Figure 5.

Comparison of abnormal alveoli at peak inspiration and end expiration. Abnormal alveoli at peak inspiration and end expiration as seen with an in vivo microscope (a, b) and as a histologic comparison (c, d). (a) Normal alveoli fill the microscopic field at peak inspiration, and (b) collapse during expiration. (c) Alveolar walls are very thin at peak inspiration, and (d) become thickened at end expiration.