cardiac circulation
DESCRIPTION
Blood flow Reynolds and Ohms LawTRANSCRIPT
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Overview of the Circulation; Biophysics
of Pressure, Flow, and Resistance
UNIT IV
Chapter 14:
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Overall Objectives: Chapter 14
Physical characteristics of the circulation:
distribution of blood volumetotal cross sectional area
velocity
blood pressure
Determinants of blood flow
Define and calculate blood flow, resistance, and pressure
Define and calculate conductance
Know Poiseulle
s law
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Systemic circuitRight HeartPulmonary circuit
Pulmonary circuitLeft HeartSystemic circuit
Cardiovascular system consists of two pumps (right/left
ventricles) and two circuits (pulmonary/systemic)connected
in series
when circuits are connected in series, flow must be
equal in two circuits
Cardiac output is output of either left or right ventricle
because of series system they are equal
Cardiac Output is ~5000ml/min (mean ~100ml/sec)
CO=SV*HR= 70ml*70bpm = 4900ml/min = ~82ml/sec
Organization:
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Components of
Circulation
Blood flows in
a circuit at rate
of 5 L/min
Transporting nutrients,
hormones to, and wastefrom, the tissues
Systemic Circulation:
84% blood volume
64% venous
13% arteries
7% arterioles/capillaries
Pulmonary Circulation:
16% blood volume
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Components of
Circulation
Transports blood to
tissues under high pressure(100mmHg)& high velocity
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Components of
Circulation
Control site for BF
major resistancesite of
the circulation
Control conduits
(strong muscular walls)
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Components of
Circulation
Major site water &
solute exchange
between blood & tissues
Containcapillary pores
permeable water/ solutes
~ 0.3-1mm in length
blood is inside for 1-2 sec
for diffusion but
not plasma leakage
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Components of
Circulation
returns blood to heart
under low pressure
serves asblood reservoir
Largest cross-sectional area
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Components of
Circulation
site of oxygenand
carbon dioxide exchange
Pulmonary Circulation:16% blood volume
9% lung:
7% heart
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Capillaries have the largest total
cross-sectional area of the circulation
cm
Aorta 2.5
Small Arterioles 20
Arterioles 40Capillaries 2500
Venules 250
Small Veins 80
Venae Cavae 8
CSA of capillaries
is 1000 timeshigher than aorta
cross sectional area veins/capillaries > arteries
same volume blood must pass through each segment
of circulation each minute
Systemic circuit is branching circuit: large single vessel (aorta) branching
extensively into smaller vessels until capillaries are reached
M j it bl d
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Majority blood
volume in veins
Total blood volume
in humans is about
5 Liters
CO &HR two circuits are equal so
SV are sameLargest blood volume in systemic
veins and
2ndlargest in pulmonary system
Systemic veins/Pulmonary
vessels have high compliance
Systemic circuit has
higher resistanceand lower
compliance
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Velocity (V) blood flow (Q) is inversely proportional to vascular
cross-sectional area (A) V= Q/A
velocity is inversely related to total cross-sectional area
of all vessels in a particular segment
Velocity is greatest in Aorta(~33cm/sec) and decreases to a
minimum in capillaries (0.3mm/sec) and then increases from
venules to right atrium
low velocity (1-3 sec) capillaries (typical length 0.3-1mm) allows
for nutritional flow(exchange dissolved substances between
plasma and tissues)
Velocities of Blood
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Velocity of blood flow is
greatest in the aorta
Velocityof Blood Flow = Blood Flow = QCross sectional area A
Aorta >Arterioles > Small veins
>Capillaries
Velocity of BF : speed blood flows in circulation (mm/sec)
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force exerted by blood against any unit vessel wall
force required to push Hg against gravity to cm height
blood flows from high pressure to low pressure therefore
the sequence of vessels in any system will also be a
sequence of pressures (highest to lowest)
Pressures are higher in systemic circuit (peripheral circuit)
lower pressures mean work of RV is lower lower capillary pressure protects against development of
pulmonary edema
Pressures
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small pressure drop in major arteries (low resistance segment)
small pressure drop occurs in major veins (low-resistancesegment)
largest drop in pressure is across arterioles
(highest resistance segment)
local arteriolar dilation:
arteriolar resistance
flow and pressure downstream
local arteriolar constriction:
arteriolar resistanceflow and pressure downstream
Pressure dissipates proportional to
Resistance in that segment.
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Blood Pressure Profilein the Circulatory System
Systemic Pulmonary
Capil
laries
Pre
ssure
(m
mHg)
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
Venules
Smallviens
Large
viens
Pulmonaryarteries
Capillaries
Pulmonaryviens
High pressures in arterial tree
Low pressures in the venous side of circulation
Largest pressure drop across arteriolar-capillary junction
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Blood Pressure
Blood pressure: force exerted against unit area vessel wall
measured in millimeters of mercury (mmHg).pressure of 100 mmHg means force sufficient to push a column of
mercury 100mm high
low pressures are sometimes reported in units of cm of water.
Blood Pressure Monitoring:
discovered by Poiseuille in 1846 (~167 years ago)
Standard Measure: mmHg (occasionally water)
1mmHg = 1.36cm water
Mercury Manometer:
inertia Hg means cannot respond pressures > 1cycle/2-3 sec
Electronic Pressure Transducers: (invasive) record < 500cycles/sec
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Pressure is pulsatile 120/80 mmHg
mean ~100mmHg actually ~93mmHg @ Aorta gradually decreasing to 0mmHg
at Right Atrium)
highest resistant segments are Arterioles
lower resistant segments are major arteries & veins
Aortic pressure mean ~100 mmHg
(Systolic ~120mmHg Diastolic ~80mmHg)
Vena cavae ~ 0 mmHg
Capillaries ~ 35 mmHg (arteriolar ends)
~ 15 mmHg (venous ends)
Capillary pressures mean ~ 17 mmHg (varies in tissues)
Mean Systemic Blood Pressure
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Pulmonary Pressure is pulsatile 25/8 mmHg
Pulmonary artery mean ~ 16mmHg (versus 100mmHg systemic)Systolic ~ 25mmHgDiastolic ~ 8mmHg
Pulmonary capillary mean ~7mmHg (versus 17mmHg systemic)
Mean Pulmonary Pressure
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Blood Flow Rate (Q) is controlled to tissue needs
tissue micro-vessels monitor O, waste and act directly onlocal blood vessels (dilating/constricting) to precisely control
local BF nervous control
hormone control
Cardiac Output is controlled primarily by sum of all tissue
blood flows
heart acts as automaton responding to venous return
Arterial blood pressure is controlled independently of either
local BF control orCardiac Output control
Basic Principles:
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Variations in Tissue Blood Flow
Brain 14 700 50Heart 4 200 70Bronchi 2 100 25Kidneys 22 1100 360Liver 27 1350 95
Portal (21) (1050)Arterial (6) (300)
Muscle (inactive state) 15 750 4Bone 5 250 3Skin (cool weather) 6 300 3Thyroid gland 1 50 160Adrenal glands 0.5 25 300Other tissues 3.5 175 1.3
Total 100.0 5000 ---
Per cent ml/min
ml/min/
100 gm
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Blood flow is the amount blood passing a given point in
circulation in a given period of time (ml/min orL/min) adult person at rest total circulation ~5000ml/min
Flowmeters: Direct measurements of flow (ml/min)
non-invasive (electromagnetic) invasive (intravascular-ultrasonic Doppler)
Total blood flow through lungs (pulmonary blood flow)per
minute is equal to systemic blood flow (normal blood volume
is ~5 L) per minute or Cardiac Output
Blood Flow is directly proportional to Pressure Differences
and inversely proportional to Resistance (Q=P/R)
BLOOD FLOW
Relationship between Pressure
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Relationship between Pressure,Flow, and Resistance
Q= P/R
Flow (Q) through a blood vessel is determined by:
1) Pressure difference (
P or P1-P2) between two ends ofvessel
2) Resistance (R) of vessel
Pressure at
arterial end
Pressure at
venous end
P1 P2
Ohms Law: Flow = P1P2/R = P/R = Q
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determines blood flow (Q) via vascular resistance
Flow (Q) = Pressure difference = P
Resistance R
Resistance (R) = Pressure difference = P
Flow Q
Pressure Difference (P) = Flow * Resistance = Q * R
Ohms Law:
R l ti hi b t
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Relationship betweenPressure, Flow, and Resistance
Q= P/R
Flow (Q) through a blood vessel is determined by:1) pressure difference (P or P1-P2) between two ends
of vessel
2) Resistance (R) of vessel
Pressure at
arterial end
Pressure at
venous end
P1 P2
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Characteristics of Blood Flow
blood usually flows in streamlines with each layer of blood
remaining same distance from wall, this type of flow iscalled laminar flow
when laminar flow occurs, velocity of blood in center of vessel is
greater than that toward outer edge creating a parabolic profile
(central portion/layer is faster) essentially noiseless
Blood Vessel
Laminar flow
occurs throughout normal CV system (excluding flow in heart) in small vessels, essentially all blood is near to wall soparabolic velocity of
laminar flow does not occur
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Laminar vs Turbulent Blood Flow
Turbulent flowdisorderly rather than
streamlined
Increases Resistance
Causes of turbulent BF:
high velocitiessharp turns in the circulation
rough surfaces in the circulation
rapid narrowing of blood vessels
Laminar flow is silent, whereas Turbulent flow tend to cause murmurs
murmursor bruitsare important in diagnosing vessel stenosis,
vessel shunts, and cardiac valvular lesions (heart murmur)
Reynolds Number:
Tendency for turbulent flow>2000 = turbulent flow
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Tendency for turbulent flow (Reynolds Number)
increases directly proportional to: Velocity of blood (V)
Diameter of blood vessel (D)
Density of blood ()
Inversely proportional to Viscosity of blood ()
Re = Velocity (cm/sec) * Diameter (cm) * Density (normally~1)
Viscosity (normally 1/30 poise)
Re = V * D * / increases with high velocities and pulsations
increases Resistance
plays a role in murmurs and bruits
Reynolds Number
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Aortic Root andPulmonary Artery,
Reynolds Number is high (5000-12,000 in systole) due tohigh velocity, pulsatile nature and sudden changes in
vessel diameter or large vessel diameter
in small vessels Reynolds Number is low (little turbulence)
Reynolds number in circulation 200-400 means turbulent
flow will occur at some branches of vessels but will die out
along smooth portions of vessels
Re > 2000 suggests increased flow turbulence even in
straight smooth vessels
Reynold
s Number : Clinical Note
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Aortic Aneurysm Atherosclerosis
Effect of Wall Stress on Blood Vessels
Turbulent flow increases wall stress
Athersclerosis: reduces Re at which turbulence begins to develop.
Thrombi:more likely to develop in turbulent flow than in laminar flow.
Relationship between
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Relationship betweenPressure, Flow, and Resistance
Q= P/R
Flow(Q) through a blood vessel is determined by:
1) pressure difference (P or P1-P2)between two ends
of vessel
2) Resistance (R) of the vessel
Pressure at
arterial endPressure at
venous end
P1 P2
Relationship between
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Flow = upstream pressure minus downstream pressure
(pressure gradient) divided by Resistance (mmHg/ml/min)Q = P1 - P2
R
critical value that determines flow is the pressure gradient
P1 accompanied by an identical P2will not cause achange in flow
P2 (caused by stenosis)pressure gradientBF
Flow to organ (kidney) calculated as mean renal arterial
pressure minus renal venous pressure divided by resistance
of all vessels in renal circuit
Relationship between
Pressure, Flow, and Resistance continued
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Determinants of Blood Flow
FLOW = arterial - venous pressure (P) = Qresistance (R)
FLOW = 100 - 0 mmHg
.1 mmHg/ml/minFLOW = 100 - 20 mmHg
.1 mmHg/ml/minFLOW = 1000 ml/min FLOW = 800 ml/min
100 mmHg
0 mmHg 20 mmHg
100 mmHg
R = .1mmHg/ml/min R = .1mmHg/ml/min
A B
Relationship between
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Relationship betweenPressure, Flow, and Resistance
Q=
P/R
Flow (Q) through a blood vessel is determined by:
1) pressure difference (P or P1-P2) between two ends ofvessel
2) Resistance (R) of the vessel
Pressure at
arterial endPressure at
venous end
P1 P2
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impediment to blood flow in vessel (mmHg/ml/min)
Calculated (not measured) from Blood Flow &BP difference if P between two points is 1mmHg & BF is 1ml/sec then
resistance =1 peripheral resistance unit(PRU)(mmHg/ml/sec)occasionally a CGS (cm, gm, sec) unit is used to express resistance
(dyne sec/cm)
Systemic Resistance Total Peripheral Resistance TPR
ArterialVenous Pressure (100mmHg-0mmHg) = 1 PRU
Cardiac Output (100ml/sec)BF through circulatory system equal to CO (~100ml/sec)
pressure systemic arteries to veins (~100mmHg)
total peripheral resistance 100/100 = 1 PRU
RESISTANCE
Total Peripheral Resistance TPR
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in conditions where blood vessels throughout body are
strongly constricted PRU ~ 4 if greatly dilated PRU~ 0.2
Most important factors to determine Resistance are:
Radius of the vessel blood Viscosity
Pulmonary Circulation Resistance
PRU = mean pulmonary pressure (16-2 mmHg) = 0.14
Cardiac Output (100ml/sec)
Total Peripheral Resistance TPR
(Systemic Circulation)
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Resistance = P1 -P2 Units of Resistance = mmHg = pressure
Q mL/min volume/timeResistance of vessel is determined by three major variables: R L/r4
1.Vessel Radius (r):
most important determining resistance is radius of vesselResistance of vessel is inversely proportional to radius4 rate of BFradius4
if radius is by resistance 16X
if radius doublesresistance to 1/16thof original2/3 of Total Peripheral Resistance is Arteriolar Resistance in
small arterioles (small changes in vessel diameter due to nervoussignals or local tissue chemical signals cause significant change in blood
pressure)
Determinants of Resistance
D t i t f R i t
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2. Blood Viscosity (): R L/r4
property of fluid that measures fluids internal resistance to flow greater viscosity, greater resistance
prime determinant of blood viscosity is hematocrit
percentage whole blood is RBCs (normally ~38 women & ~42men)
standard unit is poise(blood is ~1/30 poise)
varies with temperature(important in hypothermia)
varies with anemia, physical activity, altitude Viscosity of blood increases as Hematocrit increases
elevated in Polycythemia: increased blood viscosity > 10
normal blood viscosity is equal to three times water viscosity (primarildue to RBCs exerting frictional drag against adjacent cells and wall of blood vessel)
Normal whole blood viscosity = 3
Determinants of ResistanceContinued
Hematocrit and Viscosity Q = Pr4
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Hematocrit and Viscosityeffects on Blood Flow
Hematocrit Vascular ResistanceBlood Viscosity
Q = Pr8l
Determinants of Resistance
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3. Vessel Length: R L/r4
greater the length, greater resistance if length doubles resistance doubles
if length decreases by resistance decreases by
vessel length is usually constant
(not physiologic factor in regulation of resistance, pressure or flow)
Important conclusion: determination of capillary pressure is
Resistance of arterioles
arteriolar resistance (dilation)capillary pressure
arteriolar resistance (constriction)capillary pressure
Determinants of ResistanceContinued
Parallel and Serial Resistance Sites
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Parallel and Serial Resistance Sites
in the Circulation
Serial
Resistance
flow equal at all
points in a seriessystem
if flow changes, it
changes equally atall points
total is always
greater than
individualresistances
adding resistor in
seriesresistance
Series TPR =
sum resistance
each vessel
Parallel and Serial Resistance Sites
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Parallel and Serial Resistance Sites
in the Circulation continued
Parallel arrangementallows independent
control of flow
between tissues
Parallel TPR =
sum of inverseresistance each
vessel
Total resistance
is less than
resistance of
any single
blood vessel
2. Parallel TPR = sum of the inverse of resistance
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1/RTotal= 1/R1 + 1/R2 + 1/R3 + 1/R4
Total resistance < resistance of any single blood vessel connecting parallel resistors: low-resistance system parallel blood vessels: easier for blood to flow through circuit
because each is another parallel pathway (conductance)
if BP is kept constant, altering resistance (therefore BF) in oneparallel circuit will not change flow in remaining parallel
circuits flows can be independently regulated by changing resistance
Parallel vessels are found in: (greatest to least resistance) coronary,cerebral, renal, pulmonary
2. Parallel TPR sum of the inverse of resistance
of each vessel
Therefore: amputation of limb/surgical removal of kidney removes a parallel circuit and
reduces total vascular conductance (increasing total peripheral vascular resistance)
Obesity(adds parallel circuits) which decreases TPR and increases CO to maintain BP
Conductance
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Conductance
Conductance: measure blood flow through a vessel for a
given pressure difference units: ml/min per mmHg
increases proportion to radius to 4thpower
(Poiseuilles Law)
Conductance = 1____
Resistance
Poiseuilles Lawrepresents relationship of flow, pressure and resistance
Flow = pi * pressure difference * radius to 4thpower = P r4
8 * viscosity * length of vessel 8l
Effect of Vessel Diameter
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on Blood Flow
Q = Pr4
8l
Conductanceis sensitive to change in diameter of vessel
increases proportional tofourth power of radius
Blood Flow Autoregulation
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ability of tissue to maintain normal BF during changes in
arterial BP (70-175mmHg) calledblood flow auto-regulation otherwise increases arterial BP causes proportional increases BF
through various tissues
arterial BP increase force blood through vessels andinitiates compensatory increases in vascular resistance arterial BP BF Vascular Resistance
Arterial BP Vascular Resistance
tissues such as kidneyare able to maintain BF independent
of systemic arterial BP 70-175 mmHg Autoregulation is also seen in mesentery, skeletal muscle, brain,
liver and myocardium
Blood Flow Autoregulation
Mechanisms of blood flow
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Nervous:
Sympatheticvasoconstriction resistance
Sympatheticvasoconstriction resistance
(dilation)
Hormonal:
NE, Angiotensin II, Vasopressin, Endothelin
vasoconstrictionresistance
Mechanisms of blood flow
autoregulation include:
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No autoregulation
changes in arterial BP have important effects on BFart BPforce BF distending elastic vessels
(smooth muscle stress- relaxation)vascular resistance
BP BF dilates Vessels Resistance BP
art BPresistance as elastic vessels (smooth muscle stress-
relaxation) gradually collapse due to loss of distending ability
(critical closing pressure)
Sympathetics: can alter passive pressure-flow
sympathetic (stimulate): vasoconstrictionBF
sympathetic (inhibition): vasodilationBF
Passive Vascular Beds:
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CV system is two circuits & two pumps connected in series
Systemic pressure decreases slightly through arteries,
decreases markedly through arterioles, and then
decreases only slightly more through the major veins
loss of pressure is determined by regional resistance
cross-sectional area increases from minimum in aorta to a
maximum in capillaries.
Velocity blood is inversely related to regions cross-
sectional area
Summary
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main blood reservoir is systemic veins
of factors affecting a vessels resistance, radiusis most
important
radius arterioles determines total peripheral resistance
mean arterial BPis determined only by circulating blood
volume (cardiac output CO) and resistance(R) in arterioles
CV system is a laminar flow system
factors promoting turbulence include decreased fluid
viscosity, large-diameter tubes, increased fluid velocity and
vessel branching
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structures connected in series produce high resistance,and flow is dependent and equal at all points
systemic organs are connected in parallel, which permits
independent regulation of flow
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1. A 50-year-old woman has a renal blood flow of 1,000
mL/min and hematocrit of 50. Her arterial pressure is 120
mmHg and her renal venous pressure is 20 mmHg. She also
has a plasma colloid osmotic pressure of 25 mmHg.
Which of the following is the total renal vascular resistance (in
mmHg/mL/min) in this woman?
A. 0.10
B. 0.20C. 0.50
D. 1.00
E. 1.50
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1. A 50-year-old woman has a renal blood flow of 1,000
mL/min and hematocrit of 50. Her arterial pressure is 120
mmHg and her renal venous pressure is 20 mmHg. She also
has a plasma colloid osmotic pressure of 25 mmHg.
Which of the following is the total renal vascular resistance (in
mmHg/mL/min) in this woman?
A. 0.10
B. 0.20C. 0.50
D. 1.00
E. 1.50
Q= P/R
R= P/Q = 120-20 mmHg/1000mL/min= 0.10 mmHg/mL/min
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2. Under control conditions, flow through a blood vessel is 10
mL/min under a pressure gradient of 100 mmHg. An increasein which of the following would occur in response to a
twofold increase in the diameter of the vessel and the
pressure gradient was maintained at 100 mmHg?
A. Vascular resistance
B. Hematocrit
C. Vascular conductanceD. Blood viscosity
E. Plasma oncotic pressure
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2. Under control conditions, flow through a blood vessel is 10 mL/min
under a pressure gradient of 100 mmHg. An increase in which of thefollowing would occur in response to a twofold increase in the diameter
of the vessel and the pressure gradient was maintained at 100 mmHg?
A. Vascular resistance
B. Hematocrit
C. Vascular conductance
D. Blood viscosity
E. Plasma oncotic pressure
Conductanceis sensitive to
change in diameter of vessel
Increases proportional tofourth
power of radius
Q = Pr4
8l
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3. A decrease in the diameter of an arteriole would most
likely result in which of the following sets of changes inthe microcirculation?
Conductance Blood Flow Resistance
A. B. C. D. E. F.
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3. A decrease in the diameter of an arteriole would most
likely result in which of the following sets of changes in themicrocirculation?
Conductance Blood Flow Resistance
A.
B. C. D. E.
Q=P/R R=P/Q
Conductance = 1/R
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Vessel Blood Flow
(mL/min)
Pressure Gradient
(mmHg)
A. 1,000 100
B. 1,200 60
C. 1,400 20
D. 1,600 80
E. 1,800 40
4. Which vessel has the highest vascular resistance?
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Vessel Blood Flow
(mL/min)
Pressure Gradient
(mmHg)
A. 1,000 100
B. 1,200 60
C. 1,400 20
D. 1,600 80
E. 1,800 40
4. Which vessel has the highest vascular resistance?
0.1
0.05
0.014
0.05
0.02
R=P/Q
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5. Which one the following would tend to cause an increase
in blood flow?
A. An increase in hematocrit
B. A decrease in arterial pressure
C. A twofold increase in arteriole diameter
D. A twofold increase in blood viscosity
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5. Which one the following would tend to cause an increase
in blood flow?
A. An increase in hematocrit
B. A decrease in arterial pressure
C. A twofold increase in arteriole diameter
D. A twofold increase in blood viscosity
Poiseuille
Q = Pr4
8l
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Vessel Pressure
Gradient
Radius Viscosity
A. 100 1 10
B. 50 2 5
C. 25 4 2D. 10 6 1
6. The table below depicts the pressure gradient, radius,
and viscosity in various vessels of the same length. Which
vessel has the greatest flow?
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Vessel Pressure
Gradient
Radius Viscosity
A. 100 1 10
B. 50 2 5
C. 25 4 2
D. 10 6 1
6. The table below depicts the pressure gradient, radius,
and viscosity in various vessels of the same length.
Which vessel has the greatest flow?
Poiseuille
Q= P r/8 l = pi * P1-P2 * radius/ 8*viscosity*length
= *10*6/8*1*1
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7. If the blood flow through the kidney is 1,200 mL/min and
the renal artery pressure is 100 mmHg and the renal venouspressure is 0 mmHg, which of the following is the
conductance (in mL/min/mmHg) of the renal vessel?
A. 2
B. 4
C. 8
D. 12
E. 16
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7. If the blood flow through the kidney is 1,200 mL/min and
the renal artery pressure is 100 mmHg and renal venouspressure is 0 mmHg, which of the following is the
conductance (in mL/min/mmHg) of the renal vessel?
A. 2
B. 4
C. 8
D. 12
E. 16
Q=P/RR=P/Q
=100-0/1200
=1/12
Conductance=1/R
=1/1/12