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Alveolar Dynamics during Respiration

Are the Pores of Kohn a Pathway to Recruitment?

¹ Department of Internal Medicine, ³ Department of Biomedical Engineering, and ⁴ Department of Radiology, University of Iowa, Iowa City, Iowa; and ² Department of Informatics and Engineering, Flinders University, Adelaide, Australia

Correspondence and requests for reprints should be addressed to Geoffrey McLennan, MD, PhD, FRACP, Internal Medicine, University of Iowa, 200 Hawkins Drive, C325 GH, Iowa City, IA 52242. E-mail: geoffrey-mclennan{at}uiowa.edu

The change in alveolar size and number during the full breathing cycle in mammals remains unanswered, yet these descriptors are fundamental for understanding alveolar-based diseases and for improving ventilator management. Genetic and environmental mouse models are used increasingly to evaluate the evolution of disease in the peripheral lung; however, little is known regarding alveolar structure and function in the fresh, intact lung. Therefore, we have developed an optical confocal process to evaluate alveolar dynamics in the fresh intact mouse lung and as an initial experiment, have evaluated mouse alveolar dynamics during a single respiratory cycle immediately after passive lung deflation. We observe that alveoli become smaller and more numerous at the end of inspiration, and propose that this is direct evidence for alveolar recruitment in the mouse lung. The findings reported support a new hypothesis that requires recruitable secondary (daughter) alveoli to inflate via primary (mother) alveoli rather than from a conducting airway.

Key Words: alveolar recruitment • mechanics • mouse lung • confocal microscopy • collateral ventilation

CLINICAL RELEVANCE The research presented provides new insight into alveolar mechanics in fresh intact mouse lungs and has a significant impact on the understanding of alveolar-based diseases and current clinical ventilator management practices.