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. 2021 Sep 28;21(19):6469. doi: 10.3390/s21196469

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© 2021 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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(a) Fibre-optic respiratory rate sensor (FiRRS) system, including a laser diode (SLD), spectrometer (I-MON 512USB), optical circulator, recording laptop and fibre-optic respiratory rate sensor enclosed within a 21-gauge hypodermic needle polished at the tip. (b) Integration of the sensing probe into (left) CO₂ mask (with EtCO₂ capnometry), (middle) nasal cannula and (right) non-rebreathe trauma mask. The image and caption were adapted from their original created by Sinha et al. [47] under a Creative Commons Attribution 4.0 Unsorted license.