Use of Optoelectronic Plethysmography in Pulmonary Rehabilitation and Thoracic Surgery

OEP system is an optoelectronic device able to track the three-dimensional co-ordinates of a number of reflecting markers placed non-invasively on the skin of the subject [1-4]. A varia‐ ble number of markers (89 in the model used for respiratory acquisition in seated position) is placed on the thoraco-abdominal surface; each marker is a half plastic sphere coated with a reflective paper. Two TV Sensors 2008, cameras are needed to reconstruct the X-Y-Z coordinates of each marker, so for the seated position six cameras are required. Each camera is equipped with an infra-red ring flash. This source of illumination, which is not visible, is not disturbing and lets the system also operate in the dark. The infra-red beam, emitted by the flashes, is reflected by each marker and acquired by the cameras with a maximal sampling rate of 100 Hz. The signal is then processed by a PC board able to combine the signal coming from the cameras and to return, frame by frame, the three-dimensional co-ordinates of each marker. The process is simultaneously carried out for the six TV cameras needed for the seated respiratory model. Acquired data need a further operation called ‘tracking’ that is necessary to exclude possible phantom reflections and/or to reconstruct possible lost mark‐ ers (this could happens sometimes during very fast manoeuvres such exercise); at this time the obtained files contain the X-Y-Z co-ordinates of each marker during the recorded ma‐ noeuvre, then data are stored on the PC hard disk. The spatial accuracy for each marker’s position is about 0.2 mm [1]. Volumes for each compartment is calculated by constructing a triangulation over the surface obtained volume from the X-Y-Z co-ordinates of the markers and then using Gauss’s theorem to convert the volume integral to an integral over this sur‐