ultrasound physics ch 18

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ultrasound physics ch 18
2014-07-26 21:52:28
ultrasound physics
ch 18
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  1. What is hemodynamics?
    it is the study of blood moving through the circulatory system.
  2. What is flow?
    what is the units of flow?
    Flow is the volume of blood moving during a particular time.

    Units: volume / time
  3. Flow can also be called what?
    volume flow rate
  4. What is velocity?

    velocity indicates the speed of a fluid moving from one location to another.

    distance / time
  5. What are the three basic types of flow?
    • 1. plusatile
    • 2. phasic
    • 3. steady
    • `
  6. When does pulsatile flow happen?

    Where does pulsatile flow usually happen?
    happens during cardiac contraction, blood accelerates and decelerates as a result of cardiac contraction

    appears in arterial circulation
  7. When does phasic flow happen?

    Where does phasic flow happen?
    happens during respiration, blood accelerates and decelerates as a result of respiration

    appears in venous circulation
  8. What is steady flow?

    And where does it happen?
    steady flow occurs when a fluid moves at a constant speed or velocity.

    happens in the venous circulation when individuals stop breathing for a brief moment.
  9. What is the two types of laminar flow and what makes them different?
    • Plug flow - same velocity
    • Parabolic flow - velocity is highest at the center
    • which makes it bullet shaped.
  10. What is the Reynolds number for Laminar flow?
    Less than 1,500
  11. WHat is Reynolds number for turbulent flow?
    Greater than 2,000
  12. Turbulent flow converts flow energy into what two other forms?
    • 1. Sound also called murmur or bruit
    • 2. Vibration also called a thrill or palpable murmur.
  13. What are the three forms of energy?
    • 1.) kinetic- moving object
    • 2.) pressure- stored or potential
    • 3.) Gravitational- stored or potential
  14. Blood moves from regions of __________energy to regions of ___________energy.
    higher energy to lower energy
  15. What two factors determine kinetic energy?
    • 1.) objects mass
    • 2.) the speed at which it moves
  16. As blood flows through the circulation, energy is lost in three ways:
    • 1. viscous loss
    • 2. frictional loss
    • 3. inertial loss
  17. Viscous Energy is...
    • Viscosity, which is the thickness of a fluid.
    • More energy is lost with high viscosity = thicker
  18. WHat are the units of Viscosity?
  19. What is hematocrit?

    And what is a normal value?
    the percentage of blood made up of red blood cells

    approximately 45 %
  20. What is an example of frictional energy loss?
    When blood moves through the vessels it rubs up against the vessels walls and creates heat.
  21. What is inertial energy loss?
    it is the energy lost when the speed of a fluid changes, regardless of whether the fluid speeds up or slows down.
  22. What does inertia relate to?
    the tendency of a fluid to resist changes in its velocity.
  23. Where does the maximum velocity exist at?
    where the vessel is the narrowest has the fastest velocity
  24. WHere does velocity decrease?
    velocity decreases as blood flows out of the stenosis into a vessel segment of normal diameter.
  25. What is a stenosis?
    a narrowing in the lumen of a vessel
  26. What can increase the pressure gradient?
    • flow increases
    • or
    • resistance increases
  27. What causes an increase in flow?
    • pressure gradient increases
    • or
    • resistance decreases
  28. During normal function what is true about veins? (6)
    • 1. thin walled
    • 2. collapsible
    • 3. low pressure
    • 4. partially filled with blood
    • 5. expanded
    • 6. low resistance
  29. What is hydrostatic pressure?

    pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level.

    Units: mmHg
  30. WHat does supine mean?
    when a patient lays flat on their back, all parts of the body are at the same level as the heart
  31. WHat is the hydrostatic pressure everywhere when a patient is supine?
  32. Is the hydrostatic pressure negative or positive at the head when a patient is standing upright?


    THE measured pressure will be lower than the true circulatory pressure.
  33. Is the hydrostatic pressure negative or positive at the feet when a patient is standing upright?


    The measured pressure will be higher than the true circulatory pressure.
  34. When the diaphragm moves downward during _________ what happens to the venous flow in the legs?

    When the venous flow to the legs _______, what happens to the venous flow to the heart?
    • inspiration
    • decrease to legs

    • decrease
    • increase to the heart
  35. When the diaphragm moves upward during _______ what happens to the venous flow in the legs?

    When the venous flow to the legs _______, what happens to the venous flow to the heart?
    • expiration
    • increase to legs

    • increase
    • decrease to the heart