NNPD1013 & NNBB1234:
PULMONARY VENTILATION
dr farah fauzi | fakulti sains kesihatan
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Objectives
• Overview of respiration
• Stages of respiration: pulmonary
ventilation
• Control of pulmonary ventilation
• Factors affecting ventilation
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The Goal of Respiration
The ultimate mission of the respiratory system
to make oxygen available to body tissues for
cell metabolism. This mission is carried out in
several stages of respiration.
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Stages of Respiration
A. External Respiration
(ventilation & gas exchange)
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B. Gas Transport
C. Internal Respiration
Stages of Respiration
1, 2
1
2
3
4
3
4
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Cellular Respiration
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Pulmonary Ventilation
Gas Exchange
Gas Transport
Internal Respiration
Pulmonary Ventilation
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Pulmonary Ventilation
Ventilation refers to the flow of air in and out of
the lungs (alveoli).
This process can be categorised
into minute ventilation and
alveolar ventilation.
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Pulmonary Ventilation
Minute ventilation = the amount of
air entering lungs per minute
Alveolar ventilation =
the amount of gas that
reaches the alveoli and
takes part in gas exchange
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Pulmonary Ventilation
Lungs
Alveoli
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Pulmonary Ventilation
Inhalation brings in air into the lungs, inflating
the alveoli. Exhalation drives air out of the lungs
and deflating the alveoli.
O2
CO2
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Pulmonary Ventilation
Unlike the heart, the lungs are not innervated
with nerves. The inflation and deflation of the
lungs during breathing depends solely on
movement of respiratory
muscles, i.e. diaphragm
and intercostal muscles
and special characteristics
of the lung tissue.
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Respiratory Muscles
§ Diaphragm
§ External intercostal muscles
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Diaphragm
• Innervated by phrenic nerve.
• Contracts (inhalation) à
descends and flattens.
§ increasing the vertical volume of
thoracic cavity
• Relaxes (exhalation) à
dome-shaped
§ decreases the volume of
thoracic cavity
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Ext. Intercostal muscles
• Muscles between the ribs.
• Innervated by intercostal nerve.
• Contraction (inhalation) à
elevates the ribs upward
and outward
§ increases thoracic volume
• Relaxation (exhalation) à
depresses the ribs
§ decreases thoracic volume
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Respiratory Muscles
The cycle of contraction and relaxation of the
diaphragm and intercostals muscles cause the
volume of thoracic cavity to change.
Changes in the thoracic volume
create different pressures in
the lungs (intrapulmonary pressure)
that ultimately result in
inhalation and exhalation.
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Physics of Gas and Volume
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Respiratory Muscles
• Contraction of
respiratory muscles à
thoracic volume ▲, P▼
• Relaxation of
respiratory muscles à
thoracic volume ▼, P▲
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Physics of Air Flow
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Pressure Differences
The pressure differences between atmosphere
and intrapulmonary drives air flow.
760 mmHg
760 mmHg
contraction
757 mmHg
INHALATION
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relaxation
763 mmHg
EXHALATION
The
Balloon Lung Model
The lungs are just a
pair of air bags.
They expand as a
result of air flowing
in, and not the other
way round!
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Control of Ventilation
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Although we can
consciously control
our breathing, most
of the time we do
not, especially
during sleep.
So, what controls
our breathing ?
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Control of Ventilation
Ventilation is controlled at two levels:
§ Involuntary (brain stem; respiratory centers)
§ Voluntary (cerebral cortex)
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Control of Ventilation
The respiratory centers are located in the:
§ medulla oblongata
(medullary respiratory center)
§ pons
(pontine respiratory center)
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Medullary respiratory group
The respiratory centers in the medulla oblongata
are two group of neurons; the dorsal group
(DRG) and ventral group (VRG).
The DRG is involved in generating a normal
breathing rhythm (eupnea), while
the VRG is mostly involved
in forced breathing.
Both DRG and VRG innervates
the respiratory muscles.
DRG
VRG
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DRG and VRG innervations
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Medullary Respiratory Center
• DRG generate impulse to
begin inhalation.
• Signals sent to respiratory
muscles via efferent nerves
to stimulate contraction.
• Diaphragm: phrenic nerve
• Intercostal muscles: intercostal
nerve
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Control of Eupnea
Inspiratory neurons
depolarise (‘on’)
Inspiratory neurons
repolarise (‘off’)
Impulse sent to diaphragm
and intercostal muscles
Impulse ceases
Contraction of
respiratory muscles
Relaxation of
respiratory muscles
INHALATION
EXHALATION
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Pontine Respiratory Group
The pneumotaxic centre and apneustic centre of
the PRG modifies the output of the MRC.
Not essential for basic
rhythm of breathing, but
important in fine-tuning
breathing rhythm during
singing, talking, exercising,
laughing, etc
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Pontine Respiratory Group
Pneumotaxic center - tachypnea
Apneustic center - apnea
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Voluntary Control of Breathing
• Motor cortex of the frontal lobe.
• Breath-holding, smelling, meditation.
• Signals are relayed down from the motor
cortex directly to the phrenic and
intercostal nerves, bypassing the
respiratory centers.
• Respiratory centers can override the
voluntary control if levels of blood
gases are compromised.
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Factors Affecting Ventilation
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Factors Affecting Ventilation
Factors that can affect airflow in and out of lungs:
§
§
§
§
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Resistance in airway
Lung compliance
Pulmonary surfactant
Elastic recoil
Airway resistance
Any condition that narrows or obstruct the
airways, making it difficult for air to flow in
and out of the lungs:
§ asthma
§ emphysema
§ bronchitis
asthma
emphysema
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Lung compliance
The ability of lungs to expand easily when we
inhale. Low lung compliance will need more effort
to inhale. Decreased compliance can be seen in:
§ scarring of lung tissue (TB, asbestosis)
§ lack of pulmonary surfactant
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Pulmonary surfactant
Pulmonary surfactant is an ‘oily’ coating inside the
alveoli to help loosen water surface tension in the
alveoli. Surfactant is made up of secretions rich in
lipids and proteins, secreted by type II pneumocytes.
surfactant
alveolar fluid
alveolar air
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Alveoli are moist.
During exhalation
alveoli deflate and
can become ‘sticky’,
making it hard to
re-expand..
Having pulmonary
surfactant solves this
‘stickiness’ problem!
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Pulmonary surfactant
• reduce surface tension
• prevent alveoli collapse
during exhalation
• bind to pathogens, debris
• prevent excessive moisture
in the alveoli
Helps to maintain lung
compliance by allowing the
lungs to expand easily after
exhalation
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PULMONARY SURFACTANT
INSUFFICIENCY
Newborn respiratory distress
syndrome or “blue baby” is
common in premature infants
(<35 wk), due to insufficient
surfactant production.
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Elastic recoil
Alveoli contain elastic fibers
enabling them to stretch during
inhalation and recoil during
exhalation.
Elastic recoil gives lungs the
passive ability to deflate easily
during exhalation.
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Elastic recoil
If elastic recoil is compromised, exhalation will be
DIFFICULT
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Loss of Recoil in Emphysema
• Alveoli damage à
loss of elastic fibers.
• Loss of elastic recoil
à air trapped in
alveoli.
• Less air is exhaled
out, less fresh air can
enter lungs.
• Causing low O2
levels in the blood
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Summary
The act of breathing highly depends on the
coordinated actions of the respiratory
centers and muscles to generate pressure
differences in the lungs and hence, create air
flow.
Apart from damaged lung structures,
breathing process can also be compromised
by diseases affecting respiratory nerves and
muscles.
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