The purpose of this study is the measurement of regional opening and closing pressures of lung tissue by electrical impedance tomography in lung healthy and patients with acute lung injury. These values might help the setting of positive endexpiratory pressure during artificial ventilation to avoid the cyclic opening and closing of alveoli.

During artificial ventilation the cyclic opening and closing of alveoli during artificial ventilation results in patients with acute lung injury (ALI) in a higher mortality. A positive endexpiratory pressure (PEEP) is applied with the intention to avoid these cyclic opening and closing of alveoli. The distribution of ventilation in patients with ALI is extremely inhomogeneous, consequently there are different regional opening pressures needed to open up the alveoli and avoid closing. Finding the best level of PEEP in patients with injured lungs to avoid atelectasis and alveolar strain induced by inadequately high or low PEEP levels is a challenge.

The purpose of this study is to develop a protocol for measuring regional opening and closing pressures using the method of electrical impedance tomography in lung healthy and ALI patients. A ventilator setting guided by regional opening and closing pressures might help reducing the impairment of the lung by artificial ventilation.

Inclusion Criteria:

• artificial ventilation
• acute lung injury / healthy lung (control group)

Exclusion Criteria:

• pregnancy
• Cerebral trauma / surgery
• Age < 18 years
• instable cardiovascular disease
• instable chest wall