Unit 4 - Hemodynamic Concepts Flashcards
How is cardiac output or flow measured?
Flow = perfusion pressure difference/Resistance CO= Delta P/R or Delta P = CO x R
What does ohms law measure?
the flow moving out of the ventricles
What does delta P in Ohm’s law stand for?
The change between input pressure and output pressure
What is the input pressure when measuring CO for systemic circulation?
the aorta
What is the output pressure when measuring CO for systemic circulation?
vena cava/RA
What is the input pressure when measuring CO for pulmonary circulation?
pulmonary artery
What is the output pressure when measuring CO for pulmonary circulation?
the left atrium
Where is most of the blood in the cardiovascular system ‘stored’?
veins
Why is CO from the left side of the heart and the right side of the heart the same?
Not all blood comes back to the heart at the same time because it is stored in the veins, so the right and left cardiac output can equal each other even though systemic circulation has so much more blood than pulmonary circulation
What is cross-sectional area of a vessel?
the total area of ALL vessels of a single type
In a vessel with a small cross sectional area, is velocity high or low?
high
Where is velocity the highest?
in the aorta
In a vessel with a high cross sectional area, is velocity high or low?
low
Where is velocity the lowest?
in the capillaries
What is viscosity?
internal fluid resistance of a substance
Is viscosity the same through out the cardiovascular system?
No, it can change through different vessels
What is the main determinant of viscosity?
PCV
What does a higher hematocrit indicate in relation to resistance and viscocity?
higher viscosity, more resistance
What is erythrocytosis?
abnormally high PCV
How does erythrocytosis effect O2 carrying capacity,
viscosity, and cardiac workload?
increases O2 carrying capacity, increases viscosity which increases cardiac workload
What is anemia?
abnormally low PCV
How does anemia effect O2 carrying capacity, viscosity and cardiac workload?
it decreases O2 carrying capacity, decreases viscosity, and increases cardiac workload
What is resistance?
the impediment to blood flow in a vessel
How is resistance calculated?
R= Change in Pressure/ Cardiac Output
What vessel has the highest resistance and why?
arterioles because they have muscles
What is total peripheral resistance?
net resistance of systemic circulation
What happens to vascular pressure during exercise?
vascular pressure decreases, vessels dilate, more blood flows to the needed muscles
What causes pulmonary hypertension?
the dramatic increase of pulmonary resistance
How does the right ventricle respond to pulmonary hypertension?
the right ventricle must generate increased pressure to eject blood
What is conductance?
a measure of blood flow through a vessel for a given P difference
How is conductance calculated?
1/R
What is Poisuelle’s Law?
the rate of flow is directly proportional to the 4th power of the vessels radius
In respect to vessel length and width, what has the greatest effect on blood flow through it?
vessel width
Viscosity and vessel length are ________ proportional to flow.
inversely
Viscosity and vessel length are _______ proportional to resistance.
directly
Perfusion pressure is ______ proportional to flow
directly
What is laminar flow?
the flow of blood in streamlines
Where is velocity the highest in laminar blood flow?
in the center
Where is pressure the highest in laminar blood flow?
near the wall
What is turbulent flow?
disorganized flow
What type of currents are present in turbulent flow, and how does that affect the flow?
Eddy currents increase friction (resistance) of flow
What are the causes of turbulent flow?
increased flow velocity,, obstruction, vessel turn
What is Reynold’s number?
a measure of the tendency for turbulence to occur
How is Reynold’s number calculated?
Reynolds number = (fluid density/fluid viscosity)/(average velocity of fluid x tube diameter)
How does an increase in viscosity effect turbulence?
it decreases
What causes murmurs?
when critical Reynold’s number is exceeded - high turbulence
What is post stenotic dilation?
When a vessel bulges
How does post stenotic dilation effect turbulence?
A pressure gradient is created and a murmur occurs during the contractile phase
What is the Bernoulli relationship?
it quantifies the relation between a pressure gradient and velocity
How is the Bernoulli relationship clinically useful?
it can be used to estimate the severity of a stenosis or obstruction in a vessel
How is the Bernoulli relationship calculated?
Pressure difference = 4(peak velocity)^2
