Principles of operation of a breathing simulator
A basic overview of a breathing simulator is as follows:
The machine is, at its simplest, a piston moving within a cylinder or a bellows expanding and contracting. This forces air back and forth in the same way as the human lungs do. It requires a reciprocating motion from the piston or bellows face, usually provided by a rotating motor. Some kind of mechanical linkage is used to change the rotary motion of the motor into the reciprocation of the piston or bellows. In order to change the movement of the piston, this linkage must be altered. This requires the machine to be stopped and disassembled or otherwise adjusted mechanically.
The latest generation of breathing simulators (such as the Warwick Technology Digital Breathing Machine) use an electric actuator to provide the reciprocating motion. This uses a stepper motor through a recirculating ball screw to create the linear action. The stepper motor is controlled from a computer, enabling any movement to be performed, and changes to that motion can occur instantaneously. A simple breathing machine can only create sine waves of output flow. An actuator controlled simulator can produce anything required.
The conversion of flow rate required to movement of the piston is all handled by the computer control software. Using a solid piston and cylinder rather than a bellows means there is a rigid conversion of movement of the piston to the movement of the air.