Physical Principles of
Respiratory Care
Egan Chapter 6

I.
Physical Principles of Respiratory Care
II.
III.
IV.
States of Matter
Change of State
Gas Behavior Under Changing Conditions
Fluid Dynamics

II. Change of State
A.
B.
1.
2.
5.
6.
3.
4.
1.
2.
Liquid-Solid Phase
Changes
Melting
Freezing
Properties of Liquids
Pressure in Liquids
Buoyancy (Archimedes’
Principle)
Viscosity
Cohesion and Adhesion
Surface Tension
Capillary Action
C.
D.
1.
2.
1.
2.
3.
4.
5.
6.
Liquid-Vapor Phase
Changes
Boiling
Evaporation, Vapor Pressure, and Humidity
Properties of Gases
Kinetic Activity of Gases
Molar Volume and Gas
Density
Gaseous Diffusion
Gas Pressure
Partial Pressure (Dalton’s
Law)
Solubility of Gases in Liquids
(Henry’s Law)

II. Change of State
A.
1.
2.
Liquid-Solid Phase Changes
Melting
Freezing http://www.youtube.com/watch?v=j2KZmRIKea8
Start at 3:15

A. Liquid-Solid Phase Changes
1.
Melting
?
When a solid is heated, what happens to its kinetic energy?

What happens to its intermolecular forces?
5

A. Liquid-Solid Phase Changes
2. Freezing
?
When a liquid is cooled, what happens to its kinetic energy?


What happens to its intermolecular forces?
6

A. Liquid-Solid Phase Changes

A. Liquid-Solid Phase Changes

Melting and Boiling

Melting Point:


The temperature at which a solid converts to a liquid
Boiling Point

The temperature at which a liquid converts to the gaseous state
Substance
Water
Oxygen
Melting Point
0 °C
-219 °C
Boiling Point
100 °C
-183 °C
8

A. Liquid-Solid Phase Changes

Melting and Boiling

Latent Heat:


The amount of heat needed for a substance to change its state of matter
Latent heat of fusion:


The amount of heat needed to change a solid to a liquid
Latent heat of vaporization

The amount of heat needed to change a liquid to a gas
9

A. Liquid-Solid Phase Changes
Latent heat of vaporization
Steam
Latent heat of fusion Water
Ice
10

II. Change of State
B.
1.
2.
3.
4.
5.
6.
Properties of Liquids
Pressure in Liquids
Buoyancy (Archimedes’ Principle)
Viscosity
Cohesion and Adhesion
Surface Tension
Capillary Action

B. Properties of Liquids


Liquid Oxygen http://www.youtube.com/watch?v=ndtmfDoI8PM


B. Properties of Liquids
Liquid molecules also possess attractive forces
 but these forces are much weaker in liquids than in solids

Liquid molecules have greater freedom of movement and possess more KE than solids


This is why liquids take the shape of their container
And are capable of flow

Liquids cannot be easily compressed
13

B. Properties of Liquids
1. Pressure in Liquids


Is the same at any specific depth, regardless of the container ’ s shape
Is exerted equally in all directions
14

B. Properties of Liquids
1. Pressure in Liquids


Pascal ’ s Principle:
A confined liquid transmits pressure equally in all directions
15

B. Properties of Liquids
1. Pressure in Liquids

Pascal ’ s Principle

Downward
16

B. Properties of Liquids
1. Pressure in Liquids



Liquids are capable of flow
Pascal ’ s Principle
Sideways
17

B. Properties of Liquids
1. Pressure in Liquids

Pascal ’ s Principle

Upward
18 http://www.youtube.com/watch?v=iD55ynlUH8g http://www.youtube.com/watch?v=UpwLwP0pmwk

B. Properties of Liquids
1.


Pressure in Liquids
Clinical Application
Heart Failure
19

B. Properties of Liquids
1.


Pressure in Liquids
Clinical Application
Using an air or water mattress to prevent the development of bed soars
20

B. Pressure in Liquids
2. Buoyancy (Archimedes’ Principle)

Buoyancy occurs because the pressure below a submerged object always exceeds the pressure above it

B. Pressure in Liquids
2. Buoyancy (Archimedes’ Principle)

According to Archimedes

This buoyant force must equal the weight of the fluid displaced buy the object http://www.youtube.com/watch?v=mhJ5Ybt7L2k http://www.youtube.com/watch?v=vJ36urazDu4&list=PLB76160897CFFC3F4&index=8&feature=plpp_video

B. Pressure in Liquids
2. Buoyancy (Archimedes’ Principle)



Gases also exert buoyant force
Buoyancy helps keep solid particles suspended in gases
These suspensions, called aerosols, play an important role in respiratory care.

B. Properties of Liquids
3. Viscosity

Internal force that opposes flow of a fluid, either liquids or gases



Fluid’s viscosity is directly proportional to cohesive forces between its molecules
The stronger the cohesive forces, the greater the fluid viscosity
Heart must use more energy when blood viscosity increases, as occurs in polycythemia

B. Properties of Liquids
3. Viscosity

Clinical Application


The greater the viscosity of a fluid, the more energy is needed to make it flow
The heart must perform more work when blood viscosity increases


Polycythemia: an increase in red blood cells
Polycythemia is common in patients with chronic bronchitis
25

B. Properties of Liquids
4. Cohesion and adhesion

The attractive force between like molecules is cohesion.

The attractive force between unlike molecules is adhesion.
26

Cohesion and Adhesion
Water
Concave meniscus

Adhesion > Cohesion
27

Cohesion and Adhesion
Mercury
Convex meniscus

Cohesion > Adhesion
28

B. Properties of Liquids
5. Surface Tension
 a force exerted by like molecules at a liquid’s surface

The cohesive forces between liquid molecules are responsible for this phenomenon

B. Properties of Liquids
5. Surface Tension

B. Properties of Liquids
5. Surface Tension

B. Properties of Liquids
5. Surface Tension

Explains why liquid droplets and bubbles retain a spherical shape

B. Properties of Liquids
5. Surface Tension

In bubbles

B. Properties of Liquids
5. Surface Tension

Laplace ’ s Law

The pressure within a sphere

Varies directly with the surface tension of the liquid

As the surface tension of the liquid increases, the internal pressure increases


Varies inversely with its radius

As the droplet becomes smaller and the radius decreases, the internal pressure increases
P = 4ST r
34

B. Properties of Liquids
5. Surface Tension

Laplace’s Law
35 http://www.youtube.com/watch?v=RAmx4_G9XsQ

B. Properties of Liquids
5. Surface Tension in alveoli

Surface Tension

Surface tension in alveoli

Alveoli with increased surface tension

Have a greater tendency to collapse

Require greater distending pressure to maintain their volume
37

B. Properties of Liquids
5. Surface Tension in alveoli

Clinical Application:

Atelectasis
38

B. Properties of Liquids
5. Surface Tension

Normal CXR after the application of Continuous Positive
Airway Pressure (CPAP)

B. Properties of Liquids
5. Surface Tension

The lung reduces surface tension of alveoli by the production of a complex surface tension reducing chemical mixture called
SURFACTANT http://www.youtube.com/watch?v=Gpcbetob4p4
40

B. Properties of Liquids
5. Surface Tension

Clinical Application

The first breath of life

B. Properties of Liquids
5. Surface Tension

Artificial surfactant administration in Infant Respiratory
Distress Syndrome

B. Properties of Liquids
5. Surface Tension

Clinical Application
 Liquid Ventilation http://www.youtube.com/watch?v=2OxstD2jN08

B. Properties of Liquids
6. Capillary Action

A phenomenon in which a liquid in a small tube moves upward, against gravity

B. Properties of Liquids
6. Capillary Action http://www.youtube.com/watch?v=mdkeZbm0cCI

B. Properties of Liquids
6. Capillary Action

Clinical Examples
 Capillary blood stick http://www.youtube.com/watch?v=q5J1cCyrASs

B. Properties of Liquids
6. Capillary Action

Clinical Examples
 Absorbent wick humidifiers

C. Liquid-Vapor Phase Changes
1.
2.
Boiling
Evaporation, Vapor Pressure, and Humidity

C. Liquid-Vapor Phase Changes


49
Liquid to vapor phase changes (vaporization)
2 types of vaporization

Boiling  heating liquid to temperature at which its vapor pressure exceeds atmospheric pressure


Boiling point of most liquefied gases is very low

Liquid oxygen boils at -183°C
Evaporation  when liquid changes into gas at temperature below its boiling point





Evaporation requires heat. The heat energy required for evaporation comes from the air next to the water surface. As the surrounding air loses heat energy, it cools. This is the principle of evaporative cooling, which was previously described.
Water enters atmosphere via evaporation when at temperature lower than its boiling point (water vapor)
Molecular water exerts pressure called water vapor pressure
Temperature influences evaporation most
The warmer the air, the more vapor it can hold

C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor Pressure and
Humidity

Evaporation: the change in state of substance from a liquid to a gaseous state below its boiling point.

Molecular water exerts a pressure called the water vapor pressure
50

C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor
Pressure and Humidity

State of equilibrium: for every molecule escaping into the air another returns to the water reservoir
51

2. Evaporation, Vapor Pressure and Humidity
Influence of Temperature

The warmer the air, the more water vapor it can hold


The capacity of air to hold water vapor increases with temperature
Thus, the warmer the air contacting a water surface, the faster the rate of evaporation
52

2. Evaporation, Vapor
Pressure and Humidity
Influence of Temperature

If water is heated, its kinetic energy is thus increased and thus more molecules are helped to escape from its surface.
53

2. Evaporation, Vapor Pressure and Humidity
Influence of Temperature
54

C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor Pressure and Humidity

Clinical Application
55

C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor Pressure and Humidity
Influence of Pressure

High atmospheric pressures impede vaporization

Low atmospheric pressures increase vaporization
56

C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor Pressure and Humidity
Influence of surface area

The greater the available surface area of the gas in contact with air, the greater the rate of liquid evaporation
57

C. Liquid Vapor Phase Chapges
2 Evaporation, Water Vapor Pressure, and Humdidty

Humidity: water in molecular vapor form


Water vapor pressure: the kinetic activity of water molecules in air
For the actual amount or weight of water vapor in a gas to be found, the water vapor content (absolute humidity) must be measured
58

C. Liquid-Vapor Phase Changes
2. Evaporation, Water Vapor Pressure, and Humidity

Absolute Humidity
 a.k.a
 water vapor content


Actual amount (or weight) of water vapor in gas
Measured in mg/L


Varies w/ temperature & pressure
Air that is fully saturated w/ water vapor has absolute humidity of 43.8 mg/L at 37°C, 760 mm
Hg, & water vapor pressure of 47 mm Hg
59

Egan Table 6-3, page 112

C. Liquid-Vapor Phase Changes
2. Evaporation, Water Vapor Pressure , and Humidity

Relative humidity (RH)

When gas is not fully saturated


Water vapor content can be expressed in relative terms
Ratio of its actual water vapor content to its saturated capacity at given temperature

%RH = Content (Absolute Humidity) x 100
Saturated Capacity

2. Evaporation, Water Vapor Pressure, and Humidity

Example: At a temperature of 22°C, air has the capacity to hold 19.4 mg/L of water vapor (this information comes from the table in Egan). If the absolute humidity in the air is 7.4 mg/L, what is the relative humidity?
62

2. Evaporation, Water Vapor Pressure, and Humidity

Temperature = 22°C


Capacity = 19.4 mg/L of water vapor
Water vapor content (AH) = 7.4 mg/L

%RH = water vapor content x 100 capacity
63 http://www.youtube.com/watch?v=CL5cgXwKUXc

C. Liquid-Vapor Phase Changes
2. Evaporation, Water Vapor Pressure, and Humidity
Percent Body Humidity

The ratio of the actual water vapor content of the gas to the water vapor capacity in a saturated gas at body temperature (37°C)


%BH = water vapor content x 100 capacity at 37° C
Capacity at 37°C is always 43.8 mg/L
64

Clinical Application
Aerosol Therapy
2. Evaporation, Water Vapor Pressure, and Humidity

Clinical Aplication
 Aerosol Therapy
65

C. Liquid-Vapor Phase Changes
2. Evaporation Water Vapor Pressure, and Humidity



Example: The American National Standards Institute has set a water vapor content level of 30 mg/L as the minimum absolute humidity required for patients whose upper airways have been bypassed. This equals what body humidity?
Water vapor content = 30 mg/L
%BH = water vapor content x 100 capacity at 37° C
66

C. Liquid-Vapor Phase Changes
2. Evaporation Water Vapor Pressure, and Humidity

Humidity Deficit



The difference in water vapor content between inspired air and the saturated gas conditions present in the lungs
The amount of water vapor your body must add to the inspired gas to achieve saturation at body temperature
HD=43.8 mg/L–water vapor content
67

C. Liquid-Vapor Phase Changes
2. Evaporation Water Vapor Pressure, and Humidity




Example:
Using the previous example where water vapor content =
30 mg/L
What is the humidity deficit?
HD=43.8 mg/L–water vapor content
68

C. Liquid-Vapor Phase Changes
2. Evaporation Water Vapor Pressure, and Humidity

Condensation: The change of state from gas to liquid

Dew Point: The temperature at which condensation begins
69

C. Liquid-Vapor Phase Changes
2. Evaporation Water Vapor Pressure, and Humidity

Clinical Application
70

II. Change of State
D.
1.
2.
3.
4.
5.
6.
Properties of Gases

Kinetic Activity of Gases
Molar Volume and Gas Density
Molar Volume

Density
Gaseous Diffusion

Gas Pressure
Measuring Atmospheric Pressure

Clinical Pressure Measurements
Partial Pressure (Dalton’s Law)
Solubility of Gases in Liquids (Henry’s Law)

C. Properties of Gases



Gases do not maintain their shape and volume, they expand to fill the available space
Gases are easily compressed and expanded
Gases are capable of flow (like liquids)
72

C. Properties of Gases
1. Kinetic Activity of Gases

Molecular attractive forces are extremely weak in gases, therefore gasses possess the greatest amount of KE, their PE is minimal


Gas molecules travel at high speeds in random fashion with frequent collisions.
The velocity of gas molecules is directly proportional to its temperature.

C. Properties of Gases
2. Molar Volume and Gas Density

Molar Volume

1 gram molecular weight (gmw), or mole, of any substance at a temperature of 0 ° C (273 K) and a pressure of 1 atm

 occupies 22.4 L (molar volume) contains 6.023 x 10 23 (Avogadro’s number) molecules

C. Properties of Gases
2. Molar Volume and Gas Density

Molar Volume

Equal volumes of all gases under the same conditions must contain the same number of molecules
 Molar volume = 22.4L
1 mole of Helium
1 mole of Oxygen has the same number of molecules as…

C. Properties of Gases
2. Molar Volume and Gas Density


Gas Density
Density:

 the ratio of a substance’s mass to its volume mass per unit volume

Density = gmw
22.4 L

Gas Density
•
•
A dense substance has heavy particles packed closely together (Uranium is a good example of a dense substance)
Conversely, a low density substance has a low concentration of light weight particles per unit volume (Hydrogen gas).
•
The density of any gas at STPD can be computed easily by dividing its molecular weight by the universal molar volume of 22.4 L

GMW: O2 = N2 = He = CO2 =
78


Density of Gases
GRAM MOLECULAR WEIGHTS( GMW): The molecular weight of a substance in grams. To find the GMW of a medical gas we must know the atomic weights of several common chemical elements.
Substance Symbol Atomic Weight
A) Hydrogen
B) Helium
C) Carbon
D) Nitrogen
E) Oxygen
F) Room Air
H
He
C
N
O
1
4
12
14
16
28.8
NOTE: Nitrogen and Oxygen are found in the atmosphere in gaseous form as diatomic elements. So oxygen gas will have an atomic weight of 16 X 2 or 32, and nitrogen gas will have an atomic weight of 14 X 2 or 28.


Gas Density Example #1


What is the density of oxygen at STP?
Density = gmw
22.4 L
80

Density of O2

O2 = 32 grams


O = 8x2= 16
O2 = 16 x 2 = 32

32/22.4 = 1.42

Gas Density Example #2


What is the density of air?
Density = gmw
22.4 L
82

Density of Air
N= 14 x 2 = 28; O= 16 x 2 = 32
28 x 79% = 22.12
16 x 21%= 6.72
22.12 + 6.72 = 28.84 / 22.4 = 1.28









Density of Gases
Gases are influenced by changes in temperature and pressure
Calculates under STP conditions
Calculated by dividing volume occupied by 1 mole of gas at STP, that is 22.4 liters, into the gram of molecular weight of that gas
Density = gram molecular weight / 22.4 liters
Example:
Density of O2 = Weight of O2 32g /22.4 liters = 1.43g/L
Gases such as Helium have far less density
Oxygen has higher density than air and tends to accumulate at the lowest point (Ex: oxygen enclosure)













Density of Room Air
GMW OF ROOM AIR: Room air is not a pure substance; it is a mixture of gases. It contains about 79% nitrogen (N2) and 21% oxygen (O2) and small amounts of other gases. We can determine the relative GMW for room air by multiplying the fractional concentration of each gas by its molecular weight and adding the results.
The GMW of room air can also be used to find the specific gravity of other medical gases because air is the usual standard for specific gravity of gases.
GMW air
GMW air =
=
=
28.8
Nitrogen
(.79 x 28)
( 22.1 )
Oxygen
+ (.21 x 32)
+ ( 6.7 )
NOTE: The above method can also be used to find the relative GMW of any mixture of gases, ie: 60% He and 40% O2 or 95% O2 and 5% CO2.

Practice!

Calculate the density of the following gases:
1.
CO2
2.
3.
4.
5.
N2
He
80% He and 20% O2
70% He and 30% O2
86

CO2


C= 12
O2 = 32

12 + 32 = 44 /22.4 = 1.96

N2


N= 14
N2 = 14 x2 = 28

28 /22.4 = 1.25

He

He = 4 /22.4 = 0.18

80% He and 20% O2


He = 80% x 4 = 3.2
O2 = 20% x 32= 6.4

3.2 + 6.4 = 9.6/ 22.4

0.43

C. Properties of Gases
2. Molar Volume and Gas Density

Density

Clinical Example: Helium/Oxygen
Flow Rate Conversion


An oxygen flow meter is being used to administer 8
L/min of an 80%He/20%O2 gas mixture. What is the actual flow rate of this gas mixture?
Actual flow rate of 80%he/20%O2
= Flow rate x 1.8
= 8 L/min x 1.8
FYI: the conversion factor for
70/30 Heliox = 1.6
91
= 14.4 L/min

C. Properties of Gases
2. Molar Volume and Gas Density


An oxygen flow meter is being used to administer 8
L/min of an 80%He/20%O2 gas mixture. What is the actual flow rate of this gas mixture?
Actual flow rate of 80%he/20%O2
= Flow rate x 1.8
FYI: the conversion factor for
70/30 Heliox = 1.6
92

Practice!
1.
An oxygen flow meter is being used to administer 10
L/min of an 70%He/30%O2 gas mixture. What is the actual flow rate of this gas mixture?
2.
A therapist wants to deliver 15 L/min of an
80%He/20%O2 gas mixture. What liter flow should the therapist set on the flowmeter?
93

C. Properties of Gases
3. Gaseous Diffusion

The movement of gas molecules from an area of high concentration to an area of low concentration.
 http://www.youtube.com/watch?v=_oLPBnhOCjM

C. Properties of Gases
3. Gaseous Diffusion

Graham’s Law:

The rate of diffusion of a gas is inversely proportional to the square root of its density.


Lighter gases diffuse rapidly
Heavy gases diffuse more slowly
95

C. Properties of Gases
3. Gaseous Diffusion

Practical Application:

What is the GMW of O
2
?

What is the GMW of CO
2
?

According to Graham’s Law, which gas should diffuse faster?
96

C. Properties of Gases
6. Solubility of Gases in Liquids

Henry’s Law: The amount of gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of the gas and its solubility coefficient

Solubility coefficient: the volume of a gas that will dissolve in 1 mL of a given liquid at standard pressure and specified temperature

6. Solubility of Gases in Liquids


Practical Example:
0.023 mL of O
2
37 ° C can dissolve in 1 mL of blood at


0.510 mL of CO
2
37 ° C can dissolve in 1 mL of blood at
According to Henry’s Law, which gas should dissolve faster?
98

Diffusion: CO2 vs. O2

In the end, CO2 diffuses about 19 x faster than O2 because of its much greater solubility in blood.
99

Gas Diffusion

Fick’s law
.


The rate of diffusion across a sheet of tissue (the alveolar-capillary membrane) is:

Directly proportional to the

Surface area of the tissue



Solubility of the gas
Partial pressure gradient
Inversely proportional to the

Thickness of the tissue

Fick’s Law
Diffusion is Directly Proportional to
Surface Area

What is the surface area of the alveoli?



Fick’s Law
Diffusion is Directly Proportional to
Surface Area
A decreased alveolar surface area

Alveolar collapse

Fluid in the alveoli
Decreases the diffusion of oxygen into the pulmonary capillary blood

Fick’s Law
Diffusion is Directly Proportional to the
Concentration Gradient



Fick’s Law
Diffusion is Directly Proportional to the
Concentration Gradient
Decreased alveolar oxygen pressure (P
A
O
2
)

High altitudes

Alveolar hypoventilation
Decreases the diffusion of oxygen into the pulmonary capillary blood

Fick’s Law
Diffusion is Inversely Proportional to
Tissue Thickness

Fick’s Law
Diffusion is Inversely Proportional to
Tissue Thickness


An increased alveolar tissue thickness

Alveolar fibrosis

Pulmonary edema
Decreases the diffusion of oxygen into the pulmonary capillary blood


The rate of diffusion across a sheet of tissue (the alveolar-capillary membrane) is:

Directly proportional to the

Surface area of the tissue



Solubility of the gas
Partial pressure gradient
Inversely proportional to the

Thickness of the tissue

Fick’s Law
Figure 4-8.

C. Properties of Gases
4. Gas Pressure

All gases exert pressure



Gas pressure in a liquid is known as gas “tension”
Atmospheric pressure is measured with a barometer
Pressure: the force that a gas exerts over a given area

P = Force/Area
 lb/in 2

C. Properties of Gases
4. Gas Pressure


Atmospheric Pressure: The pressure that the atmospheric gases exert on objects within the Earth’s atmosphere.
Gases that make up the atmosphere are attracted to the Earth’s surface by gravity.



Highest near the Earth’s surface
Sea level

760 mmHg
Denver: 1 mile above sea level

630 mmHg

112
Atmospheric
Pressure



Measured with a barometer
Evangelista Torricelli
The mercury barometer uses the weight of a column of mercury to equilibrate with the force of the gas molecules hitting the surface of a mercury reservoir

Atmospheric Pressure at Sea Level





760 mmHg
760 torr
29.9 inHg
1034 cmH
2
O
1034 g/cm 2





33.9 ftH
2
O
101.3 kPa
14.7 psi
14.7 lb/in 2
1 atm
113

Clinical Pressure Measurements
114

115
Aneroid
Barometer

116
Mechanical
Manometer

117
Strain-gauge Pressure
Transducer

C. Properties of Gases
5. Dalton’s Law of Partial Pressures

Dalton’s Law


Partial pressure:

118

Dalton’s Law of Partial Pressures

The partial pressure of any gas within a gas mixture is proportional to its percentage in the mixture

P
B
= PN
2
+ PO
2
+ PH
2
O + PAr + PCO
2
+ Pgases
119

Dalton’s Law of Partial Pressures




Air ≈ 21% O
2 and 79% N
2
Fractional concentration of O
Fractional concentration of N
2
2
= 0.21
= 0.79
partial pressure = fractional concentration x total pressure

PO2 =

PN2 =
120

Dalton’s Law of Partial Pressures:


What happens to PB, PO2, and FiO2 as altitude changes?
Why do mountain climbers use extra oxygen at high altitudes?
121

Dalton’s Law of Partial Pressures
Why are oxygen masks Needed on Airplanes?
122

Hyperbaric
Chambers
123