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O2 Gradient (o2 + gradient)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Quantification of myoglobin deoxygenation and intracellular partial pressure of O2 during muscle contraction during haemoglobin-free medium perfusion

EXPERIMENTAL PHYSIOLOGY, Issue 5 2010
Hisashi Takakura
Although the O2 gradient regulates O2 flux from the capillary into the myocyte to meet the energy demands of contracting muscle, intracellular O2 dynamics during muscle contraction remain unclear. Our hindlimb perfusion model allows the determination of intracellular myoglobin (Mb) saturation () and intracellular oxygen tension of myoglobin () in contracting muscle using near infrared spectroscopy (NIRS). The hindlimb of male Wistar rats was perfused from the abdominal aorta with a well-oxygenated haemoglobin-free Krebs,Henseleit buffer. The deoxygenated Mb (,[deoxy-Mb]) signal was monitored by NIRS. Based on the value of ,[deoxy-Mb],,,and,,were calculated, and the time course was evaluated by an exponential function model. Both,,and,,started to decrease immediately after the onset of contraction. The steady-state values of,,and,,progressively decreased with relative work intensity or muscle oxygen consumption. At the maximal twitch rate,,,and,,were 49% and 2.4 mmHg, respectively. Moreover, the rate of release of O2 from Mb at the onset of contraction increased with muscle oxygen consumption. These results suggest that at the onset of muscle contraction, Mb supplies O2 during the steep decline in,, which expands the O2 gradient to increase the O2 flux to meet the increased energy demands. [source]

Improved lung function after thoracocentesis in patients with paradoxical movement of a hemidiaphragm secondary to a large pleural effusion

RESPIROLOGY, Issue 5 2007
Lee-Min WANG
Background and objectives: Previous studies have shown little or no improvement in pulmonary function and arterial blood oxygenation after therapeutic thoracocentesis. This study investigated changes in pulmonary function, arterial blood gases and dyspnoea after therapeutic thoracocentesis in patients with paradoxical movement (PM) of a hemidiaphragm due to pleural effusion. Methods: Twenty-one patients with pleural effusion and PM of a hemidiaphragm and 41 patients with pleural effusion but without paradoxical movement (NPM) were studied before and 24 h after thoracocentesis. Lung function measurements included lung mechanics, blood gas exchange and the Borg dyspnoea scale. Results: At thoracocentesis a mean of 1220 mL of pleural fluid was removed from the PM group and 1110 mL from the NPM group. Post-thoracocentesis the PM group showed small but significant improvement (P < 0.05) in FEV1 (63% vs 73%), FVC (67% vs 77%), PaO2 (66 mm Hg vs 73 mm Hg), A-a O2 gradient (38 mm Hg vs 30 mm Hg), and the Borg scale (5.1 vs 2.1). The NPM group showed no significant change in any parameter. Conclusions: Statistically significant improvement in pulmonary function following thoracocentesis was observed in patients with pleural effusion and PM of the hemidiaphragm. Patient selection may therefore explain the different outcomes of thoracocentesis reported in previous studies. [source]

Fast dynamic response of the fermentative metabolism of Escherichia coli to aerobic and anaerobic glucose pulses,

BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2009
Alvaro R. Lara
Abstract The response of Escherichia coli cells to transient exposure (step increase) in substrate concentration and anaerobiosis leading to mixed-acid fermentation metabolism was studied in a two-compartment bioreactor system consisting of a stirred tank reactor (STR) connected to a mini-plug-flow reactor (PFR: BioScope, 3.5,mL volume). Such a system can mimic the situation often encountered in large-scale, fed-batch bioreactors. The STR represented the zones of a large-scale bioreactor that are far from the point of substrate addition and that can be considered as glucose limited, whereas the PFR simulated the region close to the point of substrate addition, where glucose concentration is much higher than in the rest of the bioreactor. In addition, oxygen-poor and glucose-rich regions can occur in large-scale bioreactors. The response of E. coli to these large-scale conditions was simulated by continuously pumping E. coli cells from a well stirred, glucose limited, aerated chemostat (D,=,0.1,h,1) into the mini-PFR. A glucose pulse was added at the entrance of the PFR. In the PFR, a total of 11 samples were taken in a time frame of 92,s. In one case aerobicity in the PFR was maintained in order to evaluate the effects of glucose overflow independently of oxygen limitation. Accumulation of acetate and formate was detected after E. coli cells had been exposed for only 2,s to the glucose-rich (aerobic) region in the PFR. In the other case, the glucose pulse was also combined with anaerobiosis in the PFR. Glucose overflow combined with anaerobiosis caused the accumulation of formate, acetate, lactate, ethanol, and succinate, which were also detected as soon as 2,s after of exposure of E. coli cells to the glucose and O2 gradients. This approach (STR-mini-PFR) is useful for a better understanding of the fast dynamic phenomena occurring in large-scale bioreactors and for the design of modified strains with an improved behavior under large-scale conditions. Biotechnol. Bioeng. 2009; 104: 1153,1161. © 2009 Wiley Periodicals, Inc. [source]

Perfluorocarbon facilitated O2 transport in a hepatic hollow fiber bioreactor

BIOTECHNOLOGY PROGRESS, Issue 5 2009
Guo Chen
Abstract A mathematical model describing O2 transport in a hepatic hollow fiber (HF) bioreactor supplemented with perfluorocarbons (PFCs) in the circulating cell culture media was developed to explore the potential of PFCs in properly oxygenating a bioartificial liver assist device (BLAD). The 2-dimensional model is based on the geometry of a commercial HF bioreactor operated under steady-state conditions. The O2 transport model considers fluid motion of a homogeneous mixture of cell culture media and PFCs, and mass transport of dissolved O2 in a single HF. Each HF consists of three distinct regions: (1) the lumen (conducts the homogeneous mixture of cell culture media and PFCs), (2) the membrane (physically separates the lumen from the extracapillary space (ECS), and (3) the ECS (hepatic cells reside in this compartment). In a single HF, dissolved O2 is predominantly transported in the lumen via convection in the axial direction and via diffusion in the radial direction through the membrane and ECS. The resulting transport equations are solved using the finite element method. The calculated O2 transfer flux showed that supplementation of the cell culture media with PFCs can significantly enhance O2 transport to the ECS of the HF when compared with a control with no PFC supplementation. Moreover, the O2 distribution and subsequent analysis of ECS zonation demonstrate that limited in vivo-like O2 gradients can be recapitulated with proper selection of the operational settings of the HF bioreactor. Taken together, this model can also be used to optimize the operating conditions for future BLAD development that aim to fully recapitulate the liver's varied functions. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]