Tidal Volume

V_t = V_d + V_a

Minute Respiration

V_e=V_t x f

V_e = V_a + V_d

 Alveolar Ventilation

Dead Space Ventilation

V_a = f x V_a

V_d = f x V_d

Sources of Resistance to Airflow

Elastic Resistance  of tissue

Surface tension of alveloar gas/liquid interface

Frictional Resistance of air flow down airways

Why increasing effort on expiration may not help ventilation

Despite increased pressure gradient, the pressure exerted on lung by muscles of expiration may infact collapse the airways.  This is especially true when the linings of airway are coated with inflammatory debris/

Elastic Recoil

Half due to tissue elasticity (elastance = 1/compliance)  Compliance - volume change per uniit of intra-alveolar pressure change.

The other half due to surface forces at gas/liquid interface - surface tension tends to pull in on alveolar walls which are elastic in nature. 

Poiseuille's Law

R = k/r⁴

Decrease radius by 1/2, resistance increases 16 fold. 

Hysteresis

Pressure and Volume curves different for inspiration and expiration due to the elastic nature of lung.  Under normal circumstances, inspiration should require effort, some of this energy of inspiration in stored in the form of potential energy in the elastic tissues of the lung.  Expiration is normally passive and the elastic recoil from elastic body changes the dynamics of pressure/volume curve.

Effect of Pulmonary Surfactant on Surface Tension as Surface Area Changes

Comples lipoprotein from type II pneumocytes.  As alveolus decreases in size, the surface tension decreases accordingly.