Unit 1 Hemodynamics & Doppler

viscosity

viscosity

• a measure of a fluid’s resistance to flow

• the thickness of a fluid

• units are poise or kg/m-s

density

• mass/volume

• blood is higher than water

hematocrit

• the percentage by volume of red blood cells

• normal is about 36-50

inertia

a measure of the resistance to acceleration of an object

cardiac output

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

pressure differences

flow is the result of ________________

pressure

force/area

omnidirectional

pressure is _________________

high pressure to low pressure

direction of flow is from _______________

pressure gradient

ΔP/L

volumetric flow rate (Q)

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

• only applies to a straight rigid tube, not a stenosis

volumetric flow rate (Q)

ΔP/R

resistance

• the opposition to flow

• controlled by arterioles

resistance

this is the ___________ equation

Poiseulle’s

this is ______________ equation

CSA

the total _______________ increases toward the periphery, thus decreasing velocity in the distal vessels

• presence

• direction

• speed

• character

Doppler provides info about flow, including:

Doppler effect

the change in frequency (and therefore wavelength) caused by motion of a sound source, receiver, or reflector

movement of the reflector

______________ will change the transmitted frequency into a different received frequency

higher

if the reflector is moving towards the receiver, the received frequency will be ______________ than the transmitted frequency

lower

if the reflector is moving away from the receiver, the received frequency will be ______________ than the transmitted frequency

Doppler shift

the difference between the frequency of the received sound wave and the frequency of the emitted sound

Doppler

this is the ____________ equation

Doppler angle

the angle between the direction of sound propagation and the flow direction

% of error in speed

as the Doppler angle increases, the ______________ also increases with each degree of angle degree error

Nyquist limit

the upper limit of Doppler shift that can be detected properly by pulsed instruments

PRF

if the Doppler shift frequency exceeds one half the __________ (aka the Nyquist limit), aliasing occurs

• shift baseline

• increase PRF

• increase Doppler angle

• use lower operating frequency

• use CW

ways to correct for aliasing:

vessel length, vessel radius, and viscosity

__________________ affect resistance

temporal

steady and pulsatile flow are both _______________ flow categories

steady flow

• fluid that moves at a constant speed or velocity

• blood through arterioles and peripheral veins

pulsatile flow

• non-steady flow with acceleration & deceleration over the cardiac cycle

• fluid that moves with a variable velocity

• blood through arteries, IVC, SVC

spatial

laminar, disturbed, and turbulent flow are all ____________ flow categories

laminar

___________ flow includes plug and parabolic flow

plug flow

• majority of fluid 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

disturbed flow

• streamlines persist but waver and vary

• irregular pattern which is oscillatory

• initial indication of laminar breakdown

• caused by increased velocity and altered vessel geometry

turbulent flow

• chaotic flow in many directions and speeds

• streamlines are obliterated

• vortex (swirling pattern of rotational flow)

• flow varies from instant to instant and from location to location

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

• often associated with cardiovascular pathology and increased velocities

acceleration (increase in velocity)

_____________ occurs during early systole when the ventricles are rapidly ejecting blood

deceleration (decrease in velocity)

• occurs during late systole (not during diastole)

• tends to uniformly slow down

• flow reversal

• Windkessel effect

two major characteristics of pulsatile flow are:

vessel compliance

expansion and contraction of a vessel

expands; recoils

a compliant vessel ___________ with increase pressure and ____________ when the pressure drops

expansion of elastic vessels

the _____________ leads to a brief reversal of flow during diastole as the pressure distally overcomes the pressure upstream because of the heart relaxing

Windkessel effect

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

Reynold’s number

the likelihood of turbulence is expressed in terms of ______________

critical threshold

turbulence occurs when velocity exceeds a ______________

2000

a RE above _______________ indicates turbulent flow

entrance effects

• at the origin of a vessel, plug flow appears

• friction from the vessel walls cause streamlines on the outside to slow down

• flow profiles vary at beginning of vessel in comparison to farther downstream

boundary layer separation

• when a vessel suddenly widens, 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 as a mosaic color Doppler pattern

• commonly occurs distal from a stenosis

• lower velocity than in stenosis

tapering

in _______________ vessels:

• blunted or flattened flow (plug flow)

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

diverging

in __________ vessels:

• elongated flow profile

• lamina spread out

• flow is likely to destabilize

• results in disturbed or turbulent flow

aorta

primary vessel of systemic circulation

arterioles

considered the regulators of flow

arterioles

in _______________, pulsatile flow patterns are abolished and converted to steady flow

high resistance

a large drop in pressure from proximal to the distal side of the arteriole indicates the arteriole’s ________________

arterioles

the highest drop in pressure occurs at the level of the ______________

mild arterial disease

• often undiagnosed at rest

• during periods of increased flow (exercise), the pressure drop can become noticable

severe arterial disease

• can typically be diagnosed at rest

• the pulsatile nature of the pressure wave is diminished downstream from the obstruction

high peripheral resistance

flow patterns with ________________:

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

• flow occurs only in systole

• triphasic flow patterns may result

low peripheral resistance

flow patterns with _____________:

• energy stored in the distended artery overcomes the low resistance downstream

• forward flow occurs throughout the cardiac cycle

arterial obstruction (stenosis)

• blockage that forms in arteries generally caused by atherosclerotic plaque

• may decrease distal pressure and/or flow

occlusion

the complete blockage of a vessel without any flow around it

• length and diameter of narrowing

• endothelial surface

• gradual or abrupt narrowing

• % area reduction of orifice

• flow through the obstruction

• arterial-venous pressure gradient

• peripheral resistance distal to stenosis

factors that determine the hemodynamic effects of arterial obstruction:

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

• flow speed increases at stenosis to maintain a constant flow

inversely

pressure and velocity are _____________ related

Bernoulli effect

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

pressure drop

to allow fluid to accelerate into the stenosis, there is a _____________

increase in pressure

to allow fluid to decelerate out of a stenosis, there is an _________________

upstream

effects of a stenosis: _______________

• triphasic pattern

• plug flow

• may demonstrate high resistance waveform

• may be some turbulence

within lesion

effects of a stenosis: _______________

• elevated flow velocities

• decrease in pressure

• possibility of some turbulence

downstream

effects of a stenosis: _______________

• dampened pattern

• loss of pulsatility

• delayed upstroke

• may demonstrate low resistance waveform

• loss of triphasic waveform

• turbulence, spectral broadening, murmurs and/or thrills

normal tracing of arterial pressure waveform

• rapid upstroke

• sharp peak

• prominent dicrotic notch

mildly abnormal arterial pressure waveform

• rapid upstroke

• sharp peak

• absent dicrotic notch

• bowed downslope

moderately abnormal arterial pressure waveform

• flattened peak

• upslope=downslope

• absent dicrotic notch

severely abnormal arterial pressure waveform

• low amplitude

• loss of pulsatility

series

resistances arranged in _______________:

• obstructions in the same vessel, one upstream and the other downstream

• resistances add—they combine to form a higher resistance than either individual lesion

parallel

resistances arranged in _____________:

• obstructions in different vessels, the vessels start at the same location and end at the same location

• resistances combine into a lower resistance than either individual lesion

collateral vessels

the development of alternative, secondary, or accessory vascular pathways that allow extra blood to reach tissues located downstream from an occluded artery

exercise

____________ is the most potent vasodilator

perforator veins

connect the superficial and deep systems

superficial to deep

flow direction of veins is from _______________

transmural pressure

the pressure across the vessel wall

hydrostatic pressure

• the weight of the blood pressing against the vessel walls

• equal to the weight of the column of blood from the heart to the point of measurement

• comes from gravity

zero

in a supine patient, the hydrostatic pressure is ____________

positive

below the heart, hydrostatic pressure is ______________

negative

above the heart level, hydrostatic pressure is ______________

inspiration

______________ results in increased flow from abdomen to chest

expiration

_____________ results in decreased flow from abdomen to chest

venous reflux (insufficiency)

• increased venous pressure

• decreased venous return

• mild cases—patient must be semi-erect to document

• severe cases—can also be demonstrated in supine

deep vein thrombosis (DVT)

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

• reduces blood flow to the heart

• increased venous volume below it

• can lead to damaged valves and embolus

edema

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

arteriovenous fistula

• a direct connection between an artery and vein

• a low resistance pathway

• may be congenital or acquired (from trauma or surgically created)

pseudoaneurysm

• vessel wall ruptures resulting in extravascular blood collection

• occurs as a result of trauma, in angioaccess grafts, or at puncture sites

ying-yang color Doppler and to-and-fro Doppler pattern

the sonographic appearance of a pseudoaneurysm is:

external compression

a fresh pseudoaneurysm can be treated with ________________

ultrasound guided thrombin injection

An older pseudoaneurysm cannot be compressed due to endothelization and requires ____________________