This document discusses lung volumes and capacities and how they are measured. It defines various lung volumes like tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume, and vital capacity. Lung capacities add together different volumes and include inspiratory capacity, functional residual capacity, and total lung capacity. Lung volumes and capacities can be directly measured using a spirometer or indirectly using helium dilution methods. Abnormal lung volumes and capacities can indicate restrictive or obstructive lung diseases.

1. Lung volumes and capacities
Dr. Punyalaxmi Manandhar

2. • Determination of lung volumes is used to
-assess the efficiency of the respiratory system
-diagnose respiratory diseases
• Most of these volumes can be measured using a simple
spirometer
• Static and dynamic lung volume and capacities

3. THE SPIROMETER
– spirometer bell
– kymograph pen

4. Tidal volume
• It is the volume of air
inspired or expired
each breath during
normal quiet
breathing.
• It is about 500 ml

5. Inspiratory reserve volume
(IRV)
• It is maximal volume of air which
can be inspired after a normal
inspiration.
• It is about 3000 ml

6. Expiratory reserve volume
(ERV)
• It is the maximal volume of air
which can be expired after a
normal expiration.
• It is about 1100 ml

7. Residual volume (RV)
• It is the volume of air remaining
in the lungs after maximal
expiration
• It is about 1200ml

8. A lung capacity is two
volumes or more added
together:
Inspiratory capacity (IC)
• It is the maximal volume of air
that can be inspired from the
resting expiratory volume

10. Functional residual capacity (FRC)
• It is the volume of air which remains in the lung at the resting
expiratory level (after normal expiration)
• FRC = RV + ERV
• 1100 + 1200 = 2300 ml

12. Vital capacity (VC)
• It is the maximum volume of air
that can be expelled from lung
by a maximal expiration after a
maximal inspiration
• VC = IRV + TV + ERV
• 4600= 1100+ 500+ 3000
• It is a good index for pulmonary
efficiency

13. Total lung capacity (TLC)
• It the volume of air contained in the lung at the end of maximal
inspiration
• TLC = IRV + TV + ERV + RV
• 5800ml = 1200 + 1100+ 500 + 3000 ml

14. Lung volumes and capacities are
• Decreased in
•The recumbent position than in standing
•Women than in men by about 20-25%
•Small persons and Old age
• Increased in
•Larger and athletic persons

15. • All lung volume and capacities are measured
• directly by spirometer except
• Functional Residual capacity FRC
• Total lung capacity TLC
• Residual volume RV
• Because the air in the residual volume of the lung cannot be
expired into the spirometer and this volume constitutes part
of FRC, TLC

16. Determination of RV and FRC
• They are measured indirectly using helium dilution method
• Its low solubility in respiratory membrane so it does not diffuse into
the pulmonary capillary blood
• It is an inert gas not utilized by the tissues
• The total amount of helium does not change during the test

18. Determination of RV and FRC
• Helium dilution
• Spirometer of known volume (Vs)and
He Conc.(C1) connected to the patient.
• At end of normal expiration.
-Closed circuit
- After several minutes of breathing.
• C1XV1=C2X(Vs+VL)
• C2= final He conc,VL=FRC.
• [He] initial · Vs = [He] final · (Vs + VL)
• Unknown lung volume can be calculated
At beginning After several minutes

19. Clinical significance of FRC
• FRC maintains gas exchange with blood in between breaths
• The large volume of FRC prevents marked rise in alveolar pressure of
oxygen during inspiration and its drop during expiration i.e. it
provides stability of oxygen pressure in the alveolar air and arterial
blood
• Normally the residual volume should be less than 30% of the total
lung capacity.
• It exceeds that level in some pathological conditions e.g. Bronchial
asthma (RV/TLC>30%)

20. Minute Respiratory Volume
• It is the total amount of air that moves into the respiratory passages
each minute inspired or expired (total ventilation)
• it equals = Tidal volume X Respiratory Rate
• 12 breath / minute X 500ml =6000ml/min

21. Minute Respiratory Volume
• Minute Ventilation=
• TVX breathing frequency
• 500ml/minX12= 6000
( 6L/min)

22. Maximal Voluntary Ventilation(MVV)
• It is the maximal volume of air that can be breathed per minute using
the fastest rate and the deepest respiratory effort possible
• The subject breathes as fast and as deep as possible for 15 seconds
only
• To avoid fatigue of the respiratory muscles-
• To avoid wash out of CO2 -
• Normal MVV = 80-160 L/min for male L /min for females 60-120 =
average 100 L/minute
• It is a better index for respiratory efficiency and physical fitness- 2

23. Breathing reserve (BR
• It is the difference between MVV and minute
• Respiratory volume
• BR = MVV – MRV
• 94L/min = 100 – 6
• It is a good test for the functional reserve of the respiratory system
and the higher is the BR, the better the state of physical fitness

24. Dyspneic index
• It is the ratio between BR and MVV and it is usually about 90%.
• If it is decreased below 60% dyspnea (difficulty in breathing) occurs
on slightest effect and the person is considered physically unfit

25. Factors affecting the vital capacity
• Posture
• Movement of diaphragm
• Strength of Respiratory Muscles
• Thoracic wall expansibility
• Resistance to air flow
• Lung elasticity
• Restrictive lung disease

26. Vital Capacity Based on Age & Gender
MALE
FEMALE
Age (Years)

27. Timed vital capacity
• It is the volume of expired air at the end of the first, second or third
second, when measuring vital capacity
• also called forced expiratory volume (FEV)
• The timed vital capacity is a useful test to differentiate between
obstructive lung diseases COPD as emphysema and chronic bronchitis
and restrictive lung diseases as interstitial lung fibrosis.

28. How to measure FVC
• The patient is asked to inspire as
deep as possible and expires as
deep and as rapid as he can into
the spirometer that measures
not only the volume expired but
also the time taken in expiration.
• Normally the FVC takes place in
4 seconds

29. • Normally FEV1 (which is the fraction of the forced vital capacity which
can be expired by the end of the first second using the maximal
expiratory effort)is about 80-83% of FVC.
• FEV 2 about 90-93% of FVC, andFEV3 equals 97% of FVC

30. Timed vital capacity

31. FEV1 & FVC
• Forced expiratory volume in 1
second (FEV1) in young trained
athletes: 4 L
•FVC in young trained athletes: 5 L
• FEV1/FVC %= 80%-83%
obstructive lung disease- the air way
resistance is greatly increased, the
vital capacity is reduced and FEV1 is
markedly reduced FEV1/FVC is less
than 80%.
restrictive lung disease- FEV1/FVC is
normal or even increased 90% due to
proportionate decrease in both FEV1
and FVC

32. • In obstructive lung diseases, the air way resistance is greatly
increased, the vital capacity is reduced and FEV1 is markedly reduced
FEV1/FVC is less than 80%.
• While in restrictive lung disease FEV1/FVC is normal or even
increased 90% due to proportionate decrease in both FEV1 and FVC

34. Restrictive lung diseases

35. Lung Capacity and Disease