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Wearable devices for physiological parameters monitoring are gaining broad acceptance due to their ease of use, comfortability, and reliability. Among all human joints, the knee joint is the most involved in day-to-day activities. Monitoring the knee joint movements may allow outlining an optimized and patient-specific rehabilitation process and may perform a quantitative assessment of the improvements made. In this work, we propose a washable and reusable wearable system based on a conductive textile for knee flexion-extension monitoring. We performed a biomechanical analysis to guide the design of the sensing element, to perform its metrological characterization, and to optimize its integration into a wearable knee guard. We tested the developed system on 5 healthy volunteers performing 3 different rehabilitation exercises in terms of number of flexion-extension performed and of the knee angle. This assessment was performed using a motion capture system as a reference. The results are promising and in good agreement with the reference system and enable the system to be suitable for its application in rehabilitation and day-to-day monitoring.

The presence of a large blood vessel in the proximity of tumor masses during microwave ablation (MWA) can compromise the procedure success. Blood vessels cause convective heat dissipation (i.e., heat sink effect, HSE) in the tissue surrounding the vessel. In this scenario, cytotoxic temperatures may not be achieved within the target area, resulting in ineffective cancer removal. In this paper, we investigated HSE in hepatic tissue from both an experimental and numerical perspective. MWA was performed mimicking two clinical scenarios (i.e., with and without a blood vessel near the heat source). Fiber Bragg grating sensors measured tissue temperature during the procedure, whereas numerical simulations were carried out to evaluate temperature distribution theoretically. Temperature profiles obtained by simulations and experiments confirmed the influence of HSE with a significant cooling effect nearby the vessel. The proposed approach allowed to quantify the HSE impact on MWA outcomes, laying the foundations for optimizing the treatment parameters in terms of ablated volume and malignant cells destruction.

There is a growing demand of comfortable and unobtrusive wearable systems for monitoring a variety of physiological parameters and in particular the respiratory frequency ( ${f}_{R}$ ). The most popular techniques for ${f}_{R}$ monitoring cannot be used in several clinical applications and in unstructured environment. These issues have fostered a dramatic growth of interest for wearable systems devoted to monitor ${f}_{R}$ . In this arena, fiber Bragg grating (FBG) sensors have gained due to a variety of benefits. In this work, we designed and fabricated an FBG-based wearable device for ${f}_{R}$ monitoring from the nasal airflow. The proposed design does not require a mask to improve the comfortability and acceptability of the system. The sensing element was functionalized by a hygroscopic coating material to make the FBG sensitive to relative humidity changes. This feature allows calculating ${f}_{R}$ starting from the discrimination between the inspiration and expiration phases. A pilot study on 6 volunteers was designed to assess the system during three different breathing stages (i.e., slow, normal and fast breathing). Results showed high performance of the proposed wearable device in detecting mean and breath-by-breath ${f}_{R}$ values (i.e., mean percentage errors ≤ 2.29 % and bias ≤ 0.31 breaths per minute) during slow breathing, normal breathing, and fast breathing.

Systems for cardiorespiratory monitoring hold tremendous promise for many applications in clinical settings, harsh environments, sports science and telemonitoring. However, the translation in the real world is challenging because it is difficult to develop unobtrusive and comfortable systems with high metrological performance. Recent advances in fiber optic technology in the field of sensing and their application to instrument wearable systems can tackle the main issues in this field. In this work, we focused on the recent advances in cardiorespiratory monitoring of fiber Bragg grating (FBGs) sensors which are one of the most popular sensors based on fiber optic technology. We provide an overview of the FBGs working principle and performance. We also describe the most popular and promising configurations based on FBGs used for cardiorespiratory monitoring.

Workers experiencing high levels of stress may suffer from poor motivation, low level of attention, and physical disorders which, in turn, may lead to work injuries. Respiratory frequency (fR) is considered one of the most reliable indicators of the mental load and fatigue state of workers. Monitoring this parameter through wearable devices represents an efficient solution for the maintenance of Occupational Health and Safety. We developed an innovative wearable system equipped with flexible sensors based on fiber Bragg gratings (FBGs) to monitor fR in static and dynamic conditions characterizing occupational settings. This article provides a description of the system and of the metrological characteristics of the flexible sensors in terms of response to strain and temperature changes, and hysteresis error. The performances of the device, evaluated in a laboratory during the execution of tasks mimicking real work activity, are also reported. The obtained promising results encourage the engineering of the system for use in real workplaces to collect quantitative information on the psychophysical state of workers and its relation to stress level.

Temperature monitoring inside tissue undergoing minimally invasive thermal ablation is a primary goal to improve the clinical outcomes. Existing techniques for temperature measurements, classified as invasive or contactless, have limited clinical practice applications due to several practical issues. Fiber Bragg grating sensors (FBG) can be a valid solution since they can perform accurate and multi-point temperature measurements by inserting a single and small fiber optic within the tissue. Notwithstanding, their cross-sensitivity to strain may cause measurement errors during thermal procedures. Indeed, several organs (e.g., lungs, liver, pancreas) can strain gratings due to movements caused by breathing. To date, only a few studies have specifically addressed this concern, despite the wide use of FBGs in this field. To overcome this lack, we estimated the artefact of the FBGs output in response to lungs’ movements induced by breathing. This investigation was carried out by inserting FBGs within a manually ventilated lung model ( ex vivo swine lungs). We measured both the lungs’ movements during breathing by a Motion Capture system and the related fluctuations of the FBGs’ output. Moreover, we performed the same experiments during thermal ablation of lungs to assess the mentioned artefact’s influence. In this study, we demonstrated the relevance of the respiratory artefact on FBGs, and also the possibility to correct this error during thermal ablation.

Recent advances in understanding the importance of respiratory frequency ( ${ f}_{ R}$ ) as a sensitive marker of a variety of physiopathological stressors are fostering growing interest in respiratory monitoring. This interest is further stimulated by the ever-increasing efforts that companies are devoting to the development of systems measuring ${ f}_{ R}$ . There are a variety of techniques based on different sensors and technologies for ${ f}_{ R}$ monitoring. These techniques are commonly classified as contact-based or contactless, depending on whether the system which embeds the sensor is in contact with the body or not. This review is focused on the contactless methods for ${ f}_{ R}$ monitoring. We have introduced the main fields of use where contactless respiratory monitoring is important and provided a taxonomy to classify the most popular contactless techniques for ${ f}_{ R}$ monitoring. Finally, we have described the performances of the most popular methods, the main open challenges, and the main perspectives.

This paper investigates the performances of a head-mounted wearable device for the breath-by-breath monitoring of respiratory frequency ( ${f}_{{R}}$ ) during exercise. The device exploits a new algorithm to estimate ${f}_{{R}}$ from the breathing-related pressure drops ( ${\Delta } {P}$ ) recorded at the nostrils level. Performances of the wearable device in measuring the breath-by-breath and 30-s average ${f}_{{R}}$ values were evaluated during two high-intensity cycling exercise tests performed in the laboratory. ${\Delta } {P}$ signals were collected from ten volunteers with the wearable device, and the simultaneous measurements with a reference instrument were performed for validation purposes. In addition, numerical simulations were carried out to reproduce the conditions expected in applied settings. Bland–Altman analysis, linear regression ( ${r}^{2}$ ), and percentage error (% $E$ ) were used for comparing the two instruments. Experimental tests demonstrate the robustness and validity of the proposed wearable device and the related algorithm to measure the breath-by-breath ${f}_{R}$ (overall $\%{E} = {4.03\%}$ ) and 30-s average ${f}_{R}$ (overall ${\%E} = {2.38\%}$ ) values. Biases obtained with the breath-by-breath analysis (max. −0.06 ± 6.27 breaths/min) were higher than those obtained in the 30-s window analysis (max. −0.03 ± 1.60 breaths/min). In the simulated conditions, $\%E$ increased up to 6.65%. The proposed wearable device is suitable for a wide variety of indoor applications where the ${f}_{R}$ monitoring during exercise at reduced invasiveness is of great value.

The importance of humidity control is spreading through a broad spectrum of applications, from food and pharmaceutical industries to biomedical and chemical fields. During the last decades, the growing interest in fiber Bragg gratings (FBG) led to new approaches and applications for the humidity measurement by means of the deposition of hygroscopic materials on gratings. The influence of the coating material and its features such us coating thickness (tk) and concentration (wt%) on static and dynamic metrological properties have been investigated in this paper. In this paper, four agar-coated FBG sensors for humidity measurements have been fabricated, and the influence of tk and wt% on the sensors’ sensitivity and response time has been experimentally assessed. Sensitivity increases with tk and wt%: for instance, at 1 wt% it was $0.0024\,\,\text {nm}\cdot {\%}^{\mathrm {-1}}$ and $0.0052\,\,\text {nm}\cdot {\%}^{\mathrm {-1}}$ for $\text {tk}=87\,\,\mu \text{m}$ and $\text {tk} = 212\,\,\mu \text{m}$ , respectively. Results showed that also the response time increased with tk and wt%: for instance, at 1 wt% it was 56.7 s and 107.6 s for $\text {tk} = 87\,\,\mu \text{m}$ and $\text {tk}=212\,\,\mu \text{m}$ , respectively.

This work aims at selecting the number and the body location of piezoresistive sensors to instrument wearable systems for respiratory rate (RR) estimation. We tested a novel method based on Principal Component Analysis on 10 healthy male subjects, who were asked to perform six trials on a treadmill (at rest, during walking and low speed running). We monitored RR using both a smart garment composed of six piezoresistive sensors and a flowmeter, used as reference signal. On the basis of the results, we propose the following guidelines: i) breathing assessment at rest requires one sensor, placed on the lower thorax; ii) low speed walking assessment requires three sensors, placed on upper thorax, lower thorax and abdomen; iii) high speed walking and running assessment requires a four-sensor configuration (one sensor placed on the upper thorax, one on the lower thorax and two on the abdomen); iv) an effective assessment can be performed at all speeds using the above-mentioned four-sensor configuration, denoted as General Purpose Configuration.

A review of the current status of humidity sensors based on optical fiber gratings (OFGs) is presented. Humidity monitoring and its control are gaining importance in several fields including industrial processes and health. This review aims at giving an overview of the major developments over the last decades and categorizing the recent progress in humidity sensors based on the OFGs functionalization. This review describes the measurement principle of these sensors, their metrological properties, the materials used to functionalize OFGs, and the factors which influence the sensors’ response.

Fiber Bragg grating (FBG) sensors have gained popularity in medicine for some valuable features, such as small size, immunity to electromagnetic interferences, and good metrological properties. Among several applications, this technology has been used in the analysis of gases in mechanical ventilation. In this field, in particular during invasive ventilation, the gas delivered by the ventilator must be warmed and humidified in order to reach the patients with optimal conditions (100% of relative humidity and 37 °C). The most popular device used to accomplish this task is the heated wire humidifiers (HWHs). Unfortunately, their performances are influenced by ventilatory settings (e.g., respiratory frequency) and environmental conditions. The aim of this paper is to fabricate a probe based on an FBG sensor able to monitor both the gas relative humidity and the respiratory frequency. This information can be used as a feedback to improve the performance of the HWHs. The probe consists of a needle, which houses an FBG sensor coated by hygroscopic material (i.e., agar). This solution allows an easy insertion of the probe within the ducts connecting the ventilator to the patient. The proposed system has been assessed during mechanical ventilation at different respiratory frequencies. Future testing will be focused on the development of a system able to monitor other parameters that influence the HWHs performances (e.g., gas temperature and minute volume).

Hyperthermal techniques are spreading as an alternative to conventional surgery for cancer removal. A real-time temperature feedback can be used to adjust the treatment settings, in order to improve the clinical outcomes. In this paper, we experimentally assessed the feasibility for distributed temperature monitoring of a custom probe, which consists of a needle embedding six fiber Bragg gratings (FBGs). Since FBGs are also sensitive to strain, we focused on the analysis of the measurement error (artifact) caused by respiratory movements. We assessed the artifact both on ex vivo pig liver and lung (by mimicking the movement of these organs caused by respiration) and on in vivo trial on pig liver. Lastly, we proposed an algorithm to detect and minimize the artifact during ex vivo liver laser ablation. During both ex vivo and in vivo trials, the probe insertion within the organ was easy and safe. The artifact was significant (up to 3 °C), but the correction algorithm allows minimizing the error. The main advantages of the proposed probe are: 1) spatially resolved temperature monitoring (in six points of the tissue by inserting a single needle) and 2) the needle is magnetic resonance (MR)-compatible, hence can be used during MR-guided procedure. Even if the model is close to humans, further trials are required to investigate the feasibility of the probe for clinical applications.