Experimental measurements of particle retention efficiency of filters used to prevent contamination in respiratory devices

Objective: Various types of filters have been designed to prevent cross contamination of ventilation and respiratory devices. The aim of this study was to experimentally measure the retention efficiency of four simple filters (antibacterial and antivirial and seven combined filters (antibacterial and antiviral plus heat and water exchangers). Setting: The respiratory function testing (EFR) central department of a university teaching hospital. Measurements and results: The same aerosol test with a wide range of particle sizes (0.15 to 15 micrometers) was used to compare the retention efficiency of each filter used in various conditions. The particle sizes and the concentration of the aerosol were measured by a laser velocimeter. For all the filters studied, the retention efficiency was found to be higher than 99 %, However some of them let large particles let through. Conclusion: These data, performed in vitro, should be assessed also by further clinical studies.