A novel target-type low pressure drop bidirectional optoelectronic air flow sensor for infant artificial ventilation: measurement principle and static calibration

Wearable textile based on silver plated knitted sensor for respiratory rate monitoring

Wearable systems are gaining broad acceptance for monitoring physiological parameters in several medical applications. Among a number of approaches, smart textiles have attracted interest because they are comfortable and do not impair patients' movements. In this article, we aim at developing a smart textile for respiratory monitoring based on a piezoresistive sensing element. Firstly, the calibration curve of the system and its hysteresis have been investigated. Then, the proposed system has been assessed on 6 healthy subjects. The volunteers were invited to wear the system to monitor their breathing rate. The results of the calibration show a good mean sensitivity (i.e., approximately 0.11V·%^-1); although the hysteresis is not negligible, the system can follow the cycles also at high rates (up to 36 cycle·min^-1). The feasibility assessment on 6 volunteers (two trials for each one) shows that the proposed system can estimate with good accuracy the breathing rate. Indeed, the results obtained by the proposed system were compared with the ones collected with a spirometer, used as reference. Considering all the experiments, a mean percentage error was approximately 2%. In conclusion, the proposed system has several valuable features (e.g., the sensing element is lightweight, the sensitivity is high, and it is possible to develop comfortable smart textile); in addition, the promising performances considering both metrological properties and assessment on volunteers foster future tests focused on: i) the possibility of developing and system embedding several sensing elements, and ii) to develop a wireless acquisition system, to allow comfortable and long-term acquisition in both patients and during sport activities.

Contact-Based Methods for Measuring Respiratory Rate

There is an ever-growing demand for measuring respiratory variables during a variety of applications, including monitoring in clinical and occupational settings, and during sporting activities and exercise. Special attention is devoted to the monitoring of respiratory rate because it is a vital sign, which responds to a variety of stressors. There are different methods for measuring respiratory rate, which can be classed as contact-based or contactless. The present paper provides an overview of the currently available contact-based methods for measuring respiratory rate. For these methods, the sensing element (or part of the instrument containing it) is attached to the subject's body. Methods based upon the recording of respiratory airflow, sounds, air temperature, air humidity, air components, chest wall movements, and modulation of the cardiac activity are presented. Working principles, metrological characteristics, and applications in the respiratory monitoring field are presented to explore potential development and applicability for each method.

Temperature influence on the response at low airflow of a variable orifice flowmeter

In mechanical ventilation, in particular when neonates are ventilated, it is crucial to accurately control the amount of the gas delivered to the patients. Mechanical ventilators are equipped with one of more flowmeters. The signal of the flowmeter is used as feedback to control the amount of gas delivered to the patients. Therefore, the accuracy of the flowmeter plays a crucial role in the accurate adjustment of the gas amount delivered by the ventilator. Among several solutions, variable area orifice meters (VAOMs) have several valuable features (e.g., good accuracy, and adequate frequency response), moreover they have the main advantage, with respect to orifice meters, related to the linearity of the response. Despite of their spread in this field, there are not studies focused on the analysis of the air temperature influence on VAOMs response. This study focuses on this topic by investigating the gas temperature influence on the response of a commercial VAOM. Experiments have been performed at low airflow (up to 1.5 L·min^-1) and at four different temperatures (i.e., from 22°C to 38°C) covering the range of interest in the field of artificial ventilation. Results show that the response of the VAOM under test is sensitive to temperature: at constant airflow the higher the temperature the higher the sensor output. This analysis may be useful to add correction to sensor output in order to reject the influence of temperature, so to minimize the measurement error due to this factor.

Development and calibration of an air-floating six-axis force measurement platform using self-calibration

This paper describes the design, working principle, as well as calibration of an air-floating six-axis force measurement platform, where the floating plate and nozzles were connected without contact, preventing inter-dimensional coupling and increasing precision significantly. The measurement repeatability error of the force size in the platform is less than 0.2% full scale (FS), which is significantly better than the precision of 1% FS in the six-axis force sensors on the current market. We overcame the difficulties of weight loading device in high-precision calibration by proposing a self-calibration method based on the floating plate gravity and met the calibration precision requirement of 0.02% FS. This study has general implications for the development and calibration of high-precision multi-axis force sensors. In particular, the air-floating six-axis force measurement platform could be applied to the calibration of some special sensors such as flexible tactile sensors and may be used as a micro-nano mechanical assembly platform for real-time assembly force testing.

Theoretical and Experimental Study on Wide Range Optical Fiber Turbine Flow Sensor

In this paper, a novel fiber turbine flow sensor was proposed and demonstrated for liquid measurement with optical fiber, using light intensity modulation to measure the turbine rotational speed for converting to flow rate. The double-circle-coaxial (DCC) fiber probe was introduced in frequency measurement for the first time. Through the divided ratio of two rings light intensity, the interference in light signals acquisition can be eliminated. To predict the characteristics between the output frequency and flow in the nonlinear range, the turbine flow sensor model was built. Via analyzing the characteristics of turbine flow sensor, piecewise linear equations were achieved in expanding the flow measurement range. Furthermore, the experimental verification was tested. The results showed that the flow range ratio of DN20 turbine flow sensor was improved 2.9 times after using piecewise linear in the nonlinear range. Therefore, combining the DCC fiber sensor and piecewise linear method, it can be developed into a strong anti-electromagnetic interference(anti-EMI) and wide range fiber turbine flowmeter.

A micro opto-mechanical displacement sensor based on micro-diffraction gratings: design and characterization

A micro opto-mechanical displacement sensor is here presented. It is constituted by a sensing element based on two overlapped micro-diffraction gratings (MDGs). They present a platinum layer (45 nm of thick) on a glass substrate, a period of 525 µm constituted by a width of 150 µm of platinum separated (71.4% duty cycle). The working principle is based on the modulation of light intensity induced by the relative displacement between the MDGs: when a laser light perpendicularly hits the MDGs, the intensity of the transmitted light is a periodic function of the relative displacement between the two MDGs. A fiber optic is used to transport the transmitted light to a photodetector in order to avoid concerns related to the alignment between the optical components. The sensor's output is the ratio between the light intensity measured by the photodetector during the displacement of the MDGs and largest light intensity values measured in the whole range of measurement, therefore, it is lower than 1. The proposed sensor allows to discriminate displacement lower than 10 µm, using a cost effective micro-fabrication process implemented by the technique of Lift-Off. It shows a good linear behaviour in two ranges covering about one half of the MDGs period. Within the linear ranges it shows high sensitivity (about 0.5%/µm) and good accuracy (lower than 4% in the whole range of calibration); furthermore, the results show that a design with a duty cycle of 50% overcomes the marked decrease of sensitivity in a range of measurement corresponding to a grating period.

Influence of FBG sensors length on temperature measures in laser-irradiated pancreas: theoretical and experimental evaluation

Temperature distribution T(x,y,z,t) in tissue undergoing Laser-induced Interstitial Thermotherapy (LITT) plays a crucial role on treatment outcome. Theoretical and experimental assessment of temperature on ex vivo laser-irradiated pancreas is presented. The aim of this work is to assess the influence of thermometers dimensions on temperature measures during LITT. T(x,y,z,t) inside tissue is monitored by optical sensors, i.e., Fiber Bragg Gratings (FBGs): three FBGs with lengths of 10 mm and nine FBGs of 1 mm, at different distances (2 mm, 5 mm and 10 mm) and different quotes (0 mm, 2 mm and 4 mm) from the laser fiber tip are used. Theoretical punctual T(x,y,z,t) is averaged out on both 10 mm and 1 mm in order to compare numerical predictions with experimental data. Results demonstrate the influence of FBG length on T(x,y,z,t) measures. This phenomenon depends on the distance between sensor and applicator: it is particularly significant close to the applicator tip (2 mm) because of the high spatial T(x,y,z,t) gradient within the tissue. Both theoretical results and experimental ones show that just at a distance of 10 mm from the tip, differences between T(x,y,z,t) provided by FBGs of 10 mm and 1 mm are negligible.

Medical smart textiles based on fiber optic technology: an overview

The growing interest in the development of smart textiles for medical applications is driven by the aim to increase the mobility of patients who need a continuous monitoring of such physiological parameters. At the same time, the use of fiber optic sensors (FOSs) is gaining large acceptance as an alternative to traditional electrical and mechanical sensors for the monitoring of thermal and mechanical parameters. The potential impact of FOSs is related to their good metrological properties, their small size and their flexibility, as well as to their immunity from electromagnetic field. Their main advantage is the possibility to use textile based on fiber optic in a magnetic resonance imaging environment, where standard electronic sensors cannot be employed. This last feature makes FOSs suitable for monitoring biological parameters (e.g., respiratory and heartbeat monitoring) during magnetic resonance procedures. Research interest in combining FOSs and textiles into a single structure to develop wearable sensors is rapidly growing. In this review we provide an overview of the state-of-the-art of textiles, which use FOSs for monitoring of mechanical parameters of physiological interest. In particular we briefly describe the working principle of FOSs employed in this field and their relevant advantages and disadvantages. Also reviewed are their applications for the monitoring of mechanical parameters of physiological interest.

Flow measurement in mechanical ventilation: a review

Accurate monitoring of flow rate and volume exchanges is essential to minimize ventilator-induced lung injury. Mechanical ventilators employ flowmeters to estimate the amount of gases delivered to patients and use the flow signal as a feedback to adjust the desired amount of gas to be delivered. Since flowmeters play a crucial role in this field, they are required to fulfill strict criteria in terms of dynamic and static characteristics. Therefore, mechanical ventilators are equipped with only the following kinds of flowmeters: linear pneumotachographs, fixed and variable orifice meters, hot wire anemometers, and ultrasonic flowmeters. This paper provides an overview of these sensors. Their working principles are described together with their relevant advantages and disadvantages. Furthermore, the most promising emerging approaches for flowmeters design (i.e., fiber optic technology and three dimensional micro-fabrication) are briefly reviewed showing their potential for this application.

A transistors-based, bidirectional flowmeter for neonatal ventilation: design and experimental characterization

A bidirectional, low cost flowmeter for neonatal artificial ventilation, suitable for application in mono-patient breathing circuits, is described here. The sensing element consists of two nominally identical bipolar junction transistors employed as hot bodies. The sensor working principle is based on the convective heat transfer between the transistors, heated by Joule phenomenon, and the colder hitting fluid which represents the measurand. The proposed design allows the sensor to discriminate flow direction. Static calibration has been carried out in a range of flowrate values (from -8 L·min(-1) up to +8 L L·min(-1)) covering the ones employed in neonatal ventilation, at different pipe diameters (ie., 10 mm and 30 mm) and collector currents (i.e., 500 mA, 300 mA, and 100 mA) in order to assess the influence of these two parameters on sensor's response. Results show that the configuration with a pipe diameter of 10 mm at the highest collector current guarantees the highest sensitivity (i.e., 763 mV/Lmin1 at low flowrate ± 1 L-min(-1)) and ensures the minimum dead space (2 mL vs 18 mL for 30 mm of diameter). On the other hand, the 30 mm pipe diameter allows extending the range of measurement (up to ±6 L-min 1 vs ±3.5 L· min(-1) at 10 mm), and improving both the discrimination threshold (<;0.1 L·min-(1)) and the symmetry of response. These characteristics together with the low dead space and low cost foster its application to neonatal ventilation.

Design, development and experimental validation of a non-invasive device for recording respiratory events during bottle feeding

In newborns, a poor coordination between sucking, swallowing and breathing may undermine the effectiveness of oral feeding and signal immaturity of Central Nervous System. The aim of this work is to develop and validate a non-invasive device for recording respiratory events of newborns during bottle feeding. The proposed device working principle is based on the convective heat exchanged between two hot bodies and the infants' breathing. The sensing elements are inserted into a duct and the gas exchanged by infants is conveyed into this duct thanks to an ad hoc designed system to be mounted on a commercial feeding bottle. Two sets of experiments have been carried out in order to investigate the discrimination threshold of the device and characterize the sensor response at oscillating flows. The effect of distance and tilt between nostrils and device, and the breathing frequency, have been investigated simulating nostrils and neonatal respiratory pattern. The device has a discrimination threshold lower than 0.5 L/min at both 10° and 20° of tilt. Distance for these two settings does not affect the threshold in the investigated range (10-20 mm). Moreover, the device is able to detect breathing events, and to discriminate the onset of expiratory phase, during a neonatal respiratory task delivered by a lung simulator. The results foster the successful application of this device to the assessment of the temporal breathing pattern of newborns during bottle feeding with a non-invasive approach.

An air flow sensor for neonatal mechanical ventilation applications based on a novel fiber-optic sensing technique

In this work, a simple and low-cost air flow sensor, based on a novel fiber-optic sensing technique has been developed for monitoring air flows rates supplied by a neonatal ventilator to support infants in intensive care units. The device is based on a fiber optic sensing technique allowing (a) the immunity to light intensity variations independent by measurand and (b) the reduction of typical shortcomings affecting all biomedical fields (electromagnetic interference and patient electrical safety). The sensing principle is based on the measurement of transversal displacement of an emitting fiber-optic cantilever due to action of air flow acting on it; the fiber tip displacement is measured by means of a photodiode linear array, placed in front of the entrance face of the emitting optical fiber in order to detect its light intensity profile. As the measurement system is based on a detection of the illumination pattern, and not on an intensity modulation technique, it results less sensitive to light intensity fluctuation independent by measurand than intensity-based sensors. The considered technique is here adopted in order to develop two different configurations for an air flow sensor suitable for the measurement of air flow rates typically occurring during mechanical ventilation of newborns: a mono-directional and a bi-directional transducer have been proposed. A mathematical model for the air flow sensor is here proposed and a static calibration of two different arrangements has been performed: a measurement range up to 3.00 × 10(-4) m(3)∕s (18.0 l∕min) for the mono-directional sensor and a measurement range of ±3.00 × 10(-4) m(3)∕s (±18.0 l∕min) for the bi-directional sensor are experimentally evaluated, according to the air flow rates normally encountered during tidal breathing of infants with a mass lower than 10 kg. Experimental data of static calibration result in accordance with the proposed theoretical model: for the mono-directional configuration, the coefficient of determination r(2) is equal to 0.997; for the bi-directional configuration, the coefficient of determination r(2) is equal to 0.990 for positive flows (inspiration) and 0.988 for negative flows (expiration). Measurement uncertainty δQ of air flow rate has been evaluated by means of the propagation of distributions and the percentage error in the arrangement of bi-directional sensor ranges from a minimum of about 0.5% at -18.0 l∕min to a maximum of about 9% at -12.0 l∕min.

A high sensitivity fiber optic macro-bend based gas flow rate transducer for low flow rates: theory, working principle, and static calibration

A novel fiber optic macro-bend based gas flowmeter for low flow rates is presented. Theoretical analysis of the sensor working principle, design, and static calibration were performed. The measuring system consists of: an optical fiber, a light emitting diode (LED), a Quadrant position sensitive Detector (QD), and an analog electronic circuit for signal processing. The fiber tip undergoes a deflection in the flow, acting like a cantilever. The consequent displacement of light spot center is monitored by the QD generating four unbalanced photocurrents which are function of fiber tip position. The analog electronic circuit processes the photocurrents providing voltage signal proportional to light spot position. A circular target was placed on the fiber in order to increase the sensing surface. Sensor, tested in the measurement range up to 10 l min(-1), shows a discrimination threshold of 2 l min(-1), extremely low fluid dynamic resistance (0.17 Pa min l(-1)), and high sensitivity, also at low flow rates (i.e., 33 mV min l(-1) up to 4 l min(-1) and 98 mV min l(-1) from 4 l min(-1) up to 10 l min(-1)). Experimental results agree with the theoretical predictions. The high sensitivity, along with the reduced dimension and negligible pressure drop, makes the proposed transducer suitable for medical applications in neonatal ventilation.