A method for assessing lung function in a patient is disclosed. The method comprises isolating a lung compartment. Thereafter, in one embodiment, an inhaled gas of known composition is introduced into the lung and compared to the composition of the exhaled gas. Alternatively, accumulated CO2 content is measured within the isolated lung compartment over time, and compared to a baseline CO2 content. Alternatively, a change in pressure of an isolated lung compartment may be monitored. Alternatively, the magnitude of the range of CO2 values in an isolated lung compartment can be compared to a predetermined threshold. Any of the results obtained via these alternative embodiments may be used to determine lung function.