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hemodynamics 2


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______ in a fluid system is commonly expressed as some measurement of pressure.
Units of force: _____ Units of pressure in physics: _____
pressure difference which is responsible for the flow of a fluid from one point to another (e.g., inflow pressure minus outflow pressure, or upstream pressure minus downstream pressure).
Driving pressure:
Pressure difference across the wall of a cardiac chamber or blood vessel.
a. I.e., inside pressure minus outside pressure.
b. Responsible for distending the chamber or vessel.
Transmural pressure:
the force resulting from the action of gravity on a continuous column of fluid.
Hydrostatic pressure:
hydrostatic pressure is defined as the product of these 3 quantities:
P =
P = hρg.

h = height of column of fluid or blood
ρ (rho) = density of fluid or blood
g = gravitational constant (980 cm/sec2)
______ is commonly the reference fluid
1mm Hg = ______ dynes/cm2
_____ is sometimes used for low pressures:
1mm Hg = ____ cm H2O)
Gravity and posture will affect ______ pressures (e.g., in systemic arteries )
___________ in systemic vessels is not affected by posture, because gravity and hydrostatic pressure affect both arterial and venous pressures to the same extent, but in opposite directions, and the effects cancel out.
Driving pressure
The term “hydrostatic pressure” is also commonly used by some authors to refer to the ______________, compared to atmospheric pressure, at any level relative to the heart.
blood pressure inside capillaries
Even though not technically correct, this use of the term _________ refers to the total pressure (the sum of that due to the pumping action of the heart and any P = hρg due to gravity).
“hydrostatic pressure” in capillaries
Another way to think of it is that it is a _________, rather than a colloid osmotic pressure due to protein concentration.
fluid pressure
Approximate Normal
PRESSURE (mm Hg)of Right atrium
0-5 (mean)
Approximate Normal
PRESSURE (mm Hg)of Right ventricle
25-30/0-5 *

* systolic/diastolic
Approximate Normal
PRESSURE (mm Hg)of Pulmonary artery
25-30/3-13 *
Approximate Normal
PRESSURE (mm Hg)of Pulmonary artery wedge
3-13 (mean)
Approximate Normal
PRESSURE (mm Hg)of Left atrium
3-13 (mean)
Approximate Normal
PRESSURE (mm Hg)of Left ventricle
120/3-13 *
Approximate Normal
PRESSURE (mm Hg)of Aorta
120/80 *
Approximate Normal
PRESSURE (mm Hg)of Mean systemic arterial
Approximate Normal
PRESSURE (mm Hg)of Systemic capillary
Approximate Normal
PRESSURE (mm Hg)of Systemic venous
At each branch point between aorta and capillaries the cross-Sectional Area of each individual branch _______.
At each branch point between aorta and capillaries the _____ cross-Sectional Area of all branches at a given level ______
At each point of vessel convergence between capillaries and vena cavae the CSA’s of ______ vessels _________
At each point of vessel convergence between capillaries and vena cavae the _____ CSA of all vessels at a given level _______
Total CSA is greatest at the level of the______ and ________
smallest venules
Between aorta and capillaries, velocity progressively ______ .
Between capillaries and vena cavae, velocity progressively _______.
Is the relationship between total CSA and velocity direct or inverse?
Blood pressure _______ progressively between aorta and vena cava because of resistance to flow in all vessels
The greatest decrease in pressure occurs as blood flows through the systemic ____ arteries and arterioles, which represent the greatest _____ resistance to flow.
Pulsations in pressure are normally lost by the end of the ______________. (Arteriolar dilation can result in pulsations in capillaries.)
systemic arterioles
Volume Distribution of Aorta + systemic arteries + arterioles
11 %
Volume Distribution of Systemic capillaries
5 %
Volume Distribution of Systemic venules + veins + vena cavae
67 %
Volume Distribution of Pulmonary vessels
12 %
Volume Distribution of Heart
5 %
Blood flow: more accurately, volume flow. Units are of ____/____.
Velocity: more accurately, linear velocity; the rate of movement. Units are of ______/_____ .
distance moved/time
Relationships between flow (Q) and velocity (v) of the fluid in a tube of cross-sectional area (A):

Q =

(A) can be for one large tube or total area of small tubes in parallel.
Explain why velocity of blood flow decreases progressively from aorta to capillaries.
________ energy of blood in motion is the sum of potential and kinetic energies, which result in pressures in the system.
Potential energies represented by _______ (It is the pressure exerted at right angles to the flow of the fluid.)& _________
Lateral pressure
Hydrostatic pressure
Kinetic energy represented by:
where ρ = density and v = linear velocity
1/2 ρv2
Assuming constant volume flow and negligible loss of energy due to friction, total fluid energy (E) in a short segment of a vessel or tube will remain _______.
(Bernoulli’s principle)
E =
P + 1/2 ρv2 + hρg = constant
Driving pressure (Pi - Po): In a vessel of uniform radius and length,
Q ~ Pi - Po, where Pi = _____
Po = _________
inflow pressure
outflow pressure
The resultant of all factors which oppose flow
Resistance (R)
R =
(Pi - Po) / Q
Poiseuille’s Law:
Pressure-Flow Relationships in Distensible Blood Vessels
Q =
[(Pi - Po) Ϭ r4] / ηL8
r = radius of the vessel
L = length of the vessel
η = viscosity of the fluid
(Pi - Po)/Q = ηL8/r4 Ϭ = R
R~1/r4 tells us that
very small changes in vascular radius have profound effects on resistance to blood flow.
R~L tells us that
under physiological conditions vessel length does not usually vary significantly
R~η tells us
characteristics of the fluid directly affects resistance.
Increased resistance _______ pressure upstream, and ________ pressure downstream, assuming output of the heart is unchanged.
increases / decreases
In the body, changes in blood vessel resistance are most important at the level of the _______ , and may cause simultaneous changes in upstream and downstream pressures and flow to downstream vessels.
Total Peripheral Resistance (TPR); also called Systemic Vascular Resistance (SVR) is the total vascular resistance of the __________.
systemic circulation
Pi-Po/Q = mean aortic Pressure - Right atrial pressure / cardiac output
The greatest proportion of TPR (or SVR) is located within all of the ______________ of the systemic circulation.
small arteries and arterioles
Series resistances: _____ resistance is the sum of the individual resistances
R(T) =
total resistance =
R 1 + R2 + R3, etc.
____ is greater than any individual R in the series.
The reciprocal of total resistance is the sum of the reciprocals of the individual resistances.
Parallel resistances
1/RT =
1/R1 + 1/R2 + 1/R3 etc.
RT is _____ than any one of the individual R’s arranged in parallel.
conductance (G) =
The entire systemic circulation is ______ with the entire pulmonary circulation.
in series
Splanchnic circulation: intestinal and hepatic capillaries are _____.
in series
Kidney: afferent and efferent arterioles are ______
in series.
_________ occurs when Parallel movement of adjacent fluid molecules forms a series of concentric cylinders within the tube.
Laminar Flow (Streamline Flow)
The lamina adjacent to the wall is stationary, and the velocity of each successive lamina _______ toward the tube’s center.
_________ is due to friction between adjacent laminae
occurs when parallel laminae are disrupted into swirling currents.
Turbulent Flow
With turbulence, Pi - Po (Δ P) is proportional to ___
Reynolds number:
ρDv/η, where: ρ = density
D = tube diameter
v = mean velocity
η = viscosity
When NR is less than 2000, flow will usually be _____.
When NR is greater than 3000, flow will usually be _______.
_______ flow is silent, but ________ flow commonly produces sound audible to a physician.
Laminar / turbulent
______ flow can promote formation of thrombi.
a ratio of a given viscosity to that of H2O
Relative Viscosity:
Plasma: relative viscosity ~
Whole blood: relative viscosity depends upon _______,_______, & _______.
hematocrit, vessel diameter, and flow rate.
Relative Viscosity of Whole Blood is Directly Proportional to _______.
lower than normal hematocrit.
higher than normal hematocrit.
In _______ , hematocrit and relative viscosity are lower than in larger vessels such as arteries and arterioles, venules and veins.
Fahraeus-Lindqvist effect: relative viscosity of blood decreases in vessels less than _____ in diameter.
200 μm
______,______, & ______ are all less than 200 μm in diameter.
Arterioles, capillaries and venules
At high velocity erythrocytes tend to accumulate in the _______ portion of the vessel which results in less apparent viscosity and less resistance.
center (axial)
at low velocity, erythrocytes tend to aggregate into _______, tending to increase apparent viscosity and resistance. This consequence of a low-flow state is sometimes called “anomalous viscosity”.
stacks (“rouleaux”)
Precise mathematical application of Poiseuille’s Law assumes the walls of the tubes are _____.
The walls of blood vessels are ________
As transmural pressure increases, blood vessels are distended, therefore resulting in ______.
larger radii
As transmural pressure increases, resistance ______ and volume flow ______ more than would be observed in rigid tubes.
These factors make the relationships between volume flow and driving pressure in distensible vessels ________ , rather than linear.
the concepts summarized by Poiseuille’s Law definitely can give us important ______ and ________ information about the relationships among driving pressure, volume flow, blood vessel dimensions, and blood viscosity.
directional / qualitative

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