Alveolar Dynamics during Respiration

Abstract

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.

Positive End-expiratory Pressure Increments during Anesthesia in Normal Lung Result in Hysteresis and Greater Numbers of Smaller Aerated Airspaces

“…4A). These findings are similar to those reported using ex vivo laser scanning confocal microscopy during inflation of healthy mouse lungs, 32 where mean alveolar size increased up to a threshold airway pressure (25 cmH 2 O) and thereafter decreased. While this could represent redistribution of gas from previously inflated to newly open units, 11, 23, 27 it could be due to opening of smaller alveoli.…”

“…While this could represent redistribution of gas from previously inflated to newly open units, 11, 23, 27 it could be due to opening of smaller alveoli. 32 Recruitment is consistent with reduced compliance associated with increasing PEEP (fig. 2B), which may reflect regional lung tissue compression 33 or progressive tissue stiffening due to increased airway pressure (demonstrated by MRI 34 ).…”

An implicit elastic theory for lung parenchyma

“…It is well known that the parenchyma is viscoelastic [16] with likely causes being the tissue itself [29], the surfactant film [9, 30], and alveolar recruitment [31-33]. Here we seek to understand the underlying nonlinear elastic contribution to the overall parenchymal response so that a proper viscoelastic theory for parenchyma can be constructed in the future.…”

Dynamic Multiscale Boundary Conditions for 4D CT of Healthy and Emphysematous Rats

“…The three predominant mechanisms responsible for this are believed to be the surfactant film, alveolar recruitment, and the extracellular matrix of collagen and elastin [26]–[30]. The role of surfactant was demonstrated by Hildebrandt [31] in air- and saline-filled lungs.…”

“…Without surfactant, collagen and elastin, the primary components in the extracellular matrix [28], are responsible for the relatively small hysteresis in the parenchyma and therefore contribute relatively little to the viscoelasticity of the lung. Alveolar recruitment is not a typical viscoelastic mechanism; nevertheless, an examination of the work of Namati et al [30] demonstrates that the recruitment process is hysteretic, since the distributions in alveolar size are different at the same pressure during inflation and deflation.…”