Oxygen Diffusion Gradient Research Articles

Spatial O2 Profile in Coix lacryma-jobi and Sorghum bicolor along the Gas Diffusion Pathway under Waterlogging Conditions.

While internal aeration in plants is critical for adaptation to waterlogging, there is a gap in understanding the differences in oxygen diffusion gradients from shoots to roots between hypoxia-tolerant and -sensitive species. This study aims to elucidate the differences in tissue oxygen concentration at various locations on the shoot and root between a hypoxia-tolerant species and a -sensitive species using a microneedle sensor that allows for spatial oxygen profiling. Job's tears, a hypoxia-tolerant species, and sorghum, a hypoxia-susceptible species, were tested. Plants aged 10 days were acclimated to a hypoxic agar solution for 12 days. Oxygen was profiled near the root tip, root base, root shoot junction, stem, and leaf. An anatomical analysis was also performed on the roots used for the O2 profile. The oxygen partial pressure (pO2) values at the root base and tip of sorghum were significantly lower than that of the root of Job's tears. At the base of the root of Job's tears, pO2 rapidly decreased from the root cortex to the surface, indicating a function to inhibit oxygen leakage. No significant differences in pO2 between the species were identified in the shoot part. The root cortex to stele ratio was significantly higher from the root tip to the base in Job's tears compared to sorghum. The pO2 gradient began to differ greatly at the root shoot junction and root base longitudinally, and between the cortex and stele radially, between Job's tears and sorghum. Differences in the root oxygen retention capacity and the cortex to stele ratio are considered to be related to differences in pO2.

Human cardiac organoids for the modelling of myocardial infarction and drug cardiotoxicity.

Environmental factors are the largest contributors to cardiovascular disease. Here we show that cardiac organoids that incorporate an oxygen-diffusion gradient and that are stimulated with the neurotransmitter noradrenaline model the structure of the human heart after myocardial infarction (by mimicking the infarcted, border and remote zones), and recapitulate hallmarks of myocardial infarction (in particular, pathological metabolic shifts, fibrosis and calcium handling) at the transcriptomic, structural and functional levels. We also show that the organoids can model hypoxia-enhanced doxorubicin cardiotoxicity. Human organoids that model diseases with non-genetic pathological factors could help with drug screening and development.

29 Trans Sodium Crocetinate: A Novel Kosmotropic Molecule that Enhances Oxygen Diffusion in the Treatment of Hypoxia-Driven Medical Emergencies

Tissue-hypoxia directly contributes to underlying morbidity and mortality of the top 5 leading causes of death in the US which include heart disease, cancer, chronic lower respiratory diseases, accidents (unintentional injuries) and cerebrovascular accidents. These conditions frequently present as medical emergencies requiring urgent intervention which occurs either at home, site of an accident, in an ambulance or in the emergency department. Currently, aside from oxygen therapy, there are no effective therapies approved available to reverse hypoxia and its potentially catastrophic consequences. Trans sodium crocetinate (TSC) is a kosmotrope that was developed to treat oxygen deficits in emergency cases. TSC is based on a novel mechanism of action, that of increasing the diffusion of oxygen from the erythrocytes through the plasma to the vascular wall, thereby increasing the gradient for oxygen diffusion to hypoxic tissues. The increase in the diffusion rate is caused by the influence of the intermolecular forces of the TSC molecule on the water molecules: it increases the numbers of hydrogen bonds among them. The initial investigation of TSC was part of the Battlefield Casualty Program of the US Office of Naval Research and was further developed by Diffusion Pharmaceuticals Inc. To assess the effect of treating hypoxic emergency, TSC was evaluated preclinically in animal models of three common medical emergencies; namely hemorrhagic shock, myocardial infarction and stroke. The results are summarized below: Hemorrhagic shock resulting from severe blood loss. After inducing 60% loss in estimated blood volumes in rats, studies showed that treatment with TSC; a) increased whole body oxygen consumption, b) increased blood pressure, c) preserved organ function as reflected by liver enzymes and d) resulted in 100% survival at 24 hours compared to 15% in saline treated controls. Myocardial infarction. Studies of coronary artery ligation in a swine model showed that treatment with TSC conferred a 90% survival at 4 hours compared to 33% in controls. Stroke. Studies in both rats (3 vessel occlusion: two carotids and left middle cerebral arteries) and rabbits (injection of blood clots) showed improved neuronal preservation in animals treated with TSC compared to controls in ischemic stroke. Further, studies in rats injected with collagenase to induce hemorrhagic stroke showed an increase in live neurons and a reduction in cerebral edema in TSC treated animals compared to controls. To date, about 150 patients have received TSC in clinical trials without any serious side effects attributed to TSC. TSC is currently being developed to treat hypoxia in patients with cancer. TSC appears to be a safe and potentially beneficial treatment for hypoxia related conditions. Furthermore, compelling preclinical data call for urgent clinical investigation of TSC in hypoxia related medical emergencies.

3D Printed Vascular Networks Enhance Viability in High-Volume Perfusion Bioreactor.

There is a significant clinical need for engineered bone graft substitutes that can quickly, effectively, and safely repair large segmental bone defects. One emerging field of interest involves the growth of engineered bone tissue in vitro within bioreactors, the most promising of which are perfusion bioreactors. Using bioreactor systems, tissue engineered bone constructs can be fabricated in vitro. However, these engineered constructs lack inherent vasculature and once implanted, quickly develop a necrotic core, where no nutrient exchange occurs. Here, we utilized COMSOL modeling to predict oxygen diffusion gradients throughout aggregated alginate constructs, which allowed for the computer-aided design of printable vascular networks, compatible with any large tissue engineered construct cultured in a perfusion bioreactor. We investigated the effect of 3D printed macroscale vascular networks with various porosities on the viability of human mesenchymal stem cells in vitro, using both gas-permeable, and non-gas permeable bioreactor growth chamber walls. Through the use of 3D printed vascular structures in conjunction with a tubular perfusion system bioreactor, cell viability was found to increase by as much as 50% in the core of these constructs, with in silico modeling predicting construct viability at steady state.

Pathophysiologic Mechanisms of Cerebral Ischemia and Diffusion Hypoxia in Traumatic Brain Injury.

Combined oxygen 15-labeled positron emission tomography (15O PET) and brain tissue oximetry have demonstrated increased oxygen diffusion gradients in hypoxic regions after traumatic brain injury (TBI). These data are consistent with microvascular ischemia and are supported by pathologic studies showing widespread microvascular collapse, perivascular edema, and microthrombosis associated with selective neuronal loss. Fluorine 18-labeled fluoromisonidazole ([18F]FMISO), a PET tracer that undergoes irreversible selective bioreduction within hypoxic cells, could confirm these findings. To combine [18F]FMISO and 15O PET to demonstrate the relative burden, distribution, and physiologic signatures of conventional macrovascular and microvascular ischemia in early TBI. This case-control study included 10 patients who underwent [18F]FMISO and 15O PET within 1 to 8 days of severe or moderate TBI. Two cohorts of 10 healthy volunteers underwent [18F]FMISO or 15O PET. The study was performed at the Wolfson Brain Imaging Centre of Addenbrooke's Hospital. Cerebral blood flow, cerebral blood volume, cerebral oxygen metabolism (CMRO2), oxygen extraction fraction, and brain tissue oximetry were measured in patients during [18F]FMISO and 15O PET imaging. Similar data were obtained from control cohorts. Data were collected from November 23, 2007, to May 22, 2012, and analyzed from December 3, 2012, to January 6, 2016. Estimated ischemic brain volume (IBV) and hypoxic brain volume (HBV) and a comparison of their spatial distribution and physiologic signatures. The 10 patients with TBI (9 men and 1 woman) had a median age of 59 (range, 30-68) years; the 2 control cohorts (8 men and 2 women each) had median ages of 53 (range, 41-76) and 45 (range, 29-59) years. Compared with controls, patients with TBI had a higher median IBV (56 [range, 9-281] vs 1 [range, 0-11] mL; P < .001) and a higher median HBV (29 [range, 0-106] vs 9 [range, 1-24] mL; P = .02). Although both pathophysiologic tissue classes were present within injured and normal appearing brains, their spatial distributions were poorly matched. When compared with tissue within the IBV compartment, the HBV compartment showed similar median cerebral blood flow (17 [range, 11-40] vs 14 [range, 6-22] mL/100 mL/min), cerebral blood volume (2.4 [range, 1.6- 4.2] vs 3.9 [range, 3.4-4.8] mL/100 mL), and CMRO2 (44 [range, 27-67] vs 71 [range, 34-88] μmol/100 mL/min) but a lower oxygen extraction fraction (38% [range, 29%-50%] vs 89% [range, 75%-100%]; P < .001), and more frequently showed CMRO2 values consistent with irreversible injury. Comparison with brain tissue oximetry monitoring suggested that the threshold for increased [18F]FMISO trapping is probably 15 mm Hg or lower. Tissue hypoxia after TBI is not confined to regions with structural abnormality and can occur in the absence of conventional macrovascular ischemia. This physiologic signature is consistent with microvascular ischemia and is a target for novel neuroprotective strategies.

AI-02 * HYPOXIA AS A MEASURE OF FUNCTIONAL STATUS OF GLIOBLASTOMA VASCULATURE

INTRODUCTION: Glioblastoma (GBMs) exhibit distinct histopathological features including microvascular hyperplasia and heterogenous hypoxia within the tumor microenvironment. Newly formed vessels are often leaky/dysfunctional with intravascular thrombosis and potentially contribute to the hypoxic/necrotic foci seen throughout GBMs. By analyzing orthotopic xenograft models of GBM, we have established the correlation between tumor blood vessel and oxygen diffusion gradient. Additionally, we have established the effect of anti-angiogenic therapies (AATx) such as VEGF-Trap on this correlation. METHOD: Patient derived GSCs and established GBM cell line (U87) with or without VEGF-Trap were injected orthotopically in forebrains of NOD/SCID mice. Following 3-4 weeks of cell implantation, the mice were sacrificed and brains were harvested and imbedded in paraffin blocks. The sections were then stained for CD31 (endothelial marker) and CAIX (hypoxia marker). Images were scanned and quantified; using ImageJ (http://imagej.nih.gov/ij/), measurements include distance from tumor blood vessels to nearest hypoxic foci, total percent hypoxia, and cell proliferation. RESULTS: In literature it has been shown that any functional micro-vessel in normal tissue allows oxygen diffusion up to 100 µm radius. Using this as a guideline, we have defined the functional state of microvessels in our orthoptic tumor. We found that approximately 13% of the tumor blood vessels were dysfunctional, as their distance from immediate hypoxic cells was less than 20 µm. Upon treatment with AATx, we observed significant decrease in numbers of functional tumor blood vessels and cell prolliferation with concomitant increase in hypoxic areas within the tumor. CONCLUSIONS: AATx results in a significant decrease in the number of functional blood vessels - as measured by their proximity to the nearest hypoxic cells - and cell proliferation. We have provided a quantitative measure - distinct histopathological features including hypoxic and necrotic foci, microvascular hyperplasia and increased cell proliferation - for what was previously describe in qualitive terms in literature.

Quantifying the role of oxygen pressure in tissue function

it has been suggested that oxygen had reached significant levels in the earth's oceans as early as 2.5 billion years ago and has rapidly increased to near current levels about 50 million years later ([6][1]). The appearance of oxygen dramatically changed the chemical composition of the oceans and

Cerebral blood flow and metabolism during exercise: implications for fatigue

During exercise: the Kety-Schmidt-determined cerebral blood flow (CBF) does not change because the jugular vein is collapsed in the upright position. In contrast, when CBF is evaluated by (133)Xe clearance, by flow in the internal carotid artery, or by flow velocity in basal cerebral arteries, a approximately 25% increase is detected with a parallel increase in metabolism. During activation, an increase in cerebral O(2) supply is required because there is no capillary recruitment within the brain and increased metabolism becomes dependent on an enhanced gradient for oxygen diffusion. During maximal whole body exercise, however, cerebral oxygenation decreases because of eventual arterial desaturation and marked hyperventilation-related hypocapnia of consequence for CBF. Reduced cerebral oxygenation affects recruitment of motor units, and supplemental O(2) enhances cerebral oxygenation and work capacity without effects on muscle oxygenation. Also, the work of breathing and the increasing temperature of the brain during exercise are of importance for the development of so-called central fatigue. During prolonged exercise, the perceived exertion is related to accumulation of ammonia in the brain, and data support the theory that glycogen depletion in astrocytes limits the ability of the brain to accelerate its metabolism during activation. The release of interleukin-6 from the brain when exercise is prolonged may represent a signaling pathway in matching the metabolic response of the brain. Preliminary data suggest a coupling between the circulatory and metabolic perturbations in the brain during strenuous exercise and the ability of the brain to access slow-twitch muscle fiber populations.

Poor Circulation, Early Brain Injury, and the Potential Role of Red Cell Transfusion in Premature Newborns

To the Editor .— It is the purpose of this letter to (1) define poor circulation in very premature newborns, (2) discuss the concept of stagnant hypoxia and its relation to early brain injury, and (3) discuss the potential role of adult packed red cell transfusion as an acute intervention for poor circulation. There is no simple definition of poor circulation in newborns. It may be pragmatically described by the presence of 1 of the following: low cardiac output (CO) on echocardiography,1 profound hypotension with capillary refill time of ≥3 seconds,2 or hypoxemia resulting in elevated serum lactate.3 There are a number of different forms of hypoxia, namely, stagnant (inadequate flow), anemic (inadequate hemoglobin concentration), hypoxic (inadequate inspired oxygen), and histotoxic hypoxia. Barcroft first described stagnant hypoxia in 19204 with the sentence “[the] blood is normal but is supplied to the tissues in insufficient quantities.” The principal determinants of systemic oxygen transport are CO, hemoglobin concentration, and hemoglobin saturation.5 Final tissue oxygen extraction depends on the oxygen diffusion gradient, the diffusion distance between the capillary and the cell, and cellular uptake mechanisms. The degree of oxygen extraction varies between tissues but never reaches 100%. When oxygen delivery decreases to …

A Ruler for Determining the Position of Proteins in Membranes

Both the oxygen diffusion rate and the oxygen solubility vary with depth into the interior of biological membranes. The product of these two gradients generates a single gradient, a permeability gradient, which is a smooth continuous function of the distance from the center of the membrane. Using electron paramagnetic resonance and the spin-probe method, the relaxation gradient of oxygen, which is directly proportional to the permeability gradient, is the quantity that can be directly measured in membranes under physiological conditions. The gradient obtained provides a calibrated ruler for determining the membrane depth of residues either from loop regions of membrane-binding proteins or from the membrane-exposed residues of transmembrane proteins. We have determined the relaxation gradient of oxygen in zwitterionic and anionic phospholipid membranes by attaching a single nitroxide probe to a transmembrane alpha-helical polypeptide at specific residues. The peptide ruler was used to determine the depth of penetration of the calcium-binding loops of the C2 domain of cytosolic phospholipase A(2). The positions of selected residues of this membrane-binding protein that penetrate into the membrane, determined using this ruler, compared favorably with previous determinations using more complex methods. The relaxation gradient constrains the possible values of the membrane-dependent oxygen concentration and the oxygen diffusion gradients. The average oxygen diffusion coefficient is estimated to be at least 2-fold smaller in the membrane than that in water.

Aerotaxis in Desulfovibrio.

Aerotaxis of two sulphate-reducing bacteria, the freshwater strain Desulfovibrio desulfuricans CSN (DSM 9104) and the marine strain Desulfovibrio oxyclinae N13 (DSM 11498), was studied using capillary microslides, microscopy and oxygen microsensors. The bacteria formed ring-shaped bands in oxygen diffusion gradients surrounding O2 bubbles, which were placed into anoxic sulphate-free cell suspensions in capillary microslides. The radial expansion of the oxic volume by diffusion was stopped by aerobic respiration. Bands were formed by cells avoiding high O2 levels near the O2 bubble, as well as by cells entering from the surrounding anoxic zone. At the inner edge of the bands, O2 levels of up to 20% air saturation (50 microM O2) were found, while the outer edge always coincided with the oxic-anoxic interface. Ring diameters and O2 concentrations at the inner edge of the band depended on the cell density and the strain used in the suspension. Band formation did not occur in the absence of an electron donor (5mM lactate) or when N2 gas bubbles were used. Both strains were highly motile with velocities of approximately equals 32 microm s(-1) during forward runs, and 7 microm s(-1) during backward runs respectively. Within the bands, cells moved in circles of about 20 microm diameter, while cells outside the band exhibited straighter or only slightly bent traces. It is concluded that the capacity of respiration at high rates and the positive and negative aerotactical responses of Desulfovibrio provide an efficient strategy for removing O2 from the habitat in situations where sufficient electron donors and high cell densities are present.

Oxygen dependence of flux control of cytochrome c oxidase – implications for mitochondrial diseases

The oxygen dependence of cytochrome c oxidase control on succinate oxidation was investigated in saponin-permeabilized muscle fibers and isolated mitochondria from mouse quadriceps muscle applying metabolic control analysis. For this cyanide titrations of the oxygen consumption in the presence of succinate+rotenone were performed at different oxygen concentrations in the medium. While with isolated mitochondria high flux control coefficients were detected only at oxygen concentrations close to the K M value of cytochrome c oxidase, with saponin-permeabilized fibers a significant increase of cytochrome c oxidase flux control was already observed below 130 μM oxygen. The result is in line with the high oxygen sensitivity of maximal respiration of saponin-permeabilized muscle fibers (P 50=33 μM) caused most probably by oxygen diffusion gradients through the fiber lattice. The oxygen dependence of cytochrome c oxidase flux control in muscle fibers can explain the pathological phenotype of mild cytochrome c oxidase deficiencies in mitochondrial myopathies.

Human adaptation to high altitude: regional and life-cycle perspectives.

Studies of the ways in which persons respond to the adaptive challenges of life at high altitude have occupied an important place in anthropology. There are three major regions of the world where high-altitude studies have recently been performed: the Himalayas of Asia, the Andes of South America, and the Rocky Mountains of North America. Of these, the Himalayan region is larger, more geographically remote, and likely to have been occupied by humans for a longer period of time and to have been subject to less admixture or constriction of its gene pool. Recent studies of the physiological responses to hypoxia across the life cycle in these groups reveal several differences in adaptive success. Compared with acclimatized newcomers, lifelong residents of the Andes and/or Himalayas have less intrauterine growth retardation, better neonatal oxygenation, and more complete neonatal cardiopulmonary transition, enlarged lung volumes, decreased alveolar-arterial oxygen diffusion gradients, and higher maximal exercise capacity. In addition, Tibetans demonstrate a more sustained increase in cerebral blood flow during exercise, lower hemoglobin concentration, and less susceptibility to chronic mountain sickness (CMS) than acclimatized newcomers. Compared to Andean or Rocky Mountain high-altitude residents, Tibetans demonstrate less intrauterine growth retardation, greater reliance on redistribution of blood flow than elevated arterial oxygen content to increase uteroplacental oxygen delivery during pregnancy, higher levels of resting ventilation and hypoxic ventilatory responsiveness, less hypoxic pulmonary vasoconstriction, lower hemoglobin concentration, and less susceptibility to CMS. Several of the distinctions demonstrated by Tibetans parallel the differences between natives and newcomers, suggesting that the degree of protection or adaptive benefit relative to newcomers is enhanced for the Tibetans. We thus conclude that Tibetans have several physiological distinctions that confer adaptive benefit consistent with their probable greater generational length of high-altitude residence. Future progress is anticipated in achieving a more integrated view of high-altitude adaptation, incorporating a sophisticated understanding of the ways in which levels of biological organization are articulated and a recognition of the specific genetic variants contributing to differences among high-altitude groups.

D-rice seedling development in periodically stirred water in sealed environments

Summary Large numbers of germinating seedlings of two rice cultivars exhibited d- type development consisting solely of completely white coleoptile growth after 15 days in the light in both static and periodically stirred water environments in completely sealed jars. Thus, whether germinated in static or agitated water in the sealed environments, coleoptile greening and subsequent normal seedling development were inhibited by hypoxic stress caused by the large numbers of germinating rice seedlings competing for the limited environmental oxygen supply. Consequently, the evidence presented points away from the formation of unfavourable oxygen diffusion gradients in static water environments in the sealed jars as having been responsible for d type seedling development observed in previous investigations. Continuous aeration of the 15-day-old static and periodically stirred aquatic environments, respectively, resulted in complete reversal of all d seedlings into normal green plants.

Evidence that changes in blood oxygen affinity modulate oxygen delivery: implications for control of tissue PO2 gradients.

Oxygen flux to respiring tissue depends upon the oxygen diffusion gradient between blood in the microvascular network and sites of oxygen utilization. Current knowledge of how this gradient is regulated is quite incomplete. The magnitude of the gradient is determined by a number of morphological and functional parameters, one of which is blood oxygen affinity. Experiments examining control of oxygen delivery have traditionally made use of induced changes in parameters determining systemic oxygen transport (FIO2, [Hb], and/or flow), with secondary effects on the pattern of PO2 values along the capillary. Changes in blood oxygen affinity, by contrast, allow one to observe effects of a change in PO2 downstream in the capillary while PO2 upstream and oxygen transport (CaO2 x flow) are not primarily affected.

Effects of temperature and dissolved oxygen on heart rate, ventilation rate and oxygen consumption of spangled perch,Leiopotherapon unicolor (G�nther 1859), (Percoidei, Teraponidae)

Heart, ventilation and oxygen consumption rates ofLeiopotherapon unicolor were studied at temperatures ranging from 5 to 35°C, and during progressive hypoxia from 100% to 5% oxygen saturation. Biopotentials recorded from the water surrounding the fish corresponded to ventilation movements, and are thought to originate from the ventilatory musculature. Cardio-respiratory responses to temperature and dissolved oxygen follow the typical teleost pattern, with bradycardia, increased ventilation rate and reduced oxygen consumption occurring during hypoxia. However, ventilation rate did not increase at 15°C and below. Ventilation rate showed a slower response to increasing temperature (normoxic Q10=1.39) than heart rate and oxygen consumption (normoxic Q10=2.85 and 2.38).L. unicolor is unable to survive prolonged hypoxia by utilising anaerobic metabolism, but has a large gill surface area which presumably facilitates oxygen uptake in hypoxic environments. Periodic ventilation during normoxia in restingL. unicolor may improve ventilation efficiency by increasing the oxygen diffusion gradient across the gills.

Fat Emulsion Tolerance in Very Low Birth Weight Neonates: Effect on Diffusion of Oxygen in the Lungs and on Blood pH

Forty-one very low birth weight neonates (820 to 1,510 g and 27 to 34 weeks of gestation) requiring total parenteral nutrition were randomly assigned to one of three regimens of administration of fat emulsion for a period of eight days. Groups I and II received the emulsion at a constant rate for, respectively, 24 and 16 hours, beginning with a daily dosage of 1 g/kg and increasing daily by 1 g/kg to a maximum of 4 g/kg. Group III received the emulsion at a constant rate or 4 g/kg for 24 hours. Blood pH and alveolar-arteriolar gradient of oxygen diffusion in the lungs were measured at regular intervals. The various regimens and rates of fat infusion appeared to have no deleterious effect on blood pH and alveolar-arteriolar oxygen diffusion gradient. Infusion rates as used in the study for appropriate for gestational age very low birth weight neonates appear to be safe, although caution is always warranted when dealing with tiny neonates whose pulmonary reserve is minimal. In view of data from other studies, it is suggested to infuse fat at a constant rate for 24 hours to avoid overloading the clearance mechanisms of fat particles from plasma.

In situ calibration of an oxygen sensor in intervertebral discs.

Intradiscal hypoxia has been suspected of playing a role in the pathogenesis of degenerative back diseases. Investigating this hypothesis requires quantitative methods for measuring PO2 in the intervertebral disc. Tissue oxygen tensions are usually measured with a membrane-covered oxygen-consuming sensor. Calibrating this sensor is complicated by the existence of an oxygen-diffusion gradient in front of the membrane. This article describes a method based on mass spectrometry to measure the oxygen tension in the intervertebral disc and an 'in situ' calibration technique, which is able to compensate for errors caused by the oxygen-diffusion gradient. The principle of the calibration technique is to measure the signal of an inert reference gas, whose partial pressure in the intervertebral disc is known, and to utilize the measured signal to estimate the magnitude of the oxygen-diffusion gradient.

The evolution of air-breathing in crustaceans: A functional analysis of branchial, cutaneous and pulmonary gas exchange

1. 1. The evolution of aerial gas exchange in land crabs is correlated with a transition from diffusion limited gills (L diff, 0.88–0.92), via a bimodal, diffusion limited “skin” (vascularized branchial chamber epithelium)/gill system (L diff, 0.53–0.63), to the perfusion limited, invaginated lung of the mountain crab Pseudothelphusa (L diff, 0.008–0.145) (L diff, is used as an index of diffusion limitation); a glossary of terms is presented at the end of the Abstract. 2. 2. The reduction in diffusion limitation with the evolution of the lung in land crabs reduces the mean oxygen diffusion gradient (ΔPgO2) required to generate gas transfer at the exchange surface (gill and “skin”, 86–108 mmHg; lung, 59–69 mmHg). 3. 3. The reduction in (ΔPgO2) and concomitant elevation in (PaO2) (gill, 14–19 mmHg; “skin”/gill, 50–100 mmHg; lung, 120–140 mmHg) and PvO2) (gill, 7–8 mmHg; “skin”, 7–25 mmHg, lung, 20–28 mmHg) facilitates oxygen diffusion to the tissues (i.e. potential for large ΔPvO2—PcellO2). 4. 4. The elevation of mean blood oxygen tension at the gas exchange surface (PaO2 + PvO2/2) with the evolution of the land crab lung is matched by a decrease in the in vivo blood oxygen affinity (i.e. elevated blood P50: gill, 10 mmHg; “skin”/gill, 13–21 mmHg; lung, 26–28 mmHg) which ensures 100% O2 saturation at the gas exchange organ and 40–60% O2 delivery to the tissues. 5. 5. The low ventilation requirement of air-ventilated “cutaneous” and invaginated lungs, compared to water-ventilated gills, leads to an elevation in pulmonary air PMCO2) (i.e. PACO2 3–7 mmHg at PAO2 140–154 mmHg) and a concomitant increase in blood P,CO2 levels in land crabs (P,CO2: gill, 3.6–4.1 (< 5) mmHg; “skin”/gill, 7.5–15 mmHg; lung, 8–12.5 mmHg) (c.f. aquatic gill breather, PaCO2, 2–3 mmHg). 6. 6. A potential respiratory acidosis associated with elevated air and blood P,CO2 levels in the intermittently ventilated lungs of land crabs is compensated by an elevation in blood bicarbonate levels (CaCO2: gill, 8–12 mM/1; “skin”/gill, 8–19 mM/1; lung 14.5–25 mM/1) (c.f. aquatic gill breather, CaCO2 = 4–8 mM/1). At the pH of crab blood the directly measured variable C,CO2 is almost exclusively in the form of the bicarbonate ion. 7. 7. The evolution of air-breathing in land crabs leaves them poorly equipped for secondary water breathing via reduced gills as (a) gas transfer is impaired at the exchange surface (i.e. low PaO2, 17–27mmHg/high PaCO2, 5–6.5 (> 5) mmHg; L diff, 0.91–0.95, indicating predominant diffusion limitation) compared to primary water breathing crabs (PaO2, 50–100mmHg/PaCO2 2–3 mmHg; L diff, 0.45–0.48) and, (b) blood oxygen loading at the gills is impaired (48–52% of “air-breathing” C,O2) at the low post branchial oxygen tensions (17–27 mmHg) generated during submergence as a consequence of the evolution of a high “air-breathing” blood P50. 8. 8. The evolution of air-breathing in crustaceans described above closely parallels that of the vertebrates, but all land crabs retain gills and the potential for bimodal respiration if water is available. By the vertebrate analogy land crabs appear to have reached the lungfish stage of evolution into the terrestrial environment. 9. 9. Land crabs differ fundamentally from vertebrates in maintaining blood PaCO2 < 15 mmHg (c.f. mammals, birds, PaCO2, 30–40 mmHg) either (a) by CO2 excretion via the branchial aquatic route when water is available or, (b) in the instance of the “lung crab” Pseudothelphusa, by elevating blood PaO2 to exceptionally high levels (120–140 mmHg) thus “blowing off” CO2 (PaCO2 < 12.5 mmHg) across the perfusion limited lung. 10. 10. The maintenance of low P,CO2 levels in crustaceans may be associated with a limited capacity for extracellular acid-base regulation and the necessity to maintain the functional integrity of haemocyanin in the face of a potential Root effect at high P,CO2 levels. This appears to be a principal factor in limiting the terrestrial diversity of the Crustacea. 11. 11. Extending the lungfish analogy, the “lung crab” Pseudothelphusa also survives prolonged droughts (desiccation) during the dry season by virtue of having evolved a perfusion limited lung with a low ventilation requirement which enables it to limit convective and evaporative respiratory water loss. The perfusion limited lungs of crustaceans and vertebrates appear to have evolved primarily as an adaptation to conserve water at depressed levels of activity (aestivation) during the tropical dry season. The vertebrates have subsequently exploited the potential endowed by a large pulmonary diffusing capacity to elevate V,O2MAX) and diversify into a wide array of terrestrial habitats.

New transcutaneous pO2 probe based on mass spectrometry with low stirring effect.

Measurement of oxygen tensions by transcutaneous probes is complicated by the so-called stirring effect due to the existence of an oxygen diffusion gradient in the skin adjacent to the probe. The stirring effect is usually minimised by heating the transcutaneous probe to about 44°C. The elevated temperature does, however, increase the risk of skin burns and causes an unpredictable change inpO2 due to the right shift of the haemoglobin oxygen binding curve. We describe a new probe which has a low stirring effect at all temperatures in the interval between 38 and 44°C. The stirring effect is evaluated by measurement of an inert reference gas of known partial pressure.