A human acinar structure for simulation of realistic alveolar plateau slopes

Abstract

We simulated the intra-acinar contribution to phase III slope (S(acin)) for gases of differing diffusivities (He and SF(6)) by solving equations of diffusive and convective gas transport in multi-branch-point models (MBPM) of the human acinus. We first conducted a sensitivity study of S(acin) to asymmetry and its variability in successive generations. S(acin) increases were greatest when asymmetry and variability of asymmetry were increased at the level of the respiratory bronchioles (generations 17-18) for He and at the level of the alveolar ducts (generations 20-21) for SF(6), corresponding to the location of their respective diffusion fronts. On the basis of this sensitivity study and in keeping with reported acinar morphometry, we built a MBPM that actually reproduced experimental S(acin) values obtained in normal subjects for He, N(2), and SF(6). Ten variants of such a MBPM were constructed to estimate intrinsic S(acin) variability owing to peripheral lung structure. The realistic simulation of S(acin) in the normal lung and the understanding of how asymmetry affects S(acin) for different diffusivity gases make S(acin) a powerful tool to detect structural alterations at different depths in the lung periphery.

Saline aerosol bolus dispersion. I. The effect of acinar airway alteration

“…It is interesting to explore the underlying theory of N 2 washout and bolus dispersion analysis to understand how gas and aerosol transport mechanisms operating in the same lung structure can be held responsible for the increased S acin and increased bolus dispersion in the deep lung (high VLD). On the basis of N 2 washout theory (11,24) and experiments (29,28), S acin originates from convection-diffusion interaction at the acinar level, where gas convective and gas diffusive transport are of the same order of magnitude, and S acin may be considered independent of gas-mixing events occurring proximal to the acinar lung level. Also, S acin heavily depends on the asymmetry of the acinar lung structure, and a perturbation in the volumetric or cross-sectional asymmetry of parallel intra-acinar units can modify S acin .…”

Assessing and accessing the small airways; implications for asthma management

“…Patients with high airways resistance take longer to clear the nitrogen, and the test can distinguish between obstructions in the large or small airways. Dutrieue et al [43] and Verbanck et al [44] used the MBW test to derive the two variables, Scond (index of conductive ventilation heterogeneity) and Sacin (index of acinar ventilation heterogeneity). In asthmatic subjects, the clinical application of MBW includes evaluation of ventilation heterogeneity after an airway challenge, and analysis of response differences to inhaled steroids when comparing non-extrafine and extrafine particles [45,46].…”

A Novel Interpretation of Closing Volume Based on Single-Breath Nitrogen Washout Curve Simulation

“…As mentioned in METHOD, the deformation model did not consider intra-acinar nitrogen concentration inhomogeneity. Simulation studies by Dutrieue et al [11] suggested that diffusion-convection-dependent inhomogeneity in the pulmonary acinus generated phase III slopes. According to their study, it is reasonable that phase III slopes in the present simulation were zero.…”

“…8 and 10, respectively. The density change is expressed as ρ(z,t) = ρ 0 (t) (1 -6gtCρ 0 (t)z) -1/2 , if ρ(z,t) < ρ m ρ(z,t) = ρ m , else (11) Accordingly, the displacement function is f(Z, t) = 1.5gtCρ 0 (t) Z 2 , if ρ(z, t) < ρ m f(Z, t) = f(Z m , t) + ρ 0 (Z m -Z)/ρ m , else (12) where (Z m , t m ) are the values of (Z, t) with which the righthand side of Eq. 11 is equal to ρ m .…”

“…Although several simulation studies have been released on phase III [9][10][11][12], there have been no model studies reported on phase IV. In this paper, we have reproduced phase IV in the SBNW curve based on a lung deformation model in which the lung tissue is regarded as a porous elastic body similar to a sponge.…”