The sloping alveolar plateau at synchronous ventilation

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Abstract
We performed model calculations on the slope of the alveolar plateau at single breath washout of helium (He) and sulphurhexafluoride (SF6). Calculations were carried out on an extensible axissymmetric lung model, which was synchronously ventilated either equally or unequally. The calculated slopes of the alveolar plateau were small (<0.3%), which is in agreement with the results of other investigators. However, calculations carried out on a synchronously equally ventilated axis-asymmetric lung model related to the terminal lung unit (acinus), yielded slopes for the alveolar plateau ranging from 0 up to 14% per liter between 1.2 and 1.8 l expired volume. Even with a post inspiratory apnea of 1 s, we still found slopes ranging from 0–4%. Our findings are in contrast to the conclusions of Engel et al. (1979), who ascribe the slope of the alveolar plateau to asynchronous unequal ventilation.