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Session: Poster session 2 (Odd numbers)
Session starts: Friday 27 January, 10:00
Presentation starts: 10:00

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Maartje Leemans (Netherlands Cancer Institute - Antoni van Leeuwenhoek)
Maarten van Alphen (Netherlands Cancer Institute - Antoni van Leeuwenhoek)
Wim Vallenduuk (Netherlands Cancer Institute - Antoni van Leeuwenhoek)
Richard Dirven (Netherlands Cancer Institute - Antoni van Leeuwenhoek)
Michiel van den Brekel (Netherlands Cancer Institute - Antoni van Leeuwenhoek)
Saar Muller (Netherlands Cancer Institute - Antoni van Leeuwenhoek)

Abstract:
Background: Small passive Heat and Moisture Exchangers (HMEs) are standard treatment for pulmonary rehabilitation after a total laryngectomy. These HMEs consists of a plastic cassette containing a foam material coated with hygroscopic salt (wet core), which acts as a condensation and evaporation surface. During each breathing cycle, part of the moisture from the exhaled air is stored on the wet core and used to humidify the inhaled air (water exchange). Currently, the passive HMEs’ performances are not as high as the upper airways before laryngectomy, and the influence of the HME design on its performance is difficult to predict. We developed a numerical HME model to improve the physical understanding and design of these small passive HMEs. Methods: The numerical HME model was implemented in Matlab 2020b (Mathworks Inc. USA). The physical processes inside the HME are described by four discrete physical equations for the conservation of mass and energy in the air and wet core. The HME model was tuned and verified with experimental data sets of the HME’s performance (water exchange and temperature data) at standardized tidal volumes and flows. Finally, the HME model was applied to HME design variations and environmental conditions outside the scope of the experimental data. Results: Verification of the model’s results to the experimental data shows that the tuned model yields reliable results. The physical understanding as found using the model leads to the following design recommendations: the mass wet core, determining the HME’s total heat capacity, is the driving factor of the HME’s performance. Increasing the HME’s diameter is an effective way to improve an HME as it yields a higher performance and lowers breathing resistance. Furthermore, the model simulations led us to the insight that hygroscopic HMEs are not passive but are actually “reactive” to its environmental conditions. Therefore, HMEs intended for use in warm or dry climates should contain more and those for use in cold humid climates less hygroscopic salt. Conclusions: The numerical HME model improves the physical understanding of small passive HME’s, predicts the HME’s performance and aids the developmental process towards better performing HMEs.