Wall Folding Research Articles

Exploring alveolar recruitability using positive end-expiratory pressure in mice overexpressing TGF-β1: a structure–function analysis

Pre-injured lungs are prone to injury progression in response to mechanical ventilation. Heterogeneous ventilation due to (micro)atelectases imparts injurious strains on open alveoli (known as volutrauma). Hence, recruitment of (micro)atelectases by positive end-expiratory pressure (PEEP) is necessary to interrupt this vicious circle of injury but needs to be balanced against acinar overdistension. In this study, the lung-protective potential of alveolar recruitment was investigated and balanced against overdistension in pre-injured lungs. Mice, treated with empty vector (AdCl) or adenoviral active TGF-β1 (AdTGF-β1) were subjected to lung mechanical measurements during descending PEEP ventilation from 12 to 0 cmH2O. At each PEEP level, recruitability tests consisting of two recruitment maneuvers followed by repetitive forced oscillation perturbations to determine tissue elastance (H) and damping (G) were performed. Finally, lungs were fixed by vascular perfusion at end-expiratory airway opening pressures (Pao) of 20, 10, 5 and 2 cmH2O after a recruitment maneuver, and processed for design-based stereology to quantify derecruitment and distension. H and G were significantly elevated in AdTGF-β1 compared to AdCl across PEEP levels. H was minimized at PEEP = 5–8 cmH2O and increased at lower and higher PEEP in both groups. These findings correlated with increasing septal wall folding (= derecruitment) and reduced density of alveolar number and surface area (= distension), respectively. In AdTGF-β1 exposed mice, 27% of alveoli remained derecruited at Pao = 20 cmH2O. A further decrease in Pao down to 2 cmH2O showed derecruitment of an additional 1.1 million alveoli (48%), which was linked with an increase in alveolar size heterogeneity at Pao = 2–5 cmH2O. In AdCl, decreased Pao resulted in septal folding with virtually no alveolar collapse. In essence, in healthy mice alveoli do not derecruit at low PEEP ventilation. The potential of alveolar recruitability in AdTGF-β1 exposed mice is high. H is optimized at PEEP 5–8 cmH2O. Lower PEEP folds and larger PEEP stretches septa which results in higher H and is more pronounced in AdTGF-β1 than in AdCl. The increased alveolar size heterogeneity at Pao = 5 cmH2O argues for the use of PEEP = 8 cmH2O for lung protective mechanical ventilation in this animal model.

Specific metabolic and cellular mechanisms of the vegetative desiccation tolerance in resurrection plants for adaptation to extreme dryness.

Substantial advancements have been made in our comprehension of vegetative desiccation tolerance in resurrection plants, and further research is still warranted to elucidate the mechanisms governing distinct cellular adaptations. Resurrection plants are commonly referred to as a small group of extremophile vascular plants that exhibit vegetative desiccation tolerance (VDT), meaning that their vegetative tissues can survive extreme drought stress (> 90% water loss) and subsequently recover rapidly upon rehydration. In contrast to most vascular plants, which typically employ water-saving strategies to resist partial water loss and optimize water absorption and utilization to a limited extent under moderate drought stress, ultimately succumbing to cell death when confronted with severe and extreme drought conditions, resurrection plants have evolved unique mechanisms of VDT, enabling them to maintain viability even in the absence of water for extended periods, permitting them to rejuvenate without harm upon water contact. Understanding the mechanisms associated with VDT in resurrection plants holds the promise of expanding our understanding of how plants adapt to exceedingly arid environments, a phenomenon increasingly prevalent due to global warming. This review offers an updated and comprehensive overview of recent advances in VDT within resurrection plants, with particular emphasis on elucidating the metabolic and cellular adaptations during desiccation, including the intricate processes of cell wall folding and the prevention of cell death. Furthermore, this review highlights existing unanswered questions in the field, suggests potential avenues for further research to gain deeper insights into the remarkable VDT adaptations observed in resurrection plants, and highlights the potential application of VDT-derived techniques in crop breeding to enhance tolerance to extreme drought stress.

Elastic and collapsible: current understanding of cell walls in succulent plants.

Succulent plants represent a large functional group of drought-resistant plants that store water in specialized tissues. Several co-adaptive traits accompany this water-storage capacity to constitute the succulent syndrome. A widely reported anatomical adaptation of cell walls in succulent tissues allows them to fold in a regular fashion during extended drought, thus preventing irreversible damage and permitting reversible volume changes. Although ongoing research on crop and model species continuously reports the importance of cell walls and their dynamics in drought resistance, the cell walls of succulent plants have received relatively little attention to date, despite the potential of succulents as natural capital to mitigate the effects of climate change. In this review, we summarize current knowledge of cell walls in drought-avoiding succulents and their effects on tissue biomechanics, water relations, and photosynthesis. We also highlight the existing knowledge gaps and propose a hypothetical model for regulated cell wall folding in succulent tissues upon dehydration. Future perspectives of methodological development in succulent cell wall characterization, including the latest technological advances in molecular and imaging techniques, are also presented.

The Cell Wall Proteome of Craterostigma plantagineum Cell Cultures Habituated to Dichlobenil and Isoxaben.

The remarkable desiccation tolerance of the vegetative tissues in the resurrection species Craterostigma plantagineum (Hochst.) is favored by its unique cell wall folding mechanism that allows the ordered and reversible shrinking of the cells without damaging neither the cell wall nor the underlying plasma membrane. The ability to withstand extreme drought is also maintained in abscisic acid pre-treated calli, which can be cultured both on solid and in liquid culture media. Cell wall research has greatly advanced, thanks to the use of inhibitors affecting the biosynthesis of e.g., cellulose, since they allowed the identification of the compensatory mechanisms underlying habituation. Considering the innate cell wall plasticity of C. plantagineum, the goal of this investigation was to understand whether habituation to the cellulose biosynthesis inhibitors dichlobenil and isoxaben entailed or not identical mechanisms as known for non-resurrection species and to decipher the cell wall proteome of habituated cells. The results showed that exposure of C. plantagineum calli/cells triggered abnormal phenotypes, as reported in non-resurrection species. Additionally, the data demonstrated that it was possible to habituate Craterostigma cells to dichlobenil and isoxaben and that gene expression and protein abundance did not follow the same trend. Shotgun and gel-based proteomics revealed a common set of proteins induced upon habituation, but also identified candidates solely induced by habituation to one of the two inhibitors. Finally, it is hypothesized that alterations in auxin levels are responsible for the increased abundance of cell wall-related proteins upon habituation.

Dissecting Serial Immune Response Stages of Chronic Rejection after Murine Orthotopic Lung Transplantation

<h3>Purpose</h3> "Chronic rejection" (CR) after lung transplantation (LTx) is considered to be a cellular and humoral immune response, accompanied by angiogenesis and fibrosis, clinically denominated as chronic lung allograft dysfunction (CLAD). We aimed to reinvestigate the chronological stages and spatial organization of the immune response of CR. <h3>Methods</h3> Orthotopic single LTx was performed to create isograft (n=9; C57BL/6N to C57BL/6N) and two allograft (n=16; BALB/c to C57BL/6N) subgroups: 1/ observational group (n=8), with serial sacrifice at week 1, 3, 5 and 8 to evaluate the sequential, spatial and cellular events of CR; and 2/ validation group (week 10; n=8) to assess variation within CR. All mice received daily immunosuppression of 10 mg/kg cyclosporine A and 1.6 mg/kg methylprednisolone. <h3>Results</h3> In 1 isograft technical failure occurred and 8 had normal lung architecture at week 10. In 3 allografts failure occurred: 2 in the observational, 1 in the validation group. Histological evaluation of allografts allowed reconstruction of CR: STAGE 1: innate inflammation around end-arteries; STAGE 2: innate immune cells around end-arteries and end-venules; STAGE 3: adaptive immune cell organization around end-arteries; innate immune cells around end-venules; pleural infiltration of lymphocytes; STAGE 4: fibrosis around end-arteries with end-arteritis obliterans; adaptive immune cells around the end-venules; pleural lymphatic vessel growth and fibrosis; bronchiolar wall folding and sporadic intraluminal fibrotic plugging. In the validation group, we identified 2 mice in STAGE 2, 2 in STAGE 3 and 3 in STAGE 4. µCT confirmed the progression of severe (stage 4) vs mild (stage 2-3) in lung attenuation (1.05±0.04 vs 1.14±0.01; p=0.002) (Figure) and total and tidal volume. <h3>Conclusion</h3> CR demonstrated an innate onset, evolving to adaptive organization and fibrosis, starting at end-arteries and then spreading towards venules, pleura and airways. This pattern seems to resemble RAS after human LTx.

The dehydration- and ABA-inducible germin-like protein CpGLP1 from Craterostigma plantagineum has SOD activity and may contribute to cell wall integrity during desiccation

Main conclusionCpGLP1 belongs to the large group of germin-like proteins and comprises a cell wall-localized protein which has superoxide dismutase activity and may contribute towards ROS metabolism and cell wall folding during desiccation.The plant cell wall is a dynamic matrix and its plasticity is essential for cell growth and processing of environmental signals to cope with stresses. A few so-called resurrection plants like Craterostigma plantagineum survive desiccation by implementing protection mechanisms. In C. plantagineum, the cell wall shrinks and folds upon desiccation to avoid mechanical and oxidative damage which contributes to cell integrity. Despite the high toxic potential, ROS are important molecules for cell wall remodeling processes as they participate in enzymatic reactions and act as signaling molecules. Here we analyzed the C. plantagineum germin-like protein 1 (CpGLP1) to understand its contribution to cell wall folding and desiccation tolerance. The analysis of the CpGLP1 sequence showed that this protein does not fit into the current GLP classification and forms a new group within the Linderniaceae. CpGLP1 transcripts accumulate in leaves in response to dehydration and ABA, and mannitol treatments transiently induce CpGLP1 transcript accumulation supporting the participation of CpGLP1 in desiccation-related processes. CpGLP1 protein from cell wall protein extracts followed transcript accumulation and protein preparations from bacteria overexpressing CpGLP1 showed SOD activity. In agreement with cell wall localization, CpGLP1 interacts with pectins which have not been reported for GLP proteins. Our data support a role for CpGLP1 in the ROS metabolism related to the control of cell wall plasticity during desiccation in C. plantagineum.

Dynamics of intracellular mannan and cell wall folding in the drought responses of succulent Aloe species.

Plants have evolved a multitude of adaptations to survive extreme conditions. Succulent plants have the capacity to tolerate periodically dry environments, due to their ability to retain water in a specialized tissue, termed hydrenchyma. Cell wall polysaccharides are important components of water storage in hydrenchyma cells. However, the role of the cell wall and its polysaccharide composition in relation to drought resistance of succulent plants are unknown. We investigate the drought response of leaf‐succulent Aloe (Asphodelaceae) species using a combination of histological microscopy, quantification of water content, and comprehensive microarray polymer profiling. We observed a previously unreported mode of polysaccharide and cell wall structural dynamics triggered by water shortage. Microscopical analysis of the hydrenchyma cell walls revealed highly regular folding patterns indicative of predetermined cell wall mechanics in the remobilization of stored water and the possible role of homogalacturonan in this process. The in situ distribution of mannans in distinct intracellular compartments during drought, for storage, and apparent upregulation of pectins, imparting flexibility to the cell wall, facilitate elaborate cell wall folding during drought stress. We conclude that cell wall polysaccharide composition plays an important role in water storage and drought response in Aloe.

Perspectives on Structural, Physiological, Cellular, and Molecular Responses to Desiccation in Resurrection Plants.

Resurrection plants possess a unique ability to counteract desiccation stress. Desiccation tolerance (DT) is a very complex multigenic and multifactorial process comprising a combination of physiological, morphological, cellular, genomic, transcriptomic, proteomic, and metabolic processes. Modification in the sugar composition of the hemicellulosic fraction of the cell wall is detected during dehydration. An important change is a decrease of glucose in the hemicellulosic fraction during dehydration that can reflect a modification of the xyloglucan structure. The expansins might also be involved in cell wall flexibility during drying and disrupt hydrogen bonds between polymers during rehydration of the cell wall. Cleavages by xyloglucan-modifying enzymes release the tightly bound xyloglucan-cellulose network, thus increasing cell wall flexibility required for cell wall folding upon desiccation. Changes in hydroxyproline-rich glycoproteins (HRGPs) such as arabinogalactan proteins (AGPs) are also observed during desiccation and rehydration processes. It has also been observed that significant alterations in the process of photosynthesis and photosystem (PS) II activity along with changes in the antioxidant enzyme system also increased the cell wall and membrane fluidity resulting in DT. Similarly, recent data show a major role of ABA, LEA proteins, and small regulatory RNA in regulating DT responses. Current progress in “-omic” technologies has enabled quantitative monitoring of the plethora of biological molecules in a high throughput routine, making it possible to compare their levels between desiccation-sensitive and DT species. In this review, we present a comprehensive overview of structural, physiological, cellular, molecular, and global responses involved in desiccation tolerance.

Energy Absorption Capacity of Basalt Sandwich Composite Cylinder Subjected to Axial Compression Loadings

In this report presented the investigation of axial progressive compression on sandwich composite cylinder made from basalt fibre reinforced composite tube as skins and polyurethane (EPU) foam as core of the structure. The effect of braid orientation angle of the sandwich skins and foam core thickness were evaluated on the parameter performance namely peak force, average force, total energy absorption, crush force efficiency, and specific energy absorption. The primary failure mode observed was progressive failure fibre cracking and tube’s wall folding and crumping. Experiment result showed that the effect of outer wall braid angle of sandwich tube structure was the dominant factor contributed to high energy absorption capacity. Furthermore, the foam thickness has no significant influences on the SEA value; however, the total diameter size of sandwich tube skins was.

Mechanisms of desiccation tolerance in the bromeliad Pitcairnia burchellii Mez: biochemical adjustments and structural changes

Rocky outcrops represent the diversity center of vascular desiccation tolerant (DT) plants. Vegetation in this environment is exposed to an extended dry season and extreme conditions due to rocky soils and high sun exposure. In this study, we demonstrated that Pitcairnia burchellii, a bromeliad from rocky outcrops, tolerates intense desiccation for about 90 days due to strategies as accumulation of compatible osmolytes and antioxidant substances together with leaf morphological changes. In dehydrated plants, an increase in antioxidant activity was observed and the vacuolization of parenchyma cells was accompanied by proline accumulation in leaves and rhizomes. Precursors related to phenylpropanoid pathway increased significantly during plant dehydration. Accordingly, increases in anthocyanin and phenolic contents as well as lignin deposition were observed in leaves of dehydrated plants. Cell divisions and a decrease in stored starch were observed in the rhizomes indicating starch mobilization. Anatomical analyses revealed the presence of a more developed water-storage tissue in dehydrated leaves. During desiccation, leaves curl upwards and the adaxial V deep water-storage tissue is supported by two larger lateral vascular bundles. Cell wall folding and an increased proportion of arabinose-containing polymers was observed in leaves under dehydration, suggesting increasing of cell wall flexibility during desiccation. Such biochemical and morphological changes are consistent with the ability of P. burchellii to tolerate intense desiccation and behave as a resurrection species.

Iron (Fe2+)-induced toxicity produces morphological and physiological changes in roots in Panax ginseng grown in hydroponics

ABSTRACTRusty roots markedly influence on ginseng cultivation, and this phenomenon often attributed to iron (Fe) induced toxicity. To examine the physiological mechanisms underlying Fe-initiated toxicity as evidenced by rusty roots in Panax ginseng, morphological and physiological changes in roots were investigated in hydroponics using Fe2+ concentrations of 50 (control), 100, 200, 400 or 600 µM. Compared with control, reddish-brown deposition at the root surface increasingly appeared as Fe2+ concentration increased (≥200 µM). The pH also rose as Fe levels were elevated. Higher external Fe2+ concentrations produced changes in root organelles and cell structures. Structural alterations in mitochondria due to excess Fe storage, protoplast shrinkage and cell vacuolation as well as formation of central vacuole with deposits in roots were observed. In addition, apparent cell wall thickening, cell wall folding and shrinkage, damage of cell membranes and a large amount of cell debris occurred at higher external Fe2+ concentrations (≥400 µM). The Fe2+ mediated damage resulting in morphological and physiological changes in ginseng roots was concentration and pH dependent.

Tripogon loliiformis elicits a rapid physiological and structural response to dehydration for desiccation tolerance.

Resurrection plants can withstand extreme dehydration to an air-dry state and then recover upon receiving water. Tripogon loliiformis (F.Muell.) C.E.Hubb. is a largely uncharacterised native Australian desiccation-tolerant grass that resurrects from the desiccated state within 72h. Using a combination of structural and physiological techniques the structural and physiological features that enable T. loliiformis to tolerate desiccation were investigated. These features include: (i) a myriad of structural changes such as leaf folding, cell wall folding and vacuole fragmentation that mitigate desiccation stress, (ii) potential role of sclerenchymatous tissue within leaf folding and radiation protection, (iii) retention of ~70% chlorophyll in the desiccated state, (iv) early response of photosynthesis to dehydration by 50% reduction and ceasing completely at 80 and 70% relative water content, respectively, (v) a sharp increase in electrolyte leakage during dehydration, and (vi) confirmation of membrane integrity throughout desiccation and rehydration. Taken together, these results demonstrate that T. loliiformis implements a range of structural and physiological mechanisms that minimise mechanical, oxidative and irradiation stress. These results provide powerful insights into tolerance mechanisms for potential utilisation in the enhancement of stress-tolerance in crop plants.

Success rates and prognosis of heart valvuloplasty and valve replacement performed for elderly patients.

Objective:To analyze the success rates and prognosis of heart valvuloplasty and valve replacement for elderly patients, and to provide clinical evidence.Methods:A total of 1240 patients who received heart valve surgeries in our hospital from June 2004 to October 2014 were selected and retrospectively analyzed. They were divided into two groups based on age (60), and those older than 60 (Group B) suffered from rheumatic valvular heart disease and nonrheumatic valvular heart disease including degenerative valve disease. Mitral valve replacement (MVR), tricuspid valve replacement (TVR), aortic valve replacement (AVR), double valve replacement (DVR), mitral valvuloplasty (MVP) and tricuspid valvuloplasty (TVP) were performed by using bioprosthetic and mechanical valves. Before surgery, coronary angiography, coronary artery bypass grafting (CABG), left atrial thrombectomy, left atrial wall folding and radiofrequency ablation were conducted. For the patients younger than 60 (Group A) who had congenital heart disease, rheumatic valvular heart disease and valvular heart disease, MVR, AVR, DVR, MVP, TVP and closed cuspid commissurotomy were performed with bioprosthetic and mechanical valves. The two groups were then monitored.Results:The mortality rates of Group A and Group B were 2.7% (16 cases) and 3.1% (20 cases) respectively. They died mainly of malignant ventricular arrhythmias, multiple organ failure, left ventricular rupture, low cardiac output syndrome, acute renal failure, respiratory failure, upper gastrointestinal bleeding, mechanical valve failure and cerebrovascular accident. The two groups had significantly different application rates of bioprosthetic valve, times of auxiliary ventilation and hospitalization stay lengths (P<0.05), but left ventricular ejection fractions, left ventricular end-diastolic diameters (LVEDDs), mortality rates as well as times of aortic cross-clamping and cardiopulmonary bypass were similar (P>0.05). LVEDD, complicated coronary artery disease, CABG and grade of the New York Heart Association Functional Classification were independent risk factors for postoperative death.Conclusion:When heart valvuloplasty and valve replacement were performed for elderly patients, the success rate and prognosis could only be improved by optimizing preoperative preparation, shortening the times of cardiopulmonary bypass and aortic cross-clamping, and paying particular attention to myocardial protection and postoperative treatment.

Embryo cell wall properties in relation to development and desiccation in the recalcitrant-seeded Encephalartos natalensis (Zamiaceae) Dyer and Verdoorn.

Plant cell walls are dynamic entities that may change with development, differ between plant species and tissue type and play an important role in responses to various stresses. In this regard, the present investigation employed immunocytochemistry to determine wall composition and possible changes during development of immature and mature embryos of the recalcitrant-seeded cycad Encephalartos natalensis. Fluorescent and gold markers, together with cryo-scanning and transmission electron microscopy (TEM) were also used to analyse potential changes in the cell walls of mature embryos upon desiccation. Immature cell walls were characterised by low- and high methyl-esterified epitopes of pectin, rhamnogalacturonan-associated arabinan, and the hemicellulose xyloglucan. Arabinogalactan protein recognised by the LM2 antibody, along with rhamnogalacturonan-associated galactan and the hemicellulose xylan, were not positively localised using immunological probes, suggesting that the cell walls of the embryo of E. natalensis do not possess these epitopes. Interestingly, mature embryos appeared to be identical to immature ones with respect to the cell wall components investigated, implying that these may not change during the protracted post-shedding embryogenesis of this species. Drying appeared to induce some degree of cell wall folding in mature embryos, although this was limited by the abundant amyloplasts, which filled the cytomatrical space. Folding, however, was correlated with relatively high levels of wall plasticisers typified by arabinose polymers. From the results of this study, it is proposed that the embryo cell walls of E. natalensis are constitutively prepared for the flexibility required during cell growth and expansion, which may also facilitate the moderate cell wall folding observed in mature embryos upon drying. This, together with the abundant occurrence of amyloplasts in the cytomatrix, may provide sufficient mechanical stabilisation if water is lost, even though the seeds of this species are highly desiccation-sensitive.

Repair of mitral paravalvular leak with double left atrial wall folding

Mitral paravalvular leaks can be repaired by alternative repair techniques instead of direct suture repair of the leak site. We report our technique of double left atrial wall folding for repair of posterior mitral paravalvular leaks.

Hysteroscopic Visualization of Bubaline Uterus

Hysteroscopic visualization of buffalo uteri (n=20) was performed using a rigid endoscope. The genitals from estrus buffaloes (20.0%) revealed the presence of uterine wall folding and presence of mucus whereas; haemorrhages on the uterine wall could be visualized in 5% of the genitalia. It was concluded that hysteroscopic visualization of bubaline uterus can provide additional information on the internal uterine structures.

Understanding desiccation tolerance using the resurrection plant Boea hygrometrica as a model system.

Vegetative tissues of Boea hygrometrica, a member of the Gesneriaceae family, can tolerate severe water loss to desiccated state and fully recover upon rehydration. Unlike many other so called “resurrection plants,” the detached leaves of B. hygrometrica also possess the same level of capacity for desiccation tolerance (DT) as that of whole plant. B. hygrometrica is distributed widely from the tropics to northern temperate regions in East Asia and grows vigorously in areas around limestone rocks, where dehydration occurs frequently, rapidly, and profoundly. The properties of detached B. hygrometrica leaves and relative ease of culture have made it a useful system to study the adaptive mechanisms of DT. Extensive studies have been conducted to identify the physiological, cellular, and molecular mechanisms underlying DT in the last decade, including specific responses to water stress, such as cell wall folding and pigment-protein complex stabilizing in desiccated leaves. In this review, the insight into the structural, physiological, and biochemical, and molecular alterations that accompany the acquisition of DT in B. hygrometrica is described. Finally a future perspective is proposed, with an emphasis on the emerging regulatory roles of retroelements and histone modifications in the acquisition of DT, and the need of establishment of genome sequence database and high throughput techniques to identify novel regulators for fully understanding of the matrix of DT.

Tailored sizes of constrictive external vein meshes for coronary artery bypass surgery

External mesh constriction of vein grafts was shown to mitigate intimal hyperplasia by lowering circumferential wall stress and increasing fluid shear stress. As under-constriction leaves vein segments unsupported and thus prone to neointimal proliferation while over-constriction may cause wall folding optimal mesh sizing holds a key to clinical success. Diameter fluctuations and the occurrence of wall folding as a consequence of external constriction with knitted Nitinol meshes were assessed in saphenous vein grafts from 100 consecutive coronary artery bypass (CABG) patients. Subsequently, mesh dimensions were identified that resulted in the lowest number of mesh sizes for all patients either guaranteeing tight continual mesh contact along the entire graft length (stipulation A) or preventing wall folding (stipulation B). A mathematical data classification analysis and a statistical single-stage partitioning approach were independently applied alternatively prioritizing stipulation A or B. Although the risk of folding linearly increased when constriction exceeded 24.6% (Chi squared test p = 0.0004) the actual incidence of folding (8.6% of veins) as well as the degree of lumenal encroachment (6.2 ± 2.1%) were low. Folds were always single, narrow longitudinal formations (height: 23.3 ± 4.0% of inner diameter/base: 16.6 ± 18.1% of luminal circumference). Both analytical methods provided an optimum number of 4 mesh sizes beyond which no further advantage was seen. While the size ranges recommended by both methods assured continual tight mesh contact with the vein the narrower range suggested by the mathematical data classification analysis (3.0–3.7 mm) put 20.6 ± 12.5% of length in 69% of veins at risk of folding as opposed to 21.3 ± 25.9% being at risk in the wider size range (3.0–4.2 mm) suggested by the statistical partitioning approach. Four mesh sizes would provide uninterrupted mesh contact in 98% of vein grafts in CABG procedures with only 26% of their length being at risk of relatively mild wall folding.

Onset of airflow limitation in a collapsible tube model: impact of surrounding pressure, longitudinal strain, and wall folding geometry

We studied the impact of wall strain and surrounding pressure on the onset of airflow limitation in a thin-walled "floppy" tube model. A vacuum source-generated steady-state (baseline) airflow (0-350 ml/s) through a thin-walled latex tube (length 80 mm, wall thickness 0.23 mm) enclosed within a rigid, sealed, air-filled, cylindrical chamber while upstream minus downstream pressure, chamber pressure (Pc), and lumen geometry [in-line digital camera; segmentation (Amira 5.2.2) and analysis (Rhinoceros 4) software] were monitored. Longitudinal strain (S; 0-62.5%) and Pc (0-20 cmH(2)O) combinations were imposed, and Pc associated with onset of 1) reduced airflow and 2) fully developed airflow limitation recorded. At any strain, increasing Pc resulted in a decrease in airflow. Across all baseline airflow, threshold pressure was 1-7 cmH(2)O for S < 25%, 6-8 cmH(2)O at S = 25% and 37.5%, and 5-7 cmH(2)O at S = 50% and 62.5%. Pc associated with fully developed airflow limitation was 4-6 cmH(2)O for S < 25%, >20 cmH(2)O at S = 25% (i.e., no flow limitation), 18 cmH(2)O at S = 37.5%, and 8-12 cmH(2)O at S = 50% and 62.5%. Lumen area decreased with increasing Pc but was 1) larger at S = 25% and 2) characterized by bifold narrowing at S < 25% and trifold narrowing at S ≥ 25%. In conclusion, tube function was modulated by Pc vs. S interactions, with S = 25% producing trifold lumen narrowing, maximal patency, and no airflow limitation. Findings may have implications for understanding peripharyngeal tissue pressure and pharyngeal wall strain effects on passive pharyngeal airway function in humans.

Dehydration‐induced expression of a 31‐kDa dehydrin in Polypodium polypodioides (Polypodiaceae) may enable large, reversible deformation of cell walls

Current and predicted climate changes caused by global warming compel greater understanding of the molecular mechanisms that plants use to survive drought. The desiccation-tolerant fern Polypodium polypodioides exhibits extensive cell wall folding when dried to less than 15% relative water content (RWC) and rapidly (within 24 h) rehydrates when exposed to water and high humidity. A 31-kDa putative dehydrin polypeptide expressed in partially and fully dry tissues detected via western blotting was present only during drying and rapidly dissipated (within 24 h) upon tissue rehydration. Immunostaining indicates the presence of dehydrin near the cell wall of partially and fully dried tissues. Atomic force microscopy of tracheal scalariform perforations indicates that dry vascular tissue does not undergo significant strain. Additionally, environmental scanning electron microscopy reveals differential hydrophilicity between the abaxial and adaxial leaf surfaces as well as large, reversible deformation. The ability to avoid cell wall damage in some desiccation-tolerant species may be partially attributed to cell wall localization of dehydrins enabling reversible, large cell-wall deformation. Thus, the de novo synthesis of dehydrin proteins and potential localization to the cell walls of these desiccation-tolerant species may play a role in avoiding mechanical failure during drought.