
Silent
Most efficient
Normal
What are characteristics of turbulent flow?
Cross mixing Vibrational noise Least efficient Frequently associated with vessel disease (bruit)--thrombus Partially occluded vessels
What is Reynold’s number?
Probability statement for turbulent flow R# = vDp/n v = velocity D = tube diameter p = density n = viscosity
The greater the R#, the greater the probability for….?
Turbulance
If R#
Laminar
If R# > 3000, flow is usually laminar or turbulent?
Turbulent
What is a doppler ultrasonic flow-meter used for?
To determine velocity of flow
RBCs moving towards the doppler transmitter compress sound waves, therefore increasing or decreasing frequency of returning waves?
Increasing
Broad band is associated with laminar or turbulent flow?
Turbulent
Narrow band is associated with laminar or turbulent flow?
Laminar
What 2 things do we use to determine cardiac output?
Fick principle and indicator of dilution
What 3 things do we use to determine vessel flow?
Venous occlusion plesthymography
Doppler ultrasonic flowmeter
Vascular flow cuffs
What are the 3 parts to the Fick principle?
Input blood concentration of substance
output blood concentration of substance
Addition/removal of substance from tissue
Flow = ?
amount of substance per min / AV difference
Pulmonary blood flow = ?
Cardiac output
What is indicator of dilution?
A way to determine flow based on the area under the curve
-Inject dye, measure volume under curve
-Based on conservation of mass
CO is inversely proportional to average duration of the curve (dye concentration)
Is CO proportional to average duration of the curve (dye concentration) in indicator dilution?
No, inversely proportional
What is distensibility?
The ability of a vessel to stretch
Change in volume / change in pressure x initial volume
What is compliance?
The ability of a vessel to stretch and hold volume
Change in volume / change in pressure
Distensibility x initial volume
Is compliance = distensibility?
No
Is compliance proportional to distensibility?
Yes
In systemic arteries, a small change in volume is associated with a large change in ….?
pressure
In systemic veins, a large change in volume is associated with a small change in ….?
pressure
Veins are how much more distensible and compliant than systemic arteries?
8 x more distensible
3 x larger
24 x more compliant
Local blood flow is regulated in proportion to what?
metabolic demand in most tissues
What does short term control of blood flow involve?
Vasodilation/vasoconstriction of precapillary resistance vessels
What is long term control of blood flow involve?
Changes in tissue vascularity
- Formation/dissolution of vessels
- Vascular endothelial growth factor and angiotenin
What is the role of arterioles in control of flow?
- Integrator of multiple inputs
- Innervated by SNS vasoconstrictor fibers and have alpha receptors
- Effected by local factors (vasodilators, circulating substances)
When pressure is kept relatively constant, vasodilation will result to what changes in resistance and flow?
Decreased resistance leads to increased flow
When pressure is kept relatively constant, vasoconstriction will result to what changes in resistance and flow?
Increased resistance leads to decreased flow
What is the local vasodilator theory?
Active tissues release local vasodilator (metabolites) which relax vascular smooth muscle
What is the oxygen demand theory?
As tissue uses up oxygen, vascular smooth muscle cannot maintain constriction
What is autoregulation?
The ability to keep blood flow (F) constant in the face of a changing arterial BP
Are renal flow and glomerular filtration rate autoregulated?
Yes
What is angiogenesis?
Production of new microvessels
What is arteriogenesis?
Shear stress caused by enhanced blood flow velocity associated with partial occlusion
What are angiogenic factors?
Small peptides that stimulate growth of new vessels
-Vascular endothelial growth factor (VEGF)
What is up-regulated when endothelium is activated by stress?
Monocyte chemoattractant protein-1 (MCP-1)
- Inflammation
- Remodeling and development of new and enlarged collateral arteries and arterioles
Hypoxia causes release of what peptide?
VEGF
What does VEGF stimulate?
capillary proliferation and development of collateral arterial vessels
Is NPY from SNS angiogenic?
Yes
What may hyperactive SNS compromise?
Collateral blood flow by vasoconstriction
What is vasculogenesis?
Mesenchymal cell differentiate into endothelial cells
What is angiogenesis?
Formation of new blood vessels by sprouting from pre-existing small vessels usually lacking developed tuinca media
What is arteriogenesis?
Rapid proliferation of pre-existing collateral vessels with fully developed tunica media
What are the 3 types of angiogenesis triggers?
Mechanical, chemical, and molecular
What are the mechanical angiogenesis triggers?
Hemodynamic
Shear stress
What are the chemical angiogenesis triggers?
Hypoxia
NO
What are molecular angiogensis triggers?
Decreased glucose -- increased VEGF Inflammation angiogenic growth factors -Fibroblast gf -VEGF -Placenta gf -angiopoietin
What is therapeutic angiogensis?
Clinical enhancement/promotion of collateral blood vessels/flow in ischemic tissues
What are the 3 methods of therapeutic angiogenesis?
- Protein therapy (use GF proteins)
- Gene therapy (manipulate gene expression)
- Cellular therapy (introduce angiogenic factors)
What are 3 things that endothelium release to give it a vasoactive role?
Prostagyclin (PGI2) Nitric Oxide (NO) Endothelin
What does prostacyclin do?
Inhibit platelet aggregation
Relaxes vascular smooth muscle
What does nitric oxide do?
Vasodilator
Stimulated by shear stress associated with increased flow
and acetelcholine binding to endothelium
What is the functional unit of the circulation where the bulk of exchange takes place?
Capillary
What is vasomtion?
The intermittent contraction of metarterioles and precapillary sphincters
What are 3 mechanisms of exchange in microcirculation?
Diffusion
Ultrafiltration
Vesicular transport
What are 2 ways that blood can bypass the capillary bed and go straight to the venule?
AV shunt
Metarteriole
What is oxygen uptake equal to?
the product of flow (F) x the arterial-venous oxygen difference
O2 uptake = (F)(A-VO2 difference)
Functional/nutritive flow (F) is associated with increased what?
Oxygen uptake/utilization
Non-nutritive flow increases is associated with what?
Shunting of blood through a bed
What does passive diffusion require?
Permeability
Concentration gradient
What does ultrafiltration require?
Bulk of flow goes through filter (capillary wall)
Starling forces
-Hydrostatic pressure
-Colloid osmotic pressure
What does vesicular transport require?
Larger molecular weight non-lipid soluble substances
Does hydrostatic pressure gradient favor filtration or reabsorption?
Filtration
Does colloid osmotic pressure (low to high) favor filtration or reabsorption?
Reabsorption
What is the equation for net filtration pressure?
(capillary hydrostatic pressure-interstitial hydrostatic pressure) - (capillary colloid osmotic pressure-interstitial colloid osmotic pressure)
The colloid osmotic pressure is a function of what?
protein concentration
albumin, globulins, fibrinogen
What is the calculated colloid effect?
19 mmHg
What is the actual colloid effect?
28 mmHg
What is the discrepancy between calculated and actual colloid effect due to?
Donnan effect
What effect does the Donnan Effect have on colloid osmotic effect? (increase or decrease)
Increase
How does the Donnan effect increase colloid osmotic effect?
Large molecular weight proteins (albumin) carry negative charges which attract positive ions. This increases the osmotic effect by 50%
Where would we find tight junctions in capillary walls?
Blood brain barrier
Where would we find discontinuous junctions in capillary walls?
Liver
Where would we find filtration slits (fenestrations) in capillary walls?
Glomerular capillaries
What kind of protein can exert osmotic pressure?
That protein that cannot cross capillary wall
What does the reflection coefficient express?
How readily protein can cross a capillary wall
0-1
What does a reflection coefficient of 0 mean?
All colloid proteins freely cross wall, none are reflected = no colloid effect
What does a reflection coefficient of 1 mean?
All colloid proteins are reflected, none cross capillary wall = full colloid effect
