Structured light plethysmography

Structured Light Plethysmography (SLP) technology is a noninvasive method for collecting accurate representations of chest and abdominal wall movement. A checkerboard pattern of light is projected from a light projector onto the chest of an individual. Movements of the grid are viewed by two digital cameras, digitalised, and processed to form a 3D model and can be interrogated to assess lung function. The system has been tested on over 70 adults (data presented at clinical meetings). SLP is simple to use, accurate and cost effective, is self-calibrating and does not require the use of plastic consumables, reducing cost, risk of cross infection and the device's carbon footprint. In conjunction with the Cambridge Veterinary School, proof of concept studies have indicated that the device is sensitive enough to noninvasively pick up respiratory movements in domestic animals (cats and dogs).

A totally “non-invasive” technique using structured light to measure pulmonary function was developed as long ago as the mid-1980s by a London group at the Royal Brompton Hospital working in close association with IBM (1-4). The technique used the distortion with movement of a structured pattern of light to calculate a volume or change in volume of a textured surface. At that time structured light pattern was shone on to the anterior chest and abdominal wall surfaces, and movie camera film footage was taken and sent to IBM for processing. The digital information was used to compute automatically the volume of the trunk and the position of any point on its surface and its cross-sectional shape at any level. The group found that linear dimensions could be calculated to within 0.5mm and a cross-sectional area within 5% and volume within 3-7%. The group suggested that non-invasive technique measurements were of sufficient accuracy to be tried in clinical practice. However, probably due to technology limitations, data processing and storage, the methodology was never commercialised.

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