AN EXPERIMENTAL SET-UP TO TEST HEAT-MOISTURE EXCHANGERS

Objectives: The purpose of this study was to build an experimental set -up to assess continuously the humidification, heating and resistance properties of heat-moisture exchangers (HMEs) under clinical condition s. Design: The experimental set-up consists of a patient model, measur ement systems and a ventilator. Setting: Surgical ICU, University Hosp ital of Rotterdam. Materials: A clinically used HME. Measurements and results: The air flow, pressure in the ventilation circuit, pressure d ifference over the HME, and partial water vapour pressure and temperat ure at each side of the HME were measured. The resistance, absolute hu midity, humidification efficiency and temperature difference at the pa tient side of the HME were calculated. Measurements were performed dur ing 24 h. The temperature output, humidity output and lung mechanics o f the patient model were similar to values found in mechanically venti lated patients. The measurement system was in agreement with the ISO d raft standard and was capable of measuring dynamic variation of water and heat exchange over the range of a clinically used ventilator setti ng. Conclusion: The experimental setup described is reliable for evalu ating HMEs and can also be used for future clinical evaluation of HMEs . The main advantages of this set-up over those described previously a re: (i) measurements of dynamic variations of water and heat exchange; (ii) on-line measurements of expiratory, as well as inspiratory resis tance.