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PubMed1991

Oxygen consumption is independent of changes in oxygen delivery in severe adult respiratory distress syndrome.

We asked whether oxygen consumption is dependent on oxygen delivery in 17 patients who had severe adult respiratory distress syndrome (ARDS), 10 of whom had increased concentrations of plasma lactate. We determined oxygen consumption using analysis of respiratory gases while increasing oxygen delivery using blood transfusion. Oxygen consumption did not change after transfusion (from 227 +/- 83 to 225 +/- 82 ml/min, p less than or equal to 0.38). Oxygen delivery increased from 1,043 +/- 468 ml/min (24%, p less than or equal to 0.001). Even in the 10 patients who had increased concentration of plasma lactate and metabolic acidosis, oxygen consumption remained constant after increasing oxygen delivery (pretransfusion, 224 +/- 101 ml/min; post-transfusion, 225 +/- 99 ml/min; p less than or equal to 0.83). These data have more than 99% power of detecting a change in oxygen consumption of 20 ml/min after transfusion. Therefore, we conclude that directly measured oxygen consumption remains constant and independent of increases in oxygen delivery in our patients with severe ARDS. Because simultaneously determined oxygen consumption calculated from variables shared with the calculation of oxygen delivery yielded a dependent relationship, we speculate that finding dependence of calculated oxygen consumption on oxygen delivery may be the result of methodologic error.

Aged↗
PubMed2006

Peritoneal perfusion with oxygenated perfluorocarbon augments systemic oxygenation.

BACKGROUND: Despite maximal ventilatory support, many patients die from hypoxia in the setting of potentially reversible pulmonary failure. There remains a pressing need for additional pulmonary supportive care measures, especially techniques that do not require systemic anticoagulation. The objective of our experiments was to determine whether systemic oxygenation could be increased in a large animal, with induced hypoxia, by perfusing the abdominal cavity with oxygenated perfluorocarbons. METHODS: Fifteen pigs with a mean (+/- SD) weight of 45 +/- 5 kg were intubated and rendered hypoxic by ventilating them with a blend of nitrogen and oxygen to achieve subatmospheric concentrations of inspired oxygen ranging from 18 to 10%, resulting in baseline mean Pao(2) range of 65.9 +/- 9.7 to 26.6 +/- 2.8 mm Hg, respectively. Peritoneal perfusion was performed in eight animals with oxygenated perfluorocarbon and in seven control animals with oxygenated saline solution. RESULTS: The average increase in Pao(2) with oxygenated perfluorocarbon perfusion, compared to oxygenated saline solution perfusion, ranged from 8.1 to 18.2 mm Hg. A common treatment effect was estimated across all fraction of inspired oxygen (Fio(2)) values, representing the average mean difference in oxygen uptake between oxygenated perfluorocarbon and saline solution, irrespective of the level of Fio(2). This average was 12.8 mm Hg (95% confidence interval, 7.4 to 18.2; p < 0.001). The most clinically relevant results occurred at an Fio(2) of 14%, resulting in a baseline mean Pao(2) of 39.4 +/- 5.0 mm Hg with oxygenated saline solution perfusion, and a mean Pao(2) of 55.3 +/- 7.6 mm Hg with oxygenated perfluorocarbon perfusion. This corresponded to an increase in arterial oxygen saturation from 73 to 89%. CONCLUSION: These results of our principle experiments demonstrate that the peritoneal cavity can be used for gas exchange and, in our model, yielded clinically relevant increases in systemic arterial oxygen levels. This technique may have the potential for the supportive care of patients dying from hypoxia in the setting of reversible lung injury.

Animals↗
PubMed1996

[Oxygen transport and consumption and oxygen saturation in the right atrium in an experimental model of neonatal septic shock].

UNLABELLED: Mixed venous oxygen saturation monitoring is useful to know about the balance of oxygen supply and consumption in patient with shock as well as a form of assessing the effects of different therapeutic maneuvers. Because of newborn peculiarities this measurement is difficult and therefore, the monitoring of the shock state is limited. OBJECTIVES: To investigate the validity of central venous oxygen saturation at right atria as a reflection of mixed venous oxygen saturation in an experimental model of neonatal sepsis. METHODS: In six newborn piglets septic shock was induced by 180 minutes continuous infusion of Group B Streptococcus. Blood samples were obtained from aortic and pulmonary arteries and from right atrium at baseline and at 30-minutes intervals after the bacterial infusion was begun. Changes in arterial pressures, vascular resistances, cardiac index, oxygen delivery and consumption and the oxygen extraction index were also analyzed. RESULTS: Group B Streptococcus infusion induced significant decreases versus baseline situation of both, oxygen delivery and oxygen tissular extraction index, without changes in oxygen consumption, at 30 minutes of bacterial infusion, with a significant correlation between mixed venous and central venous oxygen saturations. Mixed venous oxygen saturation significantly correlates with right atrium oxygen saturation, r2 = 0,88, along all the period of study. CONCLUSIONS: Mixed venous oxygen saturation is a useful measurement of the oxygen delivery and consumption state in the critically ill newborn infant, and central venous oxygen saturation at the right atrium can be a sure, efficient and easy alternative for the neonatal patient.

Animals↗
PubMed2001

The effect of supplemental oxygen on the transarterial wall oxygen gradients at a prosthetic vascular graft to artery anastomosis in the rabbit.

Artery wall hypoxia has been proposed to contribute to many kinds of artery wall pathology, including atherosclerosis and intimal hyperplasia. The purpose of this study was to determine the effect of supplemental oxygen on the transarterial wall oxygen gradients at a prosthetic vascular device (PVG)-to-artery anastomosis. The transarterial wall oxygen gradient in the infrarenal aorta of New Zealand White rabbits housed for 42 days in a 40% supplemental oxygen was measured with an oxygen microelectrode 2 mm distal to a PVG-to-artery anastomosis. Oxygen tensions were significantly increased throughout the artery wall at all time points in the supplemental oxygen groups compared to those in non-oxygen-supplemented groups. Within the oxygen-supplemented groups, the outer artery wall had diminished oxygen tensions immediately following creation of the anastomosis, with a slow return to control oxygen tensions on postanastomosis day 42 which correlated with a return of the vasa vasorum. These changes were noted without differences in blood pressure or arterial blood oxygen concentrations within the oxygen-supplemented group. Artery wall hypoxia noted following the creation of a PVG-to-artery anastomosis can be eliminated and artery wall oxygen tensions significantly increased by the administration of supplemental oxygen.

Animals↗
PubMed1996

Reactions of the Escherichia coli flavohaemoglobin (Hmp) with NADH and near-micromolar oxygen: oxygen affinity of NADH oxidase activity.

The soluble flavohaemoglobin (Hmp) of Escherichia coli, product of the hmp gene, contains haem B and FAD in a single polypeptide of molecular mass 44 kDa. The function of this protein (and of the similar proteins identified in several bacteria and yeast) is unknown, but the observation that the binding of oxygen to haem modulates the reduction level of FAD has suggested that Hmp could act as an oxygen sensor. Here, stopped-flow, rapid-scan spectroscopy has shown that the oxidized protein reacts rapidly with NADH to form an oxygenated species, even when efforts are made to reduce oxygen concentrations to sub-micromolar levels, suggesting a high affinity for this ligand. As is the case at high oxygen concentrations (130 microM), oxygenated species formation was kinetically and spectrally heterogeneous. Between 12 ms and 1 s after mixing, following transient formation of the deoxy form and its reaction with dioxygen, a steady-state level of the oxygenated species was attained. During the oxygenated steady state, the flavin remained largely oxidized, as observed previously at 130 microM oxygen. Hmp is an NADH oxidase; on exhaustion of oxygen by reduction (in < 10 s under these conditions), the oxygenated species disappeared to generate the deoxy Fe(II) haem, whereupon the flavin was reduced. The affinity for oxygen during NADH oxidation was measured by continuous dual-wavelength monitoring of the deoxygenation of oxymyoglobin. The Km for oxygen was 2.6 microM, much higher than the Km values determined, using the same method, for the membrane-bound terminal oxidases cytochromes bo' and bd. These results show that the oxidase activity of Hmp, but not necessarily oxygen binding, would be minimal at oxygen concentrations that limit terminal oxidase function.

Bacterial Proteins↗
PubMed2004

Oxygen distribution in murine tumors: characterization using oxygen-dependent quenching of phosphorescence.

In the present work, a novel method for detecting hypoxia in tumors, phosphorescence quenching, was used to evaluate tissue and tumor oxygenation. This technique is based on the concept that phosphorescence lifetime and intensity are inversely proportional to the oxygen concentration in the tissue sample. We used the phosphor Oxyphor G2 to evaluate the oxygen profiles in three murine tumor models: K1735 malignant melanoma, RENCA renal cell carcinoma, and Lewis lung carcinoma. Oxygen measurements were obtained both as histograms of oxygen distribution within the sample and as an average oxygen pressure within the tissue sampled; the latter allowing real-time oxygen monitoring. Each of the tumor types examined had a characteristic and consistent oxygen profile. K1735 tumors were all well oxygenated, with a peak oxygen pressure of 37.8 +/- 5.1 Torr; RENCA tumors had intermediate oxygen pressures, with a peak oxygen pressure of 24.8 +/- 17.9 Torr; and LLC tumors were all severely hypoxic, with a peak oxygen pressure of 1.8 +/- 1.1 Torr. These results correlated well with measurements of tumor cell oxygenation measured by nitroimidazole (EF5) binding and were consistent with assessments of tumor blood flow by contrast enhanced ultrasound and tumor histology. The results show that phosphorescence quenching is a reliable, reproducible, and noninvasive method capable of providing real-time determination of oxygen concentrations within tumors.

Animals↗
PubMed1999

[The study of oxygen-conserving nasal cannula and evaluation of it's oxygen saving ratio in treatment].

OBJECTIVE: To study the oxygen-conserving nasal cannula(CNC), and to evaluate it's oxygen saving benefit ratio in COPD patients. METHODS: (1) CNC was designed as a device which conserved oxygen during exhalation and given oxygen during inhalation; (2) Evaluation of the effect of oxygen therapy: blood analysis was measured at different flows of oxygen (0.5, 1.0, 1.5, 2.0 L/min) before and after oxygen therapy. The test is randomized; Oxygen saturation(SPO2) was measured at 1, 2, 3, 5, 10, 15, 30, 60, 120 minutes by pulse oximeter; (3) Evaluation of the oxygen saving benefit ratio: SPO2 was measured at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 L/min using CNC, the standard nasal cannula (SCN) and the new CNC. RESULTS: (1) During two hours of oxygen therapy, the values of PaO2 and SaO2 in the CNC group were always higher than those in the SNC group (P < 0.05); (2) When the supply flow to CNC was set at 0.5 L/min, 1.0 L/min, 1.5 L/min, 2.0 L/min seperately, the oxygen saving benefit ratio of CNC to SNC was 2.6:1, 1.8:1, 1.8:1 and 1.5:1 respectively. (3) The oxygen saving benefit ratio was comparable between CNC made in China and that made in foreign country. CONCLUSIONS: It was confirmed that CNC saved oxygen at different flows of oxygen, and the oxygen saving benefit ratio was higher at lower flows than that at higher flows.

Adult↗
PubMedDate not supplied

Greenhouse gases in non-oxygenated and artificially oxygenated eutrophied lakes during winter stratification.

Concentrations of dissolved methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were measured in the water columns of non-oxygenated and artificially oxygenated, ice-covered eutrophied lakes in the mid-boreal zone in Finland during late winter 1997 and 1999. Sampling was conducted during winter stratification, the critical period for oxygen (O2) deficiency in seasonally ice-covered, thermally stratified lakes. Oxygen concentrations were maintained at least at a moderate level throughout the oxygenated water columns, whereas the non-oxygenated columns suffered anoxic hypolimnia. The mean concentrations of dissolved CH4 exceeding the atmospheric equilibrium were greater in the non-oxygenated water columns (20.6-154 microM) than in the oxygenated ones (0.01-1.41 microM). In contrast, the mean excess CO2 concentrations varied less between the non-oxygenated and oxygenated sites (0.28-0.47 and 0.25-0.31 mM, respectively). Oxygenated water columns had greater mean excess concentrations of N2O (0.018-0.032 microM) than the non-oxygenated ones (0.005-0.024 microM). If the accumulated greenhouse gas stores in the water columns during winter are assumed to be released to the atmosphere during the spring overturn, the global warming potentials (GWP, time horizon 100 yr) of these potential emissions at the non-oxygenated, eutrophic study sites ranged from 177 to 654 g CO2 equivalent (CO2-e) m-2 compared with 144 to 173 g CO2-e m-2 at the oxygenated sites. The increase in the accumulation of CH4 was the main reason for the higher GWP of the non-oxygenated sites. Anthropogenic eutrophication of lake ecosystems can generate increased CH4 emissions due to associated O2 depletion of their sediment and water column.

Carbon Dioxide↗
PubMed1980

Diffusion coefficients of oxygen and hemoglobin as obtained simultaneously from photometric determination of the oxygenation of layers of hemoglobin solutions.

The oxygenation of layers of deoxygenated hemoglobin solutions after a sudden exposure to a gas containing oxygen at a partial pressure P1 has been studied by a photometric method. Layer thicknesses varied between 50 and 250 micron, hemoglobin concentrations between 0.1 and 0.34kg/l, and oxygen partial pressures between 4.65 and 93.1 kPa (35 and 700 mmHg). The diffusion chamber containing the layer of hemoglobin solution permitted a step change in gas atmosphere without changing the optical apparatus constant. The following results were obtained: 1. The oxygen saturation increase is independent of the layer thickness when expressed as a function of time divided by layer thickness squared (normalized oxygenation time). This justifies the assumption of chemical equilibrium between oxygen and hemoglobin in the range considered. 2. The oxygen saturation increases proportionally to the square root of time over a wide range of oxygenation as expected. This range reaches to almost 100% oxygenation at P1=93.1kPa (700mmHg) but less far as P1 is lower. Thus at high P1 values there is a sharp boundary between the oxygenated and deoxygenated part of the layer allowing the application of the advancing front concept. 3. Fitting the theoretical equations derived in a preceding paper to the experimental results provides simultaneous values of the oxygen permeability (or, knowing oxygen solubility, of the oxygen diffusion coefficient) and of the hemoglobin diffusion coefficient. These values agree fairly well with values obtained by other authors from experiments yielding the diffusion coefficients of oxygen or hemoglobin separately.

Diffusion↗
PubMed1991

Mixed venous oxygen saturation as a guide to tissue oxygenation and prognosis in patients with acute myocardial infarction.

The relation of mixed venous oxygen saturation and the cardiac index to tissue oxygenation and prognosis was investigated in 119 patients with acute myocardial infarction. There was a positive correlation between mixed venous oxygen saturation and the cardiac index in 97 survivors and 22 nonsurvivors, but a significantly lower mixed venous oxygen saturation level at the same level of cardiac index was observed in nonsurvivors compared with survivors. Results of multivariate analysis with mixed venous oxygen saturation and the cardiac index indicated that only mixed venous oxygen saturation was significantly related to survival and to hyperlactacidemia. Oxygen delivery to tissues declined significantly in nonsurvivors because of a lower cardiac index and a lower hemoglobin concentration in these patients than in survivors. However, at the same level of oxygen delivery to tissues, nonsurvivors had a significantly higher rate of oxygen consumption leading to a correspondingly greater decrease in mixed venous oxygen saturation, suggesting that a greater increase in oxygen demand was also observed in nonsurvivors than in survivors. Thus mixed venous oxygen saturation after acute myocardial infarction is a better predictor of hyperlactacidemia and survival than the cardiac index, and this may be associated with an increased oxygen demand and an impaired oxygen transport system in seriously ill patients.

Aged↗
PubMed2005

Mitochondrial hydrogen peroxide production alters oxygen consumption in an oxygen-concentration-dependent manner.

Metabolic responses of mammalian cells toward declining oxygen concentration are generally thought to occur when oxygen limits mitochondrial ATP production. However, at oxygen concentrations markedly above those limiting to mitochondria, several mammalian cell types display reduced rates of oxygen consumption without energy stress or compensatory increases in glycolytic ATP production. We used mammalian Jurkat T cells as a model system to identify mechanisms responsible for these changes in metabolic rate. Oxygen consumption was 31% greater at high oxygen (150-200 microM) compared to low oxygen (5-10 microM). Hydrogen peroxide was implicated in the response as catalase prevented the increase in oxygen consumption normally associated with high oxygen. Cell-derived hydrogen peroxide, predominately from the mitochondria, was elevated with high oxygen. Oxygen consumption related to intracellular calcium turnover was shown, through EDTA chelation and dantrolene antagonism of the ryanodine receptor, to account for 70% of the response. Oligomycin inhibition of oxygen consumption indicated that mitochondrial proton leak was also sensitive to changes in oxygen concentration. Our results point toward a mechanism in which changes in oxygen concentration influence the rate of hydrogen peroxide production by mitochondria, which, in turn, alters cellular ATP use associated with intracellular calcium turnover and energy wastage through mitochondrial proton leak.

Adenosine Triphosphate↗
PubMed1988

Protection of the neonatal heart following normothermic ischemia: a comparison of oxygenated saline and oxygenated versus nonoxygenated cardioplegia.

Optimal methods of myocardial preservation in the neonate remain unknown. Hypothermia and cardioplegia have been shown to protect neonatal hearts, but few studies have examined the effects of cardioplegia when administered at normothermia. Accordingly, the role of 37 degrees C St. Thomas' cardioplegic solution in protecting the neonatal heart during 1 hour of ischemia in an isolated working rabbit heart model was examined. Both oxygenated and nonoxygenated cardioplegic solutions (CSs) were evaluated and compared with an oxygenated physiological saline solution (PSS). Following ischemia, control hearts were characterized by severely impaired left ventricular function, whereas all three treatment groups recovered well, indicating that the treatments provided substantial protection. Aortic flow recovered to 62, 63, and 57% of preischemic values for the oxygenated CS, nonoxygenated CS, and oxygenated PSS groups, respectively. Similarly, rate of change of pressure recovered to 76, 80, and 76% of preischemic values for oxygenated CS, nonoxygenated CS, and oxygenated PSS groups. All values were significantly greater than those for the control group. Recovery of developed pressure was significantly improved in all three groups. End-diastolic pressure rose markedly following ischemia in control hearts, was not increased after ischemia in hearts receiving oxygenated and nonoxygenated CS, but was increased in the oxygenated PSS group. These data indicate that crystalloid cardioplegia and oxygenated PSS provide substantial protection in neonatal rabbit hearts, even when delivered at 37 degrees C. No additional benefit was seen when the cardioplegic solution was oxygenated. Therefore, either method of balancing the oxygen supply/demand ratio appears to be beneficial: supplying oxygen intermittently during ischemia (oxygenated PSS group) or decreasing oxygen demand during the ischemic period (cardioplegia groups).

Animals↗
PubMedDate not supplied

Numerical simulation of oxygen delivery to muscle tissue in the presence of hemoglobin-based oxygen carriers.

This work represents a culmination of research on oxygen transport to muscle tissue, which takes into account oxygen transport due to convection, diffusion, and the kinetics of simultaneous reactions between oxygen and hemoglobin and myoglobin. The effect of adding hemoglobin-based oxygen carriers (HBOCs) to the plasma layer of blood in a single capillary surrounded by muscle tissue based on the geometry of the Krogh tissue cylinder is examined for a range of HBOC oxygen affinity, HBOC concentration, capillary inlet oxygen tension (pO(2)), and hematocrit. The full capillary length of the hamster retractor muscle was modeled under resting (V(max) = 1.57 x 10(-4) mLO(2) mL(-1) s(-1), cell velocity (v(c)) = 0.015 cm/s) and working (V(max) = 1.57 x 10(-3) mLO(2) mL(-1) s(-1), v(c) = 0.075 cm/s) conditions. Two spacings between the red blood cell (RBC) and the capillary wall were examined, corresponding to a capillary with and without an endothelial surface layer. Simulations led to the following conclusions, which lend physiological insight into oxygen transport to muscle tissue in the presence of HBOCs: (1) The reaction kinetics between oxygen and myoglobin in the tissue region, oxygen and HBOCs in the plasma, and oxygen and RBCs in the capillary lumen should not be neglected. (2) Simulation results yielded new insight into possible mechanisms of oxygen transport in the presence of HBOCs. (3) HBOCs may act as a source or sink for oxygen in the capillary and may compete with RBCs for oxygen. (4) HBOCs return oxygen delivery to muscle tissue to normal for varying degrees of hypoxia (inlet capillary pO(2) < 30 mmHg) and anemia (hematocrit < 46%) for the hamster model.

Biological Transport↗
PubMedDate not supplied

Tissue engineering of articular cartilage under the influence of collagen I/III membranes and low oxygen tension.

The objective of this study was to study the matrix production and phenotype stability of articular chondrocytes cultured on collagen I/III membranes (CM) under the influence of low oxygen tension (Po(2)). Primary bovine and osteoarthritic human chondrocytes were cultured for 2 weeks under 5-21% Po(2) on CM, in alginate, or as monolayers. Dedifferentiated cells were produced by 2-week monolayer culture under 21% Po(2). Collagen (Coll) type II and I expression was demonstrated immunohistochemically, by Western blotting (Coll II), and by semiquantitative RT-PCR; proteoglycan synthesis was demonstrated histochemically (toluidine blue); and biosynthetic activity was indicated by radiolabel incorporation ([(3)H]proline and [(35)S]sulfate). Bovine chondrocytes on CM showed an increase in Coll II expression and proteoglycan synthesis under low Po(2) conditions, whereas Coll I decreased. This oxygen-dependent phenotype-stabilizing effect was even more pronounced in alginate cultures. Biosynthesis of bovine and human chondrocytes was also increased by low Po(2), except for proline incorporation, which decreased in bovine CM cultures (low-oxygen effects were significantly higher in alginate than in CM cultures). Dedifferentiated chondrocytes reexpressed Coll II protein when cultured under low Po(2) on CM or in alginate only, but not under high Po(2) or in monolayer culture. We conclude that CM and, even more, alginate foster phenotype stability and cartilage-specific matrix production of bovine chondrocytes, especially when cultured under in vivo-like oxygen conditions.

Animals↗
PubMed2006

Mild hypercapnia increases subcutaneous and colonic oxygen tension in patients given 80% inspired oxygen during abdominal surgery.

BACKGROUND: Supplemental perioperative oxygen increases tissue oxygen tension and decreases incidence of wound infection in colorectal surgery patients. Mild intraoperative hypercapnia also increases subcutaneous tissue oxygen tension. However, the effect of hypercapnia in patients already receiving supplemental oxygen is unknown, as is the effect of mild hypercapnia on intestinal oxygenation in humans-although the intestines are presumably the tissue of interest for colon surgeries. The authors tested the hypothesis that mild intraoperative hypercapnia increases both subcutaneous tissue and intramural intestinal oxygen tension in patients given supplemental oxygen. METHODS: Patients undergoing elective colon resection were randomly assigned to normocapnia (n = 15, end-tidal carbon dioxide tension 35 mmHg) or mild hypercapnia (n = 15, end-tidal carbon dioxide tension 50 mmHg). Intraoperative inspired oxygen concentration was 80%. The authors measured subcutaneous tissue oxygen tension in the right upper arm and intramural oxygen tension in the left colon. Measurements were averaged over time within each patient and, subsequently, among patients. Data were compared with chi-square, unpaired t, or Mann-Whitney rank sum tests; P < 0.05 was significant. RESULTS: Morphometric characteristics and other possible confounding factors were similar in the groups. Intraoperative tissue oxygen tension in hypercapnic patients was significantly greater in the arm (mean +/- SD: 116 +/- 29 mmHg vs. 84 +/- 25 mmHg; P = 0.006) and colon (median [interquartile range]: 107 [81-129] vs. 53 [41-104] mmHg; P = 0.020). CONCLUSIONS: During supplemental oxygen administration, mild intraoperative hypercapnia increased tissue oxygen tension in the arm and colon. Previous work suggests that improved tissue oxygenation will reduce infection risk via the proposed pathomechanism, although only an outcome study can confirm this.

Abdomen↗
PubMed2005

Pericellular oxygen depletion during ordinary tissue culturing, measured with oxygen microsensors.

Recent research has found important differences in oxygen tension in proximity to certain mammalian cells when grown in culture. Oxygen has a low diffusion rate through cell culture media, thus, as a result of normal respiration, a decrease in oxygen tension develops close to the cells. Therefore, for the purpose of standardization and optimization, it is important to monitor pericellular oxygen tension and cell oxygen consumption. Here, we describe an integrated oxygen microsensor and recording system that allows measurement of oxygen concentration profiles in vertical transects through a 1.6-mm deep, stagnant, medium layer covering a cell culture. The measurement set-up reveals that, when confluent, a conventional culture of adherent cells, although exposed to the constant oxygen tension of ambient air, may experience pericellular oxygen tensions below the level required to sustain full oxidative metabolism. Depletions reported are even more prominent and potentially aggravating when the cell culture is incubated at reduced oxygen tensions (down to around 4% oxygen). Our results demonstrate that, if the pericellular oxygen tension is not measured, it is impossible to relate in vitro culture results (for example, gene expression to the oxygen tension experienced by the cell), as this concentration may deviate very substantially from the oxygen concentration recorded in the gas phase.

Calibration↗
PubMed1993

Capillary oxygen transport during severe hypoxia: role of hemoglobin oxygen affinity.

The efficacy of an increased hemoglobin oxygen affinity [decreased oxygen half-saturation pressure of hemoglobin (P50)] on capillary oxygen transport was evaluated in the hamster retractor muscle under conditions of a severely limited oxygen supply resulting from the combined effects of a 40% reduction in systemic hematocrit and hypoxic ventilation (inspired oxygen fraction 0.1). Two groups of hamsters were utilized: one with a normal oxygen affinity (untreated; P50 = 26.1 +/- 2.4 Torr) and one with an increased oxygen affinity (treated; P50 = 15.7 +/- 1.4 Torr) induced by the chronic short-term administration of sodium cyanate. Using in vivo video microscopy and image analysis techniques, we determined oxygen saturation and associated hemodynamics at both ends of the capillary network. During hypoxic ventilation, the decrease in oxygen saturation across the network was 3.6% for untreated animals compared with 9.9% for treated animals. During hypoxia, estimated end-capillary PO2 was significantly higher in the untreated animals. These data indicate that, at the capillary level, a decreased P50 is advantageous for tissue oxygenation when oxygen supply is severely compromised, because normal oxygen losses in capillaries are maintained in treated but not in untreated animals. The data are consistent with the presence of a diffusion limitation for oxygen during severe hypoxia in animals with a normal hemoglobin oxygen affinity.

Animals↗
PubMed1986

Preliminary study of the effects of low flow oxygen on oxygen delivery and right ventricular function in chronic lung disease.

This study was designed to test the feasibility of using the noninvasive radionuclide measurement of the right ventricular ejection fraction (RVEF) to identify which patients with chronic lung disease objectively benefit from low flow oxygen therapy. Two categories of benefit, pulmonary artery pressure/resistance and peripheral oxygen delivery, were examined in 19 patients. Fourteen subjects returned after at least 3 wk of continuous low flow oxygen therapy for restudy; 12 patients had complete radionuclide and hemodynamic data. The change in RVEF, in response to continuous oxygen, correlated significantly with the change in coefficient of oxygen delivery (r = 0.59, p less than 0.05) and the change in cardiac output (r = 0.62, p less than 0.05). The change in RVEF did not correlate significantly with the change in pulmonary artery pressure (r = 0.06) or the change in total pulmonary resistance (r = -0.35). The change in coefficient of oxygen delivery, representing oxygen delivery corrected for oxygen consumption, correlated positively with change in cardiac output (r = 0.58, p less than 0.05) and negatively with change in oxygen consumption (r = -0.63, p less than 0.05), arterial oxygen content (r = -0.63, p less than 0.05), and arterial oxygen tension (r = -0.61, p less than 0.05). That is, the fall in hemoglobin in these patients more than compensated for any increase in Pao2 so that improved oxygen delivery frequently occurred despite a decrease in arterial oxygen content, and improved oxygen delivery occurred for the most part among patients with smaller improvement in Pao2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗