Chapter 12
Pulmonary Structure and Function
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Chapter Objectives
 Diagram and label the main structures of the
ventilatory system components
 Describe the ventilatory system’s conducting,
transitional, and respiratory zones
 Discuss the mechanical and muscular aspects
of inspiration and expiration during rest and
physical activity
 Define and quantify static and dynamic lung
function measures at rest and exercise
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Chapter Objectives, cont.
 Describe two effects of cold-weather exercise
on the respiratory tract
 Discuss the contributions of breathing rate
and tidal volume to minute ventilation and
alveolar minute ventilation at rest and
physical activity
 Discuss two factors that account for variations
in the ventilation–perfusion ratio among
healthy individuals
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Chapter Objectives, cont.
 Explain the four phases of the Valsalva and
discuss the physiologic consequences of this
maneuver
 Define minute ventilation, alveolar ventilation,
ventilation perfusion ratio, and anatomic and
physiologic dead space
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Anatomy of Ventilation
• Pulmonary ventilation moves and exchanges
ambient air with air in the lungs
• Ambient air enters the nose and
mouth
trachea (and adjusts to body
temperature), is filtered and
humidified
two bronchi
bronchioles
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alveoli
Pulmonary Structures in the Thoracic Cavity
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The Lungs
• Provide the gas exchange surface that separates
blood from surrounding gaseous environment
• O2 transfers from alveolar air into alveolar
capillary blood while the blood’s CO2 moves into
the alveolar the alveoli and then into ambient air
• An average-sized adult’s
lung weighs about 1
kg with a volume of 4 to 6 L
 The lungs consists of
10% solid tissue, with the
remainder filled with air and blood
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The Alveoli
• More than 600 million alveoli provide the surface
for gas exchange between lung tissue and blood
• Alveoli receive the largest blood supply of all organs
• Capillaries and alveoli lie side-by-side with thin
surfaces to facilitate rapid gas exchange
• Pores of Kohn within alveoli evenly disperse
surfactant over respiratory membranes to reduce
surface tension for easier alveolar inflation
• Each minute at rest, 250 mL O2 leave the alveoli
and enter the blood and 200 mL CO2 diffuse in
the opposite direction
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Ventilation Mechanics
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Zones of Ventilation
1. Ventilatory subdivisions
 Conducting zones: Trachea and terminal bronchioles
- Considered anatomic dead space
- Function in air transport, humidification, warming,
particle filtration, vocalization, immunoglobulin secretion
 Transitional and respiratory zones: Bronchioles,
alveolar ducts, and alveoli
- Function in gas exchange, surfactant production,
molecule activation and inactivation, blood clotting
regulation, and endocrine function
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Zones of Ventilation,
cont.
• More than 600 million
alveoli provide the
surface for gas
exchange between
lung tissue and blood
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Lung Airflow
Related to Total
Cross-sectional
Tissue Area
• Forward airflow
velocity during
inspiration
decreases
because of the
large increase in
tissue crosssectional area in
the terminal
bronchiole region
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Fick’s Law of Diffusion
• Governs gas diffusion across a fluid membrane
 Gas diffuses through a sheet of tissue at a rate:
- directly proportional to tissue area, a diffusion
constant, and pressure differential of the gas
on each side of the membrane
- inversely proportional to tissue thickness
• The pressure differential between air in the
lungs and lung–chest wall interface causes
lungs to adhere to the chest wall and follow
its every movement
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Inspiration
• Phases:
 Diaphragm contracts, flattens, and moves
downward toward the abdominal cavity
 Elongation and enlargement of the chest
cavity expands air in the lungs, causing its
intrapulmonic pressure to decrease slightly
below atmospheric pressure
 Lungs inflate as nose and mouth suck air inward
 Completed when thoracic cavity expansion
ceases; this causes equality between
intrapulmonic and ambient atmospheric pressures
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Expiration
• The passive process during rest and light
exercise as air moves out of lungs from:
 Natural recoil of stretched lung tissue and
relaxation of inspiratory muscles
• Expiration Phases
 Sternum and ribs drop, diaphragm rises (decreasing
chest cavity volume and compressing alveolar gas),
moving air from respiratory tract to the environment
 Completes when compressive force of expiratory
muscles (activated in vigorous exercise) cease and
intrapulmonic pressure decreases to atmospheric
pressure
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Surfactant (Surface Active Agent)
• “Wetting agent” lipoprotein mixture of proteins,
phospholipids, and calcium ions produced by
alveolar epithelial cells (to reduce surface tension)
 Mixes with fluids encircling alveolar chambers
• Interrupts the surrounding water layer,
reducing the alveolar membrane’s surface tension,
thereby increasing overall lung compliance
• Reduces the energy required for alveolar inflation
and deflation
• Without surfactant, small alveoli would collapse
(atelectasis ) from high collapsing pressures
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Lung Volumes and Capacities:
Static Lung Volumes
• Tidal volume: Air moved during the inspiratory or
expiratory phase of each breathing cycle (0.4 to 1.0 L of air
per breath)
• Inspiratory reserve volume: Inspiring as deeply as
possible following a normal inspiration (2.5 to 3.5 L
above inspired tidal air)
• Expiratory reserve volume: After a normal exhalation,
continuing to exhale and forcing as much air as
possible from the lungs (1.0 to 1.5 L)
• Forced vital capacity: Total volume of air voluntarily moved
in one maximal breath; it includes TV plus IRV and ERV
(4 to 5 L in young men) and (3 to 4 L) in young women
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Static Measures of Lung Volume
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Residual Lung Volume
• Air volume remaining in the lungs after a forced
maximal exhalation
 Averages 0.8 to 1.2 L for healthy college-aged
women, and 0.9 to 1.4 L for college-aged men
 Increases with age
• Allows an uninterrupted exchange of gas between
the blood and alveoli to prevent fluctuations in
blood gases during phases of the breathing cycle
• RLV plus FVC = total lung capacity (TLC)
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Effects of Previous Exercise Effects on RLV
• RLV temporarily increases from an acute bout of
either short-term or prolonged exercise due to:
 Closure of small peripheral airways
 Increase in thoracic blood volume
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Dynamic Lung Volumes
• Dynamic pulmonary ventilation depends on:
 Maximum “stroke volume” of the lungs (FVC)
 Speed of moving a volume of air (breathing rate)
- Determined by lung compliance (the resistance
of respiratory passages to air movement and
“stiffness” imposed by the chest and lung
tissues)
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FEV-to-FVC Ratio
• Forced expiratory volume (FEV)
 Maximal airflow measured over 1 s (FEV1.0)
 FEV1.0 ÷ FVC indicates pulmonary airflow capacity
 Reflects pulmonary expiratory power and overall
resistance to air movement upstream in lungs
 FEV1.0 ÷ FVC = ~85% in healthy individuals
 FEV1.0 ÷ FVC ≤70% = delineation point for
airway obstruction
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Examples of Pulmonary Function Tests
in Normal Subjects and in Patients with
Obstructive or Restrictive Lung Disease
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Maximum Voluntary Ventilation (MVV)
• Evaluates ventilatory capacity with rapid and deep
breathing for 15s
 Extrapolated to volume if continued for 1 min
 MVV typically ranges between 35 to 40 times FEV1.0
• MVV ranges between 140 and 180 L/min in healthy,
college-age men, and 80 and 120 L/min in healthy,
college-age women
• Exercise training of the ventilatory muscles improves their
strength and endurance, increasing inspiratory muscle
function and MVV
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Physical Activity Implications of Gender
Differences in Static and Dynamic Lung
Function Measures
• Compared to men, women have a reduced lung size
and airway diameter, a smaller diffusion surface, and
lower static and dynamic lung function measures
 Leads to expiratory flow limitations, greater respiratory
muscle work and use of ventilatory reserve during maximal
exercise (particularly in highly trained women)
 A smaller lung volume plus a high expiratory flow rate
demands in trained women during intense exercise places
considerable demand on maximum flow–volume envelope of
the airways; this adversely affects the maintenance of
alveolar-to-arterial oxygen exchange
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Lung Function, Aerobic Fitness,
and Physical Performance
• Regular endurance exercise does not stimulate
large increases in pulmonary system functional
capacity
• Dynamic lung function tests indicate severity of
obstructive and restrictive lung diseases, but
provide little information about aerobic fitness or
exercise performance when values fall within the
normal range
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Pulmonary Ventilation
• Can be viewed from two perspectives:
1. Volume of air moved into or out of the
respiratory tract each minute
2. Air volume that ventilates only alveolar
chambers each minute
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Minute Ventilation (VE)
• The volume of air breathed each minute
VE = Breathing rate × Tidal volume
- can be increased by an increase in breathing
rate or breathing depth, or both
- breathing rate can increase to 35 to 45
breaths/min during strenuous exercise in
healthy young adults and 60 to 70 breaths/min
in some elite endurance athletes
Tidal volume for trained and untrained individuals
rarely exceed 60% of vital capacity
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Alveolar Ventilation
• Anatomic dead space: air in each breath that
does not enter alveoli and participate in gaseous
exchange with blood (range 150 to 200 mL)
• Alveolar ventilation: portion of inspired air
reaching the alveoli and participating in gas
exchange
 Determines the gaseous concentrations at the
alveolar–capillary membrane
 About 350 mL of the 500 mL of inspired TV at rest
enters into and mixes with existing alveolar air
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Typical Values for Pulmonary Ventilation
During Rest and Physical Activity
Breathing Rate
(Breaths ∙ min−1)
Tidal Volume
(L ∙ min−1)
Pulmonary
Ventilation
(L ∙ min−1)
Rest
12
0.5
6
Moderate
exercise
30
2.5
75
Intense
exercise
50
3.0
150
Condition
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Dead Space Versus Tidal Volume
• Anatomic dead space increases as TV becomes
larger; it often doubles during deep breathing
from stretching of respiratory passages with
a fuller inspiration
• Any increase in dead space represents
proportionately less volume than the
increase in TV
 Deeper breathing provides more effective
alveolar ventilation than similar minute
ventilation achieved through increased
breathing rate
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Ventilation-Perfusion (V-P) Ratio
• The ratio of alveolar ventilation to pulmonary
blood flow
 ~4.2 L of air ventilates alveoli each min at rest
and ~5.0 L of blood flows through pulmonary
capillaries each min
 Average V-P Ratio = 0.84
- An alveolar ventilation of 0.84 L matches each
liter of pulmonary blood flow
 In light exercise, V-P Ratio remains ~0.8 L
 In intense exercise V-P Ratio = 5.0L
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Physiologic Dead Space
• The portion of the alveolar volume with a ventilation–
perfusion ratio that approaches zero
 Sometimes alveoli may not function adequately
in gas exchange because of two factors:
- Underperfusion of blood
- Inadequate ventilation relative to alveolar surface
• In certain pathologic conditions, physiologic dead space
increases to 50% of TV
• Adequate gas exchange becomes impossible when dead
space of the lung exceeds 60% TLV
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Distribution of Tidal Volume
• TV includes about 350 mL of ambient air mixed with alveolar air,
150 mL ambient air remaining in air passages (anatomic dead
space), and a small portion of air in the physiologic dead space
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Breathing Rate Versus Tidal Volume
• Increasing the rate and depth of breathing
increases alveolar ventilation in physical activity
• In moderate activity, well-trained athletes
maintain alveolar ventilation by increasing
TV with only a small increase in breathing rate
 In exercise, breathing becomes deeper and alveolar
ventilation increases from 70% at rest to >85% of
exercise minute ventilation
• Each person develops their “style” of breathing;
breathing rate and TV blend to provide effective
alveolar ventilation
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Pulmonary
Volumes
and
Capacities
During
Rest and
Exercise
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Variations from Normal Breathing Patterns
• Hyperventilation
 Increase in pulmonary ventilation that exceeds the O2
consumption and CO2 elimination needs of metabolism
• Dyspnea
 Inordinate shortness of breath or subjective breathing distress
• Valsalva Maneuver
 Closing glottis following a full inspiration while maximally
activating expiratory muscles, creating compressive forces
that increase intrathoracic pressure above atmospheric
pressure
- Occurs commonly in activities that require a rapid,
maximum application of force for short duration
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Physiologic Consequences of Performing
the Valsalva Maneuver
• Performing a prolonged Valsalva maneuver during static,
straining-type exercise dramatically reduces venous
return and arterial blood pressure
 Diminishes brain’s blood supply, producing dizziness or fainting
 Once the glottis reopens and intrathoracic pressure
normalizes, blood flow reestablishes with an “overshoot”
in arterial blood pressure
- Does not cause the large increases in blood
pressure during heavy resistance exercises;
these exercises greatly increase resistance
to blood flow in active muscle with a resulting
rise in systemic blood pressure
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Valsalva Maneuver
• Valsalva reduces return
of blood to the heart
because increased
intrathoracic pressure
collapses inferior vena
cava that runs through
the chest cavity
Normal
breathing
Straining exercise
with Valsalva
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Valsalva Maneuver, cont.
• Valsalva reduces return
of blood to the heart
because increased
intrathoracic pressure
collapses inferior vena
cava that runs through
the chest cavity
Normal aortic pulse pressure with
Valsalva during calibrated muscle strain
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Respiratory Tract During
Cold-Weather Activity
• Cold ambient air normally does not damage respiratory
passages because of relatively rapid airway warming
 This air-conditioning process greatly increases
air’s capacity to hold moisture, which produces
measurable water loss from the respiratory passages
 In cold weather, the respiratory tract loses considerable
water and heat, especially during strenuous exercise
• Fluid loss from the airways contributes to dehydration,
dry mouth, burning sensation in the throat, and
generalized irritation of the respiratory passages
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Summary
1. The lungs provide a large surface between the
body’s internal fluid environment and the
gaseous external environment. During any 1 s
of physical activity, no more than 1 pint of blood
flows in the pulmonary capillaries.
2. Fick’s law of diffusion governs gas movement
across a fluid membrane
3. Surfactant consists of a lipoprotein mixture
secreted within lung tissue that reduces surface
tension between the alveolar membrane and
surrounding tissues
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Summary, cont.
4. Pulmonary airflow depends on small pressure
differentials between ambient air and air within
the lungs. Ventilatory muscle action produces
these pressure differences
5. Lung volumes vary with age, gender, and body
size (particularly stature)
6. The residual lung volume represents air remaining
in the lungs following maximal exhalation
7. FEV and MVV dynamically measure the ability
to sustain a high airflow level
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Summary, cont.
8. Measures of static and dynamic lung function
within the normal range poorly predict aerobic
fitness and exercise performance
9. Breathing rate and tidal volume (TV) determine
pulmonary minute ventilation
10. Alveolar ventilation reflects the portion of
minute ventilation that enters the alveoli for
gaseous exchange with the blood
11. The ventilation–perfusion ratio reflects the
association between alveolar minute
ventilation and pulmonary blood flow
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Summary, cont.
12. TV increases during physical activity by
encroachment into inspiratory and expiratory
reserve volumes
13. During intense exercise, TV plateaus at
approximately 60% of the vital capacity; minute
ventilation increases further through increases
in breathing rate
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Summary, cont.
14. A Valsalva maneuver describes a forced
exhalation against a closed glottis, which
causes large pressure increases within the
chest and abdominal cavities that compress the
thoracic veins (thereby reducing venous return
to the heart)
15. Breathing cold ambient air normally does
not damage respiratory passage
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Image Sources
Slide 12: Adapted with permission from West JB. Respiratory Physiology—The
Essentials. 8th ed. Baltimore: Lippincott Williams & Wilkins, 2008.
Slide 40: Data from Hébert J-L, et al. Pulse pressure response to the strain of the
Valsalva maneuver in humans with preserved systolic function. J Appl Physiol
1998;85:817.
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