A fluidic-controlled, miniature respirator with a new positive airway pressure device.

Abstract

A simple and miniature respirator was developed providing controlled ventilation and application of a positive airway pressure. The positive airway pressure is achieved by an airflow through a canula into the airways. During expiration the direction of this insufflated air-flow is changed and the dynamic pressure necessary for it manifests itself as a positive airway pressure. Mechanical ventilation functions according to the principle of the Ayre-T-Piece: flow direction and, therefore ventilation, is controlled by occlusion of the expiratory limb. Occlusion is brought about by inflating a balloon. The inflation of the balloon is controlled by fluidic-circuits. They allow setting of frequency, duration of inspiration and pressure limit. As the above mentioned system for creating a positive airway pressure is integrated, mechanical ventilation with PEEP is achieved. Tests on a lung model were performed to establish the variables which influence the amount of positive pressure produced by an air-flow through a canula into a tube. Results indicate that the positive pressure obtained is inversely correlated to the diameter of tube and canula and varies with the angle of inflow (Tab. I, II, Fig. 4). The pressure-rise-velocity depicted in Fig. 5 suggests that sighing is possible in an open system. On an anencephalic newborn pressure-flow-ratios were established (Fig. 6). Pressure-time curves during spontaneous breathing, CPAP assisted breathing and sighing combined with CPAP were recorded in a 3 month old baby (Fig. 7, 8, 9). The discussion states the technical performance of the respirator (frequency 100/min-1/3 min., tidal volume 5-100 ml, controlled ventilation with pressure limitation, application of PEEP) and additional advantages (no apparatus deadspace, disposable i.e. sterile air supply-system, the miniature dimensions 10 x 10 x 5 cm, versatility and simple therefore technically reliable construction).