Fiber-Optic Flow Sensor for the Measurement of Inspiratory Efforts in Mechanical Neonatal Ventilation
A novel fiber-optic flow sensor has been developed for monitoring inspiratory efforts during neonatal mechanical ventilation. The considered sensor is based on fiber-optic sensing techniques, allowing the reduction of the effects due to electromagnetic in
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Introduction
Measurements of air flow rate in neonatal mechanical ventilation are carried out mainly for monitoring air flows supplied by a mechanical ventilator to support infants in intensive care units and for the evaluation of lung ventilator performances [1–4]. Flow measurements in infant mechanical ventilation are typically performed by means of electrical and electromagnetic sensors [5, 6] that are exposed to errors due to electromagnetic interferences. The reduction of the above-quoted shortcomings, achieved by means of fiber-optic sensing techniques, is widely reported in scientific literature and is due to optical fiber features, i.e., immunity to electromagnetic interferences and electrical insulation allowing the improvement of electrical safety conditions [7–9]. By the way, even if various optical fiber sensors have been proposed, it is difficult to find an exhaustive investigation on the design and testing of optical fiber air flow meters in mechanical ventilation applications.
L. Battista (*) Department of Engineering, University of Rome “ROMA TRE”, Via della Vasca Navale 79/81, 00146 Rome, Italy CNR – National Institute of Optics, Via Campi Flegrei 34, 80078 Pozzuoli, NA, Italy e-mail: [email protected] A. Scorza • S.A. Sciuto Department of Engineering, University of Rome “ROMA TRE”, Via della Vasca Navale 79/81, 00146 Rome, Italy 453 C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_87, © Springer International Publishing Switzerland 2014
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Materials and Methods
In former works [10, 11], authors proposed a fiber-optic air flow sensor based on an arrangement that provides immunity to light intensity variations not related to the air flow, developed for monitoring air flows supplied by a neonatal ventilator to support infants in intensive care units. The principle of operation of the proposed sensor is based on the measurement of transversal displacement of an emitting fiber-optic cantilever due to action of air flow acting on it, performed by means of a photodiode linear array. The aforementioned transducer can detect air flow rates up to 18.0 l/min (i.e., flow rates normally encountered during neonatal ventilation in infants [12]); nevertheless, the minimum detectable air flow rate is 2.0 l/min, in monodirectional configuration, and 3.0 l/min in bidirectional configuration, due to resolution of the photodiode array. The poor lower limit of measurement range and resolution at low flow rates implies that the considered flow sensor cannot discriminate flow variations in the range between 0.5 l/min and 5 l/min that are the typical flow trigger levels set during assist-control ventilation (ACV) [13], i.e., a ventilation mode used when a patient is able to initiate breaths but requires ventilatory assistance. In order to reduce the minimum detectable flow allowing the measurement of air flow rates lower th
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