New Respiratory Inductive Plethysmography (RIP) Method for Evaluating Ventilatory Adaptation during Mild Physical Activities

Abstract

The pneumotachometer is currently the most accepted device to measure tidal breathing, however, it requires the use of a mouthpiece and thus alteration of spontaneous ventilation is implied. Respiratory inductive plethysmography (RIP), which includes two belts, one thoracic and one abdominal, is able to determine spontaneous tidal breathing without the use of a facemask or mouthpiece, however, there are a number of as yet unresolved issues. In this study we aimed to describe and validate a new RIP method, relying on a combination of thoracic RIP and nasal pressure signals taking into account that exercise-induced body movements can easily contaminate RIP thoracic signals by generating tissue motion artifacts. A custom-made time domain algorithm that relies on the elimination of low amplitude artifacts was applied to the raw thoracic RIP signal. Determining this tidal ventilation allowed comparisons between the RIP signal and simultaneously-recorded airflow signals from a calibrated pneumotachometer (PT). We assessed 206 comparisons from 30 volunteers who were asked to breathe spontaneously at rest and during walking on the spot. Comparisons between RIP signals processed by our algorithm and PT showed highly significant correlations for tidal volume (Vt), inspiratory (Ti) and expiratory times (Te). Moreover, bias calculated using the Bland and Altman method were reasonably low for Vt and Ti (0.04 L and 0.02 s, respectively), and acceptable for Te (<0.1 s) and the intercept from regression relationships (0.01 L, 0.06 s, 0.17 s respectively). The Ti/Ttot and Vt/Ti ratios obtained with the two methods were also statistically correlated. We conclude that our methodology (filtering by our algorithm and calibrating with our calibration procedure) for thoracic RIP renders this technique sufficiently accurate to evaluate tidal ventilation variation at rest and during mild to moderate physical activity.

Validity of thoracic respiratory inductive plethysmography in high body mass index subjects

“…Further details are available in our previous paper (Retory et al, 2016b). Data from Nox T3 were exported in an .edf file and converted in ASCII file with EDFbrowser© software version 1.52 (GNU general public license).…”

“…Recordings were performed in a quiet, warm lab room at rest and during submaximal exercise to stimulate ventilatory drive and generate tissue motion artifacts as previously described in our recent paper (Retory et al, 2016b). Exercise consisted of marching on the spot due to the non-portative aspect of our pneumotachometer, and knee-raising with swinging arms at various frequencies.…”

“…Each measurement resulted in calculation of the median for one minute of tidal volume (Vt), Respiratory rate (RR), inspiratory time (Ti) and expiratory time (Te). Data processing including filtering of artifacts was made by using a previously described algorithm (Retory et al, 2016b). (Fig.…”

“…The alternative Respiratory Inductive Plethysmography (RIP) relies on the measurement of the current induced by an alternating magnetic field in coils, which is a function of the surface encircled by the coil (Gastinger et al, 2014), and has been industrialized and validated to evaluate tidal breathing during rest (Grossman et al, 2010;Zhang et al, 2012) and exercise (Witt et al, 2006). We aimed to use RIP during a 6MWT in obese populations, which lead us to develop a method to use RIP as a replacement of the pneumotachometer (PT) to avoid bias in measurement (Retory et al, 2016b), taking into account some concerns raised by Hollier et al when using RIP in obese populations (Hollier et al, 2014). We thought to assess a one degree of freedom method independent of abdominal A c c e p t e d M a n u s c r i p t 5 motion because of the inaccuracy of the two degree of freedom model described by Konno and Mead is related to adiposity, which is particularly increased in the abdominal compartment in obese subjects (Avraam et al, 2016;Boudarham et al, 2013;Hollier et al, 2014; Konno and Mead, 1967).…”

“…These results suggested that this increase could at least partly explain ventilatory discomfort. However, it seemed necessary to add unpublished data related to high BMI subjects regarding the previously validated method in low BMI subjects (Retory et al, 2016b).…”