Lung volume and capacities
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Transcript of Lung volume and capacities
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
Four types
1. Tidal volume
2. Inspiratory reserve volume
3. Expiratory persevere volume
4. Residual volume
Normal volume of air inspired or expired
during quiet breathing
TV = 500 ml
Extra volume of air inhaled after tidal
volume by max inspiratory effort
3000ml in adult male
(or)
3300 / 1900 = M/F
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
Volume of the air left out in lungs after
forceful expiration or complete
expiration
1200/1100 = M/F
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
Max volume of air that can be inspired
after normal tidal expiration
IC = TV+IRV
= 500 +3000
= 3500 ml
Max volume of air that can be expired
after normal tidal inspiration
EC=TV+ERV (500+1100=1600ml)
Volume of air remaining in lungs after
normal tidal expiration
FRC= ERV + RV ( 1100 + 1200 = 2300ml)
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
Old age
Obstructive and restrictive lung diseases
Max Amount of air expelled after
deepest possible inspiration
VC = TV+IRV+ERV
500+3000+1100= 4600ml
To asses strength of respiratory muscles
Factors affecting VC
› Age
› Sex
› Strength of respiratory muscles
› Gravity
› Pregnancy
› Ascites
› Pulmonary diseases
Volume of air present in lung after max
inspiration
TLC = VC + RV ( 4600+1200 = 5800ml )
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
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 %
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%
Low in obstructive lung diseases
Normal or high in restrictive lung diseases
It’s the mean expiratory flow rate during
the middle 50% of FVC
Normal is 300L/min in 0.5 sec
Aka pulmonary ventilation
Volume of air inspired or expired per
minute
RMV = TV * RR ( 500* 12 = 6000 ml)
6 – 7.5 L/min
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
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
Normal DI is 60 – 90%
Average of 75%
Importance is dyspnoeia results when DI
becomes less than 60%