Reliability and minimal detectable change of thoracoabdominal mobility measurements using photogrammetry

The knowledge about measurement errors of the measuring tool is important before its use, as clinical decisions are going to be made based on its results. Here we investigate intrarater and interrater reliability and the minimal detectable change (MDC) of thoracoabdominal mobility measurements using photogrammetry, considering novice and experienced raters. Thoracoabdominal mobility of 17 healthy participants was assessed; photographs during apnea in maximal inspiration and expiration were used to calculate latero-lateral and anteroposterior diameters of the thorax (at axillary and xiphoid level) and abdomen. One novice and one experienced rater measured the same photographs three times. We found good reliability for the experienced rater (average Intraclass Correlation Coefficient (ICC): 0.98; average MDC: 0.3) and for interrater comparison (average ICC: 0.97; average MDC: 0.35) for all measures, with poorer results for latero-lateral mobility of abdomen. The novice rater presented moderate reliability for latero-lateral mobility of the thorax at axillary level and abdomen (ICC: 0.52 and 0.61; MDC: 1.42 and 2.05, respectively) and good reliability for the other measures (average ICC: 0.81; average MDC: 1.52). The photogrammetric analysis of thoracoabdominal mobility presented itself as a reliable method when used by an experienced professional. However, considering that the measurement of latero-lateral mobility is more subjected to errors, it should be used with caution. The MDC presented should be taken into account as a threshold to be certain that the measure is not under the measurement error due to rater variability.