Methods and systems of maintaining, evaluating, andproviding therapy to a lung ex vivo. The methods and systems involvepositioning the lung in an ex vivo perfusion circuit； circulating a perfusionfluid through the lung, the fluid entering the lung through a pulmonary arteryinterface and leaving the lung through a left atrial interface； andventilatingthe lung by flowing a ventilation gas through a tracheal interface.Maintaining the lung for extended periods involves causing the lung torebreath a captive volume of air, and reaching an equilibrium state betweenthe perfusion fluid and the ventilation gas. Evaluating the gas exchangecapability of the lung involves deoxygenating the perfusion fluid andmeasuring a time taken to reoxygenate the perfusion fluid by ventilating thelung with an oxygenation gas.
