2 Arterial Hemodynamics

what type of flow do arteries have?

pulsatile ; directly affected by heart’s pumping

what is the principle function of the arterial system?

distribute blood to capillary beds throughout body

what is systolic pressure?

FORCE blood exerts against arterial walls as heart contracts

what is diastolic pressure?

FORCE exerted during max relaxation of heart muscle

what is stroke volume?

amount of blood pumped by left ventricle in one contraction

what causes blood to move?

pressure gradient

blood moves from areas of

high to low pressure

where does the heart have highest pressure? lowest pressure?

highest : LV (120)

lowest : RA (2-6)

a greater pressure difference will result in

faster flow

what is kinetic energy?

energy of something in motion (movement of blood within a vessel)

kinetic energy is dependent on? formula?

mass and velocity

KE = m/2 v²

how does inertia relate to KE?

inertia decreases velocity of flow

what happens to inertia with an object at rest

inertia remains at rest

what is potential energy?

energy of something at rest (energy present in distended vessel walls)

potential energy is made up of

Intravascular pressure and gravitational PE

fluid energy is

KE + PE

What is intravascular pressure and what is it driven by?

force of blood pushing against vessel walls ; driven by heart pumping

what is gravitational PE?

ability of blood to do work relative to a reference point

how does gravity affect blood?

acts on blood to move it downward

what is the purpose and mechanism of the windkessel effect?

allows blood to continue to flow through the body when heart is not pumping (late diastole)

during cardiac contraction, some energy dissipates as KE and the rest is stored as PE ; during diastole the elastic recoil of arterial walls converts the stored PE into flow

intravascular pressure is a combination of

muscular contraction

hydrostatic pressure

static filling pressure

what is hydrostatic pressure

pressure exerted by fluid in a CLOSED system ; pressure related to reference point of right atrium

where is hydrostatic pressure highest? lowest?

highest : lower portions (ankles)

lowest : higher portions (head)

what is the reference point in the body relating to hydrostatic pressure?

heart ; RA

what are the hydrostatic pressures of parts of the body?

head : -30mmHg

heart : 0

hip : 50

knee : 75

ankles : 100

what is the relationship between hydrostatic pressure and gravitational PE?

INVERSE

where is gravitational PE highest? lowest?

highest : head

lowest : ankles

what is the formula for hydrostatic pressure/gravitational pressure?

HP : -pgh

GPE : +pgh

(p= density; g = gravitational acceleration; h= height of column of blood)

what is the GPE in a person who is recumbent?

gravitational pressure constant throughout

what is the hydrostatic pressure in a supine pt?

0; everything is at level of heart

what are the factors contributing to energy loss?

inertia

viscosity

friction

what is inertia?

tendency of objects to maintain status quo

when does inertial loss in vascular system occur?

when blood is forced to change direction or velocity

whre does inertial energy loss occur?

tortuous vessel and bifurcations

what is viscosity?

stickiness/thickness of fluid

viscosity is related to

hematocrits (% of RBC)

increased hematocrits creates

thicker blood

what is the main resistance to flow?

viscosity

what is friction?

resistance to motion

frictional energy loss occurs from

interaction of moving partices against stationary vessel walls

what is laminar flow? aka?

layers of blood cells closest to wall travel slowest

aka parabolic flow

what type of flow does normal arterial blood have?

laminar

what is plug flow?

when blood cell layers move at relatively constant speed

what is turbulent flow?

when blood cells move in random directions

what is turbulent flow due to?

high velocities through irregular shaped vessels

what is reynold’s number?

predicts whether flow is laminar or turbulent

turbulent flow is indicated when reynolds number

exceeds 2000