1777 NEW LIGHT ON STUDIES OF CHEST WALL DISTORTION

Abstract

Chest wall distortion (CWD) has been studied with magnetometers, strain gauges, and inductance plethysmography – all methods for estimating the volume excursion of the chest wall (CW). To quantitatively describe the movement and volume changes of the CW, we developed a system to optically map the CW of small infants. We project a grid onto the torso, and view the infant with a video camera from an angle of 45° from the axis of the projected grid. The video information is later played back frame-by-frame, and a cursor is superimposed on the intersections of the grid to determine their positions. The viewing angle and the calibration of the projector and camera are used to calculate 130 X-Y-Z coordinates for the surface. We studied an infant with this system, weighing 1980g. The right half of the CW was divided into four axial slices, 1.4 cm thick, located in the upper, middle, lower, and costal portion of the CW. Volume changes of each slice were calculated at 4 equally spaced times during 5 breaths, expressed in ml, as the difference from end-expiration. The total volume of the slices represents the overall CW volume change. The uncertainty of the volume measurements was ±3.6%, based on measurements of test objects. The variability of the volumes from breath to breath averaged ±5.4% of the volumes shown.

The upper and lower CW moved paradoxically during inspiration, with an overshoot in expiration, whereas the middle CW moved paradoxically throughout breathing. The costal portion had no paradox. The total CW volume is consistent both in pattern and volume change with estimates made with the inductance plethysmograph.

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