By using the same method to measure FRC, the positive end expiratory pressure ( PEEP ) was changed. PEEP was elevated by 2 and 4 cmH 2O, and then decreased by 2 and 4 cmH 2O in healthy group;

• (2 )改变呼气末正压 (PEEP) ,健康组先增加 2、4cmH2 O、然后减少 2、4cmH2 O ;