Essay of any ventilators by means of a pulmonary model with adjustable resistance, compliance and vital capacity.

After a critical study of classic lung models, showing that linear resistances are not faithful nor justified and that pneumotachograph is not a good measuring apparatus because of its inaccuracy (it changes calibration according to the nature of gas mixture and needs integration to determine volumes), authors present their own lung "model". In this model, it is possible to adjust resistance, compliance, vital capacity and residual volume. Parabolic resistances are used, because they more approach physiologic ones. Building of resistances (diaphragms), compliances (rigid tanks with adjustable elements), vital capacity (elastic membrane between two grills) is simple to realise and easy to reproduce. Measures of pressure and volume are given directly by gauges and are insensitive to gas nature, which is important in respiratory physiology. Flow-rates are deducted from volume values. The lung model can be used in a twin-cell shape to show the effects of artificial ventilation in case of pulmonary asymmetry. Examples given underline the interest of having a model with resistances easy to build and an adjustable vital capacity.