Hemodynamics Notes

Flashcards for Hemodynamics Review

Hemodynamics

The study of blood moving through the circulatory system.

Flow

The volume of blood moving at a particular time.

Velocity

The speed of a fluid moving from one location to another.

What are the three basic forms of flow

Pulsatile, phasic, and steady flow

Pulsatile flow

Occurs when blood moves with a variable velocity due to cardiac contraction (e.g., arterial blood flow).

Phasic flow

Fluid moves with a variable velocity as a result of respiration. (e.g. venous blood flow)

Steady flow

Fluid moving at a constant speed/velocity (e.g., venous circulation when an individual stops breathing).

Laminar flow

Flow streamlines are aligned and parallel, characterized by layers of blood that travel at individual speeds.

What is the two types of laminar flow

Plug and parabolic flow

Plug flow

All layers and blood cells travel at the same velocity.

Parabolic flow

Has a bullet-shaped profile; velocity is highest in the center and decreases to a minimum at the vessel wall.

Reynold’s number

A unitless number indicating laminar or turbulent flow.

Turbulent flow

Chaotic flow in many directions and speeds, often associated with cardiovascular pathology and elevated blood velocities.

Eddy current/Vortex

Small, hurricane-like, rotational patterns that appear in turbulent flow.

Murmur/Bruit

Sound associated with turbulence.

What does turbulent flow do

It converts flow energy into other forms such as sound and vibration

Thrill

Tissue vibration associated with turbulence; also described as a palpable murmur.

Energy Gradient

Blood moves from regions of higher energy to lower energy. The energy is imparted to blood by the contraction of the heart

Kinetic energy

Energy associated with a moving object, determined by mass and speed.

Pressure energy

A form of stored or potential energy with the ability to perform work.

Gravitational energy

Stored or potential energy associated with any elevated object.

Viscosity

Describes the thickness of a fluid; more energy is lost with movement of high viscosity fluids.

Viscous energy loss

Energy loss associated with blood overcoming its internal stickiness.

Viscosity is measured in units of

poise

How is viscous energy loss determined

by hamatocrit

Hematocrit

The percentage of red blood cells in the blood.

Frictional energy loss

Occurs when flow energy is converted to heat as one object rubs against another (e.g., blood sliding across vessel walls).

Inertial energy loss

Energy loss that occurs during pulsatile flow, phasic flow and velocity changes at a stenosis.

Inertia

The tendency of a fluid to resist changes in its velocity.

Stenosis

A narrowing in the lumen of a vessel.

What are the effects of a stenosis

Change in flow direction, increased velocitiesas vessels narrow, turbulent flow downstream from where the stenosis is, loss of pulsatility

Bernoulli’s Principle

Describes the relationship between velocity and pressure in a moving fluid; the sum of kinetic and pressure energy remains constant.

What type of resistance do veins have

low resistance

During normal function what is the pressure in veins

They are low pressure and only partially filled with blood and expanded

Hydrostatic pressure

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