RESPIRATORY SYSTEM
(LUNG VOLUMES & CAPACITIES)
Dr. Mohammed Sharique Ahmed Quadri
Assistant Prof. physiology
Al maarefa college
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Lung normally operate at about
“half full “
• During normal breathing, lungs are not
totally full nor totally deflated.
• At the end of normal quiet expiration,
the lungs contain about 2200 ml of air.
• Important benefit of it that we get is
– Gas content of lungs leaving lungs remains
constant
– Work of breathing is reduced
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Spirometer
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Lung Volumes
 Tidal Volume [TV]
It is volume of air we breathe in or breathe out during
single breath. Under resting condition It is about 500ml.
 Inspiratory Reserve Volume [IRV]
• It is extra volume of air that can be breathed in [inspired]
forcefully, over and above normal tidal volume.
• IRV is about 3000ml.
• It is achieved by maximal contraction of diaphragm,
external inter-costal muscles and accessory muscles of
inspiration.
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Lung Volumes
 Expiratory Reserve Volume [ERV]
• It is maximum volume of air that can be
expired forcefully after normal tidal
expiration.
• ERV is about 1000ml.
• It is done by contracting the accessory
expiratory muscles of expiration [abdominal
and internal-intercostal muscles].
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Lung Volumes
 Residual Volume ( RV )
• It is volume of air remaining in the lungs even
after maximal expiration.
• RV is about 1200ml.
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Lung Capacities
 Inspiratory Capacity [IC]
• It is maximum volume of air that can be
inspired after normal tidal expiration.
• It includes tidal volume and inspiratory
reserve volume.
• (IC = IRV + TV)
• It is about 3500ml.
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Lung Capacities
 Functional Residual Capacity [FRC]
• It is volume of air that remains in the lungs
after normal tidal expiration.
• (FRC = ERV + RV)
• Average value FRC = 2200ml.
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Lung Capacities
 Vital Capacity [VC]
• It is maximum volume of air that can be
expired after taking maximum inspiration
[during a single breath].
• (VC = IRV + TV + ERV)
• Average value VC = 4500ml.
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Vital Capacity
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Lung Capacities
 Total Lung Capacity [TLC]
• It is the maximum volume of air that the lungs
can hold.
• (TLC = TV + IRV + ERV + RV)
• Average volume TLC = 5700ml [5.5-6 liter].
• TLC is affected by Age, Build, Height and
Weight, and presence of Lung disease.
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Forced Expiratory Volume In One
Second [FEV1]
• It is volume of air that can be expired forcefully
during the first second of expiration [normally we
expire in 3sec].
• FEV1 = 80% [80% of vital capacity(VC)]
• FEV2 = 92%
• FEV3 = 99%
• FEV1 indicates maximal air flow rate from the
lungs.
• FEV1 is decreased in obstructive lung disease e.g.
bronchial asthma.
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Normal FEV1, FVC Curve
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Respiratory Dysfunction
• Obstructive Lung Disease e.g. bronchial asthma.
• Restrictive Lung Disease e.g. pulmonary fibrosis.
 Obstructive Lung Disease
• Patient has difficulty in expiration [due to obstruction of
bronchi].
• Therefore, FEV1 and FEV1% is decreased.
• Example: Normal VC = 5 liters, FEV1 = 4 liters.
• FEV1% = (FEV1/FVC) * 100
= (4/5) * 100
= 80%
• In Obstructive Lung Disease, VC = 4 liters, FEV1 = 2 liters
• FEV1% = (2/4)*100
= 50%
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Respiratory Dysfunction
 Restricted Lung Disease
• Lungs compliance is reduced , therefore, vital capacity[VC],
TLC, all are decreased as lungs can not expand.
• When we do respiratory function test:
• FEV1 is decreased, FVC is also decreased but FEV1% is
normal [80% or more].
• Example: Normal VC = 5 liters, FEV1 = 4 liters.
• FEV1% = (FEV1/FVC) * 100
= (4/5) * 100
= 80%
• In Restricted Lung Disease, VC = 3 liters, FEV1 = 2.7 liters
• FEV1% = (2.7/3)*100
= 90%
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Obstructive
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Flow Volume Loops
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Pulmonary Ventilation & Alveolar Ventilation
• Pulmonary Ventilation or Minute Ventilation: It
is volume of air we breathe in and out in 1min.
• Pulmonary Ventilation
= Tidal Volume × Respiratory rate
= 500ml × 12 = 6000ml or 6 liter
• Normal respiratory rate is 12 -18/min.
• Adult young person can increase pulmonary
ventilation 25-fold to 150 liters/min [to increase
pulmonary ventilation one has to increase tidal
volume and respiratory rate].
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Anatomic Dead Space
• As we breath in, all air does not go to alveoli
for gas exchange but some of the air remains
in trachea and bronchi [conducting zone] and
does not take part in gas exchange.
• It is 150ml. It is called ‘Anatomic Dead Space’.
• As our tidal volume is 500ml, anatomic dead
space is 150ml, therefore, 350ml goes to lungs
for gas exchange.
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Alveolar Ventilation
• It is volume of air exchange between atmosphere
and the alveoli/min.
• It is more important than pulmonary ventilation.
• It is alveolar air that takes part in gas exchange.
• Alveolar Ventilation
= (TV – Dead Space )× Respiratory Rate[RR]
= (500 – 150) × 12
= 350 × 12 = 4200 ml/min
• Alveolar Ventilation is less than Pulmonary
Ventilation.
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Effect of Breathing Pattern on
Alveolar Ventilation
• Rapid shallow breathing is not good, as TV is
decreased and most of the air is lost in dead
space and little or no air goes to alveoli.
• Person may get unconscious within few
minutes.
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Alveolar Dead Space
• Normally air going into the alveoli, takes part in
gas exchange, therefore, there is no alveolar dead
space in healthy person.
• In case of disease, where alveoli are abnormal
e.g. pneumonia, gas exchange does not take
place in affected alveoli, therefore, alveolar dead
space is there.
• Physiological Dead Space
= Anatomical Dead Space + Alveolar Dead Space
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Dead Space
• In Health,
Physiological dead space=Anatomical dead
space
[As all alveoli are functioning].
• In Disease,
Physiological dead space is more than
Anatomical dead space
[As many alveoli are not functioning].
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Ventilation and Perfusion in the Lungs
• Regional difference exist at the top and
bottom [apex and base] of the lung due to
gravitational effect.
 Standing upright
• Gravity effect is more on blood flow than on
airflow.
• Effect on Ventilation/Perfusion ratio.
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Ventilation and Perfusion in the Lungs
• Top of the lung receives relatively more air
than blood, therefore, ventilation perfusion
ratio is increased.
• Bottom of the lung receives relatively less air
than blood, therefore, ventilation perfusion
ratio is decreased.
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Local control to match the ventilation & perfusion
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Local control to match the ventilation & perfusion
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References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition