Doppler Flashcards
Flow
aka volume flow rate. Indicates the volume of blood moving during a particular time.
Velocity
indicates speed or swiftness of a fluid moving from one location to another.
Pulsatile flow
occurs when blood moves with a variable velocity. Blood accelerates and decelerates as a result of cardiac contraction; therefore, pulsatile flow commonly appears in the arterial circulation.
Phasic Flow
Also occurs when blood moves with a variable velocity. Blood accelerates and decelerates as a result of respiration; therefore, phasic flow often appears in venous circulation.
Steady Flow
Occurs when a fluid moves at a constant speed or velocity. Water flowing through a garden hose is an example of steady flow. Steady flow is present in the venous circulation when individuals stop breathing for a brief moment.
Laminar Flow
is when the flow streamlines are aligned and parallel. The word lamina means layer. Laminar flow is characterized by layers of blood that travel at individual speeds. Laminar flow patterns are commonly found in normal physiologic states.
Plug Flow
occurs when all of the layers and blood cells travel at the same velocity
Parabolic Flow
has a bullet-shaped profile. Velocity is highest in the center of the lumen, and gradually decreases to its minimum at the vessel wall
Turbulent Flow
characterized by chaotic flow patterns in many different directions and at many speeds. The streamlines are often obliterated.
Buit
Sound associated with turbulence
Thrill
Tissue vibration associated with turbulence.
Reynolds number
predicts whether flow is laminar or turbulent. The Reynolds number of turbulent flow is greater than 2,000
Energy gradiant
Blood moves from higher energy to lower energy
Forms of energy- Kinetic pressure gravitational
Kinetic is associated with a moving object
Pressure is a form of stored of potential energy. It is a major form of energy for circulating blood and creates flow by overcoming resistance
Gravitational is a form of stored or potential energy. is associated with any elevated object.
Energy losses in circulation - Viscous, Frictional, Inertial
Viscous- describes the thickness of fluid.
Frictional- frictional losses occur when flow energy is converted to heat as one object rubs against another.
Inertial- relates to the tendency of a fluid to resist changes in its velocity
Stenosis
a narrowing in the lumen of a vessel
Effects of stenosis
changes in direction as blood flows into and out of the narrow portion of the vessel increased velocity within the stenosis Turbulence downstream from stenosis pressure gradient across the stenosis loss of pulsatility
Bernoulli’s Principle
describes the relationship between velocity and pressure in a moving fluid. It is derived from the principle of conversation of energy. This principle states that with a steady flow, the sum of all forms of energy is the same everywhere.
Pressure Flow Relationships
pressure gradient=flow x resistance
pressure gradient increases when either flow increases or resistance increases
Flow increases when pressure gradient increases or resistance decreases.
Ohm’s Law
voltage = current x resistance
Hydrostatic pressure
pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level.
units= mmHg
Breathing & Venous flow- Expiration & Inspiration
Breathing effects venous flow because venous system is low pressure and muscles responsible for respiration alter pressures in the thorax and abdomen.
Inspiration- diaphragm moves down, thoracic pressure decreases, abdominal pressure increases, venous return to the heart increases, venous flow in legs decrease
Expiration- diaphragm moves up, thoracic pressure increases, abdominal pressure decreases, venous return to the heart decreases, venous flow in legs incease.
