Gas-filled Spaces Research Articles

An overview of oxygen transport in plants: diffusion and convection.

The movement of gases within plants is crucial for species that live in flood-prone areas with limited soil oxygen. These plants adapt to hypoxia/anoxia not by using oxygen more efficiently, but by ensuring a steady oxygen supply to their cells. Wetland plants typically form gas-filled spaces (aerenchyma) in their tissues, providing a low-resistance pathway for gas movement between shoots and roots, especially when the shoots are above water, and the roots are submerged. Oxygen movement in plant roots is mainly through diffusion. However, in certain species, such as emergent and floating-leaved plants, pressurized flows can also facilitate the movement of gases within their stems and rhizomes. Three types of pressurized (convective) flows have been identified: humidity-induced pressurization (positive pressure), thermal osmosis (positive pressure with air flow against the heat gradient), and venturi-induced suction (negative pressure) caused by wind passing over broken culms. A clear diel variation in pressurized flows exists, with higher pressures and flows during the day and negligible pressures and flows during the night. This article discusses some key aspects of these mechanisms for oxygen movement.

Lipid-Coated Nanobubbles in Plants.

One of the more surprising occurrences of bulk nanobubbles is in the sap inside the vascular transport system of flowering plants, the xylem. In plants, nanobubbles are subjected to negative pressure in the water and to large pressure fluctuations, sometimes encompassing pressure changes of several MPa over the course of a single day, as well as wide temperature fluctuations. Here, we review the evidence for nanobubbles in plants and for polar lipids that coat them, allowing nanobubbles to persist in this dynamic environment. The review addresses how the dynamic surface tension of polar lipid monolayers allows nanobubbles to avoid dissolution or unstable expansion under negative liquid pressure. In addition, we discuss theoretical considerations about the formation of lipid-coated nanobubbles in plants from gas-filled spaces in the xylem and the role of mesoporous fibrous pit membranes between xylem conduits in creating the bubbles, driven by the pressure gradient between the gas and liquid phase. We discuss the role of surface charges in preventing nanobubble coalescence, and conclude by addressing a number of open questions about nanobubbles in plants.

A numerical study of the double-glazed solar air heater (DG-SAH) performance using optimized gas-filled interspaces

The reduction of energy losses and destroyed exergy requires the optimization of the double-glazing space. The poor thermophysical characteristics of the air are a limiting factor in the attenuation of heat loss through the double-glazing of the solar collector.The aim of this study is to examine the effect of trapped gases (argon, xenon, krypton, and SF6) within the double-glazing and between the inner glass and the absorber on the efficiency, useful energy, overall heat loss coefficient, and outlet temperature of the back-plate solar air heater. This research was conducted by applying constant solar radiation of 1000 W/m2. The new Eismann correlation is implemented to iteratively evaluate the heat transfer coefficients in gas-filled interspaces and to optimally define these distances. Furthermore, the impact of these gases on exergy efficiency, destruction exergy, and system exergy has been studied. Among these rare gases, xenon leads to the best thermal performance, followed by krypton and argon, compared to air. Respectively, the efficiencies obtained are 51.8%, 50.6%, 48.8%, and 45.8% for xenon, krypton, argon, and air. The optimal gas-filled spaces corresponding to these efficiencies are 4 mm, 5 mm, 9 mm, and 10 mm. Similarly, the exergy approach leads to the same optimal widths of the gas-filled spaces.

LARGE BILATERAL PNEUMATOCELES COMPLICATING COVID-19 RECOVERY

LARGE BILATERAL PNEUMATOCELES COMPLICATING COVID-19 RECOVERY

MicroCT as a Useful Tool for Analysing the 3D Structure of Lichens and Quantifying Internal Cephalodia in Lobaria pulmonaria

High-resolution X-ray computer tomography (microCT) is a well-established technique to analyse three-dimensional microstructures in 3D non-destructive imaging. The non-destructive three-dimensional analysis of lichens is interesting for many reasons. The examination of hidden structural characteristics can, e.g., provide information on internal structural features (form and distribution of fungal-supporting tissue/hypha), gas-filled spaces within the thallus (important for gas exchange and, thus, physiological processes), or yield information on the symbiont composition within the lichen, e.g., the localisation and amount of additional cyanobacteria in cephalodia. Here, we present the possibilities and current limitations for applying conventional laboratory-based high-resolution X-ray computer tomography to analyse lichens. MicroCT allows the virtual 3D reconstruction of a sample from 2D X-ray projections and is helpful for the non-destructive analysis of structural characters or the symbiont composition of lichens. By means of a quantitative 3D image analysis, the volume of internal cephalodia is determined for Lobaria pulmonaria and the external cephalodia of Peltigera leucophlebia. Nevertheless, the need for higher-resolution tomography for more detailed studies is emphasised. Particular challenges are the large sizes of datasets to be analysed and the high variability of the lichen microstructures.

Tolerance to partial and complete submergence in the forage legume Melilotus siculus: an evaluation of 15 accessions for petiole hyponastic response and gas-filled spaces, leaf hydrophobicity and gas films, and root phellem.

Submergence is a severe stress for most plants. Melilotus siculus is a waterlogging- (i.e. root zone hypoxia) tolerant annual forage legume, but data were lacking for the effects of partial and full submergence of the shoots. The aim was to compare the tolerance to partial and full submergence of 15 M. siculus accessions and to assess variation in traits possibly contributing to tolerance. Recovery ability post-submergence was also evaluated. A factorial experiment imposed treatments of water level [aerated root zone with shoots in air as controls, stagnant root zone with shoots in air, stagnant root zone with partial (75 %) or full shoot submergence] on 15 accessions, for 7 d on 4-week-old plants in a 20/15 °C day/night phytotron. Measurements included: shoot and root growth, hyponastic petiole responses, petiole gas-filled spaces, leaflet sugars, leaflet surface hydrophobicity, leaflet gas film thickness and phellem area near the base of the main root. Recovery following full submergence was also assessed. Accessions differed in shoot and root growth during partial and full shoot submergence. Traits differing among accessions and associated with tolerance were leaflet gas film thickness upon submergence, gas-filled spaces in petioles and phellem tissue area near the base of the main root. All accessions were able to re-orientate petioles towards the vertical under both partial and full submergence. Petiole extension rates were maintained during partial submergence, but decreased during full submergence. Leaflet sugars accumulated during partial submergence, but were depleted during full submergence. Growth resumption after full submergence differed among accessions and was positively correlated with the number of green leaves retained at desubmergence. Melilotus siculus is able to tolerate partial and full submergence of at least 7 d. Leaflet surface hydrophobicity and associated gas film retention, petiole gas-filled porosity and root phellem abundance are important traits contributing to tolerance. Post-submergence recovery growth differs among accessions. The ability to retain green leaves is essential to succeed during recovery.

Respiration of thermogenic inflorescences of skunk cabbage Symplocarpus renifolius in heliox.

The respiration rate of the thermogenic inflorescences of Japanese skunk cabbage Symplocarpus renifolius can reach 300nmol s-1 g-1 , which is sufficient to raise spadix temperature (Ts ) up to 15°C above ambient air temperature (Ta ). Respiration rate is inversely related to Ta , such that the Ts achieves a degree of independence from Ta , an effect known as temperature regulation. Here, we measure oxygen consumption rate (Ṁo2 ) in air (21% O2 in mainly N2 ) and in heliox (21% O2 in He) to investigate the diffusive conductance of the network of gas-filled spaces and the thermoregulatory response. When Ts was clamped at 15°C, the temperature that produces maximal Ṁo2 in this species, exposure to high diffusivity heliox increased mean Ṁo2 significantly from 137±17 to 202±43nmol s-1 g-1 FW, indicating that respiration in air is normally limited by diffusion in the gas phase and some mitochondria are unsaturated. When Ta was clamped at 15°C and Ts was allowed to vary, exposure to heliox reduced Ts 1°C and increased Ṁo2 significantly from 116±10 to 137±19nmol s-1 g-1 , indicating that enhanced heat loss by conduction and convection can elicit the thermoregulatory response.

Nitrous Oxide

*Department of Anaesthetics and Critical Care, Nelson R. Mandela School of Medicine, University of KwaZulu-Natal; and †Department of Anaesthetics and Critical Care, King Edward VIII Hospital, Durban, South Africa; and ‡Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, United Kingdom.

Hyperbaric oxygen therapy and its mechanisms of action: implication of several molecular processes along with reactive species

Hyperbaric oxygen (HBO2) treatment is an interesting therapeutic modality (HBOT; hyperbaric oxygen therapy) in which the patient breathes 100% oxygen while exposed to increased atmospheric pressure. Generally, the therapeutic mechanisms for HBOT have been based on both the increased ambient pressure and the elevated partial oxygen pressure (pO2). Increasing the ambient pressure leads to reduction in the volume of gas-filled spaces according to Boyle’s law. This action is directly related to the treatment of pathological conditions in which gas bubbles are present in the patient’s body, i.e., decompression sickness or gas embolism. However, most of the pathologies for which HBOT is used rely on an inflammatory background and have no pathophysiologic relation with gas bubbles. Thus, the mechanistic basis of HBOT in indications such as problematic wounds, traumatic injuries, necrotizing fasciitis, ischemia-reperfusion processes, refractory osteomyelitis, and compromised flap and grafts depends on the elevation in pO2 in bodily fluids and tissues. Oxygen is needed to support cellular respiration and consequently provides energy. Reduced delivery of oxygen...

Investigations on the stratification of forestomach contents in ruminants: an ultrasonographic approach

The degree of stratification in the reticulorumen contents is considered a major explanatory factor for other morphological and physiological differences between ruminant feeding types. However, information on reticulorumen (RR) contents is usually gathered from dead animals or indirect such as passage kinetics. We hypothesized that, although the contents of the gastrointestinal tract can usually not be evaluated by ultrasonography, the three typical layers of stratified RR contents (gas dome, fibre mat, fluid) can be demonstrated by this technique. In three domestic cows, the gas dome in the cows’ rumens could be demonstrated sonographically by reverberation lines running in parallel to the line demarcating the rumen mucosa, as is typical for the sonographic image of large, gas-filled spaces. More ventrally, the area behind the rumen mucosa showed typical pattern indicating gaseous inclusions, corresponding to the fibre mat inside the rumen. Further ventrally, in two of the animals, the area behind the demarcation line appeared dark without reverberation lines, as is typical for large fluid-filled spaces. When the technique was applied to a captive, habituated, browse-fed moose, no gas dome could be demonstrated, supporting the hypothesis that the reticulorumen contents of browsers are less stratified. The results of this study indicate that sonography represents a useful tool for the demonstration of RR contents stratification in live animals.

Pneumatosis coli due to pharmacological constipation

A 56-year-old woman was being treated with tramadol (up to 300 mg/day) for joint pain. After 20 days of treatment, tramadol was discontinued because of intense constipation followed by severe lower abdominal pain, diarrhea, and tenesmus. On admission to the hospital, symptoms persisted; results of standard laboratory tests were unremarkable. A CT scan of the abdomen and pelvis showed a myriad of gas-filled cysts in the wall of the rectum, sigmoid, and descending colon (A, middle). Colonoscopy revealed these lesions to be 5 to 20 mm, subepithelial cyst-like lesions protruding into the lumen; the overlying mucosa was normal (B). CT and colonoscopic findings were confirmed by EUS (C). Histopathologic analysis showed a submucosal dissection by gas-filled spaces (D, H&E, orig. mag. x40). Pneumatosis coli due to pharmacological constipation was diagnosed. Antibiotics and high-flow oxygen therapy were followed-up by rapid symptomatic and radiological improvement (A, upper-left corner).

Oxygen dynamics during submergence in the halophytic stem succulentHalosarcia pergranulata

This study elucidated O2 dynamics in shoots and roots of submerged Halosarcia pergranulata (Salicornioideae), a perennial halophytic stem succulent that grows on floodprone mudflats of salt lakes. Oxygen within shoots and roots was measured using microelectrodes, for plants when waterlogged or completely submerged, with shoots in light or in darkness, in a controlled environment. Net photosynthesis (PN) when underwater, at a range of dissolved CO2 concentrations, was measured by monitoring O2 production rates by excised stems. The bulky nature and apparently low volume of gas-filled spaces of the succulent stems resulted in relatively high radial resistance to gas diffusion. At ambient CO2, quasi-steady state rates of PN by excised succulent stems were estimated to be close to zero; nevertheless, in intact plants, underwater photosynthesis provided O2 to tissues and led to radial O2 loss (ROL) from the roots, at least during the first several hours (the time period measured) after submergence or when light periods followed darkness. The influence of light on tissue O2 dynamics was confirmed in an experiment on a submerged plant in a salt lake in south-western Australia. In the late afternoon, partial pressure of O2 (pO2) in the succulent stem was 23.2 kPa (i.e. approximately 10% above that in the air), while in the roots, it was 6.2-9.8 kPa. Upon sunset, the pO2 in the succulent stems declined within 1 h to below detection, but then showed some fluctuations with the pO2 increasing to at most 2.5 kPa during the night. At night, pO2 in the roots remained higher than in the succulent stems, especially for a root with the basal portion in the floodwater. At sunrise, the pO2 increased in the succulent stems within minutes. In the roots, changes in the pO2 lagged behind those in the succulent stems. In summary, photosynthesis in stems of submerged plants increased the pO2 in the shoots and roots so that tissues experience diurnal changes in the pO2, but O2 from the H2O column also entered submerged plants.

Nitrous oxide increases the incidence of bowel distension in patients undergoing elective colon resection

Nitrous oxide rapidly inflates gas-filled spaces such as the intestines; but whether the resulting bowel distension is clinically important remains unclear. We therefore tested the hypothesis that nitrous oxide produces clinically important bowel distension. Patients scheduled for colon resection were anesthetized with isoflurane and 35% oxygen and randomly assigned to 65% nitrous oxide (n = 175) or 65% nitrogen in air (n = 169). At the end of surgery, blinded surgeons rated the degree of bowel distension as none, mild, moderate, or severe. Patients reported pain, and nausea and vomiting (PONV) 2 h after surgery. Data are reported as means (SD). P < 0.05 was statistically significant. Morphometric and demographic data were similar in the groups. The duration of surgery was 3.0 (1.2) h in the nitrous oxide group and 3.4 (1.5) h in the air group (P = 0.017). Postoperative self-reported pain scores (visual analog scale, 0-100 mm) were greater in the nitrous oxide group (43 [30] mm) than in the air group (35 [31] mm, P = 0.018). Although the incidence of PONV was similar in the groups, VAS scores for nausea were significantly greater in the nitrous oxide group (P = 0.040). Moderate-to-severe bowel distension was observed in 23% of nitrous oxide patients, but in only 9% of patients in the air group (P < 0.001). The number-needed-to-harm for moderate or severe bowel distension from nitrous oxide was thus seven. Our results suggest that avoiding nitrous oxide administration during prolonged bowel operations will minimize bowel distension and possibly reduce postoperative pain related to it.

Tight junction-related structures in the absence of a lumen: Occludin, claudins and tight junction plaque proteins in densely packed cell formations of stratified epithelia and squamous cell carcinomas

Tight junctions (TJs), hallmark structures of one-layered epithelia and of endothelia, are of central biological importance as intramembranous "fences" and as hydrophobic "barriers" between lumina represented by liquid- or gas-filled spaces on the one hand and the mesenchymal space on the other. They have long been thought to be absent from stratified epithelia. Recently, however, constitutive TJ proteins and TJ-related structures have also been identified in squamous stratified epithelia, including the epidermis, where they occur in special positions, most prominently in the uppermost living epidermal cell layer, the stratum granulosum. Much to our surprise, however, we have now also discovered several major TJ proteins (claudins 1 and 4, occludin, cingulin, symplekin, protein ZO-1) and TJ-related structures in specific positions of formations of epithelium-derived tissues that lack any lumen and do not border on luminal or body surfaces. Using immunohistochemistry and electron microscopy we have localized TJ proteins and structures in peripheral cells of the Hassall's corpuscles of human and bovine thymi as well as in specific central formations of tumor nests in squamous cell carcinomas, including the so-called "horn pearls". Such structures have even been found in carcinoma metastases. In carcinomas, they often seem to separate certain tumor regions from others or from stroma. The structural significance and the possible functional relevance of the locally restricted synthesis of TJ proteins and of the formations of TJ-related structures are discussed. It is proposed to include the determination of the presence or absence of such proteins and structures in the diagnostic program of tumor pathology.

Differential expression of hydrophobins DGH1, DGH2 and DGH3 and immunolocalization of DGH1 in strata of the lichenized basidiocarp of Dictyonema glabratum

Summary • The expression of hydrophobin genes DGH1, DGH2 and DGH3 in the lichenized fruitbody of Dictyonema glabratum (syn. Cora pavonia) is reported here, as well as immunolocalization of the DGH1 protein. • In situ hybridization was conducted to determine expression patterns of hydrophobin genes DGH1, DGH2 and DGH3. The DGH1 protein was expressed in Escherichia coli and used to raise antibodies for immunolocalization of the DGH1 protein. • DGH1 and DGH2 are expressed by hyphae in the photobiont layer and the lower stratum. DGH3 is newly expressed by hyphae in the boundary layer. DGH1 is immunolocalized in the electron-dense outer layer of fungal walls lining gas-filled spaces in the photobiont layer, in aerial hyphae in the gas-filled lower stratum and in the transition zone between the two strata. • Dictyonema glabratum hydrophobins surround wall surfaces in the photobiont layer of the fruitbody. Hydrophobin layers probably function to keep interhyphal spaces water-free, seal the apoplast to enable water translocation, and define strata within the basidiocarp.

Hydrophobins DGH1, DGH2, and DGH3 in the Lichen-Forming Basidiomycete Dictyonema glabratum

Dictyonema glabratum is a lichen-forming basidiomycete whose symbiotic phenotype shares similarities to both lichens and its non-lichen-forming relatives. In the photobiont layer of D. glabratum intercellular gas-filled spaces are present even when the lichen is water-saturated. The walls of hyphae lining air cavities are covered by a hydrophobic, rodlet-patterned layer, assumed to be formed by hydrophobins. Hot SDS-insoluble, but trifluoroacetic acid-soluble lichen cell wall extracts contained seven proteins. The N-terminal sequence of the most abundant 14-kDa protein was used to carry out cDNA cloning by RT-PCR. The deduced amino acid sequence of the amplified fragment encoded a class I hydrophobin, called DGH1. The cDNA sequence encoding the signal peptide was cloned by RACE-PCR, which also coamplified cDNA fragments encoding two additional class I hydrophobins, DGH2 and DGH3. The three proteins share 54 to 66% amino acid identity. The D. glabratum hydrophobin extract containing either all proteins or primarily DGH1 self-assembled and formed a rodlet mosaic similar to the one observed in situ. Concentration of the protein extract was shown to influence the length of the self-assembled rodlets.

Freeze-induced sap absorption in Acer pseudoplatanus: a possible mechanism

Xylem sap pressure changes in response to imposed temperature regimes were studied using excised stems of young sycamore seedlings (Acer pseudoplatanus L). Experiments confirmed that a rapid decrease in sap pressure (inducing an uptake of water) occurred within the xylem core during freezing. The sequence was reversed by thawing. Measurement of wood diameter or bark thickness revealed no significant changes which might accommodate this sap during freezing. Indeed, investigation of the sapwood density showed an overall increase on freezing. The absorption of water in response to freezing was shown to be operative in deliberately killed tissue, although high tissue water content above about 60% disrupted the response. Experiments using twigs at suprafreezing temperatures induced sap exudation also, but it was only a small fraction of the amounts which could be expected after freeze-induced absorption. Apparently suprafreezing exudation can be explained by thermal expansion effects of gas and sap in the wood. A mechanism is proposed based on sap uptake induced by apoplastic ice formation in gas-filled spaces, such as fibre cells, which may also account for the familiar maple sap exudation.

Assessment of ventilation-perfusion inequality by aADN2 in newborn infants.

The contribution (Qo/Qt) of gas-filled air spaces with reduced ventilation-perfusion ratio (VA/Qc) to the production of total venous admixture in nondistressed premature infant and newborn infants with transient tachypnea was assessed by the aADN2 and AaDo2. The mean value for Qo/Qt in both nondistressed prematures and infants with transient tachypnea was 0.08. In both groups this represented about 30% of total venous admixutre.

Function of Theswimbladder-Inner Ear-Lateral Line System of Herring in the Young Stages

INTRODUCTIONThe preceding paper (Allen, Blaxter &amp; Denton, 1976) describes the development of the swimbladder-inner ear-lateral line system of the herring.In the larval stage of herring the pro-otic bullae start to develop at a body length of about 18 mm. Between 18 and 30 mm the bullae become filled with gas. At 26 mm the lateral recess membrane starts to develop, becoming silvered at about 42 mm. The lateral line develops between 19 and 45 mm. The swimbladder silvers and contains gas from about 38 mm. The adult system is complete at 50–60 mm body length, some four months after hatching.This paper concerns the system in its intermediate stages of development. It examines the problems of how the bullae are filled with gas and how the gas spaces are maintained. It gives evidence on the possible roles of the gas-filled spaces as hydrostatic pressure receptors and as aids to buoyancy and discusses the limitations of the system before it can gain or lose gas to a gas-filled swimbladder.

Normal Tubal Function

JUST AS DIVING and flying directed at tention to tubal function under these special conditions where the middle ear is exposed to large and rapid pressure changes, so aeration of the tympanic cavity in reconstructive ear surgery has directed attention to tubal function under normal barometric conditions. The behavior of the tube in transmitting large and rapid movements of air to and from the middle ear is now fairly well documented. On the other hand, despite a great deal of study, the development and maintenance of gas-filled spaces in the middle ear and mastoid under normal conditions are not clearly understood. While there is general agreement about the gross and microscopic anatomy of the structures involved, the normal physiological role of the component parts is more difficult to determine. The behavior of the tube and middle ear under normal barometric conditions needs further study. Some of the questions that one