A video-based optical system for rapid measurements of chest wall movement

We tested apparatus developed to measure the movement of the surface of the chest and abdomen, during breathing in the supine subject. A line of light is projected onto the chest wall. The line image from a video camera is analysed to estimate of the height of the surface profile, so that the shape and volume of the object can be derived. The data can provide direct or inferential volume estimates. We compared this system with the widely used inferential system of inductance bands in supine volunteers who breathed using patterns designed to emphasize variability in movements: normal and large breaths, and breathing through an expiratory resistance. We calculated the differences between a spirometer signal and continuous volume estimates using the linear regression method, obtained using signals from the two methods. The volume estimate differences obtained by the optical system and induction bands were not significantly different, but the optical system was more precise. Using the optical device, an acceptable interquartile range of differences from spirometric volume (50 ml) was significantly likely when the optical device was used. During resistive loaded breathing (mean tidal volume 390 ml) direct optical measurements of volume, and inductance band estimates, were compared with tidal volume. The optical system showed distortion of the shape of the abdomen during this breathing pattern. Mean error with the optical system was 64 ml and with the inductance band system was 108 ml (p < 0.05). The optical system gives accurate reproducible results in supine human subjects and additional valuable information on shape changes.