CONSTRUCTION OF LINEAR RESISTANCE UNITS FOR A MODEL LUNG

A description of the design, construction and performance of a linear resistance unit for a model lung required for testing lung ventilators in breathing machines is presented. The resistance elements comprise a sandwich of layers of stainless-steel mesh. Different resistances were obtained by altering the number of layers, the type of mesh, and the aperture of the mask. Three types of mesh were used, the coarsest was 2/80/1050 mesh with an effective pore size of 25 μm, the medium mesh was 165/1400 with an effective pore size of 16 μm and the finest mesh was 250/1400 with an effective pore size of 2 μm. Measurements of resistance were made at 23°C and at ambient atmospheric pressure (102.8 kPa) using dry air. The measured resistance of the lowest resistance unit deviates from the required value over the required flow range by less than ± 5 percent. The other resistances show similarly small deviations.