LAUSR

Dear Editor, We read the article published by Bahgat and coworkers [1] in this journal, and we believe that a word of caution should be risen in terms of the quality of the studies in this field. The authors’ methodology to measure thickness of the diaphragm and therefore the diaphragm thickening fraction (DTF) is not optimal. They used the subcostal view, where the posterior diaphragm domes are visualized. However, the optimal location for this purpose is the apposition zone (see Fig. 1). In this zone, the diaphragm is parallel to the thoracic wall, where it is easier to measure the thickness of the muscle, and the insonation angle of the beam is not oblique. This measurement was originally described [2] to maintain the angle of incidence close to 90°, and in these conditions, the expected error in thickness measurements due to the angle of the beam was calculated very small (< 2%). This approach is used in most recent previous studies about DTF in adults [3–5], children [6–8], and neonates [9–11], most of which are cited by the authors. Researchers should also carefully assess the reliability of new methods before its diagnostic accuracy can be stablished with clinical purposes. In this sense, this article [1] deserves several comments.