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%