 1. history of any lung disease, use of immunosuppressive medication, recent infections, previous thromboembolic disease, recent ventilatory support, and participation in another clinical trial. Absence of lung disease was defined by the following clinical criteria: a no evidence of respiratory infection white blood cell count 10x103μl, temperature 380C, purulent sputum, b normal chest roentgenogram, c PaO2FIO2 ratio 300, d and a normal clinical respiratory history. 