Q=ΔPπr⁴/8Lη

(Q=flow, ΔP=pressure change, r=radius, L=length, η=viscosity)

↓ΔP → ↓Q

↓r → ↓↓↓↓Q

↓L → ↑Q

↓η → ↑Q

[image]

Plug

During systole in larger vessels (~>3mm).

At the enteranceof a stenosis

At the enterance of a bifurcation

Parabolic

All the time throughout cardiac cycle in smaller vessels (~<3mm)

During diastole in larger vessels (~>3mm)

Further distal in a stenosis

An object that creates a major reduction of flow and pressure.

(typically a ≥ 50% in diameter structure)

1. CHF
2. COPD

Carotid bifurcation flow: Where is shear force highest?

What is the name for the swirling area of flow at the carotid bifurcation?

Inner wall

Boundry layer separation

Re=Vρ2r/η

(V=velocity, ρ=density, r=radius, η=viscosity)

Velocity

Density

Radius

Pressure√

Kinetic

V/t

example: 5L/min

d/t

example: 200 cm/s

1. pulsatile
2. phasic
3. steady

1. Liminar
2. Turbulent

1. Plug flow
2. Parabolic flow

What is TURBULENT FLOW?

What type of flow is being described?

• arterial
• cardiac contraction
• high rate
• higher pressure

What type of flow is being described?

• venous
• respiration
• low rate
• lower pressure

What is being described?

• volume
• how much?
• volume/time

What is being described?

• speed
• how fast?
• distance/time

• sound--murmurs and/or bruits
• vibration--thrill

• Vortex: a swirling pattern of rotational flow
• Eddy currents: turbulent flow

a unitless number indicating whether flow is laminar or turbulent.

<1500 laminar

1500-2000 mixed

>2000 turbulent

1. kinetic
2. pressure
3. gravitational

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

What 2 factors is kinetic energy determined by?

• an object's mass
• the speed at which it moves

Thus, heavy, swiftly moving objects have lots of kinetic energy. Light, slowly moving objects have little kinetic energy.

1. viscous loss
2. frictional loss
3. inertial loss

Relates to the tendency of a fluid to resist changes in its velocity. "Objects at rest, tend to stay at rest..." Thus, energy is lost when the velocity of a fluid changes. 

Inertial loss results from:

>>pulsatile flow during both acceleration and deceleration

>>velocity changes at a stenosis

change in flow direction

increased velocity in the stenosis, highest velocity at the point of maximum narrowing

turbulent flow at exit

pressure gradient across the stenosis

loss of pulsatility in arterial flow

1. radius of lumen (most important)
2. length
3. viscosity of fluid

Where is the pressure lowest?

A, B, or C

[image]

The pressure is lowest at location B.

Velocity is highest at the narrowest part of the vessel, the stenosis (location B). Kinetic energy is associated with moving object and kinetic energy increases with higher velocities. Therefore, the kinetic energy of blood increases as it speeds up through the stenosis from location A to location G. Since kinetic energy increases, another form of energy, in this case pressure, simultaneously decreases. Pressure energy is converted in to kinetic energy as the blood accelerates. As a result, pressure energy drops within the stenosis and is lowest at location B

1. Venous system is low pressure
2. The muscles producing respiration change the pressure in the thorax (chest cavity) and the abdomen

When does the diaphragm move downward?

What happens to blood flow above the diaphragm and why?

What happens to blood flow below the diaphragm and why?

When does the diaphragm move upward?

What happens to blood flow above the diaphragm and why?

What happens to blood flow below the diaphragm and why?

correlates; diaphragm

diaphram ↓→↓venous flow in legs

(downward→decrease)

diaphram↑→↑venous flow in legs

(upward→increase)