Hemodynamics

• The volume or amount of blood that moves through a vessel in a given time.
• It may be called volume flow rate.
• Unit of Flow: volume divded by time. (mls/sec)

• a mesause of the speed of blood flowing through circulation.
• Unit of velocity: distance divided by time. (cm/s)

Energy stored (nozzled hose)

Energy in action (Waterfall)

Potential energy due to gravity (elevational)

Gravitational energy is called hydrostatic pressure and is expressed in mm of mercury. (mmHg)

The total energy at a specific location is the sum of all three energy forms.

There must be difference in energy at two different sites.

Blood flows from a region of higher energy to a region of lower energy.

Q=P(Pressure Gradient)/R(Resistance)

• The difference in PRESSURE bwn two points is the PRESSURE GRADIENT
• Increase the pressure gradient; flow increases
• Pressure gradient and flow are directly proportional
• Increase Resistance; Flow decreases
• Resistance and flow are indirectly proportional

• Viscosity describes the thickness of the fluid
• Viscous energy loss is associated with blood overcoming its interneal stickness

• Occurs when flow energy is converted to heat
• Blood sliding across vessel walls creates heat

• The tendency of a fluid to resist changes in velocity
• Energy is lost when the speed of a fluid changes

• If pressure differences increases, flow rate increases
• if length of vessel increases, flow rate decreases (bc of more resistance)
• if diameter increases, flow rate increases (decrease in resistance)
• if visocity increases, flow rate decreases (bc of more resistance)
• longer vessel, more resistance (double length, double resistance)

• 1. Length of vessel
• 2. Radius of vessel
• 3. Viscosity of Fluid

• -Viscosity is the thickness of blood.
• -Increase Viscosity, Increase resistance to flow

• 1) Polycythemia-high concentration of RBC's
•       Viscosity Increases
• 2) Anemia- Low concentration of RBC's
•        Viscosity Decreases

• The relationship between radius of a vessel and its resistance to flow is an inverse relationship.
• Resistance to Flow= 1/raidus⁴
• Only true if the same length and same type of liquid flowing!!

• Predicts whether flow is laminar or turbulent
• is unitless
• In a stiff tube, flow will change from laminar to disturbed/turbulent when the Re passes 2000.

• Body movement
• pulsatility of blood flow
• irregularities of vessel wall and plaque

• The higher the velocity the higher the Re
• Larger vessels tends to have higher Re
• The thinner the blood the higher the Re
• The more dense the fluid the higher the Re (higher the Re, the more potential for turbulene)
• The more viscous the more laminar flow
• Lower viscosity (thinner blood) can cause higher turbulence

Converts flow energy into other forms such as sound and vibration.

• High velocities within large vessels
• Distal to an obstruction
• Along a rough surface
• Within a sharp turn of a vessel

the audible sound associated with turbulent flow.

The tissue vibration associated with turbulent flow (also called palpable murmur).

• As severity of an obstructive lesion progresses from mild to moderate, the duration and amplitude of the bruit increases.
• Turbulence becomes more severe and more fluid energy is converted to sound energy.
• As severity of the lesion progresses from moderate to pre-occlusive, the duration and amplitude of the bruit decreases.
• Blood flow decreases, therefore the amplitude of the bruit decreases.
• (IE, ICA is the one that get stopped up the most)

Blood moves with variable velocity; blood accelerates and decelerates from cardiac contraction; commonly seen in arterial circulation (in arteries)

Blood moves with variable velocity; accelerates and decelerates from respiration; commonly seen in venous circulation. (IVC) [Venous pump in calf pump push blood up against gravity]

a fluid moves at constant velocity. (veins)

resistance of a fluid to flow due to the attraction of the molecules(also can be described as thickness or stickness of fluid)

Measure of the impediment that must be overcome for flow to occur.

• Ability of vessels walls to expand and contract; related to the ability to hold a change in volume.
• When the pressure pulse forces fluid into a complaint vessels, it expands and increases the volume within it.
• (Veins are a lot more complaint)

measure of force per unit area

Energy that is stored which has ability to perform work (pressure and gravitational energy are both forms of potential energy)

Energy related to movement; directly related to velocity

Flow pattern is random and chaotic with particvles moving at different speeds in a different directions.

Flow where streamlines are not straight; particles of fluid still flow in the forward direction.

at the entrance of a vessel.

Streams of different velocities.

A Type of laminar flow downstream from the entrance of a vessel.

• Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level.
• *Right atrium of the heart is considered the zero pressure reference point.
• *When Pt is supine, hydrostatic pressure is Zero at all parts of the circulatory system bc every part is at the heart level.
• *When Pt is standing, hydrostatic Pressure is zero at the heart level; positive below heart level and negative above the heart level bc against gravity.

Circulatory pressure + hydrostatic pressure

To maintain volume flow across vessel and body.

• Causes an increases resistance over a short distance.
• In order to maintain volume flow, velocity increases through the stenosis.
• As the stenosis gets narrower, the velocity must increase to maintain flow.

• Radius of Vessel is directly proportional to volume flow (changing the radius of the full length of the vessel)
• The size of the vessel is inversely proportional to the velocity of blood flow.
• As vessel radius decreases, resistance increases and velocity increases
• As vessel radius increases, velocity decreases but flow increases.
• The volume of blood flow through a stenotic vessel remains constant (continuity principle).

• As the vessel narrows, flow velocity increases and pressure simultaneously decreases.
• The equation shows that velocity and pressure are inversely related.
• Q=P/R