Spherical indentation of lungs: Experiments, modeling and sub-surface imaging
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Zhijia Yuana) Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York 11794
Jae Hun Kima) Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York 11794
Zhenguo Wang Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York 11794
Melissa Hoyos Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York 11794
Yingtian Pan Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York 11794
Andrew Gouldstoneb) Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02199 (Received 1 August 2008; accepted 21 November 2008)
Knowledge of mechanics in atelectasis (alveolar collapse) and reinflation would be useful during anesthesia and critical care. Here an investigation is presented in which atelectasis is induced in a controlled manner on excised inflated lungs using spherical indentation, and noninvasive imaging of the deformed subsurface region is performed using optical coherence tomography (OCT). Indentation loads are physiologic, and spatial dimensions are far larger than alveolar size to allow continuum discussions. Experimental observations of atelectasis are compared with finite element model calculations of maximum stresses. Finally, atelectasis is compared during inflation of lungs with different gases (e.g., air, oxygen/anesthesia mixture).
I. INTRODUCTION AND BACKGROUND
Of all the internal organs, the lung has arguably the strongest connection between physiologic function and mechanical behavior. For normal breathing, it requires sufficient compliance and recoil for effective inflation and deflation, respectively. Accordingly, lung mechanics, particularly elasticity during physiology, has received large attention in the medical and engineering literature. Also, a number of pathologic and clinical conditions require mechanical ventilation of patients, due to decreased lung function.1–3 These include acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD) and extreme cases of asthma. Unfortunately, ventilation treatment may cause ventilator a)
These authors contributed equally to this paper. Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0148 b)
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J. Mater. Res., Vol. 24, No. 3, Mar 2009 Downloaded: 01 Apr 2015
induced lung injury (VILI) resulting in further insult to the lung. This is often related to the nonoptimum reinflation of collapsed alveoli, or atelectatic regions. Atelectasis is also an important issue in anesthesia and critical care, and its removal is crucial to long-term recovery.4,5 Alveoli are, by natural design, stable structures that tend to resist collapse, mainly due to surfactant that imparts stretch-dependent surface tension; nevertheless atelectasis occurs at low lung volumes or during injury. The specific mechanisms of atelectasis and its recovery are not well known, mak
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