Abstract: A system and method of controlling the termination of the inhalation phase in a pressure support ventilation system is disclosed, in which an expiratory trigger sensitivity, or ratio of inspiratory flow rate to peak inspiratory flow rate at which the inspiration phase is terminated, is varied in proportion to variations in a calculated respiratory time constant. The system includes sensors for monitoring pressure and flow of gas during each breath, and, based on the sensor outputs, calculates the respiratory time constant for one breath or a series of breaths. The expiratory trigger sensitivity is automatically increased with increasing patient respiratory time constant, providing a closed loop control of expiratory trigger sensitivity. The expiratory trigger sensitivity may also be varied in response to changes in supra-plateau pressure.

Abstract: A fast switching broadband signal synthesizer method and structure are provided which not only has the ability to change frequency and amplitude quickly, but with a minimal dwell time required before switching can again take place. A signal translator can also be constructed in accordance with this invention in order to convert the output frequency of a companion signal source to any desired frequency while retaining the fast switching speed and switching rate of the signal synthesizer. Amplitude, phase, and frequency modulation of the companion signal are preserved during the translation process. A direct frequency synthesizer is provided wherein internal signals which are combined to generate any output frequency are derived from a single fixed frequency oscillator. By utilizing a single reference frequency oscillator in accordance with this invention, the amount of circuitry required to construct a direct frequency synthesizer is greatly reduced.