[A new isotope technic for the determination of residual volume]

A new isotope method for the determination of the residual volume of the lungs by means of stable, non-radioactive nitrogen isotope 15N is described. Normal air is breathed in a closed system. One part of the air nitrogen is replaced by 15N labelled molecular nitrogen. 15N2 physiologically acts like normal nitrogen so that the so-called secondary effects by using He or H2 are eliminated. By combination of a spirograph and an emission spectrometric 15N analyser the residual volume can be determined and mixing curves can be obtained. The determination of the residual volume in 10 healthy persons gives a range of normal values from 19 to 31% of the total capacity. In three persons with emphysema values from 45 to 50% of the total capacity are found. The analysis of mixing curves leads to additional informations concerning the intrapulmonary gas mixing conditions in the lungs. The relative error of the residual volume determination is about 8%.