Chest wall and lung volume estimation by optical reflectance motion analysis

Cala, S. J., C. M. Kenyon, G. Ferrigno, P. Carnevali, A. Aliverti, A. Pedotti, P. T. Macklem, and D. F. Rochester. Chest wall and lung volume estimation by optical reflectance motion analysis.J. Appl. Physiol. 81(6):2680-2689, 1996.Estimation of chest wall motion by surfacemeasurements only allows one-dimensional measurements of the chestwall. We have assessed an optical reflectance system (OR), which tracksreflective markers in three dimensions (3-D) for respiratory use. Weused 86 (6-mm-diameter) hemispherical reflective markers arrangedcircumferentially on the chest wall in seven rows between the sternalnotch and the anterior superior iliac crest in two normal standingsubjects. We calculated the volume of the entire chest wall andcompared inspired and expired volumes with volumesobtained by spirometry. Marker positions were recorded by four TVcameras; two were 4 m in front of and two were 4 m behind the subject.The TV signals were sampled at 100 Hz and combined with gridcalibration parameters on a personal computer to obtain the 3-Dcoordinates of the markers. Chest wall surfaces were reconstructed bytriangulation through the point data, and chest wall volume wascalculated. During tidal breathing and vital capacity maneuvers andduring CO₂-stimulated hyperpnea, there was a very close correlation of the lung volumes(VL) estimated by spirometry[VL(SP)] and OR[VL(OR)]. Regressionequations of VL(OR)(y) vs.VL(SP)(x,BTPS in liters) for the two subjects were given by y = 1.01x  0.01 (r = 0.996) andy = 0.96x + 0.03 (r = 0.997), and byy = 1.04x + 0.25 (r = 0.97) andy = 0.98x + 0.14 (r = 0.95) for the two maneuvers,respectively. We conclude spirometric volumes can be estimated veryaccurately and directly from chest wall surface markers, and wespeculate that OR may be usefully applied to calculations of chest wallshape, regional volumes, and motion analysis.