Effects of Heat and Moisture Exchangers Designed to Allow Aerosol Delivery on Airflow Resistance and Aerosol Deposition .Heat and moisture exchangers (HME) are passive devices that conserve a patient’s heat and moisture. To provide this conservation, our devices capture and retain the heat and moisture from a patient’s expired breath and then release it into the next inspired breath. HMEs thereby help create normal conditions in patient airways and lungs, reducing the risk of breathing complications.