Fig. 1

A (1) The microsampling probe (model BC-402C, Olympus Tokyo, Japan) used for collecting bronchial epithelial lining fluid (ELF). (2) The probe tip is comprised of a 2.5-mm outer polyethylene sheath and a 1.9-mm inner polyester fiber rod probe, 20 mm in length, attached to a stainless-steel guide wire. (3) The process of extracting ELF by centrifugation. B The study analyzed cytokine concentrations in COVID-19 patients (normal) with acute hypoxemic respiratory failure (AHRF) compared to healthy volunteers (covid). (1) Cytokine concentrations in the ELF and (2) plasma are presented. C The ratio of bronchial ELF/plasma concentrations. The data included a box plot representing the 25th to 75th percentiles (interquartile range, IQR), the median (centerline), and whisker lines extending to the furthest data points within Q1–1.5 × IQR and Q3 + 1.5 × IQR. Outliers were identified beyond these limits. Significant differences (*p < 0.05) between the normal and COVID-19 patient groups are marked with an asterisk and were assessed using the Kruskal‒Wallis test with Bonferroni correction