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. المحاضرة السادسة

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

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 Factors Affecting Vital Capacity (V.C.) : 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 circula­ tion due to the left heart failure, 3.After cardiac surgery Composition of inspired, expired and alveolar air Gas% Inspired air% Expired air% Alveolar air Oxygen CO N2N Water vapor

Partial pressure and tension of gases in inspired air, expired air and alveolar air: GasInspired airExpired airAlveolar air O2O2 159 m.m. Hg CO H2OH2O N2N Summation m.m. Hg