Pressure, Flow, Tension

Front 1

Pressure

Back 1

the force applied or distributed over a surface as force per unit area

Front 2

Pressure equation

Back 2

P= F/A

Front 3

2 Sources of Force

Back 3

1. force of gravity
2. Energy within atom or molecule (kinetic molecular theory)

Front 4

Units of force

Back 4

Newton
N = kg m/s squared

Front 5

1 mmHg = ? cm water

Back 5

1mmHg = 1.36 cm water

Front 6

Absolute pressure

Back 6

Gauge pressure + Atmospheric pressure

Front 7

Gauge pressure

Back 7

what the gauge states

Front 8

Flow

Back 8

the quantity of a fluid (gas or liquid) passing a point in unit time

Front 9

PRESSURE represents what type of energy

Back 9

Potential or stored energy

Front 10

FLOW represents what type of energy

Back 10

Kinetic energy (energy of motion)

Front 11

Flow equation

Back 11

F = Q/T
Q = quantity (mass or volume)
T = time

Front 12

Laminar Flow

Back 12

- occurs in smooth tubes
- occurs at low flow rates
- Flow is greatest at the center & approaches zero at the walls
- there must be a pressure gradient across the ends of the tube
- linear relationship between Pressure and Flow
- increase polarity increases viscosity

Front 13

In Laminar Flow there is a linear relationship between:

Back 13

Linear relationship between Pressure and Flow

Front 14

In Laminar Flow what is the key factor

Back 14

Viscosity

Front 15

Viscosity

Back 15

- a measure of a liquid's resistance to flow
- the greater the viscosity, the greater the interaction between adjacent fluid layers so there is decreased flow

Front 16

Poiseuille's Equation relationships

Back 16

Flow is directly proportional to Pressure

Flow is inversely proportional to Viscosity and Length of tube

Front 17

According to Poiseuille's Equation if radius doubles what happens to flow?

Back 17

If radius doubles than Flow Increases by 16 times
- (diameter is radius doubled)

Front 18

The greatest role in determining the rate of flow thru a vessel

Back 18

radius or diameter of the blood vessel plays the most important role in determining the rate of flow

Front 19

2/3 of systemic vascular resistance is due to what?

Back 19

is due to blood flow in the smallest arterioles ranging diameter from 4-25 micrometers

Front 20

OHM's Law (Equation)

Back 20

Q = (P1-P2)/R

R = (P1-P2)/Q

Front 21

What does OHM's Law allow us to do?

Back 21

it allows us to calculate SVR and C.O.
- use this law to describe blood flow through a vessel

Front 22

Turbulent Flow

Back 22

- molecules travel in nonparallel paths leading to eddy currents
- occurs at points of constriction causing increased fluid velocity
- Non-linear between Flow and Pressure
- Pressure is approximately proportional to the square root of the flow rate
- Occurs with increased or variable Velocity
- Density is the important property
- greater resistance than for laminar flow at the same flow rate

Front 23

In Turbulent Flow what is the important property

Back 23

Density is the important property in Turbulent flow

Front 24

Reynold's Number

Back 24

Determines if the flow is laminar or turbulent
- relates ratio of density of a gas to its viscosity

Front 25

Reynold's Number Equation

Back 25

Re = 2rvd/n

Front 26

Critical Flow rate

Back 26

Change from Laminar to Turbulent flow
- depends on velocity of gas which...
- depends on volume flow and diameter of tube

Front 27

Critical Flow is defined by what?

Back 27

Defined by the gas and temperature
- with warming of anesthetic gases as they enter the airway, the critical flow rises due to the decreased density from increased temperature

Front 28

Examples of Laminar Flow

Back 28

- Quiet breathing
- Blood flow except at bifurcations

Front 29

Examples of Turbulent Flow

Back 29

- Coughing, speaking, deep breathing
- Increased secretions
- Carotid stenosis

Front 30

Heliox

Back 30

clinical use of density and viscosity to decrease resistance to flow
- used in acute, sever airway obstruction: subglottic edema, foreign bodies, tracheal tumors
- Only Helium has a lower density to viscosity ratio

Front 31

Bernoulli's Law

Back 31

when liquids flow through a tube, a pressure is exerted against the sides of the tube. The faster the flow rate, the less side pressure is generated. If the pathway is varried in cross-sectional area, forward velocity is FASTEST and side pressure is LEAST at the point of greatest constriction
- rational behind Venturi's Priniciple

Front 32

Venturi's Principle

Back 32

pressure is lowest at area of constriction d/t fast flow in the middle and when there's a pressure decrease than air can be entrained from outside
- how nebs and venturi masks work

Front 33

Jet Ventilation

Back 33

used in upper airway lesions in OR.
- inhalation is by pressing toggle and expiration is passive.
- measure ventilation by O2 sat and chest rise

Front 34

Tension

Back 34

a tangential force in Newtons/meters acting on a length of the wall.
- caused by the smooth muscle and elastic tissue
- balance between tension and the fluid pressure inside the tube to prevent it from collapsing or distending

Front 35

Law of Laplace for a tube or cylinder

Back 35

P = Tension/Radius

Front 36

Law of Laplace for a sphere

Back 36

P = 2 Tension/Radius

Front 37

transmural pressure (hydrostatic pressure)

Back 37

pressure that distends the tube

Front 38

Explanation of Law of Laplace

Back 38

- explains how aorta can sustain high pressures and how capillary with much smaller radius can also sustain pressure of 100mmHg
- Tiny, thin-walled capillaries can withstand surprisingly large pressures because of their tiny radius
- aorta has elastin, collagen, and smooth muscle where as capillaries only have elastin and collagen

Front 39

What happens to the wall tension required to sustain a developing aortic aneurysm when the radius increases from 2cm to 3cm

Back 39

Tension Increases with Increased Radius to be able to withstand pressure

Front 40

Law of Laplace regarding Aneurysms

Back 40

Wall tension is proportional to vessel radius for cylindrical vessels. Approaching a spherical shape gives less tension than the same radius cylinder, but continued expansion produces wall tension exceeding that of the original cylinder

Front 41

Law of Laplace regarding blood pressure measurements

Back 41

- as the distended heart fails the radius increases and the pressure falls unless the muscle contracts proportionally more forcefully
- as distended heart fails the radius increases