Respiratory dead space measurements in a model lung and healthy human subjects according to the single breath method

¹ Respiratory Function Laboratory, Renströmska Sjukhuset, Gothenburg, Sweden

Observations on the dead space (Fowler's method) in a lung model were compared to observations on three human subjects. Corresponding to the theoretical gas front between dead space O₂ and alveolar N₂, a point in the model experiment was found dividing the S-shaped form of the N₂ curve in a ratio of 2:3. The washout volume for the model dead space was about twice its volume. Similar findings were noted in the human subjects. Washout time did not influence the dead space values at flow rates of 5–37 l/min. In the human subjects the dead space values increased by 2.4–3.3 ml/100 ml of increasing end-inspiratory lung volume. The values for the dead space fell during an inspiratory pause even in the normal interval of quiet breathing. The accuracy of the method in tests on the model with a known dead space of 190 ml was 189 ± 1.4 ml with a standard deviation of ±7.0 ml. In human subjects the standard deviation was about 10%.