Oxygen Partial Pressure Distribution Research Articles

Determining the Wafer Temperature in Atmospheric Thermal Silicon Oxidation Reactors

It has been shown that, in ultrathin gate oxidation processes, temperature ramp‐up in atmospheric thermal silicon oxidation reactors subjects the wafers to severe temperature nonuniformities. The extent of this nonuniformity has been determined via a method based on the principle that for a given type of silicon substrate, in the absence of nonuniform oxygen partial pressure distributions, the oxidation rate of silicon depends only on substrate temperature. By experimentally determining within‐wafer and wafer‐to‐wafer growth rate variabilities, and by using an growth rate computer simulation model, substrate temperature has been determined.

Relationship between radiobiological hypoxia in tumors and electrode measurements of tumor oxygenation

Purpose : To determine whether electrode measurements of tumor oxygenation, made in a variety of murine tumor models, correlate with estimates of radiobiological hypoxia in the same tumor systems. Methods and Materials : The tumor models used were a C3H mammary carcinoma grown in the feet of CDF1 mice; the SCCVII, KHT and RIF-1 tumors grown in the feet or flanks of C3H/Km mice; and the CaNT and SaF tumors grown on the backs of CBA mice. All treatments were performed when tumors were about 200 mm 3 in size. Radiobiological hypoxic fractions were determined using either a paired survival curve assay, with survival measured 0–24 h after irradiation, or using a clamped tumor control assay, with percent local tumor control estimated 90 days after treatment. Measurements of tumor oxygen partial pressure (pO2) distributions were performed using Eppendorf oxygen electrodes. Results : The hypoxic fractions determined from the radiation response data were about 1% in RIF-1 and SCCVII, 12% in C3H and KHT, 28% in CaNT and up to 38% in SaF tumors. When this data was compared with the tumor oxygenation measurements it was found that as hypoxic fraction increased the mean, median, and the percentage of pO 2 values ≤ 5 mmHg showed a trend towards poorer oxygenation status. However, none of these pO 2 changes were significantly correlated with hypoxia. Moreover, the pO 2 values ≤ 2.5 mmHg indicated an improvement in oxygen status with increasing hypoxic fraction. Conclusion : Electrode measurements of tumor oxygenation alone may, therefore, not be a good indicator of tumor hypoxia across different tumor cell lines.

Formulation and realization of a multicompartmental model for O2-CO2 coupled transport in the microcirculation.

A multicompartmental model for gas transport in the microcirculation (M.C.M) is a lumped form of the corresponding distributed models. This idea can be understood by the sketch shown in Fig.l. The microcirculation consists of a series of arteriole beds, capillary beds, venule beds and the surrounding tissue, with an oxygen partial pressure distribution and a carbon dioxide partial pressure distribution in both the radial and longitudinal directions. Distributed models, based on either the modified Krogh cylinder or a nonKroghian geometry, usually simulate the radial and axial distributions in one vessel segment or within a local region of the microcirculation. If every vessel group is lumped into a compartment with a unique oxygen partial pressure and a unique carbon dioxide partial pressure, and the tissue is also lumped into one compartment (or more compartments, cf. Ye and Silverton, 1994), then a multicompartmental model is constructed. The model’s block diagram in Fig.1 shows that axial convection of both blood flow and gas occurs along the sequential vessel compartments, and that simultaneous gas diffusions take place between the tissue compartment and every vessel compartment. Thus the global relationship of gas transport and blood supply is quite clear for a M.C.M. It is also easier for a M.C.M to be linked to a global multielement-lumped model for the whole cardiovascular system. Moreover, a compartmental model is described by algebraic equations (for steady-state) or by ordinary differential equations (for time-varying state), whereas a distributed model is described by ordinary differential equations (for one-dimension distributed, steady state) or by partial differential equations (otherwise).

Soil Water Relations and Aeration Status of Single Soil Aggregates, Taken from a Gleyic Vertisol

AbstractClayey soils have the potential to swell and to shrink depending on their hydraulic and hydrological status. Thus bulk density values vary in a range of 1.0 to 2.0 g cm−3 in the case of a gleyic Vertisol, by which also other soil physical properties e.g. the pore size distribution of the bulk soil as well as of the soil aggregates are affected. Intraaggregate airfilled porosities are reduced by shrinkage and are relatively low. Thus it appeared to be difficult to determine the airfilled porosity of the aggregates below pF 1.5. For that reason and because of the influence of pore forms we were not able to get a clear relation of diffusion constant K with airfilled porosity.Regarding soil aeration status, the existence of anoxic microsites in the interior of unsaturated soil aggregates has been proved by microelectrode measurements of oxygen partial pressure and redox potential distribution in single soil aggregates. We verified restrained oxygen supply to the aggregate center as well as reduced redox potentials only for aggregates of the A horizon. There the microbial activity, measured as soil respiration as well as the source for C and N was by a factor 2 to 4 higher than in the subsurface horizons.

Tissue alterations by the penetration of a pO2 sensing needle probe.

Oxygen partial pressure measurements in living tissue with needle probes inevitably lead to tissue alterations. The recent introduction of microprobe based pO2 measuring methods for clinical applications (Weiss and Fleckenstein, 1986) has invigorated research addressing the influence of anaesthetic gases on liver oxygen partial pressure distribution. Thus far, histological changes due to the penetration of this pO2 probe have been studied in skeletal muscle by Schramm et al. (1990).KeywordsMethylene BlueCresyl VioletPyknotic NucleusTissue AlterationLiver SinusoidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Peripheral oxygen availability within skeletal muscle in sepsis and septic shock: Comparison to limited infection and cardiogenic shock

In 40 intensive care patients, tissue oxygen partial pressure distribution within skeletal muscle was measured in order to estimate peripheral oxygen availability. In septic patients with multiple organ failure (n = 20) mean skeletal muscle pO2 was abnormally high (48.8 +/- 8.5 mmHg, p less than 0.001) in contrast to patients with limited infection without sepsis (28.3 +/- 5.9 mmHg, n = 10). Mean muscle pO2 also discriminated between septic and cardiogenic shock (22.6 +/- 6.9 mmHg, p less than 0.001). The characteristic pattern of oxygen availability in septic patients--but not in patients with limited infection--was high skeletal muscle pO2 high whole body oxygen delivery and low whole body oxygen extraction, which was not influenced by the type of pathogenic agent of sepsis. In our patients in severe stage of sepsis, we did not observe local skeletal muscle hypoxia due to microcirculatory disorder. High mean skeletal muscle pO2 suggested reduced oxygen consumption within tissue rather than reduced oxygen transport to tissue in sepsis.

Nonideal Flow Behavior Analysis of Atmospheric Thermal Silicon Oxidation Reactors by the Residence Time Distribution Technique

Flow nonidealities in high‐throughput, atmospheric, thermal silicon oxidation reactors have been investigated by the residence time distribution technique using mass spectrometric residual gas analysis. The resulting cumulative age distribution has been used to determine the effect of baffle configuration, gas flow rate, and injector nozzle design on the local mean residence time and local mean internal age of gas molecules within the reactor. The residence time distribution technique, which has traditionally been employed at the exit stream of flow systems, has been extended in this study to investigate nonideal flow behavior in radial as well as longitudinal locations within the reactor. Uniform gas distribution has been observed in the radial direction of the reactor. The use of coaxial injector nozzles has been shown to be unsuitable for performing ultra‐thin dry oxidation processes due to the formation of sluggish‐flow regions throughout the system. Non‐homogeneities in the oxygen partial pressure distribution across the wafer load have been partially eliminated by reducing the magnitude of the local mean residence time as well as its variability in the longitudinal direction of the reactor. This has been achieved by increasing the gas flow rate and by incorporating the maximum number of baffles at both ends of the wafer load. Having determined that both continuously stirred tank reactors (CSTR) and plug flow reactors can result in ideal silicon dioxide uniformities, the one‐parameter CSTRs‐in‐Series reactor model has been used to characterize the nature of fluid flow under various operating conditions. Except for the entrance region of the reactor, no correlation has been observed between the number of CSTRs‐in‐Series and gas flow rate. The results have indicated the attainment of CSTR conditions throughout the entire wafer load to be virtually impossible. However, it has been shown that incorporating the maximum number of baffles at both ends of the wafer load significantly promotes plug flow characteristics and can be used to reduce the nonideal flow behavior of atmospheric thermal silicon oxidation systems.

Tumors growing in irradiated tissue: Oxygenation, metabolic state, and pH

Experimental tumors growing in irradiated tissue have been used to study the biological differences characteristic of locally recurrent tumors. Animal tumors were early generation isotransplants of a spontaneous fibrosarcoma in a C3Hf/Sed mouse, designated FSa-II. Since the hypoxic cell fraction of tumors growing in irradiated tissue is increased, these tumors are assumed to be metabolically deprived with hypoperfusion and acidosis. In this study we directly measured the oxygen partial pressure (pO 2) distribution, metabolic state, and pH of tumors growing in an irradiated tumor bed using oxygen sensitive electrodes and 31P-NMR. The results confirmed a three-fold increase in the number of pO 2 readings ≤ 2.5 mmHg and also showed increased acidosis with a 0.17 unit decrease in pH NMR. When tumors growing in pre-irradiated tissue reached ≈100 mm 3 in volume, a high frequency of gross and microscopic necrosis and hemorrhage was already observed. Consistent with these observations, the phosphocreatine/inorganic phosphate (PCr/P i) and nucleoside triphosphate/inorganic phosphate (NTP/P i) ratios were significantly lower in the tumors in a pre-irradiated bed compared to tumors in a non-irradiated bed (PCr/P i: 0.51 vs 0.79, p < 0.05; and NTP/P i,: 0.64 vs 0.93, p < 0.05). The longitudinal relaxation time (T 1) of P i was numerically shorter in control tumors (consistent with the better tissue oxygenation), but this did not reach statistical significance (2.09 ± .11 sec vs 2.25 ± .16 sec).

A dynamic method to determine the O2‐partial pressure distribution within soil aggregates

AbstractDuring amperometric measurements of oxygen concentration an electrode itself consumes oxygen. To make sure that oxygen concentration at a soil microsite is not lowered by the measurement itself, but determines the in situ situation, the sensitive tip of the electrode should not be in a static position for a longer time than is necessary to reach equilibrium. If the electrode is moved stepwise through the soil aggregate and is allowed to reach equilibrium at every position, it is possible to measure profiles of oxygen partial pressure distribution from the surface to the center of single soil aggregates. We used a small electromotor attached to a micromanipulator to push the pO2‐sensitive microelectrode at a constant speed through the soil aggregate. As an advantage this ‘dynamic’ method needs no man power and gives continuous profiles of oxygen concentration from the surface to the center of the aggregate.

Theoretical evaluation of expected changes in oxygenation of tumors associated with different hemoglobin levels

A mathematical computer-based model was developed which analyzes the influence of hemoglobin concentration; shape of oxygen dissociation curve; red cell velocity; capillary network geometry; and oxygen consumption on the oxygen partial pressure (PO2) distribution in tissue. In this study, the influence of acute hemoglobin concentration changes on the oxygen supply to tissue was analyzed. The specific question, whether moderate changes in the hemoglobin concentration of only 20% (e.g., from 15 g/dl to 12 g/dl i.e. baseline is 15 g/dl), as they may often occur clinically, are able to produce a significant change in the tissue oxygenation, was addressed. This is of importance for the estimation of the possible effects of blood transfusions prior to radiation therapy. The model predicts that even a moderate 20% increase in the hemoglobin concentration is able to decrease the anoxic tissue volume by 30%. The results indicate that hemoglobin levels should not be subnormal at the beginning of chemotherapy or radiotherapy. Transfusions or the application of artificial oxygen carriers could be helpful.

Distribution of oxygen partial pressure in the carotid body region and in the carotid body (rabbit).

In the specific tissue of the rabbit carotid body as well as in the connective tissue surrounding the organ, pO2 distribution was measured with membrane-covered needle electrodes (tip diameter 1-2 microns). The histograms resulting from measurements in the specific tissue were shifted to low pO2 values as compared to other tissues. The oxygen blowing test, i.e. exposure of the carotid body to humidified 100% oxygen was employed to decide upon the site of measurement: pO2 increased when the electrode measured in the surrounding tissue (type 1 response); pO2 remained stable or slightly decreased when the electrode sampled in the specific carotid body tissue (type 2 response). After the experiment, the electrode track was reconstructed from histological serial sections and the type of reaction was related to the type of tissue. Low pO2 values were found to prevail in the specific carotid body tissue, which leads to the conclusion that the amount of low pO2 values determines the degree of chemoreceptor activity.

Application of the relaxation method for the calculation of the distribution of oxygen partial pressure in two-dimensional tissue models

The differential equations and respective difference equations arrived at in a previous article, which describe the course of oxygen partial pressure in capillaries and tissues, are solved by the application of the method of “successive overrelaxation.” Calculations prove that for a fortyfold subdivision of one square of the capillary network and a subdivision of the concurrent and countercurrent systems into 10 × 200 nodes, a relaxation parameter of about 1.85 was favorable. The accuracy of the results obtained by the method of successive overrelaxation is in the region of 2%−3% of the arterial concentration value.

Distribution of oxygen partial pressure in a two-dimensional tissue supplied by capillary meshes and concurrent and countercurrent systems

For the calculations of oxygen partial pressure in a two-dimensional tissue model supplied by a capillary network (inhomogeneously perfused tissue), two differential equations are given that describe the process in the tissue and capillaries. The differential equations are coupled by the boundary conditions. Results obtained by using the method of successive displacements are given for the two-dimensional problem. This method exhibits a satisfactory convergence. The accuracy of the results is about ±5% based on the initial concentration. The results for the network model are compared with those for equivalent concurrent and countercurrent systems. Equivalence means in this connection that the area of tissue, the total length of capillaries, and the constants characterizing blood and tissue are the same. Our results for the two-dimensional models permit us to conclude that the differences between the lowest partial pressure in the tissue and the venous partial pressure are smallest in the countercurrent system and largest in the capillary network.

Local effects of O2 and CO2 on limb, renal, and coronary vascular resistances.

Local effects of O2 and CO2 on limb, renal, and coronary vascular resistances.