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Physical Principles of
Respiratory Care
Egan Chapter 6
Physical Principles of Respiratory Care
I.
II.
III.
IV.
States of Matter
Change of State
Gas Behavior Under Changing Conditions
Fluid Dynamics
II. Change of State
Liquid-Solid Phase
Changes
A.
1.
2.
Melting
Freezing
Properties of Liquids
B.
1.
2.
3.
4.
5.
6.
Pressure in Liquids
Buoyancy (Archimedes’
Principle)
Viscosity
Cohesion and Adhesion
Surface Tension
Capillary Action
Liquid-Vapor Phase
Changes
C.
1.
2.
Boiling
Evaporation, Vapor Pressure,
and Humidity
Properties of Gases
D.
1.
2.
3.
4.
5.
6.
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
Liquid-Solid Phase Changes
A.
1.
2.
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
Melting Point
Boiling Point
Water
Oxygen
0°C
-219°C
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
Water
Ice
10
Latent heat of fusion
II. Change of State
Properties of Liquids
B.
1.
2.
3.
4.
5.
6.
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:

15
A confined liquid
transmits pressure
equally in all
directions
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
http://www.youtube.com/watch?v=iD55ynlUH8g
http://www.youtube.com/watch?v=UpwLwP0pmwk
18
B. Properties of Liquids
Pressure in Liquids
 Clinical Application
 Heart Failure
1.
19
B. Properties of Liquids
Pressure in Liquids
 Clinical Application
 Using an air or water mattress to prevent the
development of bed soars
1.
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&feat
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
37

Have a greater tendency to collapse

Require greater distending pressure to maintain
their volume
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


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
49
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
C. Liquid-Vapor Phase Changes
2. Evaporation, Vapor Pressure and Humidity
Influence of Temperature

The warmer the air, the more water vapor it can hold


52
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
C. Liquid-Vapor Phase Changes
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
C. Liquid-Vapor Phase Changes
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
C. Liquid-Vapor Phase Changes
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
C. Liquid-Vapor Phase Changes
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
http://www.youtube.com/watch?v=CL5cgXwKUXc
63
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

65
Aerosol Therapy
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



67
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
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
Properties of Gases
D.
Kinetic Activity of Gases
Molar Volume and Gas Density
1.
2.


Gaseous Diffusion
Gas Pressure
3.
4.


5.
6.
Molar Volume
Density
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 1023 (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 =
78
N2 =
He =
CO2 =
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.

Nitrogen
Oxygen
=
(.79 x 28)
+
(.21 x 32)
=
(
+
(



GMW air


22.1 )
6.7
)


GMW air =
28.8



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.
2.
3.
4.
5.
86
CO2
N2
He
80% He and 20% O2
70% He and 30% O2
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
FYI: the conversion factor for
70/30 Heliox = 1.6
= 8 L/min x 1.8
= 14.4 L/min
91
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 O2?

What is the GMW of CO2?

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
C. Properties of Gases
6. Solubility of Gases in Liquids
 Practical Example:
 0.023 mL of O2 can dissolve in 1 mL of blood at
37°C
 0.510 mL of CO2 can dissolve in 1 mL of blood at
37°C
 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
.
Fick’s Law of Diffusion

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 (PAO2)
 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
Fick’s Law of Diffusion

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/in2
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
Atmospheric
Pressure



112
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 cmH2O
1034 g/cm2
113





33.9 ftH2O
101.3 kPa
14.7 psi
14.7 lb/in2
1 atm
Clinical Pressure Measurements
114
Aneroid
Barometer
115
Mechanical
Manometer
116
Strain-gauge Pressure
Transducer
117
C. Properties of Gases
5. Dalton’s Law of Partial Pressures
 Dalton’s Law
 the sum of the partial pressures of a gas
mixture equals the total pressure.

Partial pressure:
 the pressure exerted by a single gas in a
mixture
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

PB = PN2 + PO2 + PH2O + PAr + PCO2 + Pgases
119
Dalton’s Law of Partial Pressures

Air ≈ 21% O2 and 79% N2
Fractional concentration of O2 = 0.21
Fractional concentration of N2 = 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
Dalton’s
Law of
Partial
Pressures
Hyperbaric
Chambers
123

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