Use of Angle-Independent M-Mode Sonography for Assessment of Diaphragm Displacement

Objectives-Sonographic assessment of diaphragm displacement has conventionally been conducted with M-mode sonography via an anterior subcostal approach. This method is subject to measurement errors when diaphragm displacement is not in line with the M-mode plane. We aimed to compare measurements obtained by offline angle-independent (anatomic) M-mode sonography with conventional M-mode sonography. Methods-Fifty healthy adults were imaged with conventional and angle-independent M-mode sonography of the bilateral hemidiaphragms at 60% maximal inspiratory capacity using an inspiratory spirometer. Results-Left hemidiaphragm displacement was successfully imaged by conventional M-mode sonography in only 70% (n = 35), as lung expansion obscured imaging, whereas 92% (n = 46) were assessable by angle-independent M-mode sonography. All right hemidiaphragm displacement could be assessed. Conventional M-mode results were higher than angle-independent M-mode results on the right (mean +/- SD, 4.9 +/- 1.4 versus 4.6 +/- 1.2 cm, respectively; P=.003) and left (5.4 +/- 1.3 versus 4.6 +/- 1.0 cm; P<.001). Displacement values were different for right versus left hemidiaphragms on conventional M-mode sonography (mean difference, 0.6 +/- 0.2 cm; P=.005), with only mild agreement (R-2 = 0.35; P<.001). There was no laterality seen in the diaphragm displacement on angle-independent M-mode sonography (mean difference, 0.1 +/- 0.1 cm; P=.47), with good agreement (R-2=0.76; P<.001). Conclusions-Angle-independent M-mode sonography leads to better visualization and assessment of the left hemidiaphragm. It records lower displacement than conventional M-mode sonography in the bilateral diaphragms, likely because of fewer orientation and translation errors. Future study is indicated to assess the clinical utility of angle-independent M-mode sonography in a population with diaphragm dysfunction.