Distributions of aeration (column A), perfusion (column B), and aeration/perfusion (, column C) during biphasic positive airway pressure/airway pressure release ventilation (BIPAP/APRV) at four different levels of spontaneous breathing in total minute ventilation (0%, >0 to 30%, >30 to 60%, and >60%, rows 1–4, respectively) in a representative animal. Single scans represent the maximal cross-sectional areas of the respective whole lung images. Horizontal color bars denote the respective scales. Hyper = hyperaerated compartment; non = nonaerated compartment; normal = normally aerated compartment; poor = poorly aerated compartment.