Displacement of nitrogen from normal human lungs during oxygen breathing.

Abnormalities of intrapulmonary distribution and mixing of inspired gases occur in diseases of the lungs, particularly in pulmonary emphysema. Interest in this problem began in 1864, and has been pursued with many different methods (1). However, uncertainty and even confusion still exists not only in the definition but also in the quantitative measurement of intrapulmonary distribution and mixing. One means of investigating the problem is the measurement of nitrogen displacement from the lung as it occurs during oxygen breathing, reported by Cournand and his associates (2-4). As an index of impaired distribution and mixing of the inspired gas with alveolar gas, they proposed an end-expired nitrogen concentration exceeding 2.5 per cent, delivered by a forced expiration at the end of a seven minute period of quiet oxygen-breathing (3). With such a technique only two points in the course of the nitrogen dilution were known-the initial alveolar nitrogen concentration while breathing air, and the final nitrogen concentration produced by the terminal forced expiration. Subsequently, a mathematical expression was presented (4) for ideal intrapulmonary mixing of oxygen and nitrogen, enabling predictions of the intrapulmonary nitrogen concentration at the end of any given number of breaths of oxygen. Divergence was found even in normal persons between the actual course of nitrogen dilution and the predicted course. With the help of continuous rapid automatic gas analyzers such as the nitrogen meter (5) and the mass spectrometer (6), later investigators could follow the breath-by-breath dilution of nitrogen during the breathing of oxygen. After graphical analysis of the displacement curves they proposed interesting concepts of well-ventilated and poorly-