Increase In Oxygen Tension Research Articles

Divergent effects of extracellular oxygen on the growth, morphology, and function of human skin microvascular endothelial cells.

Partial pressure of extracellular oxygen influences a number of major cellular functions. The purpose of this study was to determine if the proliferation, morphology, and synthesis of proteins important in the function of skin microvascular endothelial cells were significantly altered by an extracellular oxygen tension used to culture endothelial cells. Microvascular endothelial cells were isolated from the dermis of neonatal foreskins and were studied at a venous capillary oxygen level (5% O(2), 38 mm Hg) and at an atmospheric oxygen level (20.8% O(2,) 158 mm Hg). At all time points studied and at all passage numbers, a significant inhibition of proliferation was observed at 20.8% O(2) compared to identical cultures grown and subcultured at 5% O(2). Two morphologically distinct endothelial cell populations were observed at 5% O(2). When mediators of angiogenesis and inflammation-such as basic fibroblast growth factor (bFGF), phorbol myristate acetate (PMA), and interleukin-1beta (IL-1beta)-were studied, additional differences in proliferation were observed. Atmospheric O(2) inhibited the synthesis of a major basement membrane protein (Type IV collagen), a major surface protein (PECAM-1), and increased the synthesis of von Willebrand factor (vWf). The rate of vascular channel formation induced by collagen gels was decreased at 5% O(2). These results demonstrate that an increase in extracellular oxygen tension from 5 to 20.8% can significantly alter the cellular physiology of human skin microvascular endothelial cells.

Effect of supplemental oxygen on blood plasma organic acids within embryos from selected lines of turkeys

The hypothesis was tested that increased oxygen tensions during the plateau stage of oxygen consumption (25 and 26 d of incubation) would cause different metabolic responses from embryos selected for increased egg production or growth. Embryos were exposed to 171 or 152 mm Hg partial pressure of oxygen from 25 to 28 d of incubation, a time when the oxygen conductance properties of the eggshell are exceeded by the embryonic tissue demands for oxygen. Carbohydrate and lipid metabolism were observed by measuring plasma organic acids in embryos from selected lines and randombred controls. (E was selected for increased egg production; RBC1 is the randombred line from which it was selected. F was selected for increased BW; RBC2 is the randombred line from which it was selected.) During the plateau stage in oxygen consumption, RBC2 embryos responded to added oxygen by utilizing fat rather than carbohydrate, whereas F embryos responded by using less fat as well as less carbohydrate from the liver and kidney. The response of F embryos to added oxygen is the opposite that might be expected for aerobic metabolism. The reason that selection for growth has resulted in such a metabolism is unknown. The E embryos displayed depressed lactate and beta-hydroxybutyrate levels, but plasma urates were elevated compared with RBC1, suggesting that the selection for egg production has also resulted in a unique metabolism. The embryonic processes described in the current study suggest that selected embryos are unable to respond to elevated partial pressure of oxygen by adjusting energy metabolism, which may result in increased embryonic mortality during this stage.

Abnormal Vasoreactivity in the Pathophysiology of Persistent Pulmonary Hypertension of the Newborn

1. Steven H. Abman, MD1,* 1. 2. *Professor, Department of Pediatrics, University of Colorado School of Medicine and The Children’s Hospital, Denver CO. After completing this article, readers should be able to: 1. Describe the factors that modulate the transition of pulmonary circulation from in utero to after birth. 2. Delineate temporal changes in pulmonary vascular resistance during fetal life. 3. List the substances that play a role in vasoregulation of normal fetal pulmonary circulation. 4. Delineate the role of nitric oxide in increasing pulmonary blood flow at birth. 5. Describe the common physiologic characteristics of persistent pulmonary hypertension of the newborn. 6. Delineate how abnormalities in production and responsiveness to nitric oxide affect developing lung circulation. 7. Explain why inhaled nitric oxide therapy may not be effective in all cases of pulmonary hypertension. Successful adaptation of the newborn to postnatal conditions requires a dramatic transition of the pulmonary circulation from a high resistance state in utero to a low-resistance state within minutes after birth. This fall in pulmonary vascular resistance (PVR) allows for a nearly 10-fold rise in pulmonary blood flow that ensures that the lung can assume its postnatal role in gas exchange. Over the past 50 years, experimental studies have demonstrated that several mechanisms contribute to the normal fall in PVR at birth, including the establishment of a gas-liquid interface in the lung, increased oxygen tension, rhythmic distension of the lung (respiration), and shear stress. In addition to these physical stimuli, pulmonary vascular tone is modulated by altered production of vasoactive products, especially the release of potent vasodilator substances, such as nitric oxide (NO) and prostacyclin (PgI2). Within minutes of this vasodilator response, increased pulmonary blood flow distends the vasculature, causing a “structural reorganization” of the vascular wall that includes flattening of the endothelium and thinning of smooth muscle cells and matrix. Thus, the ability to accommodate this marked rise in blood flow requires rapid functional and structural adaptations to ensure that the normal postnatal fall in …

Paradoxical Role of Inhaled Nitric Oxide in Advanced Liver Disease

Because an increased level of exhaled nitric oxide has been noted in patients with severe liver cirrhosis, it seems unlikely that inhaled nitric oxide would ameliorate portopulmonary hypertension or hepatopulmonary syndrome. However, a few reports have suggested a beneficial effect. Therefore, we designed a prospective study of the effects of inhaled nitric oxide in patients with end-stage liver disease. Patients presenting for orthotopic liver transplantation who were identified as having moderate to severe portopulmonary hypertension or hepatopulmonary syndrome were treated with inhaled nitric oxide, and its effects on pulmonary hemodynamics and oxygenation were studied. In portopulmonary hypertension, a positive effect was defined as a ≥20% decline in mean pulmonary artery pressure or pulmonary vascular resistance. In hepatopulmonary syndrome patients, a positive effect was defined as an increase in arterial oxygen tension of ≥20%. Of 434 consecutive patients evaluated, 20 patients met the study criteria. Sixteen patients had portopulmonary hypertension, and 4 patients had hepatopulmonary syndrome. Two patients with portopulmonary hypertension responded to inhaled nitric oxide, as did 1 patient with type 2 hepatopulmonary syndrome. In conclusion, the role of nitric oxide in end-stage liver disease may not be consistent and may vary with different pathophysiological states.

Treatment of Experimental Avascular Necrosis of the Femoral Head with Hyperbaric Oxygen in Rats: Histological Evaluation of the Femoral Heads during the Early Phase of the Reparative Process

The healing of vascular deprivation-induced necrosis of the femoral head of rats exposed to hyperbaric oxygen was compared with that in untreated rats. The amount of necrotic bone, extent of osteoneogenesis, degree of remodeling, and changes of the articular cartilage were histologically graded on a semiquantitative scale of 0 to 3+. On the 2nd, 7th, and 21st postoperative days, there were no differences between the two groups. Newly formed appositional and intramembranous bone was more abundant and remodeling was more advanced in the femoral heads of the hyperbaric oxygen-treated than untreated rats sacrificed on the 42nd postoperative day; also there was less necrotic debris in the femoral heads of the treated rats. There were no differences in the severity of the degenerative changes of the articular cartilage of the treated and untreated rats. Exposure of rats to hyperbaric oxygen does not preserve tissue viability after all arteries supplying the femoral head are severed. Yet, resulting in an increased oxygen tension of the tissues, it seems to provide the optimal settings for reparative processes. The results suggest that hyperoxygenation-mediated relief of ischemia enhances the fibroblastic, angioblastic, osteoblastic, and osteoclastic activities such that healing of the rats' necrotic femoral heads is expedited.

Effect of carbogen breathing on the physiological profile of human glioma xenografts.

The aim of this study was to evaluate the effect of carbogen breathing on the physiological profile of human glioma xenografts. Near infrared spectroscopy was used to investigate changes in oxy- and deoxyhemoglobin concentrations in tumor blood. Oxygen tension changes in tumor tissue were evaluated by (19)F-MR relaxometry, using perfluoro-15-crown-5-ether, and modifications of tumor blood perfusion (TBP) were analyzed by fast dynamic (1)H-MR imaging of Gd-DTPA uptake. Finally, changes of the bioenergetic status and pH of tumor cells were analyzed by (31)P-MRS. After 5 to 8 min of carbogen breathing, the average oxygen tension increase in tumor tissue was 4.6 +/- 1.3 mm Hg, which is in agreement with an increase of the oxyhemoglobin concentration in tumor blood (Delta[O(2)Hb] = 9. 2 +/- 3 microM). However, simultaneously the TBP was reduced, the bioenergetic status was diminished, and pH was decreased. As 100% O(2) breathing alone did not result in a detectable increase of oxyhemoglobin in tumor blood, the increase of the tumor oxygenation by carbogen appears to be mediated by its CO(2) content. This component may cause a nutrient-limited decrease of oxidative energy metabolism, indirectly via a steal-effect and/or by inhibition of the glycolytic rate resulting from tissue acidification. Magn Reson Med 42:490-499, 1999.

Increases in oxygen tension stimulate expression of ICAM-1 and VCAM-1 on human endothelial cells.

Leukocyte infiltration plays a major role in ischemia-associated organ dysfunction and damage. A crucial step for extravasation of white blood cells is binding of leukocyte beta-integrins to endothelial adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1). To test for direct effects of oxygen on this process we studied ICAM-1 and VCAM-1 expression in human dermal microvascular and umbilical vein endothelial cells (EC) exposed to different oxygen tensions in the absence or presence of tumor necrosis factor-alpha (TNF-alpha). Hypoxia (95% N2-5% CO2) resulted in a downregulation of basal but not TNF-alpha-induced expression of ICAM-1 and VCAM-1. Subsequent rises in oxygen (21, 40, or 95% O2) led to marked increase of ICAM-1 and VCAM-1 cell surface and mRNA expression in both EC types, which after 16 h amounted to about one-third to one-half of maximal TNF-alpha-induced expression. This increase was greatest after 0.5-h hypoxia and was blunted with prolonged hypoxic preincubation. Exposure of cells preincubated under "normoxic" (21% O2) conditions to hyperoxia (40 or 95% O2) also enhanced expression of both adhesion molecules, but the increase was lower than in cells preexposed to hypoxia. The nitric oxide synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) enhanced ICAM-1 and VCAM-1 expression under basal and hypoxic conditions, but in the presence of L-NAME, levels in reoxygenated cells were not higher than basal levels. Moreover, the oxygen-induced rise could be mimicked by addition of H2O2 to normoxic cells, and the oxygen-induced expression of VCAM-1 but not of ICAM-1 was inhibited by addition of the free radical scavengers superoxide dismutase, N-acetyl-L-cysteine, and pyrrolidinedithiocarbamate. These data indicate that an increase in oxygen availability stimulates ICAM-1 and VCAM-1 expression on micro- and macrovascular EC, which may contribute to adhesion and transmigration of different leukocyte populations in ischemia-reperfusion injuries.

Molecular characterization of the nitrite-reducing system of Staphylococcus carnosus.

Characterization of a nitrite reductase-negative Staphylococcus carnosus Tn917 mutant led to the identification of the nir operon, which encodes NirBD, the dissimilatory NADH-dependent nitrite reductase; SirA, the putative oxidase and chelatase, and SirB, the uroporphyrinogen III methylase, both of which are necessary for biosynthesis of the siroheme prosthetic group; and NirR, which revealed no convincing similarity to proteins with known functions. We suggest that NirR is essential for nir promoter activity. In the absence of NirR, a weak promoter upstream of sirA seems to drive transcription of sirA, nirB, nirD, and sirB in the stationary-growth phase. In primer extension experiments one predominant and several weaker transcription start sites were identified in the nir promoter region. Northern blot analyses indicated that anaerobiosis and nitrite are induction factors of the nir operon: cells grown aerobically with nitrite revealed small amounts of full-length transcript whereas cells grown anaerobically with or without nitrite showed large amounts of full-length transcript. Although a transcript is detectable, no nitrite reduction occurs in cells grown aerobically with nitrite, indicating an additional oxygen-controlled step at the level of translation, enzyme folding, assembly, or insertion of prosthetic groups. The nitrite-reducing activity expressed during anaerobiosis is switched off reversibly when the oxygen tension increases, most likely due to competition for electrons with the aerobic respiratory chain. Another gene, nirC, is located upstream of the nir operon. nirC encodes a putative integral membrane-spanning protein of unknown function. A nirC mutant showed no distinct phenotype.

Uncoupling of growth and exopolysaccharide production by Lactococcus lactis subsp. cremoris NIZO B40 and optimization of its synthesis

Exopolysaccharide (EPS) production by Lactococcus lactis subsp. cremoris NIZO B40 was found to be most efficient with glucose as a substrate. The optimal temperature and pH for EPS synthesis were 25°C and pH 5.8, respectively. EPS production could not be identified as a stress response: increased oxygen tension and reduced water activity negatively affected both growth and EPS synthesis. It is often assumed that there is a competition between growth and EPS formation. Within the range of 0.5 and 0.1 h −1, reducing the growth rate resulted indeed in an increase of the specific EPS production but the polymer formation decreased again at even lower growth rates. Most of the applied fermentation conditions influenced both growth and EPS formation. As the growth rate itself also influenced EPS formation, we studied the linking between growth and EPS synthesis. Interestingly, EPS production was not strictly coupled to growth. Significant de novo synthesis of EPS was observed in non-growing cultures. Consequently, the influence of different culture conditions on EPS production could be studied independent of growth.

Tissue Oxygenation in Sepsis

The effect of sepsis on tissue oxygenation is complex and often confusing. This is in part due to the paucity of data from patients (excluding whole-body studies), and in part to the huge variation in laboratory models which have utilised different species, organs and cell lines, different insults, study durations and methods, fluid resuscitation regimens, and end-points. An organ-variable redistribution in microvascular flow undoubtedly occurs though its significance in causing tissue hypoxia remains questionable. A lower oxygen consumption is recognised in patients with an increasing severity of sepsis, with a better prognosis being seen in those spontaneously achieving higher values of global oxygen delivery and consumption. However, septic patients and (well-resuscitated) animal models demonstrate an increase in tissue oxygen tension. This suggest adequate delivery but impaired utilisation of oxygen. As over 90% of oxygen consumed by the body is for mitochondrial generation of ATP by oxidative phosphorylation, a cellular defect is strongly implicated. Mitochondrial dysfunction has been inconsistently demonstrated; on closer inspection, short-term and/or ‘milder’ insult models often show no change or an increase in mitochondrial activity whereas the longer duration and/or more severe models show depressed function. This is borne out by preliminary human studies. Reactive oxygen and nitrogen species appear instrumental in causing this dysfunction; they may also act as signalling mediators for cellular ‘shutdown’, possibly as a protective mechanism to reduce ATP turnover in the face of a decrease in production.

Developmental changes in endothelium-dependent vasodilation and the influence of superoxide anions in perinatal rabbit pulmonary arteries.

ACh-induced vasodilation was investigated in pulmonary arteries from 8 and 2 day pre-term foetal, neonatal (0-12 h and 4 day old) and adult rabbits. The effects of superoxide anion generation [with hypoxanthine (HX, 0.1 mM)/xanthine oxidase (XO, 15 mu ml(-1))], endogenous superoxide dismutase (SOD) inhibition [with the Cu-Zn SOD inhibitor triethylenetetramine (TETA, 1 mM)], endogenous superoxide anion scavenging [by superoxide dismutase (SOD, 50 u ml(-1))] and inhibition of endothelial nitric oxide synthase (eNOS) [with, Nomega-nitro-L-arginine methylester (L-NAME, 0.1 mM)], on basal and ACh-induced NO activity were studied by examining phenylephrine-induced contraction and ACh-induced vasodilation respectively. L-NAME and endothelium removal abolished all ACh-induced vasodilation and 1 microM sodium nitroprusside fully dilated all vessels. ACh-induced vasodilation was absent in the 8 day pre-term foetus and 0-12 h neonate but present at all other ages. L-NAME itself contracted 2 day pre-term foetal vessels. At 0 12 h, SOD, but not the phosphodiesterase 5 inhibitor zaprinast (1 microM), uncovered ACh-induced vasodilation. At this age SOD reduced phenylephrine-induced contraction which was not influenced by TETA, L-NAME or HX/XO, and L-NAME itself did not cause contraction. This suggests both ACh-induced and basal NO activity are compromise in these vessels by endogenous superoxide anion production and deficiencies in endogenous SOD activity. In 4 day vessels, but not adult vessels, L-NAME, TETA and HX/XO augmented contractions to phenylephrine, and L-NAME itself induced vasoconstriction, suggesting that basal NO and SOD activities were present by 4 days but were not evident in the adult. ACh-induced NO activity, and the influence of endogenous SOD on this, were present in the adult (and 4 day) vessels as superoxide generation with HX/XO significantly reduced ACh-induced vasodilation and this effect was inhibited by SOD and augmented by TETA. Increased oxygen tensions > 500 mmHg attenuated ACh-induced vasodilation in the foetal but not neonatal rabbits. Raising the oxygen tension from approximately 20 to approximately 120 mmHg revealed ACh-induced vasodilation in the 8 day pre-term vessels. In summary, superoxide anion accumulation combined with deficiencies in SOD activity may transiently compromise basal and ACh-induced NO activity at birth. Experimental oxygen tensions markedly influence ACh-induced vasodilation in foetal rabbit pulmonary arteries.

Acute effects of inhaled nitric oxide in adult respiratory distress syndrome.

This study evaluated the dose-response effect of inhaled nitric oxide (NO) on gas exchange, haemodynamics, and respiratory mechanics in patients with adult respiratory distress syndrome (ARDS). Of 19 consecutive ARDS patients on mechanical ventilation, eight (42%) responded to a test of 10 parts per million (ppm) NO inhalation with a 25% increase in arterial oxygen tension (Pa,O2,) over the baseline value. The eight NO-responders were extensively studied during administration of seven inhaled NO doses: 0.5, 1, 5, 10, 20, 50 and 100 ppm. Pulmonary pressure and pulmonary vascular resistance exhibited a dose-dependent decrease at NO doses of 0.5-5 ppm, with a plateau at higher doses. At all doses, inhaled NO improved O2 exchange via a reduction in venous admixture. On average, the increase in Pa,O2, was maximal at 5 ppm NO. Some patients, however, exhibited maximal improvement in Pa,O2 at 100 ppm NO. In all patients, the increase in arterial O2 content was maximal at 5 ppm NO. The lack of further increase in arterial O2 content above 5 ppm partly depended on an NO-induced increase in methaemoglobin. Respiratory mechanics were not affected by NO inhalation. In conclusion, NO doses < or =5 ppm are effective for optimal treatment both of hypoxaemia and of pulmonary hypertension in adult respiratory distress syndrome. Although NO doses as high as 100 ppm may further increase arterial oxygen tension, this effect may not lead to an improvement in arterial O2 content, due to the NO-induced increase in methaemoglobin. It is important to consider the effect of NO not only on arterial oxygen tension, but also on arterial O2 content for correct management of inhaled nitric oxide therapy.

Negative-Pressure Dressings as a Bolster for Skin Grafts

Contoured wounds needing closure with skin grafts are often located in complex anatomic regions or are in unusual positions, which make conventional skin graft stabilization techniques cumbersome and ineffective. Often after 72 hours, a skin graft covered with a bolstered dressing has poor take secondary to shear stresses, as well as hematoma formation or serum collection, negating the effectiveness of the stabilizing dressing. The Food and Drug Administration has recently approved vacuum-assisted closure (V.A.C.), an innovative technique using negative pressure, for closure of chronic wounds. This reportedly leads to enhanced granulation tissue formation and consequently more rapid reepithelialization of wounds compared with conventional packing with saline-moistened gauze. Experimental studies have demonstrated increased oxygen tension, decreased bacterial counts, and increased granulation formation occurring under negative-pressure systems. Extending the use of this concept, we have coupled skin grafting with negative-pressure dressings for closure of large, complex open wounds. Our results indicate greater than 95% graft take in all patients in this study. This technique is extremely efficacious, with increased graft take due to total immobilization of the graft, thereby limiting shear forces, elimination of fluid collections, bridging of the graft, and decreased bacterial contamination. Moreover we have noted decreased edema in rotated muscle flaps, improved contour conformity, and shortened hospitalizations.

Correlation of Magnetic Resonance and Oxygen Microelectrode Measurements of Carbogen-Induced Changes in Tumor Oxygenation

Purpose: The aim of this work was to test the hypothesis that decreases in the linewidth of magnetic resonance (MR) water signals in tumors caused by oxygenating treatments are due to increases in capillary and venous oxygen saturation of hemoglobin, which are tightly coupled to increases in extravascular oxygen tension (pO 2). To establish this link, changes measured by MR were compared to changes in tissue pO 2 measured directly by oxygen microelectrodes during carbogen (95% O 2/5% CO 2) inhalation. Methods and Materials: Mammary adenocarcinomas (R3230AC) in nine rats were imaged at 4.7 Tesla. T 1-weighted (TR = 200 ms, flip angle = 45°) spectroscopic images of the water resonance in a single slice through each tumor were acquired with spectral resolution of 3.9 Hz and bandwidth of ±1000 Hz. In the same slices in these tumors, microelectrode measurements were made using a non-Clark style oxygen electrode with a 350-micron tip. MR and microelectrode measurements were made during alternating periods of air and carbogen inhalation. Results: Water resonance linewidth decreased significantly during carbogen-induced hyperoxia. Paired Student’s t-test analysis of microelectrode data indicated that pO 2 was significantly ( p < 0.05) increased as a result of carbogen inhalation. MR and microelectrode data averaged over each tumor demonstrated that decreased MR water signal linewidth is strongly correlated ( r = 0.92, p < 0.05) with increased tumor pO 2 levels. Conclusion: Although tumor oxygenating agents increase response to radiation in rodent tumors, clinical studies have shown only marginal effects on the radiosensitivity of human tumors. This may be, in part, because the effects of tumor oxygenating treatments are highly heterogeneous both within each tumor and among a population of tumors. The noninvasive, high-resolution MR methods that are validated by the present work could guide the design of new and more effective tumor oxygenating agents and optimize treatments for individual patients.

Oxygen Increases cGMP-dependent Protein Kinase (PKG) Activity and mRNA Expression of PKG Type-Iα and Iβ in Pulmonary Veins of Term Fetal Lambs • 1596

Agonist-dependent vasorelaxation in the pulmonary circulation is thought to be mediated via PKG, following changes in intracellular cGMP levels. Our preliminary data indicate that there is an increase in vasodilator response to cGMP as well as an increase in PKG activity postnatally. The stimulus for increase in PKG activity after birth in vascular smooth muscle may be exposure to increased oxygen tension. There are no reports in the literature on the effects of changes in oxygen tension on the activity and mRNA expression of PKG. Therefore, in this study we determined PKG activity and mRNA expression of PKG type-I isoforms, Iα and Iβ, in pulmonary veins (3rd-7th generation) of near-term fetal lambs (145 d gestational age, term being 150 d) incubated for 16 h under low ( 400 mmHg) oxygen tension. PKG activity was determined in the absence or presence of exogenous cGMP (5 μM) and specific exogenous peptide substrate and is expressed as pmol 32P-incorporated into peptide/min/mg protein. mRNA expression of PKG isoforms was determined by RT-PCR (36 cycles) procedure using primers designed to match PKG type-Iα and Iβ cDNA sequence from the ovine species. High oxygen caused a 2- to 4-fold increase in PKG activity in the absence and presence of cGMP. Interestingly, cGMP did not stimulate PKG activity in vessels exposed to low oxygen. Furthermore, high oxygen also caused a 4-fold increase in the mRNA expression of both the isoforms of type-I PKG. We conclude that oxygen stimulates both the activity and mRNA expression of type-I PKG isoforms, which may augment pulmonary vasodilation with onset of oxygenation at birth.

Addition Of A Mast Cell Stabilizing Compound To Organ Preservation Solutions Decreases Lung Reperfusion Injury

Objective: Research in lung transplant preservation has generally focused on free radicals and enzyme release from neutrophils, parenchymal cells, macrophages, and endothelium. The lung has a large resident population of mast cells that, when activated, release potent inflammatory mediators. We hypothesized that adding an inhibitor of mast cell degranulation, lodoxamide tromethamine (10 μmol/L), to Euro-Collins and University of Wisconsin preservation solutions, would decrease lung preservation injury. Methods: Rat lungs were isolated, flushed with the respective solution, and stored at 4° C for 6 or 12 hours. The lungs were reperfused with fresh blood and ventilated with 100% oxygen. Alveolar-arterial oxygen difference, oxygen tension, capillary filtration coefficient, and compliance were determined. Results: After 6 hours of ischemic storage: lodoxamide tromethamine–enhanced Euro-Collins solution decreased alveolar-arterial oxygen difference from 539 to 457 ( p = 0.004), increased oxygen tension from 119 to 205 mm Hg ( p = 0.006), and decreased capillary filtration coefficient from 3.9 to 2.0 ( p < 0.001); lodoxamide tromethamine–enhanced University of Wisconsin solution decreased alveolar-arterial oxygen difference from 546 to 317 ( p < 0.001), increased oxygen tension from 166 to 335 mm Hg ( p < 0.001), and decreased capillary filtration coefficient from 3.0 to 1.7 ( p < 0.001). After 12 hours of ischemic storage, lodoxamide tromethamine–enhanced Euro-Collins solution decreased alveolar-arterial oxygen difference from 588 to 485 ( p < 0.001), increased oxygen tension from 100 to 161 mm Hg ( p = 0.012), decreased capillary filtration coefficient from 6.2 to 2.6 ( p < 0.001), and increased compliance from 0.12 to 0.21 ( p < 0.001); lodoxamide tromethamine–enhanced University of Wisconsin solution decreased alveolar-arterial oxygen difference from 478 to 322 ( p < 0.001), increased oxygen tension from 214 to 335 mm Hg ( p < 0.001), decreased capillary filtration constant from 4.2 to 2.0 ( p < 0.001), and increased compliance from 0.20 to 0.25 ( p < 0.001). Conclusions: Addition of lodoxamide tromethamine to Euro-Collins or University of Wisconsin solution results in a marked decrease in lung reperfusion injury as demonstrated by increased oxygenation, decreased microvascular permeability, and increased compliance. These results are relevant as Euro-Collins and University of Wisconsin solutions are the most common clinically used lung preservation solutions. This study also highlights the deleterious role of resident mast cells in preservation injury. (J Thorac Cardiovasc Surg 1998;115:631-7)

Pulmonary Epithelial Permeability and Gas Exchange: A Comparison of Inverse Ratio Ventilation and Conventional Mechanical Ventilation in Oleic Acid-Induced Lung Injury in Rabbits

(1) To explore the interaction between mechanical ventilation and oleic acid (OA)-induced lung injury on indexes of pulmonary gas exchange and epithelial permeability, and (2) to compare this interaction using two different modes of ventilation: pressure-controlled inverse ratio ventilation (PCIRV) and volume-controlled ventilation with positive end-expiratory pressure (VCV PEEP). Randomized animal study. Experimental laboratory investigation at Södersjukhuset, Stockholm, Sweden. Twenty-four New Zealand white rabbits. (1) Ventilation with PCIRV (n=6) or VCV PEEP (n=6) for 6 h at equal end-expiratory alveolar pressure levels of 5 cm H2O followed by induction of lung injury (IV injection of OA 0.15 mL/kg). (2) Induction of lung injury followed by 6 h of ventilation with either PCIRV (n=6) or VCV PEEP (n=6) as described above. Lung mechanics, heart rate, BP, and gas exchange results were equal at baseline. In group A, after 1 h of ventilation, mean airway pressure was 11.9+/-4.4 with PCIRV and 8.3+/-1.0 cm H2O with VCV PEEP (p<0.05). Forty minutes after OA injection, PaO2/fraction of inspired oxygen (FIO2) was 24+/-10 kPa with PCIRV and 44+/-15 kPa with VCV PEEP (p<0.05). Mean airway pressure was higher and peak airway pressure was lower with PCIRV. In group B, after 6 h of ventilation, PaO2/FIO2 was 17+/-5 kPa with PCIRV and 43+/-8 kPa with VCV PEEP (p<0.01). Systemic BP was lower with PCIRV and mean airway pressure was higher. Technetium-99m diethylene triamine penta-acetic acid lung clearance: In group A, curves were monoexponential with both PCIRV (half-life time [T 1/2], 21+/-8 min and VCV PEEP (T 1/2, 126+/-59 min, p<0.005) until injection of OA. In the VCV PEEP-treated animals, a marked increase in clearance rate was observed within 60 s of OA injection (T 1/2, 13+/-9 min, p<0.001). Fifteen minutes after OA injections, T 1/2 had decreased to 38+/-17 min with VCV PEEP. In the animals treated with PCIRV, OA injection did not lead to a significant change in clearance rate, although the elimination pattern was observed to change from single-compartment to multicompartment type. In group B, clearance curves were monoexponential with both ventilatory modes. There was no significant difference in clearance rate between PCIRV (T 1/2, 25+/-9 min) and VCV PEEP (T 1/2, 36+/-16 min, not significant). The observation that PaO2 was lower in the PCIRV-treated groups must be interpreted with caution in this animal study with relatively few observations. The finding may reflect differences in the effect of OA injection in the two ventilatory modes. It is also possible that externally applied PEEP is more effective than PCIRV in increasing oxygen tension, either because of a less inhomogenous distribution of ventilation and perfusion or for other reasons. The clearance results imply that PCIRV causes an alteration in lung epithelial or membrane function in comparison to VCV PEEP. This functional difference is most likely caused by the large time-weighted lung volume produced by pressure control in combination with a prolonged inspiration. Induction of high permeability lung injury with OA eliminates the difference between PCIRV and VCV PEEP. It remains to be established whether these findings are relevant with regard to ventilator-associated structural lung injury in man.

Local Radiant Heating Increases Subcutaneous Oxygen Tension

Background: We evaluated a novel bandage that incorporates a thermostatically controlled radiant heater. We first determined optimal bandage temperature, based on increases in subcutaneous oxygen tension, a measure correlating well with resistance to infection and wound strength. We then tested the hypothesis that prolonged radiant heating would increase collagen deposition in experimental thigh wounds. Methods: The experimental bandages were positioned on the anterior thigh of 8 volunteers, and heated for 2 hours at 38°C, 42°C, or 46°C, in a random order. Subcutaneous oxygen tension under the bandage was recorded from an electrode positioned within a subcutaneous tonometer. We studied 10 volunteers in the second protocol. For 1 week, the experimental bandage was continuously applied to one thigh, and heated to 38°C using a 2-hour on/off cycle. On the alternate week, a standard gauze bandage was applied to the contralateral thigh. Treatment order was randomly assigned. Wound collagen deposition under each bandage was evaluated with subcutaneous polytetrafluoroethylene tubes, which were removed and assayed for hydroxyproline on the eighth day. Data are presented as means ± SDs. Results: Skin temperature during heating ranged from 36°C to 37.5°C. Oxygen tension increased ≈50% during heating, but the increase was comparable at the three tested temperatures. Even after heating was discontinued, subcutaneous oxygen tension remained elevated for the remaining 3 study hours. Collagen deposition after 1 week of active heating was 3.4 ± 1.0 μg/cm. After 1 week of control treatment, collagen deposition was 3.2 ± 1.1 μg/cm ( P = not significant). Conclusions: Our data suggest that radiant heating at 38°C significantly increases subcutaneous oxygen tension, and presumably resistance to infection. However, prolonged heating at this temperature does not increase wound collagen deposition.

Endophytic Establishment of Diazotrophic Bacteria in Auxin-Induced Tumors of Cereal Crops

Gramineous crops such as wheat (triticum oestivum), maize (zea mays), and rice (oryza sativa) develop tumorous structures (para-nodules) along primary and secondary roots when treated with low concentrations of various auxins. Rice forms additional tumors along its hypocotyle. Histologically, auxin-induced tumors appear as cancerous grown out root meristems and thus are comparable in origin and structure to stem nodules of the legume sesbania rostrata. Auxin-affected root meristems do not recover and develop further to large nodule-like organs. Introduced diazotrophs (Azospirillum spp., Azorhizobium caulinodans, Rhizobium spp.) potentially inhabit tissues of both stem and root tumors with the central meristem as a major colonization niche. Evidence is given that infecting bacteria follow a ‘crack entry’ invasion at sites where developing tumors have emerged through the root cortex and epidermis. Bacteria are shown to establish with high cell numbers inside intercellular spaces of cortical and meristematic tissues. Plant-cell infection of tumor cells takes place with bacteria found inside the cell-cytoplasm surrounded by membrane-like structures. Once inhabiting induced tumor tissues introduced diazotrophs colonize endophytically with high cell numbers. Mutant, ammonium-excreting and thus ecologically disadvantaged A. brasilense is shown to survive inside para-nodulating maize and rice plants with a dense population. Micro-aerobic nitrogenase activities of tumor inhabiting diazotrophic bacteria (A. brasilense, Azotobacter vinelandii, A. caulonidans) are in general highly increased when compared with untreated control plants. Additionally, bacterial nitrogenase activity is less sensitive to an increased oxygen tension in the root environment. The host plants benefit from the enhanced nitrogen fixation in their para-nodulating roots. Highest rates of incorporation of fixed nitrogen into host plant material is reported for para-nodule inhabiting ammonium excreting A. brasilense strain C3. The host plant potentially stimulates the nitrogenase activity of endophytically colonizing diazotrophs by providing energy in the form of a suitable carbon source. In conclusion, it is demonstrated that gramineous plants are potentially capable of developing an endophytical diazotrophic symbiosis through para-nodule formation.

Studies of the mechanism of the anticonvulsant effect of delta-sleep-inducing peptide in conditions of increased oxygen tension.

Studies of the protective actions of three doses of delta-sleep-inducing peptide (DSIP) given at different times before barochamber compression of animals to an oxygen tension of 0.7 MPa showed that the optimum DSIP dose is 12 micrograms/100 g. Intraperitoneal administration of this dose of DSIP delayed the onset of generalized convulsive activity by a factor of 2-2.5 in animals exposed to an oxygen tension of 0.7 MPa and promoted normalization of the sleep-walking cycle within 24 h after exposure to hyperbaric oxygen (HBO), by creating an optimal balance between excitatory and inhibitory amino acid neuromediators.