Nitrogen Clearance Rates of Right and Left Lungs in Different Positions *†‡

Uniform alveolar ventilation implies that dur- ing inspiration all alveoli simultaneously receive gas of the same chemical composition and of the same volume (relative to the previous preinspiratory volume) and that this mixes almost in- stantaneously with the preinspiratory alveolar gas. Studies with single or multiple inhalations of "reference" gases have shown that alveolar venti- lation is nonuniform (uneven) in most normal men (2). The two principal theoretic explana- tions for this observation have been a) that in- spired gases are stratified in the peripheral alveolar spaces or b) that different regions (central versus peripheral spaces of a lobe or segment; different lungs, lobes or segments) are ventilated at dif- ferent rates. Although Roos, Dahlstrom and Murphy (3) again proposed the stratification theory, it was noted by Forster (4) that some of their experimental results could be equally con- sistent with a regional explanation.