Single-breath diffusion parameters are repeatedly measured in individual patients. In COPD patients a week to week change of 1,3 mmol/min/kPa is reported as significant (Pellegrino, 2005). 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. This in-house study was conducted to estimate if SDD for single breath diffusion parameters is below the clinical significance level.

Four healthy volunteers performed four repeated single breath DLCO measurements by two Vyntus ONE^TM, two Vyntus BODY^TM and two MasterScreen^TM PFT pro systems (Vyaire Medical^TM) according to international standards in random order over a period of four days within one week. SEM was calculated from the total error variance of the measurements estimated by analysis of variance (SEM = ??²error. SDD as 1.96 * ?2* SEM)

Results

Conclusion SDD of DLCOSB parameters of all systems are within the clinically relevant range.