BAL fluid studies The initial, 20-mL portion of the BAL fluid aspirate (which corresponds to the bronchial sample) will be sent for microbiological cultures, and the rest will be stored in ice-cold tubes. Subsequently, the BAL fluid will be filtered through sterile gauze and centrifuged at 500 g for 15 min at 4 degrees Celcius. The supernatant will be used for the determination of the concentrations of Activin A, inflammatory markers, and surfactant-related proteins. The sediment will be used for total cell count, determination of cell type, and estimation of cell viability on a Neubauer plate. Both the supernatant and sediment will be stored at -70 degrees Celcius.