Reproducibility and repeatability of tidal breathing parameters derived from structured light plethysmography when compared to spirometry

Introduction: This study aimed to test the reproducibility and repeatability of data collected by Structured Light Plethysmography (SLP) when compared to pneumatach. SLP is a non invasive method of pulmonary function assessment. A grid of black and white squares is projected onto the thoraco-abdominal surface. 2 digital cameras image the grid9s movement and enable a stereoscopic representation of thoracic volume change enables Volume -Time; Flow-Time and Flow-Volume to be derived. Method: 120 datasets of 45 seconds were captured from 10 healthy adults. Spirometry data were taken simultaneously with SLP. Subjects took 5 tidal breaths. To assess reproducibility, 3 operators collected consecutive data. Data was collected in sitting and standing positions. Repeatability was assessed by collecting data a second time, after 40 mins. Statistics: The inspiratory (TI), expiratory (TE) times and tidal volume (TV) were extracted. Data was analysed using the paired Student t-test. Reproducibility was tested by paired T-tests. Comparison was carried out for 3 pairs (1vs2, 1vs3 and 2vs3), and for position. Results: Paired comparison of mean TI and TE did not reach significance, (p=0.85 and 0.72). Significance was not reached for posture or between the two measurement periods. No difference was found between operators, or position. Significant differences were found between TV results. Conclusions: Measurements of TI and TE are repeatable and reproducible. They are operator independent. TV was not reproducible but dependant on wave-form scaling. Further work has been undertaken that has removed the need data scaling.