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CHAPTER 22:
RESPIRATORY SYSTEM
(2): MECHANICS OF
VENTILATION
Human Anatomy and Physiology II –
BIOL153
Processes of Respiration
Pulmonary
ventilation
External
respiration
Transport
Internal
respiration
Respiratory
system
Circulatory
system
Goals/Objectives
Explain the functional importance of the partial vacuum that exists in the intrapleural space
Relate Boyle’s law to the events of inspiration and expiration
Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs
List several physical factors that influence pulmonary ventilation
Explain and compare the various lung volumes and capacities
Define dead space
Indicate types of information that can be gained from pulmonary function tests
Pressure Relationships in the
Thoracic Cavity Atmospheric pressure (Patm)
Pressure exerted by air surrounding body
760 mm Hg at sea level = 1 atmosphere
Respiratory pressures described relative to Patm
Intrapulmonary (intra-alveolar) pressure (Ppul)
Pressure in alveoli
Fluctuates with breathing
Always eventually equalizes with Patm
Intrapleural pressure (Pip)
Pressure in pleural cavity
Fluctuates with breathing
Always a negative pressure (<Patm and <Ppul)
Pressure Relationships in the
Thoracic CavityAtmospheric pressure (P
atm)
0 mm Hg (760 mm Hg)
Thoracic wall
Parietal pleura
Visceral pleura
Pleural cavity
Transpulmonary
pressure
4 mm Hg(the differencebetween 0 mm Hgand −4 mm Hg)
Intrapleural
pressure (Pip)
−4 mm Hg(756 mm Hg)
Intrapulmonary
pressure (Ppul
)
0 mm Hg(760 mm Hg)
Diaphragm
Lung
0
– 4
If Pip = Ppul or Patm lungs collapse
(Ppul – Pip) = transpulmonary pressure Keeps airways
open
Greater transpulmonarypressure larger lungs
Atelectasis (lung collapse)
Plugged bronchioles collapse of alveoli
Pneumothorax-air in pleural cavity From either wound in parietal or
rupture of visceral pleura
Treated by removing air with chest tubes; pleurae heal lung reinflates
Pulmonary Ventilation and Boyle's
Law
Volume changes pressure changes
Pressure changes gases flow to equalize
pressure
Boyles Law: Pressure (P) varies inversely with
volume (V):
P1V1 = P2V2 OR
P = 1/V
Relationship between pressure and volume of
a gas
Gases fill container; if container size reduced
increased pressure
In
sp
iratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1
Diaphragmmoves inferiorlyduringcontraction.
Ribs areelevated and sternumflares asexternalintercostalscontract.
Externalintercostalscontract.
Inspiratory musclescontract (diaphragmdescends; rib cage rises).
Inspiration
Inspiratory musclescontract (diaphragmdescends; rib cage rises).
Thoracic cavity volumeincreases.
In
sp
iratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1
2
Diaphragmmoves inferiorlyduringcontraction.
Ribs areelevated and sternumflares asexternalintercostalscontract.
Externalintercostalscontract.
Inspiration
Inspiratory musclescontract (diaphragmdescends; rib cage rises).
Thoracic cavity volumeincreases.
In
sp
iratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1
2
3
Diaphragmmoves inferiorlyduringcontraction.
Ribs areelevated and sternumflares asexternalintercostalscontract.
Externalintercostalscontract.
Lungs are stretched;intrapulmonary volumeincreases.
Inspiration
Inspiratory musclescontract (diaphragmdescends; rib cage rises).
Thoracic cavity volumeincreases.
Lungs are stretched;intrapulmonary volumeincreases.
In
sp
iratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1
2
3
4
Diaphragmmoves inferiorlyduringcontraction.
Ribs areelevated and sternumflares asexternalintercostalscontract.
Externalintercostalscontract.Intrapulmonary pressure
drops (to –1 mm Hg).
Inspiration
Inspiratory musclescontract (diaphragmdescends; rib cage rises).
Thoracic cavity volumeincreases.
Lungs are stretched;intrapulmonary volumeincreases.
Intrapulmonary pressuredrops (to –1 mm Hg).
Air (gases) flows intolungs down its pressuregradient until intrapulmonarypressure is 0 (equal toatmospheric pressure).
In
sp
iratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1
2
3
4
5
Diaphragmmoves inferiorlyduringcontraction.
Ribs areelevated and sternumflares asexternalintercostalscontract.
Externalintercostalscontract.
Inspiration
1
Ex
piratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
Diaphragmmovessuperiorlyas it relaxes.
Ribs andsternum aredepressedas externalintercostalsrelax.
Externalintercostalsrelax.
Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).
Expiration
1
Ex
piratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
2
Diaphragmmovessuperiorlyas it relaxes.
Ribs andsternum aredepressedas externalintercostalsrelax.
Externalintercostalsrelax.
Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).
Thoracic cavity volumedecreases.
Expiration
1
Ex
piratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
2
3
Diaphragmmovessuperiorlyas it relaxes.
Ribs andsternum aredepressedas externalintercostalsrelax.
Externalintercostalsrelax.
Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).
Thoracic cavity volumedecreases.
Elastic lungs recoilpassively; intrapulmonaryVolume decreases.
Expiration
1
Ex
piratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
2
3
4
Diaphragmmovessuperiorlyas it relaxes.
Ribs andsternum aredepressedas externalintercostalsrelax.
Externalintercostalsrelax.
Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).
Thoracic cavity volumedecreases.
Elastic lungs recoilpassively; intrapulmonaryVolume decreases.
Intrapulmonary pressurerises (to +1 mm Hg).
Expiration
1
Ex
piratio
n
Sequence of eventsChanges in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
2
3
4
5 Diaphragmmovessuperiorlyas it relaxes.
Ribs andsternum aredepressedas externalintercostalsrelax.
Externalintercostalsrelax.
Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).
Thoracic cavity volumedecreases.
Elastic lungs recoilpassively; intrapulmonaryVolume decreases.
Intrapulmonary pressurerises (to +1 mm Hg).
Air (gases) flows out oflungs down its pressuregradient until intrapulmonarypressure is 0.
Expiration
Intrapulmonary pressure.
Pressure inside lungdecreases as lung volume increases during
inspiration; pressureincreases during expiration.
Intrapleural pressure.
Pleural cavity pressure becomes more negative as chest wall expands during
inspiration. Returns to initial value as chest wall recoils.
Volume of breath. During
each breath, the pressure gradients move 0.5 liter ofair into and out of the lungs.
Pre
ssu
re
re
lative
to
atm
osp
he
ric
p
re
ssu
re
(m
m H
g)
Vo
lu
me
(L
)
Inspiration Expiration
Intrapulmonarypressure
Trans-pulmonarypressure
Intrapleuralpressure
Volume of breath
5 seconds elapsed
+2
0
–2
–4
–6
–8
0.5
0
Clicker Question
The pressure in the pleural cavity is known as
__________.
a) intrapleural pressure
b) intrapulmonary pressure
c) transpulmonary pressure
d) atmospheric pressure
Goals/Objectives
Explain the functional importance of the partial vacuum that exists in the intrapleural space
Relate Boyle’s law to the events of inspiration and expiration
Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs
List several physical factors that influence pulmonary ventilation
Explain and compare the various lung volumes and capacities
Define dead space
Indicate types of information that can be gained from pulmonary function tests
Physical Factors Influencing
Pulmonary Ventilation
Three physical factors influence the ease of air
passage and the amount of energy required
for ventilation.
Airway resistance
Alveolar surface tension
Lung compliance
Airway Resistance
Relationship between flow (F), pressure
(P), and resistance (R) is:
∆P - pressure gradient between atmosphere
and alveoli (2 mm Hg or less during normal
quiet breathing)
Gas flow changes inversely with resistance
Conducting
zone
Respiratory
zone
Medium-sized
bronchi
Re
sista
nc
eTerminal
bronchioles
1 5 10 15 20 23Airway generation
(stage of branching)
Airway Resistance
Resistance usually insignificant
Large airway diameters in first part of conducting zone
Progressive branching of airways as get smaller, increasing total cross-sectional area
Resistance greatest in medium-sized bronchi
Resistance disappears at terminal bronchioles where diffusion drives gas movement
Alveolar Surface Tension
Attracts liquid molecules to one another at gas-liquid interface
Resists any force that tends to increase surface area of liquid
Water–high surface tension; coats alveolar walls reduces them to smallest size
Lung Compliance
Measure of change in lung volume that occurs
with given change in transpulmonary pressure
Higher lung compliance easier to expand
lungs
Normally high due to
Distensibility of lung tissue
Surfactant, which decreases alveolar surface
tension
Diminished by
Nonelastic scar tissue replacing lung tissue
(fibrosis)
Reduced production of surfactant
Respiratory Volumes and
Capacities
Used to assess respiratory statusTidal volume (TV)
Inspiratory reserve volume (IRV)
Expiratory reserve volume (ERV)
Residual volume (RV)
Combinations of respiratory volumes
Inspiratory capacity (IC)
Functional residual capacity (FRC)
Vital capacity (VC)
Total lung capacity (TLC)
Measurement
Adult male
average value
Adult female
average value Description
Respira
tory
volum
es
Respira
tory
capacities
Summary of respiratory volumes and capacities for males and females
Tidal volume (TV)
Inspiratory reservevolume (IRV)
Expiratory reservevolume (ERV)
Residual volume (RV)
500 ml 500 ml
3100 ml
1200 ml
1200 ml
1900 ml
700 ml
1100 ml
Amount of air inhaled or exhaled with each breath under restingconditions
Amount of air that can be forcefully inhaled after a normal tidalvolume inspiration
Amount of air that can be forcefully exhaled after a normal tidalvolume expiration
Amount of air remaining in the lungs after a forced expiration
Maximum amount of air contained in lungs after a maximuminspiratory effort: TLC = TV + IRV + ERV + RV
Maximum amount of air that can be expired after a maximuminspiratory effort: VC = TV + IRV + ERV
Maximum amount of air that can be inspired after a normal tidalvolume expiration: IC = TV + IRV
Volume of air remaining in the lungs after a normal tidal volumeexpiration: FRC = ERV + RV
6000 ml
4800 ml
3600 ml
2400 ml
4200 ml
3100 ml
2400 ml
1800 ml
Total lung capacity (TLC)
Vital capacity (VC)
Inspiratory capacity (IC)
Functional residualcapacity (FRC)
Respiratory Volumes and
Capacities
5000
4000
3000
2000
1000
0
Millilite
rs (m
l)
Spirographic record for a male
6000
Inspiratoryreserve volume
3100 ml
Expiratoryreserve volume
1200 ml
Residual volume1200 ml
Inspiratorycapacity3600 ml
Functionalresidualcapacity2400 ml
Vitalcapacity4800 ml
Total lungcapacity6000 ml
Tidal volume 500 ml
Respiratory Volumes and
Capacities
Dead Space
Anatomical dead space
No contribution to gas exchange
Air remaining in passageways; ~150 ml
Alveolar dead space–non-functional alveoli due to collapse or obstruction
Total dead space-sum of anatomical and alveolar dead space
Clicker Question
During pulmonary tests, a patient is asked to breath in normally and then inhale additionally as much as possible into the spirometer. The capacity being measured is the:
a) Inspiratory capacity
b) Functional residual capacity
c) Vital capacity
d) Total lung capacity