A capaciflector provides continuous and accurate respiratory rate monitoring for patients at rest and during exercise

Abstract

Respiratory rate (RR) is a marker of critical illness, but during hospital care, RR is often inaccurately measured. The capaciflector is a novel sensor that is small, inexpensive, and flexible, thus it has the potential to provide a single-use, real-time RR monitoring device. We evaluated the accuracy of continuous RR measurements by capaciflector hardware both at rest and during exercise. Continuous RR measurements were made with capaciflectors at four chest locations. In healthy subjects (n = 20), RR was compared with strain gauge chest belt recordings during timed breathing and two different body positions at rest. In patients undertaking routine cardiopulmonary exercise testing (CPET, n = 50), RR was compared with pneumotachometer recordings. Comparative RR measurement bias and limits of agreement were calculated and presented in Bland-Altman plots. The capaciflector was shown to provide continuous RR measurements with a bias less than 1 breath per minute (BPM) across four chest locations. Accuracy and continuity of monitoring were upheld even during vigorous CPET exercise, often with narrower limits of agreement than those reported for comparable technologies. We provide a unique clinical demonstration of the capaciflector as an accurate breathing monitor, which may have the potential to become a simple and affordable medical device.Clinical trial number: NCT03832205 https://ichgcp.net/clinical-trials-registry/NCT03832205 registered February 6th, 2019.

Keywords: Capaciflector; Critical care; Perioperative medicine; Respiratory monitoring; Respiratory rate; Sensor.

Conflict of interest statement

NH is a part-time advisor to Klinik Healthcare Solutions, UK. MG is vice-president of CPX International. He also serves on the medical advisor board of Sphere Medical Ltd and the board of EBPOM Community Interest Company, Medinspire Ltd and Oxygen Control Systems Ltd. He has received honoraria for speaking for and/or travel expenses from BOC Medical (Linde Group), Edwards Lifesciences and Cortex GmBH and unrestricted research support from Sphere Medical Ltd and Pharmacosmos Ltd. He leads the Fit-4-Surgery research collaboration and the Xtreme Everest oxygen research consortium, which has received unrestricted research grant funding from BOC Medical (Linde Group), Deltex Medical and Smiths Medical. MG was funded in part from the British Oxygen Company Chair of the Royal College of Anaesthetists awarded by the National Institute of Academic Anaesthesia. All funding was unrestricted. The funders had no role in study design, data collection and analysis, decision to publish or the preparation of the manuscript. This work was conducted within the Anaesthesia and Critical Care Research Unit, University Hospital Southampton and the School of Electronics and Computer Science, University of Southampton, as a primary research collaboration.

© 2022. The Author(s).

Figures

Fig. 1

The capaciflector as a respiratory rate (RR) sensor. A: Photograph showing one printed capaciflector sensor on fabric, with a 20 pence coin added for scale. B: Diagram showing the structure of the capaciflector that detects changes in capacitance as the thorax moves, providing the sensor signal. C: Example of the sensor signal (capacitance change) for a 60 s measurement time. The blue and yellow shaded regions indicate exhalation and inhalation, respectively. D: Photograph of a healthy volunteer wearing a pneumotachometer mask setup and demonstrating capaciflector placement on the chest during cardiopulmonary exercise testing (CPET), who provided written informed consent for image publication. The ECG dot electrodes are labelled for comparison

Fig. 2

Bland–Altman plots presented by capaciflector channel location during the metronome breathing pattern test for healthy subjects (n = 15, 17, 15 and 8 for channels 1–4, respectively). The comparator was a strain gauge chest belt (Study 1). RR, respiratory rate; BPM, breaths per minute

Fig. 3

Bland–Altman plots presented by capaciflector channel location while subjects (n = 6, 6, 9 and 6 for channels 1–4, respectively) were lying down. The comparator was a strain gauge chest belt (Study 1). RR, respiratory rate; BPM, breaths per minute

Fig. 4

Bland–Altman plots presented by capaciflector channel location while subjects (n = 7, 6, 6 and 4 for channels 1–4, respectively) were seated. The comparator was a strain gauge chest belt (Study 1). RR, respiratory rate; BPM, breaths per minute

Fig. 5

Bland–Altman plots presented by capaciflector channel location while subjects (n = 22, 18, 18 and 20 for channels 1–4, respectively) underwent cardiopulmonary exercise testing (CPET) on an exercise bike. The comparator was a pneumotachometer (Study 2). RR, respiratory rate; BPM, breaths per minute