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Pressure, Blood Flow,
Compliance and Resistance
By
Dr Kamran Afzal
Learning Objectives
• Describe the interrelationship of pressure, flow
and resistance.
• Describe the laminar blood flow and causes of its
turbulence .
• Define vascular distensibility and compliance and
identify the difference between arterial and
venous compliance
• Identify the standard units of BP measurements
• Identify the units for measurements of resistance
• Relate these factors to control of arterial pressure
Arteries
• Away from the heart
• Thick, muscular walls
• Very elastic
• Arterioles
• Diameter varies in
response to neural
stimuli and local
chemical influences.
• Capillaries
• Consist of a single tunica
interna
• Gas, nutrient, and waste
exchange
• Brain capillaries
• Blood-brain barrier
• Capillary beds
• Precapillary sphincter
• Shunting of blood
• Digestion
Venous System
• Toward the heart
• Venules—porous—free
movement of fluids and
white blood cells.
• Veins
• 3 tunics—but thin
• Venous valves
• Varicose veins
• Incompetent valves
• hemorrhoids
• Maintenance of Blood
Pressure
– Neural control
• Shunting and vasoconstriction.
– Vasomotor center
– Baroreceptors
• Carotid and aorta
– Chemoreceptors
– Higher brain centers
– Hormones
• Catecholoamines
• Atrial natrietic peptide
• ADH
– Alcohol
– Histamine—other vasodilators
Atherosclerosis
• Damage to the tunica
interna
– Viral
– Bacterial
– Hypertension
• Reinjury
• Inflammation
• LDLs—”bad cholesterol”
• Foam cells
• Fatty streak stage
• Arteriosclerosis
• Hypertension
• Stroke
• Heart attack
• Coronary bypass
• Angioplasty
• tPA—tissue plasminogen
activator
• Clot buster
• HDL—removes cholesterol
from vessel walls.
Arteries
• Aorta—largest artery
– Ascending
– Descending
– Right and left coronary arteries
– Common carotid arteries—branch to form internal and
external carotids
• External—supply tissues of the head except the brain and orbits.
• Internal—supply the orbits and most of the cerebrum.
– Vertebral arteries—branch to the cervical spinal cord,
neck, cerebellum, pons, and inner ear.
Veins to Know
• Know the veins on the preceding chart plus:
– The veins of the arms—cephalic, axillary, brachial, radial,
ulnar.
– The veins of the legs—external iliac, femoral, popliteal,
anterior tibial, posterior tibial, great saphenous vein,
hepatic portal vein.
– The great saphenous vein is a superficial vein. Connect
with many of the deep veins of the legs and thighs.
– Be able to identify these veins on a diagram. Also know
the locations served by these arteries.
Basic Circulatory Function
• Rate of blood flow to tissues changes based on
need.
- e.g., during exercise, blood flow to skeletal
muscle increases.
- In most tissues, blood flow increases in
proportion to the metabolism of that tissue.
• Cardiac output is mainly controlled by venous
return.
• Generally, arterial pressure is controlled
independently of local blood flow or cardiac
output control.
Normal Blood Pressures in Vasculature
Ohm’s Law Applied to Blood Flow
Blood Pressure
• BP is the force exerted by the blood against the
vessel wall.
- Typically measured as mm Hg.
- E.g., 100 mm Hg is the force needed to push a
column of Hg to a level of 100 mm.
Resistance
• Resistance is the impediment to blood flow.
• Not measured directly, but determined from
pressure and flow measurements.
- If ΔP = 1 mm Hg and F = 1 ml/sec, then R = 1 PRU
(peripheral resistance unit).
- In the adult systemic circulatory system, ΔP = 100
mm Hg, and F = 100 ml/sec; so R = 1 PRU.
- In the pulmonary system, ΔP = 14 mm Hg and F =
100 ml/sec; so R = 0.14 PRU.
Conductance
• Conductance is the opposite of resistance:
Conductance = 1/resistance
• Conductance may be easier to conceptualize
than resistance and is sometimes easier to use
in calculating the total resistance of parallel
vessels.
Vessel Diameter and Blood Flow – Changes in
Resistance
Laminar Flow
Poiseuille’s Law
Turbulant Flow
Adding Resistance in Series and
Parallel
Effect of Viscosity on Resistance and
Blood Flow
Summary of Blood Flow Physics
Vascular Distensibility
• Vascular distensibility is the ability of the
vascular system to expand with increased
pressure, which
-
Increases blood blow as pressure increases.
- In arteries, averages out pulses.
- Allows veins to act as reservoirs
Calculate Distensibility
• Fractional increase in volume per rise in
pressure:
Vascular = Increase in Volume
Distensibility Incr in P x orig Vol
If 1mm Hg increases a vessel from 10mm to
11mm, the distensibility would be 0.1 per
mm Hg or 10% per mm Hg.
Distensibility of Arteries and Veins
• Artery walls are much stronger than those of
veins and thus, much less distensible.
• The larger distensibility of veins allows them
to act as blood reservoirs.
Vascular Compliance
• The quantity of blood that can be stored in a
particular portion of the vasculature for a rise
in pressure:
Vascular compliance = Increase in volume
Increase in pressure
• Compliance = distensibility x volume
Veins
•Can distend to hold
large amounts of
blood.
•Contraction of
skeletal muscles can
constrict the veins and
propel blood to the
heart and increase
cardiac output.
• The contraction-
induced constriction
and the valves prevent
the venous pressure
from building up on
the feet of standing
adults.
Veins as Blood Reservoirs
• > 60% of blood in
the circulatory system is in the veins.
• When blood
is lost, sympathetic stimulation causes veins
to constrict and make up for the lost blood.
• Conversely, veins can distend to hold excess
blood if too much is
given during a transfusion.
Blood Volume
• Distribution of H2O within the
body:
• Intracellular compartment:
– 2/3 of total body H2O within
the cells.
• Extracellular compartment:
– 1/3 total body H2O.
• 80% interstitial fluid.
• 20% blood plasma.
• Maintained by constant
balance between H2O loss and
gain.
Capillaries
• Exchange nutrients and waste with tissues.
• ~ 10 billion capillaries with 500 – 700 m2
total surface area in whole body.
THANK YOU

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Bood pressure .ppt

  • 1. Pressure, Blood Flow, Compliance and Resistance By Dr Kamran Afzal
  • 2. Learning Objectives • Describe the interrelationship of pressure, flow and resistance. • Describe the laminar blood flow and causes of its turbulence . • Define vascular distensibility and compliance and identify the difference between arterial and venous compliance • Identify the standard units of BP measurements • Identify the units for measurements of resistance • Relate these factors to control of arterial pressure
  • 3.
  • 4. Arteries • Away from the heart • Thick, muscular walls • Very elastic • Arterioles • Diameter varies in response to neural stimuli and local chemical influences. • Capillaries • Consist of a single tunica interna • Gas, nutrient, and waste exchange • Brain capillaries • Blood-brain barrier • Capillary beds • Precapillary sphincter • Shunting of blood • Digestion
  • 5. Venous System • Toward the heart • Venules—porous—free movement of fluids and white blood cells. • Veins • 3 tunics—but thin • Venous valves • Varicose veins • Incompetent valves • hemorrhoids • Maintenance of Blood Pressure – Neural control • Shunting and vasoconstriction. – Vasomotor center – Baroreceptors • Carotid and aorta – Chemoreceptors – Higher brain centers – Hormones • Catecholoamines • Atrial natrietic peptide • ADH – Alcohol – Histamine—other vasodilators
  • 6. Atherosclerosis • Damage to the tunica interna – Viral – Bacterial – Hypertension • Reinjury • Inflammation • LDLs—”bad cholesterol” • Foam cells • Fatty streak stage • Arteriosclerosis • Hypertension • Stroke • Heart attack • Coronary bypass • Angioplasty • tPA—tissue plasminogen activator • Clot buster • HDL—removes cholesterol from vessel walls.
  • 7. Arteries • Aorta—largest artery – Ascending – Descending – Right and left coronary arteries – Common carotid arteries—branch to form internal and external carotids • External—supply tissues of the head except the brain and orbits. • Internal—supply the orbits and most of the cerebrum. – Vertebral arteries—branch to the cervical spinal cord, neck, cerebellum, pons, and inner ear.
  • 8. Veins to Know • Know the veins on the preceding chart plus: – The veins of the arms—cephalic, axillary, brachial, radial, ulnar. – The veins of the legs—external iliac, femoral, popliteal, anterior tibial, posterior tibial, great saphenous vein, hepatic portal vein. – The great saphenous vein is a superficial vein. Connect with many of the deep veins of the legs and thighs. – Be able to identify these veins on a diagram. Also know the locations served by these arteries.
  • 9. Basic Circulatory Function • Rate of blood flow to tissues changes based on need. - e.g., during exercise, blood flow to skeletal muscle increases. - In most tissues, blood flow increases in proportion to the metabolism of that tissue. • Cardiac output is mainly controlled by venous return. • Generally, arterial pressure is controlled independently of local blood flow or cardiac output control.
  • 10. Normal Blood Pressures in Vasculature
  • 11. Ohm’s Law Applied to Blood Flow
  • 12. Blood Pressure • BP is the force exerted by the blood against the vessel wall. - Typically measured as mm Hg. - E.g., 100 mm Hg is the force needed to push a column of Hg to a level of 100 mm.
  • 13. Resistance • Resistance is the impediment to blood flow. • Not measured directly, but determined from pressure and flow measurements. - If ΔP = 1 mm Hg and F = 1 ml/sec, then R = 1 PRU (peripheral resistance unit). - In the adult systemic circulatory system, ΔP = 100 mm Hg, and F = 100 ml/sec; so R = 1 PRU. - In the pulmonary system, ΔP = 14 mm Hg and F = 100 ml/sec; so R = 0.14 PRU.
  • 14. Conductance • Conductance is the opposite of resistance: Conductance = 1/resistance • Conductance may be easier to conceptualize than resistance and is sometimes easier to use in calculating the total resistance of parallel vessels.
  • 15. Vessel Diameter and Blood Flow – Changes in Resistance
  • 19. Adding Resistance in Series and Parallel
  • 20. Effect of Viscosity on Resistance and Blood Flow
  • 21. Summary of Blood Flow Physics
  • 22. Vascular Distensibility • Vascular distensibility is the ability of the vascular system to expand with increased pressure, which - Increases blood blow as pressure increases. - In arteries, averages out pulses. - Allows veins to act as reservoirs
  • 23. Calculate Distensibility • Fractional increase in volume per rise in pressure: Vascular = Increase in Volume Distensibility Incr in P x orig Vol If 1mm Hg increases a vessel from 10mm to 11mm, the distensibility would be 0.1 per mm Hg or 10% per mm Hg.
  • 24. Distensibility of Arteries and Veins • Artery walls are much stronger than those of veins and thus, much less distensible. • The larger distensibility of veins allows them to act as blood reservoirs.
  • 25. Vascular Compliance • The quantity of blood that can be stored in a particular portion of the vasculature for a rise in pressure: Vascular compliance = Increase in volume Increase in pressure • Compliance = distensibility x volume
  • 26. Veins •Can distend to hold large amounts of blood. •Contraction of skeletal muscles can constrict the veins and propel blood to the heart and increase cardiac output. • The contraction- induced constriction and the valves prevent the venous pressure from building up on the feet of standing adults.
  • 27. Veins as Blood Reservoirs • > 60% of blood in the circulatory system is in the veins. • When blood is lost, sympathetic stimulation causes veins to constrict and make up for the lost blood. • Conversely, veins can distend to hold excess blood if too much is given during a transfusion.
  • 28. Blood Volume • Distribution of H2O within the body: • Intracellular compartment: – 2/3 of total body H2O within the cells. • Extracellular compartment: – 1/3 total body H2O. • 80% interstitial fluid. • 20% blood plasma. • Maintained by constant balance between H2O loss and gain.
  • 29. Capillaries • Exchange nutrients and waste with tissues. • ~ 10 billion capillaries with 500 – 700 m2 total surface area in whole body.