SPI III- Hemodynamics and Doppler

Viscosity

Viscosity

A measure of fluid’s resistance to flow

The thickness of a fluid

Unit: poise or kg/m-s

Density

Mass/Volume

Blood is higher than water

Hematocrit

the percentage of volume of red blood cells (most common type of cell)

Normal is 36-50

Intertia

A measure of the resistance to acceleration of an object

Pulmonary system is

to the lungs

Systemic system is to

the body

Cardiac output

the volume of blood that crosses part of the circulatory system per time

The cardiac cycle

controlled by the electrical system at the SA node

Systole, Diastole, EKG

Flow is the result of

pressure differences

Pressure is

omnidirectional

Direction of flow is from ______ to ______ pressure

high, low

If P1=P2 then

no flow/stationary

Pressure gradient equation

change in pressure/ length

Volumetric flow rate (Q)

Flow is quantified by the volume that passes by any given point per time

Volumetric flow rate equation

Q= Delta P/ Resistance (R)

Volumetric flow rate/ poiseullie’s law only applies to

straight rigid tubes

Resistance

the opposition to flow

is controlled by arteroiles

Resistance equation

R= 8L(visosity)/ Pie(r4)

Poiseuille equation

Delta P (pie) (r4)/ 8L*viscosity

The vascular system is a ______ system

closed loop

The total CSA increases toward the periphery thus

decreasing velocity in the distal vessels

Doppler provides information about

presence, direction, speed and character

Shift and velocity are directly

porportional

As the doppler angle increases, the % of error in speed _______ with each degree of angle degree error

increases

Flow

the movement of a fluid from one location to another

Classifications of flow

temporal and spatial

Steady flow

fluid that moves at a constant speed or velocity

blood through arterioles, peripheral veins

temporal

Pulsatile flow

non-steady flow with acceleration and deceleration over the cardiac cycle

moves with a variable velocity

blood through arteries, SVC, IVC

Acceleration

occurs during early systole when the ventricles are rapidly ejecting blood

deceleration

occurs during late systole

tends to uniformly slow down

Two major characteristics of pulsatile flow

flow reversal

windkessel effect

Compliance

expansion and contraction of the vessel

A compliant vessel….

expands with increase pressure which expands it volume

then it recoils when the pressure drops later in the cardiac cycle

Windkessel effect

the contraction (recoiling) of the compliant vessel then increases the upstream pressure and adds forward flow later in the cycle

Flow reversal

the expansion of elastic vessels leads to this during diastole as the pressure distally overcomes the pressure upstream because of the heart relaxing

Laminar flow

made up of layers that travel at individual speeds

streamlines are aligned and parallel

plug flow

the majority of fluids travels at the same speed

occurs at the entrance to a vessel

similar to the motion of a solid object that moves as a unit

parabolic flow

average velocity = ½ max velocity in the center of the vessel

laminar flow close to vessel wall

low velocity

center of lumen for laminar flow

highest velocity

disturbed flow

streamlines persist, but waver and vary

irregular pattern which is oscillatory

causes of disturbed flow

increased velocity

altered vessel geometry

turbulent flow

chaotic flow in many directions and speeds, streamlines are obliterated

flow energy converted to sound (murmurs, bruits) or vibration (thrill)

Reynold’s number

The likelihood of turbulence

A Re above _____ indicates turbulent flow

2000

At the origin of a vessel,

plug flow appears

when a vessel suddenly widens, the fluid

falls toward the new vessel boundary

results in flow reversal in the small region at the vessel expansion

Eddy current

rotational motion from turbulent flow

referred to a mosaic color doppler pattern

commonly occurs distal from a stenosis

lower velocity than in stenosis

Tapering vessels

blunted or flattened flow

most of blood cells travel at the same velocity, regardless of their position within the vessel

Diverging vessels

elongated flow profile

lamina spread out

flow is likely to destabilize

results in disturbed or turbulent flow

What is the primary vessel of systemic circulation

aorta

Vessel compliance ensures

forward flow

the energy and pressure drop from the aorta to the distal end of the arteries is normally quite small. this indicates that the resistance to flow in these vessels is

low

A low change in pressure means

low resistance

Arterioles are considered

regulators of flow

Pulsatile flow patterns are abolished in the arterioles the pattern is converted to

steady flow

The highest pressure drop is at the level of

arterioles

Pressures at the same location on the right and left sides of the body should be

similar

severity of disease is not typically

symmetrical

During periods of increased flow, such as exercise, the pressure drop across the ____ diseased segnemtn can become

mildly, noticeable

Why ankle-brachial indices are often taken with and without exercise

Severe arterial disease

can typically be diagnosed at rest

because the obstruction offers a high resistance to flow the pulsatile nature of the pressure wave is diminished downstream from the obstruction

Peripheral resistance

in a rigid straight tube, the volume of liquid inserted into one end is immediately expelled at the other end

Flow patterns with high peripheral resistance

energy stored in the distended artery is unable to overcome the high resistance downstream

triphasic flow patterns may result

Flow patterns with low resistance

energy stored in the distended artery overcomes the low resistance downstream

forward flow occurs throughout cardiac cycle

Critcal stenosis

a partial obstruction that decreases both pressure and flow

90% reduction in large arteries

Occlusion

complete blockage of a vessel without any flow around it

Factors that determine the hemodynamic effects of arterial obstruction

length and diameter of narrowing

endothelial surface (rough or smooth)

gradual or abrupt narrowing

% area reduction of orifice

flow through the obstruction

arterial-venous pressure gradient

peripheral resistance distal to stenosis

Continuity rule

blood is neither created nor destroyed as it flows through a vessel

Volumetric flow rate must be constant proximal, within and distal to a stenosis

Turbulence can occur _____ to a stenosis

distal

continuity rule equation

Qp= Qs= Qd

Bernoulli effect

to maintain flow continuity, flow speed must increase through a stenosis

to allow fluid to accelerate into the stenosis there is a

pressure drop

Pressure and velocity are _______ related

inversely

The decreased pressure in regions of high flow speed is known as the

bernoulli effect

Effects of stenosis: upstream

• triphasic patter

• plug flow

• may demonstrate high resistance waveform

  • There may be some turbulence

Effects of stenosis: within lesion

• elevated flow velocities

• decrease in pressure

• possibility of some turbulence

Effects of stenosis: downstream

• dampened pattern

• loos of pulsatility

• delayed upstroke

• loss of triphasic

• spectral broadening

• murmurs or thrills

• turbulence with flow reversal or eddies

• may demonstrate low resistance

Normal tracing

rapid upstroke, sharp peak, prominent dicrotic notch

mildly abnormal waveform

rapid upstroke, sharp peak, absent dicrotic notch, bowed downslope.

Moderately abnormal waveform

flattened peak

upslope=downslope

absent dicrotic notch

Severely abnormal waveform

low amp

loss of pulsatility

venous circulation is normally affected by

respiration

flow direction is from

superficial to deep

venous pump

return of blood from legs to heart is facilitated by compression of the veins by leg muscles

flow in the arteries equal

flow in the veins

pressure drop from the aorta to the distal arteries is the same as that from the

veins to the right atrium

continuity rule

transmural pressure is the pressure

across the vessel wall

Hydrostatic pressure

the weight of blood pressure against the vessel walls

comes from gravity

same for adjacent arteries and veins

Hydrostatic pressure is equal to the weight of the column of blood from

the heart to the point of measurement

In a supine patient

hydrostatic pressure is 0

no column of blood

Pressure at the ankle equals

circulatory pressure plus the weight of blood pressing on ankle

Hydrostatic pressure below the heart

pressure positive

measured pressure will be higher than true circulatory pressure

Hydrostatic pressure above heart level

is negative

pressure is decreased counter-acting gravitational forces

measured pressure will be lower than the true circulatory pressure

During inspiration

diaphragm pressure into abdomen

pressure in abdominal cavity increases

pressure in thoracic cavity decreases

results in increased flow from abdomen to chest

during expiration

diaphragm presses into the thorax

pressure in the thorax increases

pressure in the abdomen decreases

results in decreased flow from the abdomen to the chest

Incompetent valves

allow blood flow backward from the heart woard the periphery

Deep vein thrombosis

venous stasis can cause the blood to clot resulting in partial or complete obstruction of the vein

Edema

accumulation of abnormally large volumes of fluid in the intracellular spaces of the body

Arteriovenous fistula

a direct connection between an artery and vein

low resistance pathway

Pesudoaneurysm

vessel wall ruptures resulting in extravascular blood collection

usually because of trauma

ying yang doppler appearance