Chapter 18: Hemodynamics Flashcards
Definition of flow
Amount of blood flowing through an area. Also known as volume flow rate
What are the 3 types of flow
Pulsatile, phasic and steady
What are the characteristics of pulsatile flow
Variable velocity, results from cardiac contraction, found in arterial circulation
What are the characteristics of phasic flow
Variable velocity, caused by respiration, found in venous circulation
What are the characteristics of steady flow
Constant speed, found NORMALLY in portal system. If found in arteries or veins then it is because of changes in respiration or disease
Describe laminar flow
Consists of parallel streamlines, found in normal physiology
What are the 2 types of laminar flow
Plug flow and parabolic flow
Describe plug flow
Seen at the beginning of a vessel, happens when all of the layers travel at the same velocity
Describe parabolic flow
When blood flow starts traveling in different velocities, and forms like a bullet shape
Describe turbulent flow
Chaotic streamlines, seen following pathology, causes swirling patterns called eddy
Palpable turbulent flow is called
Thrill
Audible turbulent flow is called
Bruit
What is the Reynolds number for laminar flow
<1500
What is the reynolds number for turbulent flow
> 2000
Blood moves from ____ energy areas to ____ energy areas
High, low
What are the 3 forms of energy
Kinetic energy, pressure energy, and gravitational energy
Describe kinetic energy
Any moving object, determined by object mass and speed
Describe pressure energy
Stored or potential energy, has the ability to perform work, creates flow by overcoming resistance
Describe gravitational energy
Stored or potential energy, has the ability to do work, associated with any elevated object (above earth)
Energy gets lost in circulation in 3 ways:
Viscous loss, frictional loss, and inertial loss
Describe viscous loss
Measured in units of Poise, it’s the thickness of blood, determined by hematocrit
Describe frictional loss
Caused by blood sliding across vessel walls, creating heat and loosing energy
Describe intertial energy loss
When energy is lost when the speed of blood changes (resisting velocity)
What is stenosis
Narrowing of lumen of a vessel
What are the 5 changes to blood flow that a stenosis causes
1.Change in flow direction
2.Increased velocity through narrowing
3. Turbulence after narrowing
4. Pressure decreases across the stenosis
5. Loss of pulsatility (from pulsatile to steady)
Bernoullis principle describes the relationship between _______ and ________ in a moving fluid
Velocity and pressure
If velocity increases, pressure ______
Decreases. And viceversa
In a stenosis, velocity increases, so pressure _______
Decreases
Electrical resistance is reported in units of ____
Ohms
Hydrostatic pressure is reported in units of
mmHg
Pt lying in supine position, hydrostatic pressure is ____ everywhere
Zero
Hydrostatic pressure at heart level is ____
Zero
Hydrostatic pressure below heart level is
Positive
Hydrostatic pressure above heart level is
Negative
During inspiration, the diaphragm goes ____
Down
During inspiration, the pressure in the abdominal cavity ______
Increases. Reducing flow from lower body
During inspiration, the pressure in the thorax_____
Decreases. Allowing blood flow from upper body
During expiration the diaphragm goes___
Up
During expiration, the pressure in the abdominal cavity____
Decreases. Allowing flow from lower body
During expiration, the pressure in the thorax _____
Increases, reducing blood flow from upper body
