Optoelectronic plethysmography (OEP) has shown to be a reliable and accurate method for measuring lung volume changes during breathing in various positions and conditions. OEP enables the detection of asynchronous and asymmetric movements between the Chest Wall (CW) compartments . Typically, OEP is used to measure of volume variations of up to six CW compartments. The objective of this study is to enrich the kinematical description of the CW and thus enhance the clinical interpretation of pulmonary function tests. The kinematical methods used here are based on the Triangular Cosserat Point Element (TCPE) method , previously developed for bone pose estimation.
3 groups were examined; 10 healthy subjects, 10 patients with Duchenne muscular dystrophy (DMD), and 9 with Pompe disease. The positions of 52 markers attached to the anterior CW in anatomical positions  were recorded in the supine position during spontaneous breathing using a CX1 Codamotion system. A mesh of 78 triangles was defined by the markers (Fig.1a). Each triangle was characterized by a TCPE, and the non-rigid kinematics of each TCPE was described by 4 scalar parameters (Pi). Attention will be given here to the outward translation parameter (PT). In addition, the volume variations of the CW (Vcw) were computed by applying the Gauss divergence theorem . The phase angles θ(PT,VCW) were computed from the Lissajou figures obtained by plotting Vcw versus PT. In this method, θ=0⁰ represents complete synchrony, and θ=±180⁰ complete asynchrony .
RESULTS AND DISCUSSION:
Fig.1b shows a characteristic pattern of θ(PT,VCW) for each group. Healthy: values were close to zero over the entire CW (mean: -2⁰±10⁰ SD). DMD: negative values (-45⁰±22⁰) in the medial CW and positive (-40⁰±18⁰) in the lateral and abdominal CW. Pompe: large negative angles (-90⁰±47⁰) in the abdominal CW and positive values in the thoracic CW (80⁰±43⁰). Neuromuscular disease typically causes progressive respiratory muscles weakness. In particular, diaphragm weakness is evident in Pompe patients, which causes a lack of synchronicity and low contraction, and result in an abdominal paradoxical motion. In this study, the TCPE parameter PT appears as a good tool to analyze the kinematical pattern over the CW and distinguish this paradoxical motion, and the TPCE approach provides useful information which may assist clinicians to detect and monitor respiratory function.
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