The Area method: a new method for ultrasound assessment of diaphragmatic movement.

Background: Ultrasound can be used to assess diaphragm movement. Existing methods focus on movement at a single point at the hemidiaphragm and may not consider the anatomic and functional complexity. We aimed to develop an ultrasound method, the Area method, to assess movement of the entire hemidiaphragm dome and to compare it with existing methods to evaluate accuracy, inter-rater agreement, and feasibility.

Methods: Movement of the diaphragm was evaluated by ultrasonography in 19 healthy subjects and correlated with simultaneously performed spirometry. Two existing methods, the M-mode excursion at the posterior part of diaphragm and the B-mode at the top of the diaphragm, were compared with the Area method. Two independent raters reviewed film clips to analyze inter-rater agreement. Feasibility was tested by novice ultrasound operators.

Results: Correlation with expired lung volume was higher with the Area method, 0.88 (95% CI 0.81-0.95), p < 0.001, and with the M-mode measurement, 0.84 (95% CI 0.75-0.92), p < 0.001, than with the B-mode measurement, 0.71 (95% CI 0.59-0.83), p < 0.001. Inter-rater agreement was highest with the Area method, 0.9, p < 0.001, and M-mode measurement 0.9, p < 0.001, and lower with the B-mode measurement, 0.8, p < 0.001. The M-mode measurement could be done in only 20% at the left side. The Area method could be performed in all participants at both hemidiaphragms, and novice operators found it easy to perform.

Conclusion: A new method to evaluate diaphragm movement is introduced. Accuracy and inter-rater agreement are high. The Area method is equally feasible at both hemidiaphragms in contrast to existing methods. However, additional studies should include more participants, different types of pulmonary diseases, and investigate the role of patient position to validate the Area method fully.