Replacing fluoroscopy with ultrasound to evaluate diaphragm excursion? A method comparative study.

Introduction: The diaphragm is the most important respiratory muscle and dysfunction ultimately leads to respiratory failure. Numerous conditions may affect its function. Evaluation of diaphragm function is cumbersome. Fluoroscopy has been used in many years to measure excursion. Ultrasound can visualize diaphragm excursion and holds many advantages due to is portability and accessibility. However, correlation between fluoroscopy and ultrasound has never been studied. Aims: We aimed to compare fluoroscopy and ultrasound measures of diaphragm excursion to study if ultrasound can replace fluoroscopy. Methods: In patients with COPD or heart failure and in volunteers ultrasound and fluoroscopy was done simultaneously during sniff inspiration and in inspiratory capacity. Cranio-caudal excursion was measured om fluoroscopy recordings and compared directly to M-mode excursion, B-mode excursion, area change, resting thickness, thickening fraction and contraction velocity measured by ultrasound. Results: Forty-two participants were recruited. Pearson´s correlation between M-mode and fluoroscopy excursion was 0.61. The slope was 0.9 (90%CI 0.76 – 1.04) in a regression analysis. Using Bland-Altman method the bias was -0.39 cm (95%CI -1.04 – 0.26), p=0.24 with an error estimate on 3.8%. The correlations were lower during sniff inspiration the in inspiratory capacity breathing. Conclusion: Ultrasound has acceptable and low bias compared to fluoroscopy and can replace it as the primary tool to evaluate diaphragm excursion.