Bench testing of the CPU-1 ventilator.

An artificial patient capable of spontaneous and artificial ventilation has been used for bench testing of the Ohmeda CPU-1. This ventilator has an extensive capacity for interaction with the spontaneous breathing of the patient, and provides a wide variety of operating modes. These include spontaneous breathing with or without continuous positive pressure, volume-cycled and pressure-cycled artificial ventilation, with or without positive end-expiratory pressure or synchronization. In addition, there is a facility for ensuring a mandatory minute volume. The ventilator is controlled by a microprocessor with sophisticated decision-taking functions based on input from an expiratory hot-wire anemometer. Intended and measured ventilatory variables are displayed separately. The anemometer has satisfactory accuracy and pressure control is adequate. The synchronization permits adaptation of the ventilator to spontaneous respiration according to a wide range of harmonics. In any mode, artificial ventilation is initiated if spontaneous respiration is inadequate. The mandatory minute volume mode is based on a complicated program of a cautious nature which reacts instantly to inadequate spontaneous breathing, but is slow to discontinue artificial ventilation.