Reproducibility of diaphragmatic thickness measured by M-mode ultrasonography in healthy volunteers.

We aimed at testing M-mode ultrasound diaphragmatic thickness reproducibility and its clinical correlates in healthy volunteers. Sixty-six consecutive healthy volunteers were considered eligible, and enrolled in the study. During a single visit, all participants received three M-mode and B-mode ultrasound evaluations of Diaphragmatic Thickness (DT). We then proceeded to calculate the thickness difference and assess the association of ultrasonographic measurements with demographic and anthropometric data. Variables associated through univariate analyses were entered in multivariable models, and Intraclass Correlation Coefficient (ICC) was performed in order to determine intra- and inter-observer reproducibility. Intra- and inter-observer agreements showed to be excellent through Cronbach's Alpha, ranging from 0.81 - 0.91 and 0.86 - 0.92, respectively. Mean diaphragmatic thickness measurements were: 2.6 (±0.5) mm at inhalation and 1.8 (±0.4) mm at exhalation. The results we obtained significantly varied according to gender, showing diaphragmatic motion, inspiratory/expiratory thickness and fractional thickening to be significantly lower in women. Moreover, a significantly reduced expiratory diaphragmatic thickness emerged in the subgroup of subjects having a sedentary work (p = 0.045). The crude association between expiratory thickness and active work produced a B coefficient of 0.19 (95% CI: 0.04-0.38; p = 0.045), which was confirmed after adjustments considering age and sex (B = 0.20; 95% CI: 0.01- 0.39; P = 0.037). Diaphragmatic thickness measurements using M-mode are reproducible. Intra and inter-observer agreement is high enough to support the precision of this measurement and provide a further analytic tool for a wider application in clinical practice.