103- Fundamental Hemodynamics Flashcards
Includes concepts from Hemodynamics simulation session
Suppose a rigid tube gets 10% longer while its radius increases by 10%.
Will the resistance increase or decrease? Why?
The resistance will decrease
The increase in radius will decrease resistance more than the increased length will increase resistance
What is diastolic pressure?
The lowest pressure attained during a cardiac cycle
Occurs right before the ventricles begin to contract
Are the pulmonary and systemic ciruculations in series or in parallel?
In series
What is the most important reason for maintaining sufficient cardiac output?
To maintain the diffusion gradient at the capillary beds
What is the equation for total resistance when resistors are in parallel?
The total resistance will be less than any one resistor in the system
(Think about students leaving a lecure hall when there are 3 doors open - students have multiple doors to go through, so the total resistance to students leaving is less than the resistance through any one door on its own)
What is the relationship between flow (Q), velocity (v), and cross-sectional area (A) of a blood vessel?
What is Pouiselle’s equation?
What does it help us understand?
Pouiselle’s law helps us understand factors that affect vascular resistance in a rigid tube
- Increased length and viscosity = increased resistance
- Increased radius = decreased resistance
- 4th power -> radius is the most powerful determinant of resistance
What is the pulse pressure in a patient with a blood pressure of 110/60?
50
Pulse pressure = SBP - DBP
110 - 60 = 50
Which blood vessls are considered “capacitance vessels” in the systemic cirulation?
Veins
They can stretch to accomodate more blood if necessary
What factors might cause tubulent blood flow?
- Physiologic
- Blood pressure measurement
- When we hear Korotkoff sounds, flow through the vessel is turbulent, because it is partially occluded by the blood pressure cuff
- Increased velocity
- Blood pressure measurement
- Pathologic
- Heart murmur
In a rigid tube, what happens to resistance as the length increases?
As the length increases, resistance increases
Which number predicts whether flow will be laminar or tubulent?
What is the equation?
Reynolds Number
(density X diameter X velocity)/(viscosity
Transition from laminar to turbulent flow at Reynolds number of ~2000
Which organ recieves circulation from both the systemic and pulmonary circuits?
The lungs
- Oxygenate blood recieved from the pulmonary circulation
- Need oxygen from systemic circulation blood in order to function
Which blood vessels are considered “conduit vessels” in the circulation?
Arteries, venules
Which blood vessels are considered “resistance vessels” in the systemic ciruclation?
Arterioles
They have a substantial smooth muscle layer that can contract to increase resistance
Give an example in the systemic circulation of resistors “in series”
Any time when there are two distinct sets of arterioles along the same path
- Kidney
- Afferent arterioles (before glomeruli)
- Efferent arterioles (after glomeruli)
- The portal circulation has two capillary beds in series
- Pulmonary and systemic circulation
In the lumen of a blood vessel, where is shear greatest?
The wall of the blood vessel
What is the equation for total resistance when resistors are in series?
Give an example in the systemic circulation of resistors “in parallel”
In the systemic circulation, blood flow to any organ system is in parallel to blood flow to any other organ system
(if there are exceptions please suggest an edit!)
How can we measure pressure in the right atrium without actually puncturing the heart?
Look at the JVP (Jugular Venous Pulse)
Measure pressure in the jugular vein by looking at the height of the jugular vein pulse above the clavicle; it is a proxy for right atrial pressure
What is systolic pressure?
The highest pressure created during a cardiac cycle -
When the ventricles are contracting and ejecting blood into the systemic circulation (and pulmonary, but we measure systemic)
What is stroke volume?
The amount of blood expelled from the left ventricle with one contraction
What happens to flow (Q) if resistance (R) decreases, and the pressure gradient (P) stays the same?
Flow increases
What is pulse pressure?
Pulse pressure = Systolic pressure - Diastolic pressure
What is compliance?
How is it calculated?
Compliance is the change in volume due to change in pressure
Basically, the stretchiness of a blood vessel
More compliant vessels will increase in volume in response to increased pressure (resulting in minimal pressure increase inside the blood vessel)
Which blood vessels provide a diffusion site for waste and nutrients?
Capillaries
What is the equation that relates flow (Q), pressure (P), and resistance (R)?
Hint: The central dogma of cardiovascular medicine
What is cardiac output?
How is it calculated?
Cardiac output (CO) is the amount of blood expelled from the heart in one minute
CO = SV * HR
How do you calculate the pressure in a hydrostatic column?
Why would we ever want to do this?
Pressure = density * gravitational constant * height of column
The jugular vein acts as a hydrostatic column; pressure in the jugular vein is a proxy for pressure in the right atrium
When a patient sits up, would you expect jugular distention to rise or fall?
Fall; gravity will pull the blood down
What is shear?
Why is it important?
Lateral stress on a fluid as a consequence of travelling at different velocities.
If shear is too large, red blood cells may rupture, causing hemolytic anemia
