Measuring Ventilatory Activity with Structured Light Plethysmography (SLP) Reduces Instrumental Observer Effect and Preserves Tidal Breathing Variability in Healthy and COPD

Abstract

The use of a mouthpiece to measure ventilatory flow with a pneumotachograph (PNT) introduces a major perturbation to breathing (“instrumental/observer effect”) and suffices to modify the respiratory behavior. Structured light plethysmography (SLP) is a non-contact method of assessment of breathing pattern during tidal breathing. Firstly, we validated the SLP measurements by comparing timing components of the ventilatory pattern obtained by SLP vs. PNT under the same condition; secondly, we compared SLP to SLP+PNT measurements of breathing pattern to evaluate the disruption of breathing pattern and breathing variability in healthy and COPD subjects. Measurements were taken during tidal breathing with SLP alone and SLP+PNT recording in 30 COPD and healthy subjects. Measurements included: respiratory frequency (Rf), inspiratory, expiratory, and total breath time/duration (Ti, Te, and Tt). Passing-Bablok regression analysis was used to evaluate the interchangeability of timing components of the ventilatory pattern (Rf, Ti, Te, and Tt) between measurements performed under the following experimental conditions: SLP vs. PNT, SLP+PNT vs. SLP, and SLP+PNT vs. PNT. The variability of different ventilatory variables was assessed through their coefficients of variation (CVs). In healthy: according to Passing-Bablok regression, Rf, TI, TE and TT were interchangeable between measurements obtained under the three experimental conditions (SLP vs. PNT, SLP+PNT vs. SLP, and SLP+PNT vs. PNT). All the CVs describing “traditional” ventilatory variables (Rf, Ti, Te, Ti/Te, and Ti/Tt) were significantly smaller in SLP+PNT condition. This was not the case for more “specific” SLP-derived variables. In COPD: according to Passing-Bablok regression, Rf, TI, TE, and TT were interchangeable between measurements obtained under SLP vs. PNT and SLP+PNT vs. PNT, whereas only Rf, TE, and TT were interchangeable between measurements obtained under SLP+PNT vs. SLP. However, most discrete variables were significantly different between the SLP and SLP+PNT conditions and CVs were significantly lower when COPD patients were assessed in the SLP+PNT condition. Measuring ventilatory activity with SLP preserves resting tidal breathing variability, reduces instrumental observer effect and avoids any disruptions in breathing pattern induced by the use of PNT-mouthpiece-nose-clip combination.

ERS statement on respiratory muscle testing at rest and during exercise

“…Structured light plethysmography (SLP) is another emerging imaging tool. SLP is a non-contact, noninvasive method to assess breathing pattern [226]. The technique is based on the stereoscopic analysis of respiratory-related distortions of a black and white chequered pattern projected on the chest wall and abdomen [226][227][228].…”

Mini review shows that structured light plethysmography provides a non‐contact method for evaluating breathing patterns in children

“…In addition, the variability of tidal breathing indices was significantly lower in patients with chronic obstructive pulmonary disease than in the healthy controls and this was further supported by similar observations from a study by Nierat et al. . The latter study also showed that, compared to using a pneumotachograph, the non‐contact SLP measurements attenuated the instrumental observer effect masking the reduced variability of tidal breathing patterns evolving in chronic obstructive pulmonary disease .…”

“…In three papers, the study groups were specifically children and one paper described a paediatric case report . Otherwise, the data for this mini review had to be drawn together from published studies and abstracts covering adults and a number of abstracts covering paediatrics .…”

“…In addition, this level of agreement was sustained with increased respiratory rates after an exercise challenge . In another study with 30 adults with chronic obstructive pulmonary disease and 30 healthy adults, the timing indices inspiratory time, expiratory time and total respiratory time did not show significant differences between SLP and pneumotachograph measurements in a Passing‐Bablok regression analysis . Another study compared the respiratory impedance pneumography method in 103 adults and the respiratory rate obtained with SLP and found that it was within ± 2.0 per minute of that captured with respiratory inductance bands.…”

“…. The latter study also showed that, compared to using a pneumotachograph, the non‐contact SLP measurements attenuated the instrumental observer effect masking the reduced variability of tidal breathing patterns evolving in chronic obstructive pulmonary disease .…”