Developing a new ultrasonic method to assess diaphragm movement and comparing the accuracy with existing methods

Abstract

Introduction: Diaphragm is the most important respiratory muscle. Movement can be evaluated with ultrasound. Currently two different methods are used, M-mode and B-mode. However, diaphragm movement is complex. Aim: We hypothesized that the two existing methods are imprecise as they only measure movement of a single point at the diaphragm. Therefore, we developed a new method, Area-measurement, that assesses motion of the whole diaphragm dome. We wanted to evaluate which of the three methods is the most accurate. Methods: We examined nineteen healthy men and women, aged 21 to 26. Ultrasound and Forced Vital Capacity (FVC) measurement was performed simultaneously. We measured excursion of the right hemi-diaphragm with M-mode and cranio-caudal movement with B-mode. Using Area-measurement, we measured change in thoracic area by tracking the diaphragm. Two experienced ultrasound operators rated film clips independently to assess inter-rater variability. Results: We found a linear correlation between FVC and diaphragmatic movement. M-mode had Pearson r=0.84 (95%CI 0.76-0.89), B-mode had r=0.68 (95%CI 0.55-0.79) and Area-measurement had r=0.84 (95%CI 0.77-0.90). Inter-rater agreement was r=0.97 (95%CI 0.76-0.99) for M-mode, r=0.79 (95%CI 0.50-0.92) for B-mode and r=0.94 (95%CI 0.85-0.98) for Area-measurement. Conclusion: The new Area-measurement and M-mode excursion are equally accurate ultrasonic measurements of diaphragmatic movement. They both have high inter-rater agreement. B-mode measurement was less accurate and had lower Inter-rater agreement. M-mode can only be used at the right diaphragm whereas Area-measurement can be used at both sides and is therefore recommended.