Abstract
Respiratory rate (RR) monitoring provides crucial information on the overall health condition of patients and a reliable, low cost RR monitor for normal hospital inpatient or home use would be of significant benefit. The proposed system measures light reflection from a Fibre Bragg Grating (FBG) located near, and the total reflection spectrum from a humidity sensing film deposited at, the tip of an optical fibre. Every breath causes a shift in the wavelength reflected from the FBG and intensity change in the overall reflection spectrum. The accuracy of different techniques is investigated in a two-part study with 15 healthy volunteers. In part 1, the participants’ respiration rate followed a handheld mobile application at 5, 12 and 30 breaths per minute with simultaneous measurement using the optical fibre system, thoracic impedance pneumography (TIP) and capnometry device (where possible). Two types of medical face masks and a nasal cannula with oxygen delivery rates were investigated. In part 2, participants wore an anaesthetic face mask and breathed at normal and low tidal volumes to evaluate whether low tidal volumes could be detected. The most accurate measurement of RR was through monitoring the Bragg wavelength shift (mean accuracy = 88.1%), followed by the intensity change at the Bragg wavelength (mean accuracy = 78.9%), capnometry (mean accuracy = 77.8%), area under the overall spectrum (mean accuracy = 65.4%) and TIP (mean accuracy = 43.1%). The Fibre-optic Respiratory Rate Sensor system (FiRRS) can differentiate between normal and low tidal volumes (p-value < 0.05) and demonstrated higher accuracy than capnometry measurement of end-tidal carbon dioxide in exhaled air. These latter two monitors measured RR more accurately than TIP. A comparable accuracy in the measurement of RR was obtained when the FiRRS was implemented in nasal cannula and face masks.
Highlights
Previous research has demonstrated that there is a significant incidence of respiratory failure (3.4%) in patients following surgical procedures under epidural, general and spinal anaesthetics [1]
Clinical measurement is still frequently carried out by intermittent manual counting of chest wall movement; research and developments of respiratory rate (RR) measurement approaches have been recently classified into three modalities [5]: (a) RR from other physiological signals such as in pulse oximetry or thoracic impedance pneumography (TIP) [6, 7]; (b) RR measurement based on respiratory movements such as with accelerometers and gyroscopes recordings [8], with application of either piezoresistive/piezoelectric elements [9, 10] or Fibre Bragg Grating (FBG) sensor array [11] attached to fabrics; (c) RR measurement based on airflow such as with technologies based on hygroscopic sensors [12] and where EtCO2 capnometry has been established as one of the clinical standards for RR monitoring [13, 14]
The narrow FBG peaks of the measurement FBG1 and reference FBG2 can be clearly observed along with a broader background signal reflected from the fibre tip
Summary
Previous research has demonstrated that there is a significant incidence of respiratory failure (3.4%) in patients following surgical procedures under epidural, general and spinal anaesthetics [1]. Obesity is one of the most important contributory factors in OSA and these patients are at a higher risk of a variety of postoperative complications including apnoeas [2]. Clinical measurement is still frequently carried out by intermittent manual counting of chest wall movement; research and developments of RR measurement approaches have been recently classified into three modalities [5]: (a) RR from other physiological signals such as in pulse oximetry or TIP [6, 7]; (b) RR measurement based on respiratory movements such as with accelerometers and gyroscopes recordings [8], with application of either piezoresistive/piezoelectric elements [9, 10] or Fibre Bragg Grating (FBG) sensor array [11] attached to fabrics; (c) RR measurement based on airflow such as with technologies based on hygroscopic sensors [12] and where EtCO2 capnometry has been established as one of the clinical standards for RR monitoring [13, 14]
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