Filtration Performances of Heat and Moisture Exchangers and Filters Against Viral Aerosols: Adaptation of a Wind Tunnel

Abstract

Background:

The exhaled breath of infected, mechanically ventilated patients poses an infection risk to health care workers. Proper expiratory gas filtration with heat and moisture exchanger filters (HMEF) or filters could reduce that phenomenon. Current laboratory means of assessing the filtration efficiency are limited to the use of monodisperse aerosols at a single humidity level and flow. This study aims to examine the filtration efficiency of various devices under simulated clinical conditions, namely against a broad range of particle sizes containing viruses at different levels of gas humidity and flow.

Methods:

A wind tunnel was adapted to evaluate the filtration efficiency of 4 devices (HME, HMEF, filters, and HEPA-HMEF) against viral aerosols. Bacteriophages PhiX174 and MS2 were used as a proxy for human viruses.

Results:

In general, particulate filtration was significantly increased under dry versus humid conditions and with low versus high flows (P < .05). The HEPA filter significantly outperformed all other devices under all tested conditions in filtration efficiency. Both HMEF and filter showed approximately a 1% decrease in absolute differences compared with the reference method (∼99% vs 99.99%). This difference could represent an emission of as many as 10² SARS-CoV-2 copies per hour by an ICU patient, which is enough to spread the infection.

Conclusions:

Accurate testing of filtration function has long gone unexamined, and in preparation for the next respiratory pandemic, better evaluation of devices that filter potentially dangerous pathogens is vital for health care professionals and systems. Standard filtration testing should be adapted to mimic the clinical usage of HMEs and filters.