Imaging of the three-dimensional alveolar structure and the alveolar mechanics of a ventilated and perfused isolated rabbit lung with Fourier domain optical coherence tomography

Abstract

In this feasibility study, Fourier domain optical coherence tomography (FDOCT) is used for visualizing the 3-D structure of fixated lung parenchyma and to capture real-time cross sectional images of the subpleural alveolar mechanics in a ventilated and perfused isolated rabbit lung. The compact and modular setup of the FDOCT system allows us to image the first 500 microm of subpleural lung parenchyma with a 3-D resolution of 16 x 16 x 8 microm (in air). During mechanical ventilation, real-time cross sectional FDOCT images visualize the inflation and deflation of alveoli and alveolar sacks (acini) in successive images of end-inspiratory and end-expiratory phase. The FDOCT imaging shows the relation of local alveolar mechanics to the setting of tidal volume (VT), peak airway pressure, and positive end-expiratory pressure (PEEP). Application of PEEP leads to persistent recruitment of alveoli and acini in the end-expiratory phase, compared to ventilation without PEEP where alveolar collapse and reinflation are observed. The imaging of alveolar mechanics by FDOCT will help to determine the amount of mechanical stress put on the alveolar walls during tidal ventilation, which is a key factor in understanding the development of ventilator induced lung injury (VILI).

Alveolar dynamics in acute lung injury: Heterogeneous distension rather than cyclic opening and collapse*

“…Contact-free Fourier domain OCT was performed by a recently developed custom-built system (20). A schematic drawing of the setup is given in Figure 2.…”

A 4-Dimensional Model of the Alveolar Structure

“…To verify the hypothesis that liquid bridges cover the alveolar mouth at low lung volume, we will need a much higher magnification than any currently available on our in vivo microscope or other imaging technique. Micro CT scanners are the most promising modalities for the 3-D observation of alveolar dynamics, though the present resolutions are insufficient for observing the 4-D behavior of alveoli in vivo [8,9].…”

“…However, it is limited to an observation of subpleural alveoli in two dimensions, and it is difficult to estimate the 3-dimensional (3-D) change of the alveoli from these data. Three-dimensional micro CT images provide excellent 3-D images with high spatial resolution [8,9], but the time resolution is insufficient for acquiring 4-dimensional (4-D; 3-D space + time) alveolar images. Thus with the technology currently available, it is impossible to measure the changes in alveolar architecture in vivo; therefore new methods must be developed to study the 4-D behavior of alveoli.…”

Alveolar Dynamics during Respiration

“…The most recently proposed alternative for imaging subpleural alveolar structure is Fourier domain optical coherence tomography (7). In their feasibility study, Popp and colleagues initially evaluated formalin fixed rabbit lung followed by isolated fresh lungs.…”