12.2 B Flashcards
How does the mean arterial pressure in the various organs differ from one another?
they all have the same pressure differential (MAP-RAP)
Given that the pressure differential across each organ is the same, what accounts for the variability in flow across each?
differences in resistance
What is pulse pressure?
the systolic pressure minus the diastolic pressure
What is the runoff phase?
the part of the cardiac cycle in which blood is only leaving the arteries
What is the main factor determining the rate of blood leaving the arterial system (runoff)?
arteriolar resistance (TPR)
How can we calculate MAP from systole and diastole?
MAP = diastolic pressure + (1/3 systolic pressure)
Diastolic arterial pressure is determined by what factors?
- rate of runoff
- duration of runoff
What happens to runoff when systemic arteries are dilated?
TPR is decreased, flow increases, runoff increases, arterial diastolic pressure decreases
Diastolic arterial pressure can be increased by doing what two things?
- increasing TPR via arteriolar constriction
- increasing heart rate
What are the three determinants of arterial systolic pressure?
- ejection rate
- stroke volume
- arterial compliance
How does aortic stenosis affect the arterial systolic pressure?
- stenosis decreases ejection rate
- pressure is reduced in the arteries
Increased stroke volume will do what to arterial systolic pressure?
increase it
Decreased arterial compliance will do what to arterial pressure?
increase systolic arterial pressure
How is compliance mathematically defined?
compliance = (volume change)/(pressure change) = (stroke volume)/(pulse pressure)
If pulse pressure is different between two people, it can likely be attributed to what?
a difference in stroke volume
If pulse pressure changes in an individual over a short period of time, it can be attributed to what?
either a change in stroke volume or a change in complicance
What happens to diastolic arterial pressure when compliance is reduced?
it drops more quickly and reaches a lower value
Which blood vessels have the lowest velocity of blood flow?
capillares
How, if cardiac output must equal the flow through the whole system, do capillaries have slow flow?
because taken all together, capillaries have the most cross sectional area of any set of vessels
Most blood is found in which part of the system?
systemic veins
A small change in blood volume will have what effect on pressure in the veins versus the arteries?
with increased compliance, an increase in blood volume has little change on the pressure within veins
Why does venous constriction/dilation have little effect on venous resistance?
because the radius only changes slightly
Venous constriction significantly increases _____ without significantly altering _____. This allows for what?
- pressure without significantly altering resistance
- allowing for increased venous return with venous constriction
How are centimeters of water converted to mm Hg?
centimeters x 1.36.
What is an example of series resistance in the human body?
TPR
What is an example of parallel resistance in the human body?
resistance in the organs
TPR is (lower/higher) than the lowest organ vascular resistance?
lower since the organs are in parallel
What is the conversion rate for mm Hg to dynes?
mm Hg x 1330
What is a normal value of TPR?
1 mm Hg/ml/sec
Poiseuille’s law says what about resistance?
that a small decrease in radius will greatly increase the resistance of a tube
Poiseuille’s law says what about viscosity?
as viscosity increases, so does resistance of a tube
Viscosity of blood is largely determined by what?
the erythrocyte concentration (hematocrit)
What happens to the rate of flow when that flow becomes turbulent?
flow decreases
Turbulent blood flow is more likely if what changes?
- flow increases
- viscosity decreases
- vessel radius decreases
What happens to resistance of flow when that flow becomes turbulent?
it greatly increases
Sphygmomanometers function on the basis of what hemodynamic factor?
turbulent blood flow due to arterial collapse under the pressure of the cuff
What is an ankle brachial index?
- use doppler to identify systolic pressure in the leg
- systolic in leg/systolic in brachial artery should be between 1 and 1.4
If the ankle brachial index is below 1, it is indicative of what?
large plaques in the arteries to the legs or coarctation of the aorta
What is the skeletal muscle pump?
the idea that muscle contraction is used to drive blood flow in the veins
Inspiration does what to venous return?
increases venous return to the right heart
Inspiration has what effect on the left heart?
- pulmonary veins distend
- pressure in pulmonary veins decreases
- flow is diminished
- return to left atrium decreases
Expiration will do what to the immediate heart rate?
it slows it slightly as pulmonary vein return to the left heart increases and stroke volume increases
How does arterial pressure change during the valsalva maneuver?
- it initially increases as stroke volume in the left heart increases
- continued increased intrathoracic pressure decreases venous return
- eventually arterial pressure drops as less blood becomes available to the left heart
What happens to venous return when central venous pressure increases?
return decreases since the pressure differential in the venous system decreases
What happens to ventricular filling when central venous pressure increases?
ventricular filling increases
A venous function curve puts what to lines on a graph?
1) venous return and 2) cardiac output as functions of central venous pressure
Where is the steady state on a venous function curve?
where the two curves intersect and venous return equals cardiac output
