A preliminary set of growth adjusted reference equations for Structured light plethysmography (SLP)

Abstract

Background: Structured light plethysmography (SLP) is a non-contact tidal breathing pattern measurement technique (Motamedi-Fakhr, S. et al. Physiol Rep 2017; 5(3):e13124). Lack of reference equations for SLP parameters makes clinical decision-making difficult. We have developed a set of reference equations for 7 SLP tidal breathing parameters.

Data: Five minutes of SLP data from 198 healthy subjects [Mean (SD); 28.6 (20.8) years, 155.7 (27.2) cm, 108 Male] in seated position (at rest) were collated. Subjects were of unspecified ethnic groups.

Method: We have adopted a similar methodological approach to the global lung function initiative (GLI) work on reference spirometric equations albeit on a smaller scale (Quanjer, P.H. et al. Eur. Respir. J. 2012; 40:1324-1343). Generalised additive models for location, scale and shape (GAMLSS) was used to derive the growth adjusted reference equation for each parameter.

Results: Reference equations for respiratory rate (RR), inspiratory time (Ti), expiratory time (Te), duty cycle (Ti/Ttot), phase (thoraco-abdominal asynchrony [TAA]), relative thoracic contribution and IE50 (surrogate measure of airway obstruction) were derived. Assessment of worm plots and distribution of the residuals ensured adequate fit. A reference range calculator was also developed. The calculator takes age, height and sex as inputs and generates the predicted value of each parameter, its z-score and upper and lower limits of normal (ULN, LLN).

Conclusion: This preliminary set of reference equations for SLP will help clinicians and researchers better understand and interpret SLP data and be able to define abnormality.