Alveolar mechanics studied by in vivo microscopy imaging through intact pleural space

Abstract

In six male anesthetized, tracheotomized, and mechanically ventilated rabbits we derived indications on alveolar mechanics from in vivo imaging, using a "pleural window" technique (pleural space intact) that allows unrestrained movement of the same subpleural alveoli (N=60) on increasing alveolar pressure from 4 to 8 cmH2O. Absolute compliance (C(abs), ratio of change in alveolar surface area to the change in alveolar pressure) was significantly lower in smaller compared to larger alveoli. Specific compliance, C(sp), obtained by normalizing C(abs) to alveolar surface area, was essentially independent of alveolar size. Both C(abs) and C(sp) were affected by large variability likely reflecting the complex matching between elastic and surface forces. We hypothesize that the relative constancy of C(sp) might contribute to reduce interregional differences in parenchymal and surface forces in the lung tissue by contributing to assure a uniform stretching in a model of mechanically inter-dependent alveoli.

The effect of exogenous surfactant on alveolar interdependence

“…3). Recalling data from previous paper Salito et al, 2014), alveolar compliance was found to be directly proportional to alveolar dimension. The present data suggest that the smaller alveoli, that by nature have a lower mechanical compliance, benefit to a greater extent of surfactant distribution, as indicated by the increase in surface area.…”

“…In the present study, using an advanced imaging acquisition and data analysis method Salito et al, 2014), we estimated the geometrical changes induced by intra-tracheal surfactant administration and attempted an analysis to assess how inter-alveolar mechanical equilibrium was modified by local surfactant distribution. …”

“…The absolute compliance of the smaller alveolus (A) is lower than that of the larger one (B) as from data derived from Salito et al (2014). Before surfactant instillation, alveoli A and B were considered in equilibrium due to mechanical interdependence at P d of 2.5 cmH 2 O (as from esophageal pressure).…”

“…Recent studies from our group Salito et al, 2014) provided evidence of the existence of considerable geometrical heterogeneity in alveolar geometry and size that impact on the inter-alveolar differences in mechanical behavior that, in turn reflects the balance between elastic and surface forces (Gil et al, 1979;Tabuchi et al, 2008). The inter-alveolar differences in mechanical properties ought to be framed within a model of mechanically inter-dependent units (Bates and Suki, 2008).…”

Self-organizing pattern of subpleural alveolar ducts

“…Alveoli in the region just below the pleural surface have been examined by light microscopy since the 1930s [1][2][3][4][5][6][7] . These studies have often examined how the alveoli expand with lung inflation and how they might change with lung pathology.…”