BME 211 - Biomechanics - Exam 1

Biomechanics

the study of the mechanical laws relating to the movement or structure of living organisms.

Fluid, tissue, and solid mechanics

Cardio

Heart

Vascular

Vessel

Components of the cardiovascular system

Pulmonary circulation:

Right atrium, right ventricle, pulmonary artery, arteries, arterioles, capillaries, venules, veins, pulmonary vein

Systemic circulation:

Left atrium, left ventricle, aorta, arteries, arterioles, capillaries, venules, veins, vena cavae

Functions of Cardiovascular System

1. Transport of molecules (e.g. O2)

2. Defense and healing

3. Thermoregulation

4. Maintenance of fluid balance between organs and tissues

Cardiovascular defense and healing

white blood cells and platelets

cardiovascular thermoregulation

vasodilation/vasoconstriction

Diastole

relaxation phase; chambers are filled with blood from venous and pulmonary systems

Systole

contraction phase; blood is ejected from the left and right ventricles

how many heart valves

4 of them

heart valves

atrioventricular valves, semilunar valves

atrioventricular valves

tricuspid and bicuspid

semilunar valves

pulmonary and aortic

function of heart valves

prevent the backflow of blood and operate massively following pressure difference

arteries

transport blood AWAY from the heart

arterioles

the smallest arteries that connect with the capillaries

veins

transport blood TO the heart

venules

the smallest veins that join to form the larger veins

capillaries

Microscopic vessel through which gas exchanges (O2 and CO2) take place between the blood and cells of the body

structure of the artery wall

adventitia (tunica externa)

media (tunica media)

intima (tunica interna)

adventitia

aka tunica externa

the outermost layer of the artery wall, primarily consisting of collagen fiber layered in a spiral fashion

media

aka tunica media

a layer in the artery wall, consisting of smooth muscle, elastin sheets (layered circumferentially) and collagen fibers

intima

aka tunica interna

the innermost layer of the artery wall consisting of a single layer of endothelial cells

two main constituents of the vessel wall

elastin and collagen

elastin

A protein that is similar to collagen. however it is highly deformable with a low Young's modulus and a high breaking strength

collagen

structural protein found in the vessel wall

high young's modulus, low breaking strength

Solid mechanics uses these

-Young's Modulus

-Poisson's Ratio

-Linear elastic vs. viscoelastic

Fluid mechanics uses these

-Hydrostatic Pressure

-Shear Force and Strain Rate

-Viscosity

-Reynolds number

-Bernoulli's equation

Young's Modulus

A measure of the stiffness of an elastic material and defined by stress/strain.

Poisson's Ratio

the ratio of lateral strain to the corresponding longitudinal strain in an elastic body under longitudinal stress

Linear elasticity

as stress increases, strain increases proportionally

A type of elasticity in which the force applied is directly proportional to the degree of deformation

viscoelasticity

A type of deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation.

property of a material expressed by a changing stress-strain relationship over time

Hydrostatic Pressure

Pressure exerted by a volume of fluid against a wall, membrane, or some other structure that encloses the fluid.

as blood moves along the capillary, fluid moves out through its pores because of the pressure and into the interstitial space

blood

fluid, but not a pure fluid.

a suspension of several different particles in a fluid base

constituents of blood

-plasma

-macromolecules and other molecules

-red blood cells

-white blood cells

-platelets

plasma

-straw colored fluid

-90% water, 1% electrolytes and other molecules, 9% macromolecules and other molecules

electrolytes

1% of plasma along with other molecules. Play a role in ensuring the correct fluid content within cells

Macromolecules and other molecules in blood

-9% of the plasma

-majority of them are proteins such as globulins, albumin, fibrinogen

-some are vitamins, hormons, waste products, CO2, oxygen

globulins

Proteins found in blood involved in transport as well as immune functions as antibodies

albumin

protein in blood; maintains the proper amount of water in the blood

fibrinogen

plasma protein that is converted to fibrin in the clotting process

waste products in blood

urea, ammonia

red blood cells

-principle particle in the blood

-no nucleus

-bicocave shape

function of red blood cells

involved in the transport of oxygen from the lung to the tissue

hematocrit

the percent by volume of the red blood cells in the blood

normal hematocrit

41-52% in men

36-28% in women

diameter of red blood cell

7.5E-6 m

thickess of red blood cell

2E-6 m

white blood cells

-leukocytes; perform the function of destroying disease-causing microorganisms

-occupy 0.7% of the blood volume

neutrophils

ingest and digest bacteria and fungi

eosinophils

attack larger parasites and are involved in allergic responses

monocytes

carried by the cardiovascular system to different tissues where they transform into macrophages

lymphocytes

attack invading bacteria and viruses and help destroy cells in the body which have become diseased through virus infection or cancer

basophils

involved in response to allergic symptoms including histamine release

macrophages

Found within the lymph nodes, they are phagocytes that destroy bacteria, cancer cells, and other foreign matter in the lymphatic stream.

monocytes turn into these

platelets

-occupy 0.3% of the blood volume

-exist in activated and inactivated forms

-plate like shape when inactive

function of platelets

-involved in blood clotting and repair of the damaged endothelium

this happens once platelets become active

become sticky and more spherical with projections which help them to stick together

low platelet volume fraction

impaired clotting ability which leads to potentially life-threatening blood loss from minor wounds

increased platelet volume fraction

increased risk of thrombosis which leads to life threatening events such as heart attack and stroke

flow of blood in the smallest diameter tubes (viscous behavior of RBCs)

the red cell distorts to a bullet shape

flow of blood in the 2nd smallest diameter tubes (viscous behavior of RBCs)

the red cell distorts to a parachute shape

flow of blood in the 3rd smallest diameter tubes (viscous behavior of RBCs)

the red cell distorts to a slipper shape

viscosity

-A liquid's resistance to flowing/pouring

-a measure of the resistance of a fluid to deformation under shear stress

shear rate

-the rate of change of velocity at which one layer of fluid passes over an adjacent layer

-ratio of velocity of a moving plate and distance between the stationary plate and moving plate

viscosity equation

shear stress/shear rate

reynolds number in heart

500-20,000;

turbulent; homogeneous distribution of red cells

reynolds number in arteries

5000 (ascending), 500 (small);

turbulence post-systole in ascending;

homogeneous distribution of red cells

reynolds number in microcirculation

0.5 (largest arterioles), 0.003 (capillaries);

not turbulent;

red cell aggregation;

distribution of RBCs not homogeneous

reynolds number in veins

100 (smallest) 3000 to 4000 (vena cava);

not turbulent;

red cell aggregation;

distribution of RBCs not homogeneous

reynolds number

inertia force/viscous force

as Re increases

turbulence is increased

as Re decreases

laminar blood flow is increased

laminar flow

Flows in parallel lines in a smooth progression;

low reynolds #

vortex formation associated with arterial disease

-low shear

-suitable condition for red cell aggregation

(e.g. atherosclerotic plaques, saccular aneurysm, fusiform aneurysm)

vortex flow

Blood flow that is initially laminar, then intersects a vessel stenosis or stricture, becoming high velocity central flow and spiral near the walls of the vessel

range of blood pressure

80-120mmHg

within physiologic range of blood pressure, arterial diamater can vary by this much

can vary by 10% under this condition

elastic modulus of elastin

low (0.4-0.6 MPa)

elastic modulus of collagen

high (100 MPa)

elastic modulus of arteries

combination of both elastin and collagin; 1-5 MPa

Young's Modulus as applied to elastin and collagen in the blood vessels

-stress/strain = elastin/collagen;

-high ratio = elasticity and deformation

-low ratio = tough and no deformation

measurements of blood pressure

inflate rubber cuff with air until artery closed; released...listen for pulse sounds

reynolds number in the arterial system

the mean number decreases with distance from the heart

flow of blood in the whole cardiovascular system

high reynolds number in the aorta in systole, leading to turbulent flow post-systole, but the rest of flow is laminar

axial flow

-flow in a long straight pipe will become like this after a certain distance; it follows the axis

rotation of flow

fluid rotates-

induced in a curved pipe or in branching; in arteries, these are curvature and bifurcations, as well as twisting of shear while contracting

bifurcation

division into two

symmetric velocity profiles

these are in a long straight tube; velocity profiles that are symmetric with respect to the radius

asymmetric velocity profiles

occur when a vessel is curved or immediately downstream of a branching point; not symmetric with respect to the radius

forces that the arterial wall is subject to

-pressure

-shear stress

-circumferential/hoop stress

cyclic variation in pressure in the arteries

this is in diameter and circumference of the artery

arterial thickness variation

cyclic variation

shear stress

the tangential force of the flowing blood on the endothelial surface of the blood vessel

blood pressure force direction

perpendicular to blood flow; 90 degrees to the artery wall

circumferential stress

the stress in a vessel wall, acting circumstantially in a plane perpendicular to the longitudinal axis of the vessel

Law of Laplace

for a fixed pressure P, as the radius r increases, the tension T in the wall increases

T = P*r

circumferential stress equation

H = Pr/w

P=fixed pressure

r = radius

w = wall thickness

Murray's Law

(d1)^3 = (d2)^3+(d3)^3

blood flow causes this force

wall shear stress, resulting in diameter change