[Comparative studies of CPAP systems using a respiration simulator. I. Evaluation criteria]

Assessment of the performance of modern ventilators that combine spontaneous breathing and mechanical ventilation is orientated not only towards the assessment of the inspiratory and expiratory resistance within the system, but also towards the functional criteria for the inspiratory and expiratory valves. This conclusion is particularly valid for CPAP procedures, as in this case patients must perform the entire work of breathing by themselves. As it has proved to be extremely problematic to carry out comparative testing of ventilators on patients in the intensive care unit, a breathing simulator has been developed, the use of which has enabled us to have a "patient" at our disposal who can tolerate the procedures for measuring the performance of ventilators with IMV and with CPAP without injury. The pressure-flow characteristics and the work of breathing can thus be measured under constant conditions and with various ventilation systems. Exact analysis of the pressure curve pattern under standardized conditions proved to be of value for assessing the suitability of CPAP in the case of both demand-valve systems and continuous flow systems. Appropriate assessment criteria have been worked out; the course of the test and the results for two ventilators are discussed as an example, using these criteria.