Abstract
An array of optical fibre long period gratings (LPGs) has been demonstrated for biomedical application to monitor temperature and relative humidity (RH) changes in the air delivered by a mechanical ventilator operating in different modes. The LPG array consists of two gratings, where one was kept bare to monitor the temperature change and the second was modified with 10 layers of silica nanoparticles to measure relative humidity.A mesoporous film was deposited on the surface of an optical fibre LPG using the layer-by-layer method. The sensor was calibrated in a bench model against a commercially available temperature and relative humidity sensor and sensitivity of the sensor was 0.46 ± 0.01 nm/ oC and 0.53 nm/RH%, respectively.The tip of the sensor array was modified with reflection mirror and placed inside an endotracheal tube (ETT) and tested in typical clinical equipment to enable the in-situ real-time monitoring of humidity and temperature. Temperature and RH changes associated with the breathing frequency of 8 and 15 breaths per minute were successfully monitored using developed sensor array.
Highlights
Artificial ventilation via a tracheal tube is integral to critical care and anaesthesia [1]
We propose the simultaneous measurement of temperature and relative humidity (RH) of the air delivered by a mechanical ventilator in non-breathing and breathing modes using an long period gratings (LPGs) array
The attenuation band at ca. 679 nm for this grating period corresponds to the coupling of the core mode to the linearly polarized LP018 cladding mode, while two attenuation bands at ca 799 nm and 862 nm correspond to the coupling of the same LP019 cladding mode as LPG operates at the phase matching turning point (PMTP) [30,31]
Summary
Artificial ventilation via a tracheal tube is integral to critical care and anaesthesia [1]. Over 1 million endotracheal tubes (ETT) are placed in patients' tracheas annually in the UK to support artificial ventilation and/or protect the lungs from inhalation of blood or gastric contents. Around 2000 patients on Intensive Care Units (ICUs) in the UK are receiving artificial ventilation via ETTs, and annually around 20,000 patients require these devices in Emergency Departments [2]. Appropriate warming and humidification, is an important aspect of respiratory care in patients where normal nasal and oral passages have been bypassed by an ETT [4]. There is a correlation between humidification and ventilated associated pneumonia (VAP) risk. VAP is the device centred infection responsible for the largest number of deaths, around 100 K, and for €5.2bn hospital costs in Europe per annum [5]
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