Proposta de uma nova arquitetura de ventilador pulmonar mecânico parapequenos animais

Abstract

Mechanical ventilators are widely adopted for experimental research in small animals, both for specific studies about lung diseases as for experiments with different purposes requiring anesthesia procedure. The existing equipments for this application are based on servocontrolledpiston technology that presents limitations with respect to modern clinicalventilators in establishing certain modes of ventilation, for example, pressure controlled ventilation. This work proposes a new architecture and numerical model of ventilator with the main objective generate pressure and flow profiles relative to established modes of clinicalventilation. The architecture contains a solenoid on-off valve for control of inspiratory pressure or flow by a strategy based on sliding mode, combined with a pneumatic system able to filter high-frequency oscillations during flow. An initial architecture considers valveswitching and drain a reservoir to the atmosphere, in addition to the establishment of PEEP (positive end-expiratory pressure) by water column. In a modification of the architecture, it includes the possibility of gas recovery and generates PEEP automatically. Numerical simulations of the system dynamics were performed for the two architectures in order to determine the minimum requirements in terms of response time of the valves, performance due to the transfer of data in continuous and discrete time, and the system robustness due to the presence of measurement noise. Satisfactory results in the pressure controlled mode wereobtained in the modified architecture, considering valves with a minimum response time of 2 ms, analog or digital configuration (with sampling rate of 1 kHz) and robustness to measurement errors of up to 0.75 cmH2O. In the volume controlled mode, minor errors were found in the initial architecture, but also the modified architecture provides adequate results,with the advantage of avoiding the waste of gases.