DRUGS AFFECTING BLOOD COAGULATION Lector prof. Posokhova K.A.
Hemodynamics and Factors Affecting Blood Flow
description
Transcript of Hemodynamics and Factors Affecting Blood Flow
Hemodynamics and Factors Affecting Blood Flow
Amir GolnabiENGS 166
Spring 2008
Outline: •Blood Flow
•Blood Pressure–Facts
–Mean Arterial Pressure
–Total Blood Volume
•Vascular Resistance–Size Of The Lumen
–Blood Viscosity
–Total Length of Blood Vessel
•Conclusion–Rate of Blood Flow
•References
Blood Flow:
•Blood flow: Amount of blood that flows through any tissue
in a given period of time (mL/min)
•Total blood flow: Volume of blood that circulates through
the systemic and pulmonary blood vessels each minute →
Cardiac Output (CO)
•Cardiac output (CO) = heart rate (HR) x stroke volume
(SV)
•Distribution of CO into different body tissues:
1.Pressure difference of different parts of the body
Pressure ↑ → Blood Flow ↑
2.Resistance of specific blood vessels to blood flow
Resistance ↑ → Blood Flow ↓
1. Blood Pressure (BP):
•Blood flow: ↑ Pressure → ↓ Pressure
•BP: Contraction of the ventricles → hydrostatic pressure
exerted by blood on the walls of a blood vessel.
•Normal BP in a young adult at rest:–110 mmHg during ventricular contraction, systole
–70 mmHg during ventricular relaxation, diastole
–Systemic Circulation:
Torto
ra, G
erard, and B
ryan D
errickson. P
rinciples of A
natom
y and P
hysiology. W
iley, 2006. 747.
Blood Pressure (cont.):
•Mean Arterial Pressure (MAP): The average blood
pressure in arteries → closer to diastolic pressure during the
greater portion of the cardiac cycle
MAP = diastolic BP + 1/3(systolic BP – diastolic BP)
(80 + 1/3(120 – 80)) = 93 mmHg
•CO = HR x SV
•CO = MAP/R where R is the vascular resistance
•MAP = CO x R
•SV ↑ or HR ↑ → CO ↑
•and if R stays constant → MAP ↑
Blood Pressure (cont.):
•Total volume of blood in the cardiovascular
system:
•5 liters of blood in total
–Modest decrease in BV → Homeostatic mechanism
–More than 10% → BP ↓
–Water retention → BP ↑
2. Vascular Resistance:
•Friction between blood and the walls of blood
vessels: resists to blood flow
•Vascular resistance depends on three factors:
(1) Size of the blood vessels
(2) Blood viscosity
(3) Total blood vessels length
2.1. Size of Blood Vessels:
•Size of the lumen of a blood vessel ↓ → Resistance to
blood flow ↑
•“forth power law”: the resistance increases in proportion to
the inverse of the forth power of the diameter:
•Vasoconstriction: Narrowing of the vessels resulting from
contraction of the muscular wall of the vessels
•Vasodilation: Widening of the vessels resulting from
relaxation of the muscular wall of the vessels
•constant fluctuations → Resistance → BP
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1
dR
2.2. Blood Viscosity:
•Shearing force F
•Different layers of the blood move with different velocities
causing a shearing action (friction) between them
•Rate of shear (γ) is the relative displacement of one fluid
layer with respect to the next–slope of the velocity profile: v/h
•Blood moves by the action of shear stress–the force per area, τ = F/A
•Viscosity:–η = shear stress / shear rate = τ / γ
2.2. Blood Viscosity (cont.):
•Blood: –Plasma: 0.015 Poise
–Hematocrit (Ht): normally about 46% for men and 38% for women
•Factors: –Size of blood vessels ↓ → Velocity (shear rate) ↑ → Viscosity ↓
–Temperature ↓ → Viscosity ↑
1ºC ↓ → Viscosity ↑ by 2%
Ht.plasma 521
Poise.... 03204605210150
2.3. total length of blood vessel:
•Resistance to blood flow through a vessel ≈ total length of
blood vessel
•Hypertension → additional blood vessels in the adipose
tissue → total blood vessel length is longer → resistance to
blood flow ↑ → blood pressure ↑
•For each extra kilogram of fat, an estimated 650 km (about
400 miles) of additional blood vessels can develop in our
body!!!
Rate of Blood Flow
Poiseuille’s Law:
–F: rate of blood flow
–∆P: pressure difference between two ends of the
vessel
–r: radius of the vessel
–η: blood viscosity
–l: length of the vessel
l
rPF
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References:
•"An Introduction to Blood Pressure". Maryland Virtual High School of Science and
Mathematics. 04/27/2008 <http://mvhs.shodor.org/edgrid/bloodpressure/bptoblt.pdf>.
•Bipin , Upadhyay. "BLOOD VISCOSITY FUNCTIONAL PARAMETERS". COLLEGE OF
BIOMEDICAL ENGINEERING AND APPLIED SCIENCES. 04/28/2008
<http://www.biomedical.edu.np/biomed_files/>.
•Freeman, Scott. Biological Science. Upper Saddle River, NJ: Pearson Prentice Hall,
2005.
•Guyton, Arthur, and John Hall. Textbook of Medical Physiology. PA: Elsevier, 2006.
•Purves, William K.; David Sadava, Gordon H. Orians, H. Craig Heller (2004). Life: The
Science of Biology, 7th, Sunderland, Mass: Sinauer Associates, 954.
•Tortora, Gerard, and Bryan Derrickson. Principles of Anatomy and Physiology. Wiley,
2006.