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Respiratory physiology: new tools, old concepts
P134 Validating structured light plethysmography (SLP) as a non-invasive method of measuring lung function when compared to Spirometry
  1. S Alimohamed1,
  2. K Prosser1,
  3. C Weerasuriya1,
  4. R Iles2,
  5. J Cameron3,
  6. J Lasenby3,
  7. C Fogarty4
  1. 1School of Clinical Medicine, University of Cambridge, Addenbrookes Hospital, Cambridge, UK
  2. 2Department of Respiratory Paediatrics, Cambridge University Hospitals, Addenbrookes Hospital, Cambridge, UK
  3. 3Signal Processing and Communications Laboratory, Department of Engineering, University of Cambridge, Cambridge, UK
  4. 4Department of Statistics, Harvard University, Cambridge, Massachusetts, USA


Background Structured Light Plethysmography (SLP) is a recently developed technology for non-invasive and entirely non-contact monitoring of lung (respiratory) function. The system projects a structured light grid onto the thoraco-abdominal surface of the subject, which is imaged by two cameras giving a dynamic 3D reconstruction of the surface as the subject breathes. From this data we can infer changes in chest/abdomen volume over time, allowing us to extract parameters and generate curves (eg, Volume-Time, Flow-Time, Flow-Volume curves) directly comparable to conventional spirometry. SLP therefore hopes to provide an inexpensive replacement for conventional spirometry, which is an invasive methodology unusable in a number of patient classes (eg, neonates, young children, intensive care patients etc). This study tests the validity of SLP in terms of reproducibility, repeatability and position dependence, as compared to conventional spirometry (Pneumatach); by comparison of ventilation parameters extracted from both technologies.

Methods SLP and Pneumatach spirometry were used simultaneously to capture 120 datasets from 10 randomly chosen adult subjects. Each complete dataset contained tidal breathing and forced expiratory manoeuvres, in both sitting and standing positions. Operator-dependence (reproducibility) was tested by collecting data sets from each subject using three different operators. Repeatability was tested by collecting the data from each subject once, and then again after a 40 min break. Tidal Inspiratory Time (TI) parameters were extracted from the results and the data analysed using the paired Student t test.

Results There was no significant difference between TI values obtained from SLP compared to conventional spirometry throughout the study (n=120; p=0.8556). SLP comparisons of pooled mean TI before, and after a 40 min break were not significant (1.5589 vs 1.5595; p=0.9938); similarly, readings in different positions (sitting or standing) were not significantly different. SLP comparison of all three operator pairs (1vs2, 1vs3 and 2vs3), were not significant (p=0.7361, p=0.9765, p=0.7343, respectively).

Conclusions SLP measurements are not operator, time or position dependant. Therefore SLP shows a high degree of reproducibility and repeatability; and represents a promising, viable and non-invasive alternative to conventional spirometry.

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