Hydraulic lung analogue

This paper describes an easy-to-build, hydraulic analogue of the lungs, which has similar mechanical characteristics as an infant lung. It consist of two, clear, U-tubes filled with water (similar to two water-manometers) and connected through two capillary bundles into a T. Since the analogue is passive (it represents an unconscious subject), it is connected to a ventilator to demonstrate its characteristics. As the air enters through the T, it splits into two pathways (representing the first bifurcation present the trachea), and then passes through two capillary bundles, simulating airway resistance. The other sides of the capillary bundles are connected to the U-tubes, filled with water halfway. Since it is the tendency of the U-tube manometer is to maintain the two water columns at the same level, it provides a recoil effect that simulates lung compliance. The airway resistance can be changed by changing the size and/or number of the small tubes that make the capillary bundle. Lung compliance can be changed by selecting the size of the U-tube, or by placing a solid insert into one or both of U-tubes. This device provides an adequate model for an infant lung provided that the frequency of excitation is not too high. This lung analog is an excellent vehicle for demonstrating the air movement in the respiratory system, since by using clear PVC piping, the water level change is equivalent to the tidal volume. The respiratory system provides excellent example of a dynamic bio-system and a vehicle to model dynamic systems.