Sixty-minute ventilation significantly increased plasma neutrophil elastase levels in the VT6 ( 35.2 30.4 vs. 56.4 51.7 ng/ml , P = 0.008 ) and Clara Cell protein 16 levels in the VT10 group ( 16.4 8.8 vs. 18.7 9.5 ng/ml , P = 0.015 ) .