This model represents a compliant bronchiole with a compliant alveolar sac. The driving force for this model is a pressure gradient which represents the difference in the alveolar and the pleural pressures.

Description

 This model represents a compliant bronchiole with a compliant alveolar sac.
 The resistance offered by bronchial wall to the flow of air is represented by 
 the resistor in the model. The total resistance of the bronchiole is split into 
 two resistors in series to fecilitate smooth coupling of downstream circuits. 
 The compliance of the bronchiole is represented by the capacitor. The alveolar sac
 compliance is repsented by a capcitor. The alveolar sac changes its volume as a 
 function of inlet flow or pressure. The driving force for this model is the pressure 
 gradient which represents the pressure difference between the alveolar sac and the 
 pleural pressure. Since this model lacks a pleural cavity, a positive pressure
 gradient is imposed to drive the flow into the alveolar sac. The important difference 
 between this model and the rigid_bronchiole_compliant_alveolus model is the shape of 
 alveolar volume curve. 

Equations

Pinlet - P2 = Finlet * R1
F1 = Finlet - F2
P2 = (V1 - V1_0)/Com1
P2 - P3 = F1 * R2
P3 - P4 = F1 * R3
P4 = (V2 - V2_0)/Com2
d(V1)/dt = F2   
d(V2)/dt = F1

Where: P is pressure, F is flow, R is resistance, Com is capacitance, and V is the volume.