Uneven mixing of gas within the lungs is characteristic of pulmonary emphysema. A number of technics have been devised to demonstrate unequal gas mixing in emphysema and to grade the severity of the defect. These have depended upon measuring various consequences of impaired mixing, such as delay in washing a test gas out of the lungs, delay in introducing a test gas into the lungs, or abnormally great variation in the concentration of expired gas during the course of a single breath.
Recently it has become possible to describe defective intrapulmonary gas mixing in more complete terms. This has resulted from the finding that an unevenly ventilated lung behaves as if it consisted of several subdivisions, each evenly ventilated at its own rate.1,2 The volume and ventilation rate of these subdivisions can be measured, and these measurements provide a simple quantitative picture of the defect in intrapulmonary gas mixing.
Blair E, Hickam JB. Quantitative Study of Intrapulmonary Gas Mixing in Emphysema. Arch Intern Med. 1971;127(4):625–636. doi:10.1001/archinte.1971.00310160103009