lung volume and capacities
TRANSCRIPT
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Lung volumes and lung capacities refer
to the volume of air associated with
different phases of the respiratory cycle.
Lung volumes are directly measured;
Lung capacities are inferred from lung
volumes
Instrument is spirometry
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Four types
1. Tidal volume
2. Inspiratory reserve volume
3. Expiratory persevere volume
4. Residual volume
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Normal volume of air inspired or expired
during quiet breathing
TV = 500 ml
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Extra volume of air inhaled after tidal
volume by max inspiratory effort
3000ml in adult male
(or)
3300 / 1900 = M/F
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Extra volume of air that can be exhaled
after tidal volume by max expiratory
efforts
1100 in a normal adult male
(or)
1200/700 = M/F
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Volume of the air left out in lungs after
forceful expiration or complete
expiration
1200/1100 = M/F
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These are combinations of two or more
lung volumes 1. Inspiratory capacity
2. Expiratory capacity
3. Functional residual capacity
4. Vital capacity
5. Total lung capacity
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Max volume of air that can be inspired
after normal tidal expiration
IC = TV+IRV
= 500 +3000
= 3500 ml
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Max volume of air that can be expired
after normal tidal inspiration
EC=TV+ERV (500+1100=1600ml)
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Volume of air remaining in lungs after
normal tidal expiration
FRC= ERV + RV ( 1100 + 1200 = 2300ml)
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Significance ?
› Continues exchange of gases
› So that conc of O2 and CO2 is maintained
› Breath holding is made possible
› Dilution of toxic inhaled gases
› Prevents colapse of lungs
› reduces workload of respiratory muscles
and rt ventrcle
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Old age
Obstructive and restrictive lung diseases
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Max Amount of air expelled after
deepest possible inspiration
VC = TV+IRV+ERV
500+3000+1100= 4600ml
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To asses strength of respiratory muscles
Factors affecting VC
› Age
› Sex
› Strength of respiratory muscles
› Gravity
› Pregnancy
› Ascites
› Pulmonary diseases
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Volume of air present in lung after max
inspiration
TLC = VC + RV ( 4600+1200 = 5800ml )
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Timed vital capacity or FVC
FVC is volume of the air that can be
expired rapidly with max force following
a max inspiration , and its timed by a
spirograph
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FEV1 – volume of air expired in the first
second of FVC
Fev1 is flow rate
Fev1 is expressed in percentage
Fev1 = 80%
Fev2 = 90 %
Fev3 = 98-100 %
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0 1 2 3
5000
4000
3000
2000
1000
0
Time (sec)
Volu
me (
ml)
FEV1 = (5000 ml -1000 ml) / 5000ml
= 4000 ml / 5000 ml
= 80%
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Low in obstructive lung diseases
Normal or high in restrictive lung diseases
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It’s the mean expiratory flow rate during
the middle 50% of FVC
Normal is 300L/min in 0.5 sec
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Aka pulmonary ventilation
Volume of air inspired or expired per
minute
RMV = TV * RR ( 500* 12 = 6000 ml)
6 – 7.5 L/min
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Aka MVV
Max volume of air that can be ventilated
voluntarily for given interval of time
Subject asked to breath rapidly and deeply
, for 15 seconds
Recorded by a spirometer or Douglas bag
Normal is 80- 170 L/min
Reduced in pt with emphysema and
respiratory muscle weakness
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Maximum amount of air above the PV
that can be inspired or expired in one
min
PR = MVV – PV
Pulmonary reserve is expressed as % of
MVV and is known as dyspnoeic index
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Normal DI is 60 – 90%
Average of 75%
Importance is dyspnoeia results when DI
becomes less than 60%
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