Smallest detectable change (SDD) of absolute long volumes by bodyplethysmography

Abstract

<b>Introduction:</b>&nbsp;In clinical pratice absoute long volumes are repeatedly measured in individual patients by body-plethysmography to measure change over time. The detection of a significant change is often based on the coefficient of variation (CV). The CV is a mean value in a group of healthy subjects and gives only average information about the variation of measurement results. To determine whether a significant change in an individual patient has occurred, knowledge about the reliability of the test, expressed as the standard error of the measurement (SEM) is needed. Smallest detectable difference (SDD) estimated from the SEM is defined as the smallest statistically significant amount of change to be detected with a measurement device measured on different occasions. <b>Aim:</b>&nbsp;To estimate the reliability of total lung capicity (TLC), functional residual capacity (FRC), residual volume (RV) and vital capacity (VC), expressed by SEM and SDD. <b>Method:</b>&nbsp;Ten healthy volunteers performed two repeated TLC, FRC, RV and VC measurements by Vyntus BODY^® (Vyaire Medical) according to international standards in random order over a period of two days within one week. SEM was calculated from the total error variance of the measurements estimated by analysis of variance (SEM = √δ_error². SDD was calculated as 1.96 * √2* SEM. <b>Results:</b> <b>Conclusion:</b> SEM and therefore&nbsp;SDD of absolute lung volumes measured by Vyntus Body^®&nbsp;are&nbsp;in clinical acceptable&nbsp;range.