Oxygen Tension Gradient Research Articles

A New Method for Measuring the Oxygen Diffusion Constant and Oxygen Consumption Rate of Arteriolar Walls

Oxygen transport is believed to primarily occur via capillaries and depends on the oxygen tension gradient between the vessels and tissues. As blood flows along branching arterioles, the O(2) saturation drops, indicating either consumption or diffusion. The blood flow rate, the O(2) concentration gradient, and Krogh's O(2) diffusion constant (K) of the vessel wall are parameters affecting O(2)delivery. We devised a method for evaluating K of arteriolar wall in vivo using phosphorescence quenching microscopy to measure the partial pressure of oxygen in two areas almost simultaneously. The K value of arteriolar wall (inner diameter, 63.5 ± 11.9 μm; wall thickness, 18.0 ± 1.2 μm) was found to be 6.0 ± 1.2 × 10(-11) (cm(2)/s)(ml O(2)·cm(-3) tissue·mmHg(-1)). The arteriolar wall O(2) consumption rate (M) was 1.5 ± 0.1 (ml O(2)·100 cm(-3) tissue·min(-1)), as calculated using Krogh's diffusion equation. These results suggest that the arteriolar wall consumes a considerable proportion of the O(2) that diffuses through it.

Hypoxia-Inducible Factor Regulates Expression of Surfactant Protein in Alveolar Type II Cells In Vitro

Alveolar type II (ATII) cells cultured at an air-liquid (A/L) interface maintain differentiation, but they lose these properties when they are submerged. Others showed that an oxygen tension gradient develops in the culture medium as ATII cells consume oxygen. Therefore, we wondered whether hypoxia inducible factor (HIF) signaling could explain differences in the phenotypes of ATII cells cultured under A/L interface or submerged conditions. ATII cells were isolated from male Sprague-Dawley rats and cultured on inserts coated with a mixture of rat-tail collagen and Matrigel, in medium including 5% rat serum and 10 ng/ml keratinocyte growth factor, with their apical surfaces either exposed to air or submerged. The A/L interface condition maintained the expression of surfactant proteins, whereas that expression was down-regulated under the submerged condition, and the effect was rapid and reversible. Under submerged conditions, there was an increase in HIF1α and HIF2α in nuclear extracts, mRNA levels of HIF inducible genes, vascular endothelial growth factor, glucose transporter-1 (GLUT1), and the protein level of pyruvate dehydrogenase kinase isozyme-1. The expression of surfactant proteins was suppressed and GLUT1 mRNA levels were induced when cells were cultured with 1 mM dimethyloxalyl glycine. The expression of surfactant proteins was restored under submerged conditions with supplemented 60% oxygen. HIF signaling and oxygen tension at the surface of cells appears to be important in regulating the phenotype of rat ATII cells.

HIF-1α in Epidermis: Oxygen Sensing, Cutaneous Angiogenesis, Cancer, and Non-Cancer Disorders

Besides lung, postnatal human epidermis is the only epithelium in direct contact with atmospheric oxygen. Skin epidermal oxygenation occurs mostly through atmospheric oxygen rather than tissue vasculature, resulting in a mildly hypoxic microenvironment that favors increased expression of hypoxia-inducible factor-1α (HIF-1α). Considering the wide spectrum of biological processes, such as angiogenesis, inflammation, bioenergetics, proliferation, motility, and apoptosis, that are regulated by this transcription factor, its high expression level in the epidermis might be important to HIF-1α in skin physiology and pathophysiology. Here, we review the role of HIF-1α in cutaneous angiogenesis, skin tumorigenesis, and several skin disorders.

Impaired Lung 123I-MIBG Uptake on SPECT in Pulmonary Emphysema

The aim of this study was to evaluate impaired lung uptake of (123)I-metaiodobenzylguanidine ((123)I-MIBG) on SPECT, compared with perfusion SPECT and morphologic CT, in patients with pulmonary emphysema (PE). (123)I-MIBG SPECT was performed at 15 min and 4 h after intravenous injection of (123)I-MIBG in 36 PE patients with a history of smoking and variable-extent low-attenuation areas on CT, indicative of emphysematous changes, and in 16 controls with no history of smoking and no noticeable low-attenuation areas. The distribution of (123)I-MIBG was compared with that of low-attenuation areas on CT and perfusion on SPECT at the base of the 180 lung lobes of the PE patients. Total-lung (123)I-MIBG kinetics were calculated, including early and delayed lung-to-mediastinum uptake ratios and washout rate. The controls showed a fairly uniform lung (123)I-MIBG distribution nearly consistent with perfusion. PE patients had heterogeneous (123)I-MIBG defects showing frequent discordance with low-attenuation areas or perfusion distribution; (123)I-MIBG defects were more extensive than low-attenuation areas in 76 lobes (42.2%) of 31 patients (86%) and more extensive than perfusion defects in 44 lobes (24.4%) of 22 patients (61%). (123)I-MIBG defects were seen regardless of the absence of noticeable low-attenuation areas and perfusion defects in 19 lobes (10.5%) of 16 patients (44%). All total-lung (123)I-MIBG kinetic parameters in PE patients were significantly lower than the control values (P < 0.0001), with significant correlation with alveolar-arterial oxygen tension gradient but without correlation with the extent of perfusion defects or low-attenuation areas. (123)I-MIBG SPECT allows evaluation of lung pathophysiology in PE independently of perfusion SPECT or morphologic CT, and impairment of lung (123)I-MIBG uptake may be more extensive than perfusion or morphologic abnormalities in PE.

Design and characterization of a one‐compartment scale‐down system for simulating dissolved oxygen tension gradients

AbstractBACKGROUND: A laboratory scale one‐compartment scale‐down system (1‐CSDS), used to generate dissolved oxygen tension (DOT) gradients was designed and characterized. The system consists of a 1.5‐L stirred‐tank bioreactor coupled to an automatic DOT controller that changes the oxygen partial pressure in the inlet gas through a feedback proportional–integral–derivative algorithm, while maintaining the hydrodynamic conditions constant. Oscillatory control of DOT was achieved by employing time‐dependent square wave or sinusoidal setpoints.RESULTS: The 1‐CSDS can be modeled as a first‐order dynamic system, but showing a permanent lag between the system response and the setpoint. The 1‐CSDS had a faster response rate for generating oscillating DOT when a square wave setpoint was used rather than a sinusoidal setpoint. The 1‐CSDS generated symmetric DOT oscillations at periods above of 100 s.CONCLUSION: The 1‐CSDS is suited to investigate the responses of microorganisms and cells, of biotechnological importance, to oscillatory DOT conditions. It was found that the response of the 1‐CSDS was limited by the kLa. Copyright © 2010 Society of Chemical Industry

Intratumoral Hypoxic Gradient Drives Stem Cells Distribution and MGMT Expression in Glioblastoma

Glioblastoma multiforme (GBM) are highly proliferative tumors currently treated by surgical removal, followed by radiotherapy and chemotherapy, which are counteracted by intratumoral hypoxia. Here we exploited image guided surgery to sample multiple intratumoral areas to define potential cellular heterogeneity in correlation to the oxygen tension gradient within the GBM mass. Our results indicate that more immature cells are localized in the inner core and in the intermediate layer of the tumor mass, whereas more committed cells, expressing glial fibrillary acidic protein and beta-III-tubulin, are distributed along the peripheral and neo-vascularized area, where Smad1/5/8 and Stat3 result to be activated. Moreover, GBM stem cells, identified with the stem cell marker CD133, express high level of DNA repair protein O6-methylguanine-DNA-methyltransferase (MGMT) known to be involved in chemotherapy resistance and highly expressed in the inner core of the tumor mass. Importantly, these cells and, particularly, CD133(+) cells result to be resistant to temozolomide (TMZ), the most used oral alkylating agent for the treatment of GBM, which specifically causes apoptosis only in GBM cells derived from the peripheral layer of the tumor mass. These results indicate a correlation between the intratumoral hypoxic gradient, the tumor cell phenotype, and the tumor resistance to chemotherapy leading to a novel concentric model of tumor stem cell niche, which may be useful to define the real localization of the chemoresistant GBM tumor cells in order to design more effective treatment strategies.

Transmural Oxygen Tension Gradients in Rat Cerebral Cortex Arterioles

Modified needle oxygen microelectrodes and vital microscopy were used to measure transmural oxygen tension gradients (PO2) in pial arterioles with lumen diameters of 20-90 microm. A relationship between the magnitude of the transmural PO2 gradient and arteriole wall tone was found: in control conditions, PO2 gradients were 1.17 +/- 0.06 mmHg/microm (n = 40), while in conditions of arteriolar wall dilation the transmural PO2 gradient decreased to 0.68 +/- 0.04 mmHg/microm (p < 0.001, n = 38). These data provide the first measurements of transmural PO2 gradients in pial arterioles of different calibers at different levels of vascular tone and have fundamental importance for assessing the role of arterial microvessels in tissue oxygen supply processes. The results obtained here provide evidence that oxygen consumption by the vessel wall is within the range characteristic of enveloping tissues and that oxygen consumption by the endothelial cell layer probably has no significant effect on the magnitude of the transmural PO2 gradient.

Impact of Rat Outer Medullary Architecture on Oxygen Distribution

In this study, we examined the impact of the complex structural organization of the rat outer medulla (OM) on oxygen distribution. We extended a previous region‐based mathematical model of the urine concentrating mechanism in the rat OM to incorporate the transport of red blood cells, hemoglobin, and O2. We considered O2 consumption for basal cellular metabolism and for active transport of NaCl across medullary thick ascending limbs (mTALs). Our model predicts that the OM structural organization results in significant oxygen tension (PO2) gradients both in the axial and the radial directions. The segregation of descending vasa recta, the main supply of O2, at the center and immediate periphery of the vascular bundles gives rise to large radial differences in PO2 between regions and helps preserve O2 delivery to the inner medulla. Assuming that the mTAL active Na+ transport rate decreases when mTAL PO2 falls below a critical level, oxygen availability to mTALs has a significant impact on the concentrating capability of the model OM. The model also predicts that when the OM undergoes hypertrophy, its concentrating capability increases significantly only when anaerobic metabolism supports a substantial fraction of the mTAL active Na+ transport, which is otherwise critically reduced by the low interstitial and mTAL luminal PO2 in a hypertrophied OM.Support: NIH Grant DK‐53775 (AE and AL) and NSF Grant DMS‐0701412 (AL).

The Association of D-dimer Levels with Clinical Outcomes in Patients Presenting with Acute Pulmonary Embolism

The D-dimer fragment of fibrin degradation has been a useful adjunct in the diagnosis of venous thromboembolism (VTE). In conjunction with predictive algorithms, the high negative predictive value (NPV) of D-dimer measurements has provided this analyte with a prominent position in the diagnosis of pulmonary embolism (PE). The purpose of this study was to determine if D-dimer levels correlate with ventilation/perfusion (V/Q) derangements as assessed by the alveolar-arterial oxygen tension gradient (DeltaA-a) and to ascertain if quantitative measurements of D-dimer on admission have prognostic value in terms of during-admission mortality and recurrence over a 60-week period. The study utilized a retrospective cohort of 108 subjects admitted to a single institution and studied longitudinally. The cohort was divided into 4 groups representing degree of severity assessed by computed tomographic (CT) angiography: mild, moderate, severe, and very severe. Differences in D-dimer levels among these groups were strongly significant (P < .0001). A strong correlation was observed between D-dimer concentration and DeltaA-a (P < .0001). Logistic methods were used to calculate a "cut-off" level that would distinguish mild-moderate from severe-very severe PE. At a concentration of 12.35 mug/mL, this level yielded an odds ratio (OR) of 12.64 (P = .006) for during-admission mortality and a hazard ratio (HR) of 0.13 (P < .0001) for 60-week recurrence. These data suggest that D-dimer levels have utility beyond their NPV and should be considered as potential prognostic markers in subjects presenting with acute PE.

Pulmonary injury after cardiopulmonary bypass: Beneficial effects of low-frequency mechanical ventilation

Pulmonary dysfunction is a frequent postoperative complication after cardiac surgery with cardiopulmonary bypass, and atelectasis is thought to be one of the main causes. The aim of this study was to evaluate whether low-frequency ventilation and continuous positive airway pressure during cardiopulmonary bypass reduce postcardiopulmonary bypass lung injury. Eighteen Yorkshire pigs were subjected to 120 minutes of cardiopulmonary bypass (1 hour of cardioplegic arrest) followed by 90 minutes of recovery before being sacrificed. Six animals served as control with the endotracheal tube open to atmosphere during cardiopulmonary bypass. The remaining animals were divided into 2 groups of 6: One group received continuous positive airway pressure of 5 cm H(2)O, and one group received low-frequency ventilation (5/minutes) during cardiopulmonary bypass. Lung tissue biopsy and bronchoalveolar lavage samples were obtained before and 90 minutes after discontinuation of cardiopulmonary bypass for measurement of adenine nucleotide (adenosine-5'-triphosphate, adenosine diphosphate, adenosine monophosphate), lactate dehydrogenase, DNA levels, and histology. Hemodynamic data and arterial blood gases were also collected through the study. The hemodynamic parameters were similar in the 3 groups. After cardiopulmonary bypass, the low-frequency ventilation group showed significantly better oxygen tension and alveolar arterial oxygen gradient, higher adenine nucleotide, lower lactate dehydrogenase levels, and reduced histologic damage in lung biopsy, as well as lower DNA levels in bronchoalveolar lavage compared with the control group. The continuous positive airway pressure group showed only significantly reduced lactate dehydrogenase levels compared with control. Low-frequency ventilation during cardiopulmonary bypass in a pig experimental model reduces tissue metabolic and histologic damage in the lungs and is associated with improved postoperative gas exchange.

Longitudinal and Radial Gradients of PO2 in the Hamster Cheek Pouch Microcirculation

The aim of this study was to determine longitudinal and radial gradients in oxygen tension (PO(2)) in microvessels of the hamster cheek pouch. We measured PO(2) using the phosphorescence-quenching method in two orders of arterioles (45.8 +/- 5.5 and 19.9 +/- 1.8 micro m diameter), capillaries, and two orders of venules (50.5 +/- 3.4 and 21.4 +/- 2.0 micro m diameter) in order to determine the longitudinal PO(2) gradient. At the arteriolar and venular sites, we also measured PO(2) at four different sites for an analysis of radial PO(2) gradients: centerline, inside wall (larger arteriole and venule only), outside wall, and interstitium. We used 10 hamsters weighing 115 +/- 27 g anesthetized with pentobarbital intraperitoneally and maintained with alpha-chloralose intravenously. The cheek pouch was everted and a single-layered preparation was studied by intravital microscopy. Albumin-bound Pd-porphyrin was infused into the circulation and excited by flash illumination at 10 Hz, with a rectangular diaphragm limiting the excitation field to 5 x 25 micro m. In the longitudinal direction, intravascular PO(2) decreased significantly (P < 0.01) from large arterioles (39.5 +/- 2.3 mmHg) to small arterioles (32.2 +/- 0.3 mmHg), then to capillaries (30.2 +/- 1.8 mmHg), and on to small venules (27.3 +/- 2.1 mmHg) and large venules (25.5 +/- 2.2 mmHg). In the radial direction, PO(2) decreased significantly (P < 0.01) in and around larger arterioles, and to a lesser extent, around the smaller ones (P < 0.05). There was no significant PO(2) gradient, longitudinal or radial, associated with venules. The PO(2) difference from the centerline to the outside wall in large arterioles was 8.3 +/- 1.4 mmHg, and most of the decline in PO(2) in the radial direction was contributed by the intravascular difference (4.7 +/- 2.1 mmHg) and only about 1.0 +/- 2.7 mmHg by the transmural difference. Our data show that there are large intra-arteriolar radial PO(2) gradients, but no large transmural PO(2) differences, suggesting that the oxygen consumption of the microvessel wall is not exceptionally high.

Erythrocyte-associated transients in capillary Po2: an isovolemic hemodilution study in the rat spinotrapezius muscle

Mathematical simulations of oxygen delivery to tissue from capillaries that take into account the particulate nature of blood flow predict the existence of oxygen tension (Po(2)) gradients between erythrocytes (RBCs). As RBCs and plasma alternately pass an observation point, these gradients are manifested as rapid fluctuations in Po(2), also known as erythrocyte-associated transients (EATs). The impact of hemodilution on EATs and oxygen delivery at the capillary level of the microcirculation has yet to be elucidated. Therefore, in the present study, phosphorescence quenching microscopy was used to measure EATs and Po(2) in capillaries of the rat spinotrapezius muscle at the following systemic hematocrits (Hct(sys)): normal (39%) and after moderate (HES1; 27%) or severe (HES2; 15%) isovolemic hemodilution using a 6% hetastarch solution. A 532-nm laser, generating 10-micros pulses concentrated onto a 0.9-microm spot, was used to obtain plasma Po(2) values 100 times/s at points along surface capillaries of the muscle. Mean capillary Po(2) (Pc(O(2)); means +/- SE) significantly decreased between conditions (normal: 56 +/- 2 mmHg, n = 45; HES1: 47 +/- 2 mmHg, n = 62; HES2: 27 +/- 2 mmHg, n = 52, where n = capillary number). In addition, the magnitude of Po(2) transients (DeltaPo(2)) significantly decreased with hemodilution (normal: 19 +/- 1 mmHg, n = 45; HES1: 11 +/- 1 mmHg, n = 62; HES2: 6 +/- 1 mmHg, n = 52). Results suggest that the decrease in Pc(O(2)) and DeltaPo(2) with hemodilution is primarily dependent on Hct(sys) and subsequent microvascular compensations.

Variables Associated with the Early Failure of Nasal CPAP in Very Low Birth Weight Infants

To identify risk factors and neonatal outcomes associated with the early failure of “bubble” nasal continuous positive airway pressure (CPAP) in very low birth weight (VLBW) infants with respiratory distress syndrome (RDS). Following resuscitation and stabilization at delivery, a cohort of 261 consecutively inborn infants (birth weight #1250 g) was divided into three groups based on the initial respiratory support modality and outcome at 72 hours of age: “ventilator-started” group, “CPAP-failure” group, and “CPAP-success” group. CPAP was successful in 76% of infants #1250 g birth weight and 50% of infants ≤750 g birth weight. In analyses adjusted for postmenstrual age (PMA) and small for gestational age (SGA), CPAP failure was associated with need for positive pressure ventilation (PPV) at delivery, alveolar-arterial oxygen tension gradient (A-a DO2) >180 mmHg on the first arterial blood gas (ABG), and severe RDS on the initial chest x-ray (adjusted odds ratio [95% CI] = 2.37 [1.02, 5.52], 2.91 [1.30, 6.55] and 6.42 [2.75, 15.0], respectively). The positive predictive value of these variables ranged from 43% to 55%. In analyses adjusted for PMA and severe RDS, rates of mortality and common premature morbidities were higher in the CPAP-failure group than in the CPAP-success group. Although several variables available near birth were strongly associated with early CPAP failure, they proved weak predictors of failure. A prospective controlled trial is needed to determine if extremely premature spontaneously breathing infants are better served by initial management with CPAP or mechanical ventilation.

Role of hypoxia-inducible transcription factors (HIFs) in oxygen-dependent modulation of IGF binding protein–1 biosynthesis in primary rat hepatocytes

Higher levels of IGFBP–1 mRNA are expressed in the less aerobic perivenous zone of the liver. Since gradients in oxygen tension (pO2) may contribute to zonated gene expression, the influence of arterial and venous pO2 on IGFBP–1 biosynthesis was studied in primary cultures of rat hepatocytes. Maximal IGFBP–1 mRNA and protein levels were observed under venous pO2 whereas less than 30% of maximal levels were observed under arterial pO2. In contrast, the expression of IGFBP–4 was greatest under arterial pO2, indicating that this effect of hypoxia on IGFBP–1 gene expression is specific. The response to hypoxia appeares to involve reactive oxygen species, since treatment with H2O2 results in a dose-dependent decrease of IGFBP–1 mRNA levels under venous pO2, whereas IGFBP–1 mRNA expression under arterial pO2 was not affected. Inhibition of the hypoxia-dependent IGFBP–1 mRNA induction by actinomycin D indicates that this effect is mediated at the level of gene transcription, inhibition of IGFBP–1 mRNA by the iron chelator desferrioxamine under both venous and arterial pO2 suggested an involvement of hypoxia-inducible transcription factors (HIF). Transfection experiments demonstrated that especially HIF–3α and HIF–2α, and to a lesser extent HIF–1α, contribute to the induction of IGFBP–1 mRNA expression in isolated hepatocytes, while experiments with vectors for the HIF prolyl hydroxylases (PHD) indicated a major role of PHD–2 in destabilization of HIFs, attenuating the induction of IGFBP–1 under venous pO2. Reporter gene studies indicate that hypoxia stimulates IGFBP–1 expression through a putative HIF response element located ~250 bp upstream from the transcription initiation site. Together, these results support the concept that iron, radical oxygen species, the HIF–2 and –3 as well as the PHD pathways play important roles in mediating effects of hypoxia on IGFBP–1 gene expression in the liver.

Succinate and artificial maintenance of normal body temperature synergistically correct lethal disorders in thiopental coma rat

Under modeling of thiopental coma influence of sodium succinate and (or) external warming for the support of normal body temperature (isothermal regimen) on the gas exchange, blood gas content, acid–base status and survival rate was studied in rats. In the absence of therapy hypothermia was developed (−9.4 °C), O 2 consumption decreased by a factor 5, oxygenation of arterial blood ( pO 2) did not change while that of venous blood increased, wherewith arteriovenous oxygen tension gradient decreased by half. Blood tension of carbon dioxide ( pCO 2) increased twice, respiratory and metabolic acidosis was developed. Survival rate under absence of a therapy was 42%, with isolated use of isothermal regimen or succinate therapy alike—50%; with their use in combination drastically increased up to 92%. Succinate increased arteriovenous gradient of pO 2, decreased deficit of buffer bases, increased bicarbonate concentration. At isothermal regimen accumulation of CO 2 in the blood was diminished, its excretion was increased, pH of blood approached normal values. Combined use of both therapy agents increased O 2 consumption and potentiated their positive influence on acid–base status. The implication is that hypothermia restrains effect of succinate in barbiturate coma; prevention of hypothermia in combination with succinate administration is highly effective method of experimental therapy of barbiturate intoxication.

Transcriptional and metabolic response of recombinant Escherichia coli to spatial dissolved oxygen tension gradients simulated in a scale‐down system

Escherichia coli, expressing recombinant green fluorescent protein (GFP), was subjected to dissolved oxygen tension (DOT) oscillations in a two-compartment system for simulating gradients that can occur in large-scale bioreactors. Cells were continuously circulated between the anaerobic (0% DOT) and aerobic (10% DOT) vessels of the scale-down system to mimic an overall circulation time of 50 s, and a mean residence time in the anaerobic and aerobic compartments of 33 and 17 s, respectively. Transcription levels of mixed acid fermentation genes (ldhA, poxB, frdD, ackA, adhE, pflD, and fdhF), measured by quantitative RT-PCR, increased between 1.5- to over 6-fold under oscillatory DOT compared to aerobic cultures (constant 10% DOT). In addition, the transcription level of fumB increased whereas it decreased for sucA and sucB, suggesting that the tricarboxylic acid cycle was functioning as two open branches. Gene transcription levels revealed that cytrochrome bd, which has higher affinity to oxygen but lower energy efficiency, was preferred over cytochrome bO3 in oscillatory DOT cultures. Post-transcriptional processing limited heterologous protein production in the scale-down system, as inferred from similar gfp transcription but 19% lower GFP concentration compared to aerobic cultures. Simulated DOT gradients also affected the transcription of genes of the glyoxylate shunt (aceA), of global regulators of aerobic and anaerobic metabolism (fnr, arcA, and arcB), and other relevant genes (luxS, sodA, fumA, and sdhB). Transcriptional changes explained the observed alterations in overall stoichiometric and kinetic parameters, and production of ethanol and organic acids. Differences in transcription levels between aerobic and anaerobic compartments were also observed, indicating that E. coli can respond very fast to intermittent DOT conditions. The transcriptional responses of E. coli to DOT gradients reported here are useful for establishing rational scale-up criteria and strain design strategies for improved culture performance at large scales.

Oxygen-Dependent Modulation of Insulin-Like Growth Factor Binding Protein Biosynthesis in Primary Cultures of Rat Hepatocytes

Higher levels of IGF-binding protein 1 (IGFBP-1) mRNA are expressed in the less aerobic perivenous zone of the liver. Because gradients in oxygen tension (pO(2)) may contribute to zonated gene expression, the influence of arterial and venous pO(2) on IGFBP-1 biosynthesis was studied in primary cultures of rat hepatocytes. Maximal IGFBP-1 mRNA and protein levels were observed under venous pO(2), whereas less than 30% of maximal levels were observed under arterial pO(2). In contrast, the expression of IGFBP-4 was greatest under arterial pO(2), indicating that this effect of hypoxia on IGFBP-1 gene expression is specific. The response to hypoxia appears to involve reactive oxygen species, because treatment with H(2)O(2) results in a dose-dependent decrease of IGFBP-1 mRNA levels under venous pO(2), whereas IGFBP-1 mRNA expression under arterial pO(2) was not affected. Inhibition of the hypoxia-dependent IGFBP-1 mRNA induction by actinomycin D indicates that this effect is mediated at the level of gene transcription, and inhibition of IGFBP-1 mRNA by the iron chelator desferrioxamine under both venous and arterial pO(2) suggested the involvement of hypoxia-inducible transcription factors (HIF). Transfection experiments demonstrated that especially HIF-3alpha and HIF-2alpha, and to a lesser extent HIF-1alpha, contribute to the induction of IGFBP-1 mRNA expression in isolated hepatocytes, whereas experiments with vectors for the HIF prolyl hydroxylases (PHD) indicated a major role of PHD-2 in destabilization of HIFs, attenuating the induction of IGFBP-1 under venous pO(2). Reporter gene studies indicate that hypoxia stimulates IGFBP-1 expression through a putative HIF response element located approximately 250 bp upstream from the transcription initiation site. Together, these results support the concept that iron, radical oxygen species, and the HIF-2 and -3 as well as the PHD pathways play important roles in mediating effects of hypoxia on IGFBP-1 gene expression in the liver.

Variables Associated with the Early Failure of Nasal CPAP in Very Low Birth Weight Infants

To identify risk factors and neonatal outcomes associated with the early failure of "bubble" nasal continuous positive airway pressure (CPAP) in very low birth weight (VLBW) infants with respiratory distress syndrome (RDS). Following resuscitation and stabilization at delivery, a cohort of 261 consecutively inborn infants (birth weight < or = 1250 g) was divided into three groups based on the initial respiratory support modality and outcome at 72 hours of age: "ventilator-started" group, "CPAP-failure" group, and "CPAP-success" group. CPAP was successful in 76% of infants < or = 1250 g birth weight and 50% of infants < or = 750 g birth weight. In analyses adjusted for postmenstrual age (PMA) and small for gestational age (SGA), CPAP failure was associated with need for positive pressure ventilation (PPV) at delivery, alveolar-arterial oxygen tension gradient (A-a DO2) >180 mmHg on the first arterial blood gas (ABG), and severe RDS on the initial chest x-ray (adjusted odds ratio [95% CI] = 2.37 [1.02, 5.52], 2.91 [1.30, 6.55] and 6.42 [2.75, 15.0], respectively). The positive predictive value of these variables ranged from 43% to 55%. In analyses adjusted for PMA and severe RDS, rates of mortality and common premature morbidities were higher in the CPAP-failure group than in the CPAP-success group. Although several variables available near birth were strongly associated with early CPAP failure, they proved weak predictors of failure. A prospective controlled trial is needed to determine if extremely premature spontaneously breathing infants are better served by initial management with CPAP or mechanical ventilation.

Alteraciones gasométricas en pacientes cirróticos hospitalizados

Gas exchange alterations have been described in cirrhotic patients; but by the moment, a few prospective studies have focused in them. The aim of this study was to describe the frequency and severity of gasometric alterations in hospitalized cirrhotic patients, a their correlation with hepatocellular disfunction. 50 consecutive cirrhotic patients (41 males) admitted for liver decompensation (ascites, liver encephalopathy, alcoholic hepatitis and upper gastrointestinal bleeding) without acute or chronic cardiopulmonary disfunction were included in the study. Patients were classified according with Child-Pugh score (A, n = 13; B, n = 21; C, n = 16). Severe alcoholic hepatitis (SAH) was confirmed in 7 patients. Arterial gasometry was performed in all patients before discharge. Contrast echocardiography was performed in any case of suspicion of hepatopulmonary syndrome (HPS). Light hypoxemia was observed (80.9 mmHg), without differences with Child-Pugh. Hypocapnia was significantly more evident in Child C than in A and B (31.2 +/- 3.1 vs. 38.1 +/- 4.3 y 36.3 +/- 5 mmHg; p < 0,05), respectively. Cirrhotic patients with SAH showed a significantly higher hypocapnia by comparison with others (31.2 +/- 3.1 vs. a 36.3+/-5 mmHg; p < 0.05). In multivariate analysis, independent prognostic variables for hypocapnica were plasmatic levels of protrombin time, albumin and sodium. HPS was confirmed in 8 patients (16%). The most prevalent gas exchange abnormality in cirrhosis was the alteration of alveolar-arterial oxygen tension gradient, directly correlated with hepatocellur disfunction. Hypocapnia could be a compensatory mechanism or the result of the activation of central respiratory centres by non-depurated substances by the liver.

A New Oxygenation Index for Reflecting Intrapulmonary Shunting in Patients Undergoing Open-Heart Surgery

To assess the reliability of new and traditional oxygenation measurements in reflecting intrapulmonary shunt. Prospective study. Cardiac surgery unit at a university hospital. Fifty-five patients undergoing coronary artery bypass grafting. Simultaneous blood samples were collected from an indwelling arterial line and a catheter for determination of blood gases. Standard accepted formulas were utilized to measure a new oxygenation index: PaO(2)/fraction of inspired oxygen (FIO(2)) x mean airway pressure (Paw). The standard formulas used were the oxygenation ratio (PaO(2)/FIO(2)), PaO(2)/alveolar partial oxygen pressure (PAO(2)), alveolar-arterial oxygen tension gradient (P[A-a]O(2)), and intrapulmonary shunt (venous admixture [Qsp/Qt]). There were significant negative (p < 0.05) correlations between the PaO(2)/(FIO(2) x Paw) and Qsp/Qt (r = - 0.85), between the PaO(2)/FIO(2) and Qsp/Qt (r = - 0.74), and between the PaO(2)/PAO(2) and Qsp/Qt (r = - 0.71). There was a significant positive (p < 0.05) correlation between the P(A-a)O(2) gradient and Qsp/Qt (r = 0.66). However, the correlation was strongest between the PaO(2)/(FIO(2) x Paw) and Qsp/Qt. In this group of patients, PaO(2)/(FIO(2) x Paw) might be more reliable than other oxygenation measurements in reflecting intrapulmonary shunt.