HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Prange, H. D. Search for Related Content PubMed PubMed Citation Articles by Prange, H. D.

MISCONCEPTIONS

LAPLACE’S LAW AND THE ALVEOLUS: A MISCONCEPTION OF ANATOMY AND A MISAPPLICATION OF PHYSICS

Medical Sciences Program, Indiana University, Bloomington, Indiana 47405

Both the anatomy and the mechanics of inflation of the alveoli, as presented in most textbooks of physiology, have been misunderstood and misrepresented. The typical representation of the acinus as a "bunch of grapes" bears no resemblance to its real anatomy; the alveoli are not independent little balloons. Because of the prevalence of this misconception, Laplace’s law, as it applies to spheres, has been invoked as a mechanical model for the forces of alveolar inflation and as an explanation for the necessity of pulmonary surfactant in the alveolus. Alveoli are prismatic or polygonal in shape, i.e., their walls are flat, and Laplace law considerations in their inflation apply only to the very small curved region in the fluid where these walls intersect. Alveoli do not readily collapse into one another because they are suspended in a matrix of connective tissue "cables" and share common, often perforated walls, so there can be no pressure differential across them. Surfactant has important functions along planar surfaces of the alveolar wall and in mitigating the forces that tend to close the small airways. Laplace’s law as it applies to cylinders is an important feature of the mechanics of airway collapse, but the law as it applies to spheres is not relevant to the individual alveolus.

Key words: lung mechanics; respiratory models; surfactant; airway closure