Flashcards in Exam #2: Hemodynamics Deck (29):
In hemodynamics, how is the venous system described? What does a change in the radius of a vein lead to?
The venous system is referred to as a capacitance system.
- Change in radius= change in volume
In hemodynamics, how is the arterial system described? What does a change in the radius of an artery lead to?
The arterial system is referred to as a resistance system.
- Change in radius= change in pressure
List the characteristics of arteries,
List the characteristics of arteroles.
List the characteristics of capillaries.
List the characteristics of venules.
List the characteristics of veins
Elastic fibers vs. collagen fibers.
Pressure changes in circulatory system?
List the three basic principles of hemodynamics.
1) The rate of blood flow to an organ/ tissue is related to its need (more need= more flow)
2) Cardiac output is controlled by the sum of individual tissue needs
3) Arterial pressure regulation is independent of local blood flow or cardiac output control
How is arterial pressure regulated?
Short-term= nervous reflexes
What are the units of blood flow?
Write Ohm's law for blood flow using symbols. What is Ohm's law for blood flow?
Flow is equal to the pressure gradient, divided by the resistance.
Thus, flow is directly proportional to the pressure gradient, & flow is indirectly proportional to the resistance.
Write Poiseuill's law for rigid tubes.
What is viscosity?
Internal friction of the fluid
How is viscosity measured clinically?
Hematocrit (% RBCs in blood, which in men is ~45)
What is anomalous viscosity?
As blood flow decreases, viscosity increases & conversely, as viscosity increases, blood flow slows
*Note that this can be clinically important in burns as a loss of plasma leads to an increase in blood viscosity
What is laminar blood flow?
Blood flow that is organized into concentric circles:
- FASTEST in the middle (closest to center axis)
- SLOWEST on the edges (near the wall of the vessel)
*Results in a parabolic shape & is due to a reduction of friction in the center of the vessel & is very efficient. This is what is occurring in most blood vessels, most of the time.
What is turbulent flow?
Disorganized blood flow with a squared leading edge of movement. This type of blood flow is:
- Has increased resistance
When do we induce turbulent flow clinically?
Blood pressure measurement; Korotkoff sounds are "turbulent" flow
The blood pressure cuff is inflated to a level above systolic pressure (occluding the artery). Pressure is released until a sound is heard, which is turbulent blood flow in the constricted vessel. As the cuff pressure is reduced, blood flow is less turbulent. When flow is no longer heard, the diastolic pressure is measured. At this point, blood flow is laminar.
What is the Reynolds number? Write the equation for the reynolds number.
What do we know from the reynolds number?
- Large vessels more prone to turbulence
- Fast fluid flow is more likely turbulent
- Viscous blood is less turbulent (slower)
Draw the pressure-flow-resistance curves.
What is the Law of Laplace? Write the law of Laplace.
Law of Laplace states that the tension in a vessel (or chamber) wall is proportional to the radius & pressure.
What is flow?
Flow is equal to the pressure gradient divided by resistance.
What is resistance?
Resistance is the pressure gradient divided by flow.
Where is resistance lower, pipes in series or parallel?
What is TPR?
TPR= Total Peripheral Resistance= resistance to the entire systemic circulation, exclusive of the lungs.
TPR= pressure gradient divided by cardiac output