Lung volume and capacities

1. Lung volume and
capacities
BY SHAMA
PHYSIOLOGY DEPARTMENT

2. LUNG VOLUME
AND CAPACITIES
• Divided into 2:
• Static lung volume & capacities: no
time factor involved.
• Dynamic lung volume & capacities:
time factor is involved
This Photo by Unknown Author is licensed under CC BY-NC-ND

3. Static lung volumes
• TIDAL VOLUME: volume of air inspired or expired during
quiet respiration. 500ml
• INSPIRATORY RESERVE VOLUME: Air inspired with a
maximal inspiratory effort. 2 to 3.3 l
• EXPIRATORY RESERVE VOLUME: volume of air
expelled by an active expiratory effort after passive
expiration. 700-1200ml
• RESIDUAL VOLUME: air left in lung at the end of
maximal expiratory effort.

4. STATIC LUNG CAPACITIES
• INSPIRATORY CAPACITY: maximum amt of air that can be inhaled
after a normal tidal expiration. (TV+IRV). 2.5-3.5l
• VITAL CAPACITY: amt of air that can be exhaled with maximum
effort after maximum inspiration. (TV+ERV+IRV).
• FUNCTIONAL RESIDUAL CAPACITY: volume4 of air remain in
lungs at the end of normal tidal expiration. (RV+ERV)
• TOTAL LUNG CAPACITY: maximum amt of air the lungs can
contain. (RV+VC).

5. This Photo by Unknown Author is licensed under CC BY

6. VITAL CAPACITY
IT IS MEASURED IN 2 STAGE:
Stage1: subject is asked to breath in maximally after normal expiration then he
takes a few normal breaths.
Stage2: subject is asked to breath out maximally after normal expiration.
Sum of stage 1 and stage 2 : TV+IRV+ERV

7. Advantages
of VC
• Provide information about strength
of respiratory muscles.
• Gives information about other
aspects of PFT through FEV1.

8. Factors affecting VC
Physical
dimension
Age
Strength of
respiratory
muscles
Posture
Pregnancy
Respiratory
obstruction
ascites

9. Significance
of FRC
• It maintains residual volume
constant.
• Acts as a buffer and allows
continuous exchange of gases to
occur even during expiration
thereby prevents sudden changes
in partial pressure of gases in
blood.

10. • RV & FRC cannot be measured directly by simple spirometry.
• Measured by using dilution technique involving Helium (helium
dilution technique)
• Subject is connected to spirometer filled with 10% helium in oxygen
and subject breathes from spirometer. After the subject rebreathes
helium oxygen mixture and equilibrates with the spirometer, the
helium concentration in the lungs becomes same as in spirometer
• FRC can also be measured by body plethysmography.

11. DYNAMIC LUNG VOLUME AND
CAPACITIES
• Timed vital capacity or forced vital capacity: maximum volume of air
which can be breathed out as forcefully and rapidly as possible
following a maximum inspiration.
• Components of TVC:
FEV1 : volume of FVC expired in 1st second of exhalation. 80% of
FVC
FEV2 : volume of FVC expired in 2nd second of exhalation. 95% of
FVC
FEV3 : volume of FVC expired in first 3 seconds of exhalation. 98%-
100% of FVC.

13. Clinical
significance
• FEV1 to FVC ratio is a useful tool in
the diagnosis of airway disease.
• Help to distinguish between restrictive
and obstructive lung disorder.
• In restrictive disorder: chest
expansion is restricted. VC decreases
while FEV1 is normal.
• In Obstructive disorder: inspiration is
normal but expiration is obstructed.
FEV1 decreases.

14. • Minute ventilation or pulmonary ventilation: volume of air
expired or inspired by the lungs in one minute.
• PV = TV * RR per min
= 500*12 = 6L/min, normally
• Forced expiratory flow during 25- 75% of Expiration (FEF25-
75%): the time taken for FEF25-75% is called mid expiratory
time (MET). Normal : MET 0.5 sec, increases in obstructive lung
disorder.
• Peak expiratory flow rate (PEFR): this is the expiratory flow rate
during the peak of FVC. 400-450 L/min.

15. • Maximum breathing capacity or maximum voluntary ventilation
or maximum ventilation volume: largest volume of air that can
be moved into and out of lungs in one minute by maximum
voluntary effort.
• Normal: 90-170l /min.
• Pulmonary reserve or breathing reserve: maximum amount of
air above pulmonary ventilation which can be breathed in and
out lungs in one minute.
• It is usually expressed as percentage of MVV and called as
percentage pulmonary reserve or dyspnoeic index (DI)
• Normal DI : >60-70%

16. THANK YOU