The aim of this study was to evaluate the reproducibility of computed tomography (CT) to assess respiratory mechanics in tetraplegic subjects. Due to the lack of most expiratory muscles, tetraplegic subjects show big differences in respiratory mechanics compared to able-bodied subjects. To specify these differences, the reproducibility of chest-CT-scans at maximal in- and expiration in tetraplegic subjects was assessed.
Eight chronic tetraplegic subjects with motor complete lesions between C5 and C8 were tested. All CT-scans were performed twice in supine position, with a repositioning of the patient in-between. At maximal in- and expiration, a topogram of the whole chest and 2 slices at the bottom plate of vertebral body Th4 and the cover plate of vertebral body Th9 were recorded. The raw values for diaphragm levitation, lung areas as well as frontal and sagital expansions of the chest were calculated by visual selection of the areas and distances using ’Osiris’ medical imaging software. Coefficients of variation (CV) were calculated for the variation between the first and second measurement of the patients and for the intra-tester reproducibility of 3 independent testers, analyzing everything twice.
Mean CV of the 3 intra-tester calculations were 0.2±0.1% for lung areas, 0.6±0.2% for sagital and 0.3±0.1% for frontal distances and 2.9±1.0% for diaphragm levitation. Mean CV of the patients’ maximal in- and expiration were 3.8±2.6% for lung areas, 2.9±2.0% for sagital and 1.3±0.6% for frontal distances and 11.3±2.4% for diaphragm levitation.
Our results showed a high intra-tester reproducibility of the calculated values with CV below 1%. CV of maximal in- and expiration of the patients were below 4%, indicating the measurement error which is relevant for the practical use of this method. Concerning diaphragm levitation, the rather weak reproducibility has to be taken into account.
Computed tomography provides interesting possibilities to assess changes in respiratory mechanics due to training or degeneration in tetraplegic subjects.
Gabi Mueller, None.