Abstract
IntroductionRespiration frequency (RF) could be derived from the respiratory signals recorded by accelerometers which detect chest wall movements. The optimum direction of acceleration for accurate RF measurement is still uncertain. We aim to investigate the effect of measure site, posture, and direction of acceleration on the accuracy of accelerometer-based RF estimation.MethodsIn supine and seated postures respectively, respiratory signals were measured from 34 healthy subjects in 70 s by triaxial accelerometers located at four sites on the body wall (over the clavicle, laterally on the chest wall, over the pectoral part of the anterior chest wall, on the abdomen in the midline at the umbilicus), with the reference respiratory signal simultaneously recorded by a strain gauge chest belt. RFs were extracted from the accelerometer and reference respiratory signals using wavelet transformation. To investigate the effect of measure site, posture, and direction of acceleration on the accuracy of accelerometer-based RF estimation, repeated measures multivariate analysis of variance, linear regression, Bland-Altman analysis, and Scheirer-Ray-Hare test were performed between reference and accelerometer-based RFs.ResultsThere was no significant difference in accelerometer-based RF estimation between seated and supine postures, among four accelerometer sites, or between seated or supine postures (p > 0.05 for all). The error of accelerometer-based RF estimation was less than 0.03 Hz (two breaths per minute) at any site or posture, but was significantly smaller in supine posture than in seated posture (p < 0.05), with narrower limits of agreement in Bland-Altman analysis and higher accuracy in linear regression (R2 > 0.61 vs. R2 < 0.51).ConclusionRespiration frequency can be accurately measured from the acceleration of any direction using triaxial accelerometers placed at the clavicular, pectoral and lateral sites on the chest as well the mid abdominal site. More accurate RF estimation could be achieved in supine posture compared with seated posture.
Highlights
Respiration frequency (RF) could be derived from the respiratory signals recorded by accelerometers which detect chest wall movements
Three Scheirer-RayHare tests were performed based on the posture-direction, FIGURE 5 | Bland–Altman Plots of the accelerometer-derived and reference respiratory frequency (RF) in seated posture
The results showed that the RF estimation error was only significantly influenced by posture and its interaction with direction
Summary
Respiration frequency (RF) could be derived from the respiratory signals recorded by accelerometers which detect chest wall movements. The optimum direction of acceleration for accurate RF measurement is still uncertain. We aim to investigate the effect of measure site, posture, and direction of acceleration on the accuracy of accelerometer-based RF estimation. RR can be directly calculated from the respiratory frequency (RF) which is widely used in healthcare monitoring: RR (bpm) = RF (Hz)/60. A raised RR precedes clinical deterioration in many acute medical conditions (Hodgetts et al, 2002) and its accurate measurement is of prime importance to patient safety. The commonest method of measuring RR in non-critical care settings is manual measurement in which a healthcare worker counts the number of breaths taken within a certain time period. To yield patient safety benefits, there is an urgent clinical need for a device to achieve reliable RR (or RF) measurement
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