Low-power wireless system for temperature and humidity monitoring in artificial ventilation

Artificial ventilators are commonly used with Passive Heat-Moisture Exchangers (HME) to warm and humidify the inspired air in order to ensure a proper conditioning of inspired gases to the artificially ventilated patients. However, different aspects potentially affect their performances and this change in performance should be analyzed in-vivo during HME operation. In this paper, a wireless measurement system is proposed for the monitoring of air temperature and humidity in-vivo. The system is composed by a measuring device connected to the ventilating tube near the HME and a reading device connected to a Personal Computer (PC). Each device integrates a wireless transmission via low-power Bluetooth module that allows limiting power consumption. For the measuring device, the calculated power consumption when all the on-board components are working is about 15 mA, permitting a continuous monitoring for about 5 days and 16 hours with a rechargeable Li-Ion battery of 2050 mAh. A first prototype was manufactured and tested in the laboratory. Then, this prototype was tested with a setup specially developed to simulate human breath. The tests were conduced changing the respiratory rate and minute volume. Preliminary results are reported showing interesting aspects, such as the warm-up time of the HME. Furthermore, the results shows a direct dependence of humidity loss on frequency-volume ratio requiring future investigations. Clinicians are expected to use this system in-vivo to identify the correlations between clinical issues and HME performances.