Gas Exchange Model Research Articles

X-ray micro-CT based computation of effective diffusivity of metabolic gases in tomato fruit

The effective diffusivity is a key engineering property of fruit that affects transport of metabolic gases and, hence, ripening. It strongly depends on the microstructure of the fruit. In bulky fruit such as tomato, porosity and pore structure differ between tissues and change during maturation and ripening. Knowledge of the relationship between gas diffusivity and microstructure of tomato will aid management and control of postharvest operations. By using mathematical models of mass transport that incorporate the 3-D microscopic tissue geometry obtained from micro-computed tomography (μ-CT), the relationship between microstructural features and gas diffusivity may be computed in a direct way. In this study, a previously validated pore-scale network model (PNM) was used to simulate the effective gas diffusivity of O2, CO2 and ethylene for five types of tomato fruit tissues (i.e., outer mesocarp, inner mesocarp, septa, placenta and columella) at different maturation and ripeness stages. The effective gas diffusivity of the placenta and columella was large during the entire ripening process as these tissues contained more interconnected open intercellular spaces. The effective diffusivity of the inner mesocarp increased with increasing porosity during ripening while the microstructural changes of the outer mesocarp lagged compared to those of the inner mesocarp region, resulting in a delayed increase of the effective gas diffusivity with ripening. Regression models between the effective diffusivity of O2, CO2 and ethylene as a function of porosity, open porosity or tortuosity were established. This study provides a quantitative basis for further gas exchange modeling in intact tomato fruit to predict their ripening process.

Establishing a hemoglobin adjustment for 129 Xe gas exchange MRI and MRS.

129 Xe MRI and MRS signals from airspaces, membrane tissues (M), and red blood cells (RBCs) provide measurements of pulmonary gas exchange. However, 129 Xe MRI/MRS studies have yet to account for hemoglobin concentration (Hb), which is expected to affect the uptake of 129 Xe in the membrane and RBC compartments. We propose a framework to adjust the membrane and RBC signals for Hb and use this to assess sex-specific differences in RBC/M and establish a Hb-adjusted healthy reference range for the RBC/M ratio. We combined the 1D model of xenon gas exchange (MOXE) with the principle of TR-flip angle equivalence to establish scaling factors that normalize the dissolved-phase signals with respect to a standard (14 g/dL). 129 Xe MRI/MRS data from a healthy, young cohort (n = 18, age = 25.0 3.4 years) were used to validate this model and assess the impact of Hb adjustment on M/gas and RBC/gas images and RBC/M. Adjusting for Hb caused RBC/M to change by up to 20% in healthy individuals with normal Hb and had marked impacts on M/gas and RBC/gas distributions in 3D gas-exchange maps. RBC/M was higher in males than females both before and after Hb adjustment (p < 0.001). After Hb adjustment, the healthy reference value for RBC/M for a consortium-recommended acquisition of TR = 15 ms and flip = 20° was 0.589 0.083 (mean SD). MOXE provides a useful framework for evaluating the Hb dependence of the membrane and RBC signals. This work indicates that adjusting for Hb is essential for accurately assessing 129 Xe gas-exchange MRI/MRS metrics.

Estimation of Pulmonary Gas Exchange in the Human Respiratory System Under Normal and Abnormal Conditions

ABSTRACT: The human respiratory system is a collection of organs and tissues that regulate gas exchange in the body. There are millions of alveoli in the lungs surrounded by tiny blood capillaries. By breathing, the body inhales oxygen which moves from the alveoli to the blood capillary, and then exhales carbon dioxide in the air that diffuses across the pulmonary membrane of the blood capillary to the alveoli. We aim to develop a mathematical model of respiratory gas exchange that can handle various situations. A Model should be capable of finding the diffusion rate of oxygen that enters into the capillary from the lungs and dissolves into a different level of hemoglobin. It is also able to give the relationship between oxygen and carbon dioxide concentration with time. Numerical simulation helps us to predict the responses of the cardiorespiratory system during a heavy workout, usual activity, and inactive situations. It also considered the various factors that affect the gas exchange relation between partial pressure and saturation.

Development of a Zero-Dimensional Model for a Low-Speed Two-Stroke Marine Diesel Engine with Exhaust Gas Bypass and Performance Evaluation

Most large commercial vessels are propelled by low-speed two-stroke diesel engines due to their fuel economy and reliability. With increasing international concern about emissions and the rise in oil prices, improvements in engine efficiency are urgently needed. In the present work, a zero-dimensional model for a low-speed two-stroke diesel engine is developed that considers the exhaust gas bypass and geometry structures for the gas exchange model. The model was applied to a low-speed two-stroke 7G80 ME-C9 marine diesel engine and validated with engine shop test data, which consisted of the main engine performance parameters and cylinder pressure diagrams at different loads. The simulation results were in good agreement with the experimental data. Thus, the model has the ability to predict engine performance with good accuracy. After model validation, the variations in compression ratio, fuel injection timing, exhaust gas bypass valve opening portion, exhaust valve opening timing, and exhaust valve closing timing effects on engine performance were tested. Finally, the influence level of different parameters on engine performance was summarized, which can be used as a reference to determine the reasons for high fuel consumption in some cases. The developed engine performance model is considerable in digital twins for performance simulation, health management, and optimization.

Postharvest shelf life simulation for lettuce (Lactuca sativa L.) based on coupling dynamic models of respiration, gas exchange, and Pseudomonas fluorescens growth

Shelf life simulation of fresh-cut lettuce was established when packed in two commercial packaging materials with four levels of O2 transmission rate (OTR) from 5 to 3875 cm3/m2/d/0.1 MPa. This study has established mathematic models coupling respiration of fresh-cut lettuce and Pseudomonas fluorescens, O2 and CO2 exchange, and microbial growth. The coupling models succeeded in predicting the dynamic change of O2 and CO2 in the headspace of biaxially oriented polyamide/low-density polyethylene (BOPA/LDPE) and polyethylene (PE) films. The coupling model contained Baranyi function showed the best fitting performance when predicting P. fluorescens growth. Quality attributes of lettuce showed that the BOPA/LDPE film with the lowest OTR significantly inhibited the P. fluorescens growth, extensively maintained color and texture, and extended the shelf life of fresh-cut lettuce. The established coupling models could be further utilized for evaluating the microbial safety and shelf life of other types of leaf vegetables where pseudomonads are dominant for spoilage.

Seasonal dynamics of photosynthetic nitrogen content and partitioning in deciduous forests.

Nitrogen allocated to the photosynthetic apparatus and its partitioning into different photosynthetic components is crucial for understanding plant carbon gain and plant productivity. It is known that photosynthetic nitrogen content and partitioning are controlled by both environmental and vegetation factors and have versatile and dynamic responses. However, such responses are greatly simplified in most current gas exchange models, in which only a prescribed relationship is commonly applied to describe the effect of nitrogen on photosynthesis and with limited model performance. While within-canopy variation at a specific time in leaf photosynthetic nitrogen content and partitioning has been studied previously, far less attention has been paid to the seasonal dynamics of photosynthetic nitrogen content and partitioning, which is especially critical to deciduous forests. In this study, we integrated long-term field observations in deciduous forests in Japan to determine seasonal patterns of photosynthetic nitrogen content and partitioning (rubisco, electron transport, and light capture) and to examine how photosynthetic nitrogen content and partitioning varied seasonally in deciduous forest canopies growing at different altitudes. The results demonstrated that there were remarkable seasonal variations in both photosynthetic nitrogen content and partitioning in deciduous forests along the altitudinal gradient. Moreover, photosynthetic nitrogen use efficiency was well explained by nitrogen partitioning rather than total leaf nitrogen. These results suggest that seasonal patterns of nitrogen partitioning should be integrated into ecosystem models to accurately project emergent properties of ecosystem productivity on local, regional, and global scales.

Sensitivity Analysis of Whole-Room Indirect Calorimeters at the Steady-State Condition

Whole-Room Indirect Calorimeters (WRIC) are accurate tools to precisely measure energy metabolism in humans via calculation of oxygen consumption and carbon dioxide production. Yet, overall accuracy of metabolic measurements relies on the validity of the dynamic model for gas exchange inside the calorimeter volume in addition to experimental and environmental conditions that contribute to the uncertainty of WRIC outcome variables. The aim of this work is to formally study the sensitivity of a WRIC system operated in a push configuration at the steady-state condition to identify the optimal experimental conditions to obtain the best degree of accuracy for outcome metabolic measurements. The results of our sensitivity analysis are then validated with measurements obtained during propane combustion tests performed at the WRIC located at the University Hospital of Pisa. Our results demonstrate that achieving a fractional concentration of carbon dioxide inside the calorimeter >0.2% leads to relative uncertainty <5% for the outcome metabolic measurements when assuming an accuracy class of 1% for gas analyzer instruments.

Gas exchange and ventilation imaging of healthy and COPD subjects using hyperpolarized xenon-129 MRI and a 3D alveolar gas-exchange model.

To investigate the utility of hyperpolarized xenon-129 (HPX) gas-exchange magnetic resonance imaging (MRI) and modeling in a chronic obstructive pulmonary disease (COPD) cohort in comparison to a minimal CT-diagnosed emphysema (MCTE) cohort and a healthy cohort. A total of 25 subjects were involved in this study including COPD (n = 8), MCTE (n = 3), and healthy (n = 14) subjects. The COPD subjects were scanned using HPX ventilation, gas-exchange MRI, and volumetric CT. The healthy subjects were scanned using the same HPX gas-exchange MRI protocol with 9 of them scanned twice, 3 weeks apart. The coefficient of variation (CV) was used to quantify image heterogeneities. A three-dimensional computational fluid dynamic (CFD) model of gas exchange was used to derive functional volumes of pulmonary tissue, capillaries, and veins. The CVs of gas distributions in the images showed that there was a statistically significant difference between the COPD and healthy subjects (p < 0.0001). The functional volumes of pulmonary tissue, capillaries, and veins were significantly lower in the subjects with COPD than in the healthy subjects (p < 0.001). The functional volume of pulmonary tissue was found to be (i) statistically different between the healthy and MCTE groups (p = 0.02) and (ii) dependent on the age of the subjects in the healthy group (p = 0.0008) while their CVs (p = 0.13) were not. The novel HPX gas-exchange MRI and CFD model distinguished the healthy cohort from the MCTE and COPD cohorts. The proposed technique also showed that the functional volume of pulmonary tissue decreases with aging in the healthy group. • The ventilation and gas-exchange imaging with hyperpolarized xenon-129 MRI has enabled the identification of gas-exchange variation between COPD and healthy groups. • This novel technique was promising to be sensitive to minimal CT-diagnosed emphysema and age-related changes in gas-exchange parameter in a small pilot cohort.

Low atmospheric CO2 levels before the rise of forested ecosystems

The emergence of forests on Earth (~385 million years ago, Ma)1 has been linked to an order-of-magnitude decline in atmospheric CO2 levels and global climatic cooling by altering continental weathering processes, but observational constraints on atmospheric CO2 before the rise of forests carry large, often unbound, uncertainties. Here, we calibrate a mechanistic model for gas exchange in modern lycophytes and constrain atmospheric CO2 levels 410–380 Ma from related fossilized plants with bound uncertainties of approximately ±100 ppm (1 sd). We find that the atmosphere contained ~525–715 ppm CO2 before continents were afforested, and that Earth was partially glaciated according to a palaeoclimate model. A process-driven biogeochemical model (COPSE) shows the appearance of trees with deep roots did not dramatically enhance atmospheric CO2 removal. Rather, shallow-rooted vascular ecosystems could have simultaneously caused abrupt atmospheric oxygenation and climatic cooling long before the rise of forests, although earlier CO2 levels are still unknown.

Cropbox: a declarative crop modelling framework

AbstractWe introduce Cropbox, a novel modelling framework that supports various aspects of crop modelling in a unique yet concise style. Building a crop model can be easily riddled with technical details looking trivial at first but later becoming major obstacles that hamper the whole development or application process. This is particularly the case when implementing models from scratch without relying on an established framework. Cropbox adopts a declarative approach providing a domain-specific language to reduce technical debt and assist modellers to focus on high-level abstraction formed by relations between variables and enclosing systems, rather than tinkering with low-level implementation details. The syntax of Cropbox framework is based on the Julia programming language and is deliberately constrained to avoid unintended side effects caused by common mistakes while its architecture remains open to extension. We highlight key capabilities of the framework through case studies featuring a leaf gas-exchange model and a whole-plant simulation model. We also illustrate potential extensions for supporting functional-structural plant modelling by demonstrating a 3D root architectural model as an example.

Modulation of Bubble‐Mediated CO2 Gas Transfer Due To Wave‐Current Interactions

AbstractWave breaking modulates air‐sea fluxes of energy, momentum, heat, and gases. Building on recent advances in the modeling of CO2 gas exchange and wave breaking, we investigate the variability of bubble‐mediated gas transfer coefficients due to wave‐current interactions. Submesoscale current gradients strongly modulate wave breaking, which can enhance the bubble‐mediated gas transfer coefficient along temperature fronts and cold filaments. The enhancement of the gas transfer coefficient is over relatively small areas averaging out over larger regions. However, the correlation between positively anomalous gas transfer coefficients and regions with strong downwelling could potentially enhance CO2 exchange over regions with increased submesoscale activity. An empirical scaling based on the mean wave period, root‐mean‐square current gradients, and friction velocity can explain the root‐mean‐square differences of gas transfer coefficients computed from solutions with and without current forcing.

Effects of O2/CO2 transmission rate of BOPA/LDPE or PE film on shelf life and quality attributes of fresh-cut cherry radish

This study established models coupling Pseudomonas fluorescens growth, respiration, and dynamic O2 and CO2 change to evaluate effects of O2/CO2 transmission rates (OTR/CTR) on quality attributes of fresh-cut cherry radish (Raphanus sativus L. var. radculus pers) packed in biaxially oriented polyamide/low-density polyethylene (BOPA/LDPE) and polyethylene (PE) films during cold storage. The Baranyi model successfully modeled the growth of P. fluorescens. Microbial growth kinetics, including μmax and λ of P. fluorescens decreased with the increased OTR/CTR level of packaging films. Starting from the 4th day-storage, the respiration rates (RRs) remained unchanged until the end of cold storage, and the plateau of RR increased with the increase in OTR/CTR levels. The O2 content was significantly lower and CO2 content was higher in BOPA/LDPE films with OTR5 and OTR48 compared with that in PE films with high OTR where O2 ingress through permeation kept high and compensated O2 consumed by respiration of fresh-cut cherry radish. The difference in dynamic gas change influenced quality attributes and sensory properties as well. The BOPA/LDPE as a high barrier film extensively maintained color, total soluble solid content, firmness, nutrients and therefore, extended shelf life of cherry radish to 12 d, which was longer than that packed in the PE films (9 d) as low barrier films. The established coupling gas exchange models conjugated to the Baranyi model could be further utilized for predicting dynamic gas change and RR of other types of fresh-cut vegetables where Pseudomonas are dominant for spoilage.

Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

AbstractGas exchange at high wind speeds is not well understood—few studies have been conducted at wind speeds above 20 ms−1 and significant disagreement exists between gas exchange models at high wind speeds. In this study, noble gases (He, Ne, Ar, Kr, and Xe) were measured in 35 experiments in the SUSTAIN wind‐wave tank where the wind speeds ranged from 20 to 50 m s−1 and mechanical waves were generated as monochromatic or with a short‐crested JONSWAP frequency spectrum. Bubble size spectra were determined using shadowgraph imagery and wave statistics were measured using a wave wire array. The steady state saturation anomalies and gas fluxes initially increased as wind speeds increased but then leveled off, similar to prior studies of heat and momentum flux coefficients. Noble gas fluxes and steady state saturation anomalies are correlated most strongly with bubble volumes for the less soluble noble gases and with wind speed and wave Reynolds number for the more soluble noble gases. In the JONSWAP experiments, significant wave height was the most important predictor for gas steady state saturation anomalies with correlation coefficients of greater than 0.92 for He, Ne, and Ar (P &lt; 0.05). Furthermore, invasion fluxes were larger than evasion fluxes when other conditions were similar. Taken together, these lab‐based experiments suggest more attention should be paid to parameterizations based on wave characteristics and bubbles and that current wind‐speed based gas exchange parameterizations should not be applied to conditions with very high wind speeds.

Remotely Sensing River Greenhouse Gas Exchange Velocity Using the SWOT Satellite

AbstractTwo decades of research has shown that the global river network emits significant amounts of greenhouse gas. Despite much progress, there is still large uncertainty in the temporal dynamics of gas exchange and thus carbon emissions to the atmosphere. Much of this uncertainty stems from a lack of existing tools for studying the spatiotemporal dynamics of gas exchange velocity (the rate of this diffusive transport). We propose that the NASA/CNES/UKSA/CSA Surface Water and Ocean Topography (SWOT) satellite can provide new insights to fluvial gas exchange modeling upon launch and subsequent data collection in 2022. Here, we exploit the distinct geomorphology of SWOT‐observable rivers (&gt;50 m wide) to develop a physical model of gas exchange that is remotely sensible and explains 50% of log‐transformed variation across 166 field measurements of . We then couple this model with established inversion techniques to develop BIKER, the “Bayesian Inference of the Exchange Rate” algorithm. We validate BIKER on 47 SWOT‐simulated rivers without an in‐situ calibration, yielding an algorithm that predicts the timeseries solely from SWOT observations with a by‐river median Kling‐Gupta Efficiency of 0.21. BIKER is better at inferring the temporal variation of gas exchange (median correlation coefficient of 0.91), than reproducing the absolute rates of exchange (median normalized RMSE of 51%). Finally, BIKER is robust to measurement errors implicit in the SWOT data. We suggest that BIKER will be useful in mapping global‐scale fluvial gas exchange and improving emissions estimates when coupled with river models.

Stems matter: Xylem physiological limits are an accessible and critical improvement to models of plant gas exchange in deep time

The evolution of woody stems approximately 400 mya (middle Paleozoic) facilitated the expansion of plants and has likely affected carbon and water budgets across much of the terrestrial surface since that time. Stems are a carbon cost/sink and limit water transport from soil to leaves as it must pass through specialized xylem tissue. While leaf fossils have provided a wealth of quantitative data, including estimates of plant water fluxes utilizing biophysically based models, fossil-informed models integrating stem and leaf physiology are lacking. Integrated stem-leaf physiology may distinguish successors to ecological catastrophes like the end of the Late Paleozoic Ice Age (LPIA). The documented collapse of LPIA tropical forests provides an opportunity to assess the importance of woody stems as a key to understanding differences in survivorship among common plant taxa from the Carboniferous to the Permian. Here, we present an analysis of the limits to leaf water supply and plant function for Paleozoic forest plant types due to (1) cavitation-induced embolism and xylem blockage and (2) insufficient sapwood water transport capacity.—collectively defined here as sapwood dysfunction. We first present a modified ecosystem process model (Paleo-BGC+) that includes sapwood dysfunction. Paleo-BGC + is parameterized using measurements obtainable from fossil xylem and therefore applicable to both modern and ancient ecosystems. We then assess the effect of sapwood dysfunction on ecosystem processes based on previously published fossil leaf measurements and a new fossil xylem dataset for plant types present in the Late Paleozoic. Using daily meteorology from a GCM of the late Carboniferous (GENESIS v3) under a Glacial (low-CO2) and an Inter-glacial (high-CO2) scenario, we found that simulated sapwood dysfunction slowed plant water use and reduced carbon storage. This inhibition occurred particularly in plants with high maximum stomatal conductance and high stem vulnerability to embolism. Coincidentally, plants with these traits were predominantly reduced or missing from the fossil record from the Carboniferous to the Permian. Integrating stem and leaf physiology may improve the fidelity of model representations of soil-to-atmosphere water transport through plants, simulations of long-term climate phenomena like the LPIA, and ecosystem projections under future climate change.

Mathematical lung model for local gas exchange based on EIT-measurements

Abstract In this work we present a four compartment mathematical lung model to simulate the local gas exchange based on electrical impedance tomography (EIT) input. The model simulates the local and global time course of the volume, the gas fraction in the alveoli and the arterial partial pressure. The regional information about the distribution of ventilation and perfusion is extracted from EIT data. In order to illustrate the suitability of this approach, an ARDS patient is simulated. The results show good agreement with measurement data for large portions of the time and seem promising e.g. for the use in medical decision support systems.

Computational modeling of capillary perfusion and gas exchange in alveolar tissue

Gas exchange is an essential function of the respiratory system that couples fundamentally with perfusion in respiratory alveoli. Current mathematical formulations and computational models of these two phenomena rely on one-dimensional approximations that neglect the intricate volumetric microstructure of alveolar structures. In this work, we introduce a coupled three-dimensional computational model of pulmonary capillary perfusion and gas exchange that conforms to alveolar morphology. To this end, we derive non-linear partial differential equations and boundary conditions from physical principles that govern the behavior of blood and gases in arbitrary alveolar domains. We numerically solve the resulting formulation by proposing and implementing a non-linear finite-element scheme. Further, we carry out several numerical experiments to validate our model against one-dimensional simulations and demonstrate its applicability to morphologically-inspired geometries. Numerical simulations show that our model predicts blood pressure drops and blood velocities expected in the pulmonary capillaries. Moreover, we replicate partial pressure dynamics of oxygen and carbon dioxide reported in previous studies. This overall behavior is also observed in three-dimensional alveolar geometries, providing more detail associated with the spatial distribution of fields of interest and the influence of the shape of the domain. We envision that this model opens the door for enhanced in silico studies of gas exchange and perfusion on realistic geometries, coupled models of respiratory mechanics and gas exchange, and multi-scale analysis of lung function; furthering our understanding of lung physiology and pathology. Codes are available at https://github.com/comp-medicine-uc/num-model-alv-perfusion-gas-exchange.

Mediating heat transport by microbubble dispersions: The role of dissolved gases and phase change dynamics

• Developed a new model for buoyant convection with a dispersed microbubble phase. • Predicts microbubble phase fraction controls additional HT mechanism. • Scale of the additional heat transfer ranges from 5–45% with phase fractions 2–20%. • Demonstrates that dominant feature for HT in larger domains is the boundary layer. • Conclusions hold qualitatively with simple model for gas exchange between phases. Recently a theory for additional heat convection by microbubbles was posited. The mechanism proposed is that the latent heat of vapor of the liquid is carried by microbubbles from hot zones that vaporize more liquid to cold zones where condensation releases the latent heat. In this paper, the proposition that the additional heat flux is controlled by the phase fraction of microbubbles, is tested by steady state solutions of the canonical hot wall / cold wall buoyant convection problem. The simulations show that the range of additional heat transfer varies monotonically with length scale of the cavity, between 5 and 45% with phase fractions varying from 0.02 and 0.2. The larger characteristic lengths introduce insufficient heat flux from the hot wall to maintain a “driven cavity” flow structure, so that the steady state structure that emerges is a stable stratification with thin boundary layers near the hot and cold walls, with weak shear flow convection. The stable stratification resultant at higher characteristic lengths suppresses the additional heat flux due to microbubble mediation, yet only moderately deviating from proportionality. These conclusions hold qualitatively for a variant of the model which simply treats the gas exchange between the microbubble phase and dissolved gases in the liquid, resulting in variation of the microbubble phase fraction with temperature, hence with position in the domain. Quantitatively, the percentage increases are 3–30% in the parameter regime above, with the effects of dissolved gases captured dynamically.

Gas exchange model using heterogeneous diffusivity to study internal browning in ‘Conference’ pear

Internal gas gradients in pear fruit during controlled atmosphere storage depend on the effective gas diffusivity of the tissue. The diffusivity varies over the fruit organ due to the heterogeneous tissue microstructure across the fruit. This study implemented effective diffusivity maps reflecting the heterogeneous structure to predict internal gas gradients and relate the result to the occurrence of internal browning. Diffusivity maps of different pears were calculated from X-ray CT based porosity maps. Internal oxygen (O2), carbon dioxide (CO2) and respiratory quotient (RQ) levels were computed using a reaction-diffusion model incorporating the heterogeneous effective diffusivity map. Critical O2 and RQ levels for the shift from respiration to fermentation were defined based on the respiratory-fermentative energy balance of the cells. The model was indirectly validated by comparing RQ level contours with non-destructive 3D images of the internal browning of the pears after storage at 1.0 kPa and 0.5 kPa O2, combined with 0.7 kPa CO2 at 1 °C. The distribution of the internal gas concentrations and RQ was affected by the heterogeneity of the diffusivity. The results also confirmed the incidence of internal browning when the O2 and RQ were under or above critical O2 and RQ limits, respectively. The fermentation process was indicated to be dominant when the tissue’s RQ limit (RQ*) went above 2.12 (or at 0.044 kPa O2). The tissue volumes where O2 and RQ levels were critical corresponded reasonably well to browning-affected tissues of pears with different shapes. The pear with more shallow gas gradients showed less symptoms of browning.

Analysis and characterization of diffusive flows and movement of the human acinar region: An experimentally validated CFD model

This paper presents a study of the gas exchanges at the alveolar level to define the respiratory capacity of a subject. A numerical multidimensional approach is proposed for the prediction of the diffusive flows of gases (oxygen and carbon dioxide) in the alveoli accounting for the gas exchange phenomena including the surface variation due to the alveoli motion. The overset mesh technique is used to reproduce a realistic surface variation during inspiration and expiration and simulate the expansion and retraction of the alveolar sac. A gas-exchange model is implemented to predict the gas distribution in the alveolar sac wall by assigning a gas flow function through the membrane. The numerical analysis enables to evaluate the flow field within the single alveoli in terms of total and partial pressure of the considered alveolar gases, as well as the species distribution due to the diffusive flows. The predictive capabilities of the numerical model are addressed by comparing the calculations with the values obtained by means the mobile metabolic system K5 from COSMED. An experimental campaign on a set of healthy subjects is used to evaluate the diffusive flows through the membrane and a good agreement between the numerical results and the experimental measurements is found. These evaluations are suitable for the characterization of the breathing capacity in physiological or pathological conditions; therefore, the proposed model can be used as a valid support for bioengineering studies in terms of respiratory gas exchange prediction.