Multi-sensitive FBG-based needle for both relative humidity and breathing rate monitoring

Clinical scenarios could be characterized by several adverse conditions. For this reason, it is important to ensure a safety interaction between medical equipment and patients. In this context, optical fiber-based technologies are becoming very popular because they are considered intrinsically safe and immune to electromagnetic interferences. Among them, Fiber Bragg Grating (FBG) sensors are gaining in importance for the monitoring of physiological parameters like breathing rate (BR), heart rate, and body temperature. Moreover, among many procedures, polymer functionalization of the fiber optic allows making FBG sensitive to chemical parameters, including: relative humidity (RH), pH, gas, and biomolecules. In this study, we investigated the possibility of using a FBG-based needle for monitoring both RH and BR during mechanical ventilation. Regarding RH estimation, we performed a qualitative analysis to assess if the probe is able to follow RH changes, during mechanical ventilation. The proposed systems experienced a Bragg wavelength shift of ~0.38 nm for RH changes from ~20% to ~90% and vice versa. The performance of the needle for BR estimation was investigated at different minute volumes (MV) and BR set by using the ventilator, covering the values used in the adult ventilation. The BR values estimated by the system were compared to the ones provided by the mechanical ventilator, and used as reference. The absolute value of the percentage errors $(\varepsilon _{\mathrm {e}\mathrm {r}\mathrm {r}}\%)$ was always lower than 3.7% (in the 90% of cases it was <1.8%).