A method for assessing pulmonary stress, wherein a volume of respiratory gas is received from the lungs of a subject, an ensuing pressure is measured and the pressure-volume (P-V) relationship is analysed is disclosed. The analysis comprises the method step of determining the profile of the pressure-volume (P-V) relationship. In short, the profile is straight when no stress is present, convex when there is a risk for overdistension and concave when alveolar units are opened up. Implemented in a breathing apparatus the method can be used to assist an operator in diagnostic and therapeutic considerations in relation to a patient. <；IMAGE>；
