Studies of Lung Volumes and Intrapulmonary Mixing: Notes on Open-circuit Methods, including Use of a New Pivoted Type Gasometer for Lung Clearance Studies.

The measurement of lung volume by an opencircuit method (1, 2) is usually based on the redistribution of nitrogen contained in the lungs in such a manner that most of this gas is expelled and measured. Physically, this principle requires only the collection of the exhaled nitrogen in some diluent such as oxygen and the measurement of total volume and nitrogen concentration; the quantity of nitrogen involved can then be computed. In the usual procedure the subject breathes oxygen for a set period, the total expired air being collected in a gasometer; then the connecting tubes are washed with more oxygen and the final volume and nitrogen concentration in the gasometer are measured. Such a method could be extended to the study of the nitrogen clearance process. The physical conditions which must be satisfied, however, are much more exacting than those which apply to measurement of lung volume. It becomes necessary to determine accurately (1) respiratory volume at various instants during the clearance process and (2) the total amounts of nitrogen in the external system at these instants. These requirements demand modification of existing open-circuit methods in the following particulars: A. It is necessary to avoid continuous flow of oxygen by-passing the experimental subject. Only by using a true demand system of oxygen supply can it be assured that all the gas collected has been involved in the tidal movement. B. It is necessary either to measure separate points on the clearance curve by doing several experiments, or to arrange for serial sampling of the expired gas, with simultaneous measurement of volume. The