Breath‐by‐Breath Sampling of Alveolar (End‐Tidal) Gas

For studies of the rate of change of alveolar gas composition in transitional states, a breath‐by‐breath end‐tidal gas sampler is proposed which combines great simplicity in design with a much reduced mixing of successive samples. The validity of the method is discussed and illustrated by breath‐by‐breath comparisons of end‐tidal and arterial P co2 , the latter being followed by continuous recording of the arterial pH. It is shown that, in or near the resting conditions, the two parameters closely follow each other, even when exhibiting rapid and great fluctuations, and that the P co2 of the samples approximates the functional mean alveolar P co2 .