Laboratory evaluation of heat and moisture exchangers. Assessment of the Draft International Standard (ISO/DIS 9360) in practice.

A lung model and test method in accordance with the ISO draft standard for evaluation of heat and moisture exchangers (HME's) was designed. The trial period was 24 h. The moisture-conserving ability of the HME was determined gravimetrically and the temperature performance was calculated from graphs obtained by temperature probes near the two ports of the HME. To determine the reproducibility of the test results, the model was used without an HME and with two HMEs from different manufacturers. The performance values obtained from all three series indicated that the reproducibility of the method was good. The difference between mean inspiration and mean expiration temperatures at the patient port (dTp) provides a useful, simple and reproducible measure of the HMEs' temperature performance. Based on these data, we suggest certain changes in the test procedures outlined in the proposed ISO draft standard.