Diffusive Gas Exchange Research Articles

Ontogeny of tracheal system structure: a light and electron-microscopy study of the metathoracic femur of the American locust, Schistocerca americana.

Does oxygen delivery become more challenging for insects as they increase in size? To partially test this hypothesis, we used quantitative light and electron microscopy to estimate the oxygen delivery capacity for two steps of tracheal oxygen delivery within the metathoracic femur (jumping leg) for 2nd instar (about 47 mg) and adult (about 1.7 g) locusts, Schistocerca americana. The fractional cross-sectional areas of the major tracheae running longitudinally along the leg were similar in adults and 2nd instars; however, since the legs of adults are longer, the mass-specific diffusive conductances of these tracheae were 4-fold greater in 2nd instars. Diffusive gas exchange longitudinally along the leg is easily possible for 2nd instars but not adults, who have many air sacs within the femur. Mitochondrial content fell proximally to distally within the femur in 2nd instars but not adults, supporting the hypothesis that diffusion was more important for the former. Lateral diffusing capacities of the tracheal walls were 12-fold greater in adults than 2nd instars. This was primarily due to differences in the smallest tracheal class (tracheoles), which had thinner epidermal and cuticular layers, greater surface to volume ratios, and greater mass-specific surface areas in adults. Adults also had greater mitochondrial contents, larger cell sizes and more intracellular tracheae. Thus, larger insects do not necessarily face greater problems with oxygen delivery; adult grasshoppers have superior oxygen delivery systems and greater mass-specific aerobic capacities in their legs than smaller/younger insects.

Cardiac rhythms of late pre-pipped and pipped chick embryos exposed to altered oxygen environments

During the final stages of embryonic development in chickens, diffusive gas exchange through the chorioallantoic membrane (CAM) is progressively replaced by pulmonary respiration that begins with internal pipping (IP) of the CAM. Late chick embryos going through the transition from CAM respiration to pulmonary respiration were exposed to hyperoxic (100% O 2) and hypoxic (10% O 2/N 2) environments for 2-h and the responses of baseline heart rate (HR), and HR fluctuation patterns were investigated. 16- and 18-day-old (referred to as 18-d) embryos and 20-d externally pipped (EP) embryos were examined as pre-pipped embryos and pipped embryos, respectively. 19-d embryos were divided into two groups: embryos that had not yet internally pipped (Pre-IP embryos) and embryos that had internally pipped (IP embryos). IP was identified by detecting the breathing signal with a condenser microphone attached hermetically on the eggshell (i.e. acoustorespirogram) on day 19 of incubation. In the hyperoxic environment, HR baseline of pre-pipped embryos remained unchanged and that of pipped embryos was depressed. In the hypoxic environment, HR baseline of 16-d pre-pipped embryos was depressed and that of pipped (IP and EP) embryos elevated. These different responses in pipped embryos might be partially attributed to increased cholinergic input from the vagus nerve in hyperoxia and increased adrenergic response in hypoxia. While hyperoxia did not induce marked modification of instantaneous heart rate (IHR) fluctuation patterns, hypoxia tended to augment transient decelerations of IHR in late pre-pipped embryos and markedly depressed HR fluctuations in pipped embryos.

Reducing lung strain after pneumonectomy impairs oxygen diffusing capacity but not ventilation-perfusion matching.

After pneumonectomy (Pnx), mechanical strain on the remaining lung is an important signal for adaptation. To examine how mechanical lung strain alters gas exchange adaptation after Pnx, we replaced the right lung of adult dogs with a custom-shaped inflatable silicone prosthesis. The prosthesis was kept 1) inflated (Inf) to reduce mechanical strain of the remaining lung and maintain the mediastinum in the midline, or 2) deflated (Def) to allow lung strain and mediastinal shift. Gas exchange was studied 4-7 mo later at rest and during treadmill exercise by the multiple inert gas elimination technique while animals breathed 21 and 14% O2 in balanced order. In the Inf group compared with Def group during hypoxic exercise, arterial O2 saturation was lower and alveolar-arterial O2 tension difference higher, whereas O2 diffusing capacity was lower at any given cardiac output. Dispersion of the perfusion distribution was similar between groups at rest and during exercise. Dispersion of the ventilation distribution was lower in the Inf group at rest, associated with a much higher respiratory rate, but rose to similar levels in both groups during hypoxic exercise. Mean pulmonary arterial pressure at a given cardiac output was higher in the Inf group, whereas peak cardiac output was similar between groups. Thus creating lung strain by post-Pnx mediastinal shift primarily enhances diffusive gas exchange with only minor effects on ventilation-perfusion matching, consistent with the generation of additional alveolar-capillary surfaces but not conducting airways and blood vessels.

Selected Contribution: Lung hypoxia: antioxidant and antiapoptotic effects of liposomal α-tocopherol

The aim of this study is to examine the antioxidant and antiapoptotic activity of liposomal alpha-tocopherol (LAT) in anesthetized rats exposed to severe hypoxia. It was shown that intratracheal application of LAT normalized lung phospholipid composition and inhibited lipid peroxidation in lung tissues, which in turn decreased lung edema and damage and improved breathing pattern, oxygen diffusion, and lung gas exchange. LAT also limited the overexpression of genes encoding hypoxia inducible factor-1alpha and both studied forms of phospholipase A(2), and it increased the power of cellular antioxidant and antiapoptotic defense by overexpressing genes encoding Mn- and Cu-Zn-cofactored superoxide dismutases, Bcl-2, and heat shock 70 proteins. The overexpression of studied caspases and their activity were downregulated, which significantly (1.6-2 times) limited apoptosis in lung cells. Finally, all these positive changes decreased mortality during hypoxia from approximately 60% in untreated animals to approximately 30% in the group of rats treated with LAT. The data obtained indicate that LAT may be useful for the correction of hypoxic lung injury.

Respiration of the eggs of the giant cuttlefish Sepia apama

On the roofs of subtidal crevices, the giant cuttlefish (Sepia apama) of southern Australia lays clutches of lemon-shaped eggs which hatch after 3 to 5 mo. Diffusion of oxygen through the capsule and chorion membrane to the perivitelline fluid and embryo was modelled using the equation V˙ O2 = G O2(P O2out−P O2in), where V˙ O2 = rate of oxygen consumption, G O2 = oxygen conductance of the capsule, and P O2 values = oxygen partial pressures across the capsule. During development, V˙ O2 rose exponentially as the embryo grew, reaching 5.5 μl h−1 at hatching. Throughout development, the capsule dimensions enlarged by absorption of water into the perivitelline space, increasing G O2 by a combination of increasing surface area, and decreasing thickness of the capsule. These processes maintained P O2in high enough to allow unrestricted V˙ O2 until shortly before hatching. Diffusion limitation of respiration in hatching-stage embryos was demonstrated by (1) increased embryonic V˙ O2 when P O2out was experimentally raised, (2) greater V˙ O2 of resting individuals immediately after hatching, and (3) reduced V˙ O2 of hatchlings at experimental P O2 levels higher than P O2in before hatching. Thus, low P O2in may be the stimulus to hatch. Potential problems of diffusive gas-exchange are mitigated by the relatively low incubation temperature (12 °C), which may be a factor limiting the distribution of the species to cool, southern waters.

Respiratory system of arachnids II: morphology of the tracheal system of Leiobunum rotundum and Nemastoma lugubre (Arachnida, Opiliones)

The tracheal system of two species of harvestmen with different life styles was investigated: the long-legged, Leiobunum rotundum (Phalangioidea, Phalangiidae) and the short-legged Nemastoma lugubre (Troguloidea, Nemastomatidae). The morphology of the tracheae is very similar in both species: The branching pattern is basically asymmetric and dichotomous, and the tracheae taper between branching points. The tracheal diameters range from 160 to 0.3 μm in L. rotundum (mean body mass 25.3 mg), and from 70 to 0.5 μm in N. lugubre (mean body mass 3.8 mg). Ultrastructurally, the tracheal walls are similar to those of insects, consisting of an outer hypodermal layer and an inner cuticular layer with taenidial structures. Tracheae of all diameters have close contact with organs and muscles, indicating that diffusive gas exchange may take place through the walls of all tracheae. The finest tracheae end freely in the hemolymph or at the surface of organs and muscles. Exceptions are tracheal penetration of the central nerve mass in the prosoma in both species, and of the muscles in L. rotundum. The latter may correlate with the active perambulatory life style of L. rotundum.

Rotary Cell Culture System (RCCS): A new Method for Cultivating Hepatocytes on Microcarriers

The Rotary Cell Culture System (RCCS) is a new technology for growing anchorage dependent or suspension cells in the laboratory. The RCCS is a horizontally rotated, bubble free disposable culture vessel with diffusion gas exchange. The system provides a reproducible, complex 3D in vitro culture system with large cell masses. During cell growing the rotation speed can be adjusted to compensate for increased sedimentation rates. The unique environment of low shear forces, high mass transfer, and microgravity, provides very good cultivating conditions for many cell types, cell aggregates or tissue particles in a standard tissue culture laboratory. The system enables to culture HepG2 cells on Cytodex 3 microcarriers (mcs) to high densities. We inoculated 2 x 10(5)/ml HepG2 cells and 200 mg Cytodex 3 mcs in 50 ml Williams E medium (incl. 10% FCS) allowing them to attach to the mcs in the rotating vessel (rotation rate 14-20 rpm). HepG2 cells readily attached to the mcs while the vessel was rotating. Attachment of HepG2 to the mcs was about 50% after 24 hrs and 100 % within 48 hrs. After 72 hrs of rotary culturing small aggregates of Hep G2 on mcs were built. HepG2 cells and the aggregates rotated with the vessel and did not settle within the vessel or collide with the wall of the vessel. We conclude that this new RCCS is an excellent technology for culturing HepG2 cells on Cytodex 3 mcs. The system is easy to handle and enables to culture anchorage dependent cells to high densities in a short period.

Gas exchange potential in reptilian lungs: implications for the dinosaur–avian connection

The theory that birds evolved from a group of small terrestrial theropod dinosaurs has created much controversy. One argument proposed against this theory is that the lungs of early theropods were incapable of sustaining endothermic gas exchange requirements and could not have given rise to the lungs of birds. A reexamination of the comparative physiological and morphological literature combined with a theoretical analysis of gas exchange potential indicates that non-avian lungs would not constrain the gas exchange requirements of early endotherms. Furthermore, our analysis suggests that factors besides diffusive gas exchange were important in the evolution of the distinct morphology of the highly effective avian and mammalian lungs.

Red Blood Cells: Centerpiece in the Evolution of the Vertebrate Circulatory System

All vertebrates except cold-water ice fish transport oxygen via hemo-globin packaged in red blood cells (RBCs). Vertebrate RBCs vary in size by thirty-fold. Differences in RBC size have been known for over a century, but the func-tional significance of RBC size remains unknown. One hypothesis is that largeRBCs are a primitive character. Agnathans have larger RBCs than do mammals.However, the largest RBCs are found in urodele amphibians which is inconsistentwith the hypothesis that large RBCs are primitive. Another possibility is that smallRBCs increase blood oxygen transport capacity. Blood hemoglobin concentration([Hb]) and mean RBC hemoglobin concentration (MCHC) increase from Agnathato birds and mammals. However, the changes in [Hb] and MCHC do not parallelchanges in RBC size. In addition, RBC size does not affect blood viscosity. Thus,there is no clear link between RBC size and oxygen transport capacity. We hy-pothesize that RBC size attends changes in capillary diameter. This hypothesis isbased on the following observations. First, RBC width averages 25% larger thancapillary diameter which insures cell deformation during capillary flow. Function-ally, RBC deformation minimizes diffusion limitations to gas exchange. Second,smaller capillaries are associated with increased potential for diffusive gas ex-change. However, smaller capillaries result in higher resistances to blood flowwhich requires higher blood pressures. We propose that the large capillary di-ameters and large RBCs in urodeles reflect the evolutionary development of apulmonary vascular supply. The large capillaries reduced systemic vascular resis-tances enabling a single ventricular heart to supply blood to two vascular circuits,systemic and pulmonary, without developing high pressures on the pulmonary side.The large RBCs preserved diffusive gas exchange efficiency in the large capillaries.

Stability of foams in silicate melts

Bubble coalescence and the spontaneous disruption of high-porosity foams in silicate melts are the result of physical expulsion of interpore melt (syneresis) leading to bubble coalescence, and diffusive gas exchange between bubbles. Melt expulsion can be achieved either along films between pairs of bubbles, or along Plateau borders which represent the contacts between 3 or more bubbles. Theoretical evaluation of these mechanisms is confirmed by experimental results, enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity, surface tension, and time. Foam stability is controlled primarily by melt viscosity and time. Melt transport leading to coalescence of bubbles proceeds along inter-bubble films for smaller bubbles, and along Plateau borders for larger bubbles. Thus the average bubble size accelerates with time. In silicate melts, the diffusive gas expulsion out of a region of foam is effective only for water (and even then, only at small length scales), as the diffusion of CO 2 is negligible. The results of our analyses are applicable to studies of vesicularity of lavas, melt degassing, and eruption mechanisms.

Contrasting rates and diurnal patterns of methane emission from emergent aquatic macrophytes

Rates of methane emission associated with Florida Typha domingensis Pers. and Typha latifolia L. peaked in the early daylight hours and were two to four times higher than the relatively constant rates observed in the afternoon and night. Factors associated with methane emission peaks were increasing solar illumination which drives pressurized bulk flow ventilation in T. domingensis and T. latifolia, opening of stomata, and decreasing concentrations of methane within plant stems. Cladium jamaicense Crantz, which employs diffusive gas exchange, did not exhibit diurnal variations in methane emission rates although stomatal conductance varied diurnally. Within the Florida Everglades methane emission rates were higher in T. domingensis areas (143±19 mg CH 4 m −2 day −1) than in C. jamaicense areas (45±15 mg CH 4 m −2 day −1). These elevated rates were related to the higher above ground biomass and production in T. domingensis areas relative to C. jamaicense, which suggests that quantitative differences in plant biomass and production rather than qualitative differences between these plant species may control methane emissions. Methane emission was 2.7±1.4% of net daily ecosystem production (NEP) in a T. domingensis area and 14±5.8% and 3.4±4.2% of NEP in two C. jamaicense areas.

Suitability of polyethylene terephthalate heavy-ion track membrane for protecting the environment in clean rooms and sterile closed apparatus

In this paper the method of recirculative recovery of the air in different closed apparatus and clean rooms is proposed. The method is based on diffusive gas exchange through polyethylene terephthalate heavy-ion track membrane. Tests with the membrane process were carried out to provide sterility inside a fermenter and to create normal conditions required for the vital activity of the staff in a closed clean room.

Surfactant Improves Gas Mixing and Alveolar Ventilation in Preterm Lambs

Prophylactic treatment with ovine surfactant was evaluated in preterm lambs at risk for development of hyaline membrane disease. Eight mechanically ventilated newborn lambs were treated before delivery and 10 served as controls (gestational age 129-131 d). Lung mechanics, functional residual capacity, alveolar ventilation, efficiency of ventilation, and distribution of ventilation were tested using pressure, flow, and nitrogen elimination (nitrogen washout during 100% oxygen breathing) measurements in the endotracheal tube. The surfactant-treated animals showed significantly improved gas mixing efficiency in the lung with improved alveolar ventilation. Single exponential washout pattern dominated in both groups. Adequate functional residual capacity was established earlier after birth in the treated lambs than in the control animals. Lung mechanics in the treated group showed significant improvement in dynamic lung compliance. Surfactant treatment also improved gas exchange and reduced respirator pressure requirement. We speculate that the main functional effect of surfactant treatment in preterm lambs at risk to develop hyaline membrane disease is to maintain the patency of the peripheral airways in the lung, which improves diffusive gas mixing, alveolar ventilation, and gas exchange. The techniques used in this study should also be useful to evaluate lung function in preterm human infants after specific adaptation of the equipment size.

Water Vapor and Oxygen Exchange of Praying Mantis (Tenodera aridifolia sinensis) Egg Cases

Mantid egg cases must be capable of preventing desiccation of the developing eggs for 5-6 mo while allowing adequate respiratory gas exchange for timely hatching. This investigation examined water vapor, oxygen, and thermal exchange of Chinese mantis (Tenodera aridifolia sinensis) egg cases. Water vapor conductance was 0.277 mg · d⁻¹ · mmHg⁻¹. Results of experiments with altered vapor pressure gradients, moving air, and hypobaria were consistent with water vapor loss by simple gaseous diffusion. Experiments at 100% relative humidity showed a linear increase in the internal egg case temperature with development, peaking more than 0.3° C above ambient temperature before hatching. Egg case O₂ consumption increased with increasing hatchling mass. Oxygen consumption at 25° C increased linearly with incubation time and for a case producing 1 g of hatchlings peaked at 537.5 μL · h⁻¹. The Q10's for O₂ consumption between 15° and 25° C were typical of insects. Calculations using diffusive gas exchange equations indicate the high resistance to water vapor flux does not result in embryonic hypoxia.

Air-Conducting Porosity in Slash Pine Roots from Saturated Soils

Abstract On many sites, slash pine taproot systems extend into zones of perennially saturated, anoxic soil. Tap and sinker roots, submerged for weeks or months by periodic rising of the water table, appear to be undamaged by anoxia. On such sites, green wood of large-diameter sinkers and a taproot had unusually high air contents (48% to 69% of green volume), a consequence of low wood substance and low moisture volumes. Green root sections conducted air longitudinally when small pressures (0.06 to 0.98 kPa) were applied at one end. Mass air flow through root wood increased linearly with the pressure applied and was approximately proportional to root cross-sectional area. Since sinker roots taper, root length influenced mass flow by affecting both pressure gradient and the conducting cross-section. Using Darcy's Law, mass air flow through each root was characterized by K, an air-permeability factor, which incorporates the unique anatomic or morphologic features of each root section. The average K for the population of green sinker and taproot sections was 68.6 cm² kPa-1 min-1, which is the same magnitude of Darcy K estimates reported for mass air flow through dried pine stem wood. The findings suggest that vertical roots simultaneously conduct water up from, and air down to, submerged distal ends of the root system. The large gas-filled volume in wood likely serves as a pool for diffusive gas exchange between the atmosphere and 02-depleted tissues. For. Sci. 36(1):18-33.

Methane efflux from the pelagic regions of four lakes

Methane emission to the atmosphere was studied in the deepest, central (“pelagic”) regions of one freshwater and three meromictic, alkaline saline lakes. The range of methane emissions was 0.0004 to 2.916 mmol m−2 h−1 (n = 41). Outward flux was dominated by bubble ebullition only in the freshwater lake. Diffusive gas exchange was the sole mechanism of transfer in the meromictic lakes, and flux from these lakes was equivalent to or lower than that from the freshwater lake during its periods of ebullition. A comparison of measured flux with flux calculated using a model of gas exchange in Mono Lake suggested that floating chambers provide reasonable estimates of the magnitude of methane emissions from diffusion‐dominated systems.

Role of diffusion shunt in transfer of inert gases and O2 in muscle.

Diffusion shunt is diffusive gas exchange between arterial and venous vessels. Evidence for diffusion shunt had been obtained in washout studies in the gastrocnemius muscle of the dog. According to models, diffusion shunt is expected to be enhanced at low blood flow, and for gases of high diffusivity. Shunting of O2 should be reduced in comparison to inert gases because of chemical binding in blood.

Convective and Diffusive Gas Exchange in Nest Cavities of the Northern Flicker (Colaptes auratus)

We continuously measured O₂ and CO₂ levels within four nest cavities of the northern flicker (Colaptes auratus) after they had been flushed with a low-oxygen, high-CO₂ gas mixture. It took over 2 h for O₂ and CO₂ levels in cavities to return to free atmospheric values under isothermal conditions, even when the entrance to the cavity was open. Heating the interior of cavities with open entrances to 5, 10, or 15 C above outside air temperature reduced the time required for cavity gases to return to atmospheric levels to 5, 3, and 2 min, respectively; comparable values for sealed cavities are 65, 50, and 47 min. In open cavities, rates of O₂ influx and CO₂ efflux were not significantly increased by thermal differences greater than 5 C. Since air temperatures within occupied flicker cavities usually exceed those outside by 5 C or more, thermally induced convective exchange expectably would augment diffusive gas transfers between the cavities and free atmosphere and explain the moderate gaseous conditions within these cavities.

Sources of carbon dioxide in penguin air sacs.

CO2 tensions in the caudal air sacs of birds cannot be quantitatively predicted by current models of avian respiration, mainly because the contribution of neopulmonic parabronchial gas exchange has not been determined. To overcome this problem we studied penguins that have purely paleopulmonic lungs. Three penguins were anesthetized, intubated, and ventilated at a constant respiratory rate and different tidal volumes (VT). PO2 and PCO2 were measured in arterial blood and end-expired, mixed-expired, interclavicular air sac, and caudal thoracic air sac gas. Interclavicular air sac and end-expired gas had similar compositions. Caudal thoracic air sac gas was intermediate in composition to end-expired and inspired gas, and its PCO2 was 1.5-3.5 times greater than the value predicted from reinhaled dead space. This difference between measured and predicted caudal thoracic air sac PCO2 increased with VT but showed no relationship to changes in dead space-to-VT ratio. The difference is not explained by stratification or diffusive gas exchange across air sac walls. The results can be explained by postulating that inspired gas passes over exchange surfaces on its path to caudal air sacs. This is unexpected in the purely paleopulmonic lungs of penguins and suggests that airflow may not be caudocranial in all paleopulmonic parabronchi.

Respiratory Gas Exchange and Growth of Bonin Petrel Embryos

The constraints placed upon diffusive gas exchange by the eggshell, and parameters of embryonic respiration were examined in naturally incubated eggs of the Bonin petrel on Sand Island, Midway. The incubation period of the Bonin petrel egg was 49 days, or 184% of the predicted value based on egg mass; this is relatively longer than in larger members of the order. A low eggshell gas conductance was matched by a low egg O₂ uptake (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}${\mathrm{\dot{M}_{O_{2}}}}$\end{document}), resulting in air cell gas tensions (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepack...