Sentence:  In the lower center rack an 8 - channel recorder indicates the percentage of carbon dioxide and <WSD>nitrogen</WSD> from the upper and lower lobes of one lung , the total volume of inhalation per breath , the flow of air from both lobes , and the pressure of the two lobes with respect to each other . 
Meaning of the word marked with <WSD> tags:  a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues