Evolving topological order in the postnatal visceral pleura.

BACKGROUND: Changes in epithelial cell shape reflects optimal cell packing and the minimization of surface free energy, but also cell-cell interactions, cell proliferation, and cytoskeletal rearrangements. RESULTS: Here, we studied the structure of the rat pleura in the first 15 days after birth. After pleural isolation and image segmentation, the analysis demonstrated a progression of epithelial order from postnatal day 1 (P1) to P15. The cells with the largest surface area and greatest shape variability were observed at P1. In contrast, the cells with the smallest surface area and most shape consistency were observed at P15. A comparison of polygonal cell geometries demonstrated progressive optimization with an increase in the number of hexagons (six-sided) as well as five-sided and seven-sided polygons. Analysis of the epithelial organization with Voronoi tessellations and graphlet motif frequencies demonstrated a developmental path strikingly distinct from mathematical and natural reference paths. Graph Theory analysis of cell connectivity demonstrated a progressive decrease in network heterogeneity and clustering coefficient from P1 to P15. CONCLUSIONS: We conclude that the rat pleura undergoes a striking change in pleural structure from P1 to P15. Further, a geometric and network-based approach can provide a quantitative characterization of these developmental changes.

Vascularization of the adult mouse lung grafted onto the chick chorioallantoic membrane.

In the later stages of angiogenesis, the vascular sprout transitions into a functional vessel by fusing with a target vessel. Although this process appears to routinely occur in embryonic tissue, the biologic rules for sprout fusion and lumenization in adult regenerating tissue are unknown. To investigate this process, we grafted portions of the regenerating post-pneumonectomy lung onto the chick chorioallantoic membrane (CAM). Grafts from all 4 lobes of the post-pneumonectomy right lung demonstrated peri-graft angiogenesis as reflected by fluorescent plasma markers; however, fluorescent microsphere perfusion primarily occurred in the lobe of the lung that is the dominant site of post-pneumonectomy angiogenesis-namely, the cardiac lobe. Vascularization of the cardiac lobe grafts was confirmed by active tissue growth (p < .05). Functional vascular connections between the cardiac lobe and the CAM vascular network were demonstrated by confocal fluorescence microscopy as well as corrosion casting and scanning electron microscopy (SEM). Bulk transcriptional profiling of the cardiac lobe demonstrated the enhanced expression of many genes relative to alveolar epithelial cell (CD11b-/CD31-) control cells, but only the upregulation of Ereg and Fgf6 compared to the less well-vascularized right upper lobe. The growth of actively regenerating non-neoplastic adult tissue on the CAM demonstrates that functional lumenization can occur between species (mouse and chick) and across the developmental spectrum (adult and embryo).

High resolution propagation-based lung imaging at clinically relevant X-ray dose levels.

Absorption-based clinical computed tomography (CT) is the current imaging method of choice in the diagnosis of lung diseases. Many pulmonary diseases are affecting microscopic structures of the lung, such as terminal bronchi, alveolar spaces, sublobular blood vessels or the pulmonary interstitial tissue. As spatial resolution in CT is limited by the clinically acceptable applied X-ray dose, a comprehensive diagnosis of conditions such as interstitial lung disease, idiopathic pulmonary fibrosis or the characterization of small pulmonary nodules is limited and may require additional validation by invasive lung biopsies. Propagation-based imaging (PBI) is a phase sensitive X-ray imaging technique capable of reaching high spatial resolutions at relatively low applied radiation dose levels. In this publication, we present technical refinements of PBI for the characterization of different artificial lung pathologies, mimicking clinically relevant patterns in ventilated fresh porcine lungs in a human-scale chest phantom. The combination of a very large propagation distance of 10.7 m and a photon counting detector with [Formula: see text] pixel size enabled high resolution PBI CT with significantly improved dose efficiency, measured by thermoluminescence detectors. Image quality was directly compared with state-of-the-art clinical CT. PBI with increased propagation distance was found to provide improved image quality at the same or even lower X-ray dose levels than clinical CT. By combining PBI with iodine k-edge subtraction imaging we further demonstrate that, the high quality of the calculated iodine concentration maps might be a potential tool for the analysis of lung perfusion in great detail. Our results indicate PBI to be of great value for accurate diagnosis of lung disease in patients as it allows to depict pathological lesions non-invasively at high resolution in 3D. This will especially benefit patients at high risk of complications from invasive lung biopsies such as in the setting of suspected idiopathic pulmonary fibrosis (IPF).

MDCT-based longitudinal automated airway and air trapping analysis in school-age children with mild cystic fibrosis lung disease.

Objectives: Quantitative computed tomography (QCT) offers some promising markers to quantify cystic fibrosis (CF)-lung disease. Air trapping may precede irreversible bronchiectasis; therefore, the temporal interdependencies of functional and structural lung disease need to be further investigated. We aim to quantify airway dimensions and air trapping on chest CT of school-age children with mild CF-lung disease over two years. Methods: Fully-automatic software analyzed 144 serial spirometer-controlled chest CT scans of 36 children (median 12.1 (10.2-13.8) years) with mild CF-lung disease (median ppFEV1 98.5 (90.8-103.3) %) at baseline, 3, 12 and 24 months. The airway wall percentage (WP5-10), bronchiectasis index (BEI), as well as severe air trapping (A3) were calculated for the total lung and separately for all lobes. Mixed linear models were calculated, considering the lobar distribution of WP5-10, BEI and A3 cross-sectionally and longitudinally. Results: WP5-10 remained stable (P = 0.248), and BEI changed from 0.41 (0.28-0.7) to 0.54 (0.36-0.88) (P = 0.156) and A3 from 2.26% to 4.35% (P = 0.086) showing variability over two years. ppFEV1 was also stable (P = 0.276). A robust mixed linear model showed a cross-sectional, regional association between WP5-10 and A3 at each timepoint (P < 0.001). Further, BEI showed no cross-sectional, but another mixed model showed short-term longitudinal interdependencies with air trapping (P = 0.003). Conclusions: Robust linear/beta mixed models can still reveal interdependencies in medical data with high variability that remain hidden with simpler statistical methods. We could demonstrate cross-sectional, regional interdependencies between wall thickening and air trapping. Further, we show short-term regional interdependencies between air trapping and an increase in bronchiectasis. The data indicate that regional air trapping may precede the development of bronchiectasis. Quantitative CT may capture subtle disease progression and identify regional and temporal interdependencies of distinct manifestations of CF-lung disease.

Topography of pleural epithelial structure enabled by en face isolation and machine learning.

Pleural epithelial adaptations to mechanical stress are relevant to both normal lung function and parenchymal lung diseases. Assessing regional differences in mechanical stress, however, has been complicated by the nonlinear stress-strain properties of the lung and the large displacements with ventilation. Moreover, there is no reliable method of isolating pleural epithelium for structural studies. To define the topographic variation in pleural structure, we developed a method of en face harvest of murine pleural epithelium. Silver-stain was used to highlight cell borders and facilitate imaging with light microscopy. Machine learning and watershed segmentation were used to define the cell area and cell perimeter of the isolated pleural epithelial cells. In the deflated lung at residual volume, the pleural epithelial cells were significantly larger in the apex (624 ± 247 µm2 ) than in basilar regions of the lung (471 ± 119 µm2 ) (p < 0.001). The distortion of apical epithelial cells was consistent with a vertical gradient of pleural pressures. To assess epithelial changes with inflation, the pleura was studied at total lung capacity. The average epithelial cell area increased 57% and the average perimeter increased 27% between residual volume and total lung capacity. The increase in lung volume was less than half the percent change predicted by uniform or isotropic expansion of the lung. We conclude that the structured analysis of pleural epithelial cells complements studies of pulmonary microstructure and provides useful insights into the regional distribution of mechanical stresses in the lung.

The fatal trajectory of pulmonary COVID-19 is driven by lobular ischemia and fibrotic remodelling.

BACKGROUND: COVID-19 is characterized by a heterogeneous clinical presentation, ranging from mild symptoms to severe courses of disease. 9-20% of hospitalized patients with severe lung disease die from COVID-19 and a substantial number of survivors develop long-COVID. Our objective was to provide comprehensive insights into the pathophysiology of severe COVID-19 and to identify liquid biomarkers for disease severity and therapy response. METHODS: We studied a total of 85 lungs (n = 31 COVID autopsy samples; n = 7 influenza A autopsy samples; n = 18 interstitial lung disease explants; n = 24 healthy controls) using the highest resolution Synchrotron radiation-based hierarchical phase-contrast tomography, scanning electron microscopy of microvascular corrosion casts, immunohistochemistry, matrix-assisted laser desorption ionization mass spectrometry imaging, and analysis of mRNA expression and biological pathways. Plasma samples from all disease groups were used for liquid biomarker determination using ELISA. The anatomic/molecular data were analyzed as a function of patients' hospitalization time. FINDINGS: The observed patchy/mosaic appearance of COVID-19 in conventional lung imaging resulted from microvascular occlusion and secondary lobular ischemia. The length of hospitalization was associated with increased intussusceptive angiogenesis. This was associated with enhanced angiogenic, and fibrotic gene expression demonstrated by molecular profiling and metabolomic analysis. Increased plasma fibrosis markers correlated with their pulmonary tissue transcript levels and predicted disease severity. Plasma analysis confirmed distinct fibrosis biomarkers (TSP2, GDF15, IGFBP7, Pro-C3) that predicted the fatal trajectory in COVID-19. INTERPRETATION: Pulmonary severe COVID-19 is a consequence of secondary lobular microischemia and fibrotic remodelling, resulting in a distinctive form of fibrotic interstitial lung disease that contributes to long-COVID. FUNDING: This project was made possible by a number of funders. The full list can be found within the Declaration of interests / Acknowledgements section at the end of the manuscript.

Kinetics of Pectin Biopolymer Facial Erosion Characterized by Fluorescent Tracer Microfluidics.

Pectin is a plant-derived heteropolysaccharide that has been implicated in drug development, tissue engineering, and visceral organ repair. Pectin demonstrates remarkable biostability in a variety of physiologic environments but is biodegradable in water. To understand the dynamics of pectin biodegradation in basic environments, we developed a microfluidics system that facilitated the quantitative comparison of pectin films exposed to facial erosion. Pectin biodegradation was assessed using fluorescein tracer embedded in pectin, trypan blue quenching of released fluorescence, and highly sensitive microfluorimetry. The microfluidic perfusate, delivered through 6 um-pore synthetic membrane interface, demonstrated nonlinear erosion of the pectin film; 75% of tracer was released in 28 h. The microfluidics system was used to identify potential modifiers of pectin erosion. The polyphenolic compound tannic acid, loaded into citrus pectin films, demonstrated a dose-dependent decrease in pectin erosion. Tannic acid had no detectable impact on the physical properties of citrus pectin including adhesivity and cohesion. In contrast, tannic acid weakened the burst strength and cohesion of pectins derived from soy bean and potato sources. We conclude that facial erosion may explain the biostability of citrus pectin on visceral organ surfaces as well as provide a useful method for identifying modifiers of citrus pectin biodegradation.

Functional Adhesion of Pectin Biopolymers to the Lung Visceral Pleura.

Pleural injuries and the associated "air leak" are the most common complications after pulmonary surgery. Air leaks are the primary reason for prolonged chest tube use and increased hospital length of stay. Pectin, a plant-derived heteropolysaccharide, has been shown to be an air-tight sealant of pulmonary air leaks. Here, we investigate the morphologic and mechanical properties of pectin adhesion to the visceral pleural surface of the lung. After the application of high-methoxyl citrus pectin films to the murine lung, we used scanning electron microscopy to demonstrate intimate binding to the lung surface. To quantitatively assess pectin adhesion to the pleural surface, we used a custom adhesion test with force, distance, and time recordings. These assays demonstrated that pectin-glycocalyceal tensile adhesive strength was greater than nanocellulose fiber films or pressure-sensitive adhesives (p < 0.001). Simultaneous videomicroscopy recordings demonstrated that pectin-glycocalyceal adhesion was also stronger than the submesothelial connective tissue as avulsed surface remnants were visualized on the separated pectin films. Finally, pleural abrasion and hyaluronidase enzyme digestion confirmed that pectin binding was dependent on the pleural glycocalyx (p < 0.001). The results indicate that high methoxyl citrus pectin is a promising sealant for the treatment of pleural lung injuries.

Biomaterial-Assisted Anastomotic Healing: Serosal Adhesion of Pectin Films.

Anastomotic leakage is a frequent complication of intestinal surgery and a major source of surgical morbidity. The timing of anastomotic failures suggests that leaks are the result of inadequate mechanical support during the vulnerable phase of wound healing. To identify a biomaterial with physical and mechanical properties appropriate for assisted anastomotic healing, we studied the adhesive properties of the plant-derived structural heteropolysaccharide called pectin. Specifically, we examined high methoxyl citrus pectin films at water contents between 17-24% for their adhesivity to ex vivo porcine small bowel serosa. In assays of tensile adhesion strength, pectin demonstrated significantly greater adhesivity to the serosa than either nanocellulose fiber (NCF) films or pressure sensitive adhesives (PSA) (p < 0.001). Similarly, in assays of shear resistance, pectin demonstrated significantly greater adhesivity to the serosa than either NCF films or PSA (p < 0.001). Finally, the pectin films were capable of effectively sealing linear enterotomies in a bowel simulacrum as well as an ex vivo bowel segment. We conclude that pectin is a biomaterial with physical and adhesive properties capable of facilitating anastomotic healing after intestinal surgery.

3D analysis of microvasculature in murine liver fibrosis models using synchrotron radiation-based microtomography.

Cirrhosis describes the development of excess fibrous tissue around regenerative nodules in response to chronic liver injury and usually leads to irreversible organ damage and end-stage liver disease. During the development of cirrhosis, the formation of collagenous scar tissue is paralleled by a reorganization and remodeling of the hepatic vascular system. To date, macrovascular remodeling in various cirrhosis models has been examined using three-dimensional (3D) imaging modalities, while microvascular changes have been studied mainly by two-dimensional (2D) light microscopic and electron microscopic imaging. Here, we report on the application of high-resolution 3D synchrotron radiation-based microtomography (SRµCT) for the study of the sinusoidal and capillary blood vessel system in three murine models of advanced parenchymal and biliary hepatic fibrosis. SRµCT facilitates the characterization of microvascular architecture and identifies features of intussusceptive angiogenesis in progressive liver fibrosis in a non-destructive 3D manner.

Combination of µCT and light microscopy for generation-specific stereological analysis of pulmonary arterial branches: a proof-of-concept study.

Various lung diseases, including pulmonary hypertension, chronic obstructive pulmonary disease or bronchopulmonary dysplasia, are associated with structural and architectural alterations of the pulmonary vasculature. The light microscopic (LM) analysis of the blood vessels is limited by the fact that it is impossible to identify which generation of the arterial tree an arterial profile within a LM microscopic section belongs to. Therefore, we established a workflow that allows for the generation-specific quantitative (stereological) analysis of pulmonary blood vessels. A whole left rabbit lung was fixed by vascular perfusion, embedded in glycol methacrylate and imaged by micro-computed tomography (µCT). The lung was then exhaustively sectioned and 20 consecutive sections were collected every 100 µm to obtain a systematic uniform random sample of the whole lung. The digital processing involved segmentation of the arterial tree, generation analysis, registration of LM sections with the µCT data as well as registration of the segmentation and the LM images. The present study demonstrates that it is feasible to identify arterial profiles according to their generation based on a generation-specific color code. Stereological analysis for the first three arterial generations of the monopodial branching of the vasculature included volume fraction, total volume, lumen-to-wall ratio and wall thickness for each arterial generation. In conclusion, the correlative image analysis of µCT and LM-based datasets is an innovative method to assess the pulmonary vasculature quantitatively.

The Pathology of Severe COVID-19-Related Lung Damage.

BACKGROUND: The histomorphological changes of lung damage in severe coronavirus disease 2019 (COVID-19) have not yet been adequately characterized. In this article, we describe the sequence of pathological changes in COVID-19 and discuss the implications for approaches to treatment. METHODS: Standardized autopsies were performed on thirteen patients who had died of COVID-19. The findings were analyzed together with clinical data from the patients' medical records. RESULTS: Most (77%) of the deceased patients were men. Their median age at death was 78 years (range, 41-90). Most of them had major pre-existing chronic diseases, most commonly arterial hypertension. The autopsies revealed characteristic COVID-19-induced pathological changes in the lungs, which were regarded as the cause of death in most patients. The main histological finding was sequential alveolar damage, apparently due in large measure to focal capillary microthrombus formation. Alveolar damage leads to the death of the patient either directly or by the induction of pulmonary parenchymal fibrosis. Diffuse lung damage was seen exclusively in invasively ventilated patients. CONCLUSION: Autopsies are crucial for the systematic assessment of new diseases such as COVID-19: they provide a basis for further investigations of disease mechanisms and for the devising of potentially effective modes of treatment. The autopsy findings suggest that focal damage of the microvascular pulmonary circulation is a main mechanism of lethal lung disease due to the SARS-CoV-2 virus. It may also be a cause of persistent lung damage in patients who recover from severe COVID-19.

Assessment of the Alveolar Capillary Network in the Postnatal Mouse Lung in 3D Using Serial Block-Face Scanning Electron Microscopy.

The alveolar capillary network (ACN) has a large surface area that provides the basis for an optimized gas exchange in the lung. It needs to adapt to morphological changes during early lung development and alveolarization. Structural alterations of the pulmonary vasculature can lead to pathological functional conditions such as in bronchopulmonary dysplasia and various other lung diseases. To understand the development of the ACN and its impact on the pathogenesis of lung diseases, methods are needed that enable comparative analyses of the complex three-dimensional structure of the ACN at different developmental stages and under pathological conditions. In this study a newborn mouse lung was imaged with serial block-face scanning electron microscopy (SBF-SEM) to investigate the ACN and its surrounding structures before the alveolarization process begins. Most parts but not all of the examined ACN contain two layers of capillaries, which were repeatedly connected with each other. A path from an arteriole to a venule was extracted and straightened to allow cross-sectional visualization of the data along the path within a plane. This allows a qualitative characterization of the structures that erythrocytes pass on their way through the ACN. One way to define regions of the ACN supplied by specific arterioles is presented and used for analyses. Pillars, possibly intussusceptive, were found in the vasculature but no specific pattern was observed in regard to parts of the saccular septa. This study provides 3D information with a resolution of about 150 nm on the microscopic structure of a newborn mouse lung and outlines some of the potentials and challenges of SBF-SEM for 3D analyses of the ACN.

Comprehensive three-dimensional morphology of neoangiogenesis in pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis.

Pulmonary veno-occlusive disease (PVOD) is a rare lung disease characterized by fibrotic narrowing of pulmonary veins leading to pulmonary hypertension (PH) and finally to death by right heart failure. PVOD is often accompanied by pulmonary capillary hemangiomatosis (PCH), a marked abnormal proliferation of pulmonary capillaries. Both morphological patterns often occur together and are thought to be distinct manifestations of the same disease process and accordingly are classified together in group 1' of the Nice classification of PH. The underlying mechanisms of these aberrant remodeling processes remain poorly understood. In this study, we investigated the three-dimensional structure of these vascular lesions in the lung explant of a patient diagnosed with PVOD by µ-computed tomography, microvascular corrosion casting, electron microscopy, immunohistochemistry, correlative light microscopy and gene expression analysis. We were able to describe multifocal intussusceptive neoangiogenesis and vascular sprouting as the three-dimensional correlate of progressive PCH, a process dividing pre-existing vessels by intravascular pillar formation previously only known from embryogenesis and tumor neoangiogenesis. Our findings suggest that venous occlusions in PVOD increase shear and stretching forces in the pulmonary capillary bloodstream and thereby induce intussusceptive neoangiogenesis. These findings can serve as a basis for novel approaches to the analysis of PVOD.

Structural heteropolysaccharides as air-tight sealants of the human pleura.

Pulmonary "air leaks," typically the result of pleural injury caused by lung surgery or chest trauma, result in the accumulation of air in the pleural space (pneumothorax). Air leaks are a major source of morbidity and prolonged hospitalization after pulmonary surgery. Previous work has demonstrated structural heteropolysaccharide (pectin) binding to the mouse pleural glycocalyx. The similar lectin-binding characteristics and ultrastructural features of the human and mouse pleural glycocalyx suggested the potential application of these polymers in humans. To investigate the utility of pectin-based polymers, we developed a simulacrum using freshly obtained human pleura. Pressure-decay leak testing was performed with an inflation maneuver that involved a 3 s ramp to a 3 s plateau pressure; the inflation was completely abrogated after needle perforation of the pleura. Using nonbiologic materials, pressure-decay leak testing demonstrated an exponential decay with a plateau phase in materials with a Young's modulus less than 5. In human pleural testing, the simulacrum was used to test the sealant function of four mixtures of pectin-based polymers. A 50% high-methoxyl pectin and 50% carboxymethylcellulose mixture demonstrated no sealant failures at transpleural pressures of 60 cmH2 O. In contrast, pectin mixtures containing 50% low-methoxyl pectin, 50% amidated low-methoxyl pectins, or 100% carboxymethylcellulose demonstrated frequent sealant failures at transpleural pressures of 40-50 cmH2 O (p < 0.001). Inhibition of sealant adhesion with enzyme treatment, dessication and 4°C cooling suggested an adhesion mechanism dependent upon polysaccharide interpenetration. We conclude that pectin-based heteropolysaccharides are a promising air-tight sealant of human pleural injuries. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 799-806, 2019.

Similarities in the Computed Tomography Appearance in α1-Antitrypsin Deficiency and Smoking-Related Chronic Obstructive Pulmonary Disease in a Smoking Collective.

BACKGROUND: Emphysematous destruction of lung parenchyma visible in computed tomography (CT) can be attributed to chronic obstructive pulmonary disease (COPD) or to α1-antitrypsin deficiency (AATD). OBJECTIVES: We evaluated if visual semiquantitative phenotyping of CT data helps identifying individuals with AATD in a group of smokers with severe emphysema and airflow limitation. METHOD: n = 14 patients with AATD and n = 15 with COPD and a minimum of 10 pack years underwent CT, clinical assessment, and full-body plethysmography. The extent and type of emphysema as well as large and small airway changes were rated semiquantitatively for each lobe using a standardized previously published scoring system. Lastly, a final diagnosis for each patient was proposed. RESULTS: AATD had a significantly lower mean emphysema score than COPD, with 8.9 ± 3.4 versus 11.9 ± 3.2 (p < 0.001), respectively. Within both groups, there was significantly more emphysema in the lower lobes (p < 0.05-0.001). The COPD group showed an upper- and middle-lobe predominance of emphysema distribution when compared to the AATD group (p < 0.001). Centrilobular (CLE) and panlobular (PLE) emphysema patterns showed a uniform distribution within both groups, with a CLE predominance in the upper lung and a PLE predominance in the lower lung regions. AATD and COPD both showed significantly more airway changes in lower lobes compared to upper lobes (p = 0.05-0.001), without significant differences between both groups. CONCLUSION: The typical emphysema distribution patterns seen on CT traditionally assigned to AATD and COPD were of little use in discriminating both entities. Also, airway changes could not contribute to a more precise differentiation. We conclude that a concise standardized phenotyping-driven approach to chest CT in emphysema is not sufficient to identify patients with AATD in a cohort of smokers with advanced emphysema.

Pressure-decay testing of pleural air leaks in intact murine lungs: evidence for peripheral airway regulation.

The critical care management of pleural air leaks can be challenging in all patients, but particularly in patients on mechanical ventilation. To investigate the effect of central airway pressure and pleural pressure on pulmonary air leaks, we studied orotracheally intubated mice with pleural injuries. We used clinically relevant variables - namely, airway pressure and pleural pressure - to investigate flow through peripheral air leaks. The model studied the pleural injuries using a pressure-decay maneuver. The pressure-decay maneuver involved a 3 sec ramp to 30 cmH2 0 followed by a 3 sec breath hold. After pleural injury, the pressure-decay maneuver demonstrated a distinctive airway pressure time history. Peak inflation was followed by a rapid decrease to a lower plateau phase. The decay phase of the inflation maneuver was influenced by the injury area. The rate of pressure decline with multiple injuries (28 ± 8 cmH2 0/sec) was significantly greater than a single injury (12 ± 3 cmH2 O/sec) (P < 0.05). In contrast, the plateau phase pressure was independent of injury surface area, but dependent upon transpulmonary pressure. The mean plateau transpulmonary pressure was 18 ± 0.7 cm H2 O. Finally, analysis of the inflation ramp demonstrated that nearly all volume loss occurred at the end of inflation (P < 0.001). We conclude that the air flow through peripheral lung injuries was greatest at increased lung volumes and limited by peripheral airway closure. In addition to suggesting an intrinsic mechanism for limiting flow through peripheral air leaks, these findings suggest the utility of positive end-expiratory pressure and negative pleural pressure to maintain lung volumes in patients with pleural injuries.

Free-Floating Mesothelial Cells in Pleural Fluid After Lung Surgery.

OBJECTIVES: The mesothelium, the surface layer of the heart, lung, bowel, liver, and tunica vaginalis, is a complex tissue implicated in organ-specific diseases and regenerative biology; however, the mechanism of mesothelial repair after surgical injury is unknown. Previous observations indicated seeding of denuded mesothelium by free-floating mesothelial cells may contribute to mesothelial healing. In this study, we investigated the prevalence of mesothelial cells in pleural fluid during the 7 days following pulmonary surgery. STUDY DESIGN: Flow cytometry was employed to study pleural fluid of 45 patients after lung resection or transplantation. We used histologically validated mesothelial markers (CD71 and WT1) to estimate the prevalence of mesothelial cells. RESULTS: The viability of pleural fluid cells approached 100%. Leukocytes and mesothelial cells were identified in the pleural fluid within the first week after surgery. The leukocyte concentration was relatively stable at all time points. In contrast, mesothelial cells, identified by CD71 and WT1 peaked on POD3. The broad expression of CD71 molecule in postoperative pleural fluid suggests that many of the free-floating non-leukocyte cells were activated or proliferative mesothelial cells. CONCLUSION: We demonstrated that pleural fluid post lung surgery is a source of mesothelial cells; most of these cells appear to be viable and, as shown by CD71 staining, activated mesothelial cells. The observed peak of mesothelial cells on POD3 is consistent with a potential reparative role of free-floating mesothelial cells after pulmonary surgery.

Functional Mechanics of a Pectin-Based Pleural Sealant after Lung Injury.

Pleural injury and associated air leaks are a major influence on patient morbidity and healthcare costs after lung surgery. Pectin, a plant-derived heteropolysaccharide, has recently demonstrated potential as an adhesive binding to the glycocalyx of visceral mesothelium. Since bioadhesion is a process likely involving the interpenetration of the pectin-based polymer with the glycocalyx, we predicted that the pectin-based polymer may also be an effective sealant for pleural injury. To explore the potential role of an equal (weight%) mixture of high-methoxyl pectin and carboxymethylcellulose as a pleural sealant, we compared the yield strength of the pectin-based polymer to commonly available surgical products. The pectin-based polymer demonstrated significantly greater adhesion to the lung pleura than the comparison products (p < 0.001). In a 25 g needle-induced lung injury model, pleural injury resulted in an air leak and a loss of airway pressures. After application of the pectin-based polymer, there was a restoration of airway pressure and no measurable air leak. Despite the application of large sheets (50 mm2) of the pectin-based polymer, multifrequency lung impedance studies demonstrated no significant increase in tissue damping (G) or hysteresivity (η)(p > 0.05). In 7-day survival experiments, the application of the pectin-based polymer after pleural injury was associated with no observable toxicity, 100% survival (N = 5), and restored lung function. We conclude that this pectin-based polymer is a strong and nontoxic bioadhesive with the potential for clinical application in the treatment of pleural injuries.