In pulmonary disease the inspired air is often distributed unequally throughout the lung. The volume of the poorly aerated regions of the lung and their rate of ventilation are of importance to the clinician but quantitation of these values has been difficult.
The situation was much clarified in 1950 by Robertson, Siri, and Jones (1) who demonstrated that an unequally ventilated lung behaves as though it consisted of a number of subdivisions of smaller size, each of which is homogeneously ventilated at its own particular rate. Preliminary work which led to the same concept was also reported at this time by Fowler, Cornish, and Kety (2). By continuously following the course of nitrogen elimination from the lungs of a subject breathing oxygen, it was possible to characterize these lung subdivisions in terms of size and ventilation rate. This information describes an unequally ventilated lung in a way which permits useful,
HICKAM JB. AN OPEN-CIRCUIT HELIUM METHOD FOR MEASURING FUNCTIONAL RESIDUAL CAPACITY AND DEFECTIVE INTRAPULMONARY GAS MIXING. Arch Intern Med. 1971;127(4):615-624. doi:10.1001/archinte.1971.00310160093008