MMP9 and acute respiratory distress syndrome: In a prospective study investigating the MMP-9/TIMP-1 ratio in the pathogenesis of ARDS, 21 patients were divided into three groups: patients whose ARDS lasted less than 4 days (Group 1), patients whose ARDS lasted more than 8 days (Group 2), and a control group of patients diagnosed with hospital-acquired pneumonia in the absence of ARDS (Group 3).