‫المحاضرة‬
‫السادسة‬
1- Total lung capacity:
= tidal volume + inspriatory reserve volume + expiratory
reserve volume + residual volume ( 6 liters)
2- Normal Capacity (Functional Residual Capacity):
This is the volume of air remaining in the lungs after a
normal expriation. It comprises the expiratory reserve
volume + the residual volume (2-3 liters).
3- The Inspiration Capacity:
It is the volume of air taken by maximal inspiration at the
end of a normal expiration, it equals the tidal volume +
the inspiratory reserve.
4- The vital capacity:
It is the volume of air exhaled by a maximal expiration
after a maximal inspiration (i.e. tidal volume + inspiratory
reserve V. + expiratory reserve. V.) 5 liters.
Dead Space:
The Dead Space

CO 2 in alveolar  CO 2 in Expired
 Tidal air
CO 2 in Alveolar
Factors Affecting Vital Capacity (V.C.) :
1) Condition of respiratory muscles
2) Posture
3) Elasticity of the lung
4) Expansion and recoil of the thoracic cage
5) Volume of blood in pulmonary circulation
6) Resistance to Air Flow in Respimwry passages
Orthopnoea :
This is difficulty in respiration when lying down but not
when standing or sitting. It occurs in left sided heart
failure. It is due to decreased V.C. caused by : .
1. Pressure of viscera on the diaphragm when lying down
2. Increase and stagnation of blood in pulmonary circulation due to the left heart failure,
3. After cardiac surgery
Composition of inspired, expired and alveolar air
Gas
Oxygen
% Inspired air % Expired air % Alveolar air
20.94
16.3
14.6
CO2
N2
Water vapor
0.03
79.03
0.50
4.0
79.7
6.2
5.2
79.7
6.2
Partial pressure and tension of gases in
inspired air, expired air and alveolar air:
Gas
Inspired air
O2
159 m.m.
Hg
0.15
3.85
597
760
CO2
H2O
N2
Summation
Expired air Alveolar air
120
104
27
47
566
760
40
47
569
760 m.m.
Hg