Fourier analysis of effects of varying pressure waveforms in electrical lung analogs

Six voltage waveforms were devised to simulate pressure curves of varying configuration for use in artificial ventilation. These waveforms were subjected to Fourier analysis and terms of the resulting series applied to a simple two-branch resistive-capacitive circuit intended to represent a lung analog using computer simulation. Current (analogous to flow) and charge (analogous to volume) in each branch could be graphically displayed. Differences among the waveforms in such attributes as efficiency, inspiratory work, volume introduced per unit of mean pressure applied, and relative volume distribution between the two branches could be demonstrated. All waveforms were capable of delivering a predetermined volume to the circuit with adjustment of their peak pressure (voltage). It was not possible to designate any of the waveforms as "superior" since advantage in one attribute, such as efficiency, was accompanied by deficiencies in other characteristics such as uneven volume distribution. Despite obvious severe limitations on physiological interpretations of such data, Fourier analysis of respiratory waveforms appears to be a useful teaching, illustrative, and exploratory method.