Limiting behaviour during the hydroperoxide ion generation in a flow alkaline fuel cell

A comparative study of an O₂-diffusion cathode and a H₂-diffusion anode has been performed to ascertain the limiting processes, when they are combined in a flow alkaline fuel cell with hydroperoxide ion generation. The linear sweep voltammograms and the impedance diagrams of both electrodes show large differences. The cathode reaction is charge transfer-controlled up to current densities of at least 1 A cm^?2, whereas the dissociative adsorption, charge transfer and diffusion of H₂ appear to limit the anode reaction. The anode, with limiting current densities of about 90 and 150 mA cm^?2 for 1.0 and 6.0 M KOH, respectively, then clearly controls the hydroperoxide ion production in the fuel cell. Diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy reveal that, the carbon of the H₂-diffusion anode does not undergo significant oxygen functionalisation during hydroperoxide ion generation in the fuel cell.     

Axonal damage in the spinal cord of multiple sclerosis patients detected by magnetic resonance spectroscopy.

Axonal damage is a major factor contributing to permanent disability in patients with multiple sclerosis (MS); it has been extensively investigated in the brain using magnetic resonance spectroscopy (MRS). In this study, MRS was used to investigate the degree of neuronal damage in the cervical spinal cord in MS. Spectra were acquired from spinal cord and brain in 11 patients with MS (expanded disability status score [EDSS], range 2.5-7.0) and 11 controls. Brain lesion volume and spinal cord cross-sectional area were measured. Concentration of the neuronal metabolite N-acetyl-aspartate ([NAA]) was reduced in the spinal cord in MS patients relative to controls (reduced by 32%, P < 0.05), indicating significant neuronal damage. Additionally, the spinal cord was significantly atrophied in MS patients (15%, P < 0.001). No significant reduction in brain [NAA] was seen in the MS group. There were no correlations between clinical measures and cord atrophy or brain lesion volume on MRI; however, spinal cord [NAA] correlated with the cerebellar subscore of the neurological assessment (P < 0.005), while brain [NAA] correlated with disease duration (P < 0.05). MRS demonstrated cellular damage within the cord over and above the tissue atrophy seen by MRI. Combining MRI and MRS may therefore give a more complete picture of neurodegeneration in the spinal cord.     

MR imaging of viscoelastic properties

Mechanical waves in magnetic resonance imaging, which have been suggested for possible clinical applications, were analyzed with regard to imaging of the viscoelastic properties of large objects. The method is based on the Larmor frequency modulation caused by the application of mechanical waves. Possible clinical applications include all diseases that result in a change in the mechanical properties of biologic tissues (eg, atherosclerosis).     

Effects of exercise on muscle activation and metabolism in multiple sclerosis

We investigated the role of metabolism in muscle fatigue during voluntary exercise in persons with mild multiple sclerosis (MS). Six MS and 8 healthy control subjects performed intermittent, progressive, isometric contractions of the ankle dorsiflexors, during which we measured maximum voluntary force (MVC), inorganic phosphate (Pi), phosphocreatine (PCr), and pH. During exercise. MVC fell sooner in MS, but by the end of exercise the relative decrease in MVC was similar in both groups. In contrast, at the end of exercise Pi/PCr increased to 1.86 ± 0.22 in controls but to only 0.66 ± 0.04 in MS (P < 0.01); likewise, pH was 6.75±0.04 in controls and unchanged (7.06 ± 0.04) in MS (P <0.01). The smaller metabolic change at the same relative exercise intensity suggests a failure of muscle activation that is present even in mild MS. Neurophsyiologic measures of activation indicated some central activation failure and no neuromuscular junction impairment in MS, and suggested that activation failure beyond the muscle membrane(excitation–contraction coupling) may be important in MS. We conclude that metabolic factors do not play a significant role in the development of muscle fatigue during voluntary exercise in mild MS. © 1994 John Wiley & Sons, Inc.     

P-31 MR spectroscopy of skeletal and cardiac muscle metabolism in patients with systemic sclerosis: A multiple case study

Three-dimensionally localized proton-decoupled phosphorus-31 magnetic resonance (MR) spectroscopy of skeletal and cardiac muscle was performed in six patients with systemic sclerosis. Cardiac (n = 9) and skeletal (n = 6) spectra were also obtained in healthy volunteers. Metabolite ratios and intracellular pH were determined from the spectra of skeletal and cardiac muscle. The phosphocreatine-to-adenosine triphosphate ratio was normal for both skeletal and cardiac muscle in patients with systemic sclerosis. The pH values of skeletal muscle were similar in patients and control subjects (7.13 ± 0.02 vs 7.12 ± 0.01, respectively). In skeletal muscle, the inorganic phosphate-to-phosphocreatine ratio in patients was increased relative to that of control subjects (0.106 ± 0.014 vs 0.086 ± 0.006, respectively; P =.02). P-31 MR spectroscopy showed no abnormalities in the myocardium of patients with systemic sclerosis. Assessment of the inorganic phosphate-to-phosphocreatine ratio in peripheral skeletal muscle may be helpful for assessing disease activity.     

Applications of magnetic resonance spectroscopy to diagnosis and monitoring of mitochondrial disease

Magnetic resonance spectroscopy (MRS) can now be performed on routine high-field clinical magnetic resonance imaging systems. Over the last decade it has provided several useful insights into the pathophysiology of mitochondrial disorders. More recently, the feasibility of applications to clinical diagnosis and monitoring have been demonstrated. Exciting new work suggests that carefully supervised physical conditioning in conjunction with sodium dichloroacetate administration can markedly enhance both biochemical measures of aerobic metabolism and functional performance of patients with mitochondrial myopathies.

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Sommario La risonanza magnetica spettroscopica (MRS) può oggi essere effettuata di routine in apparecchi clinici di risonanza magnetica. Nell'ultima decade essa ha fornito importanti informazioni nella patofisiologia dei disordini mitocondriali. Più recentemente sono state dimostrate le sue possibilità di applicazione nella diagnosi clinica e nel monitoraggio di pazienti neurologici. Nuovi ed interessanti studi suggeriscono che un allenamento attentamente supervisionato in congiunzione con trattamento con dicloroacetato è capace di migliorare i parametri biochimici e la performance di pazienti con miopatie mitocondriali.

     

Metabolite changes with age measured by proton magnetic resonance spectroscopy in normal subjects

Abstract  To determine whether there are metabolite changes in the left medial temporal and frontal lobes with aging, we performed proton magnetic resonance spectroscopy in 36 normal subjects. The N-acetylaspartate/creatine-phosphocreatine ratio in the medial temporal lobe tended to be decreased in subjects over 60 years of age. The ratio decrease in the frontal lobe related to aging was lower than that in the medial temporal lobe. There were no significant differences in the metabolite ratios between males and females. These findings suggest that structures in the medial temporal lobe may be more susceptible to neuronal dysfunction associated with aging than those in the frontal lobe.     

不同状态胆囊组织的傅立叶变换红外光谱研究

目的 探索不同生理病理状态的胆囊组织各自特异的傅立叶变换红外光谱(Fourier transform infrared spectroscopy，FT-IR)表现。方法 应用FT-IR对8例正常胆囊组织、10例炎性胆囊组织和10例胆囊癌组织进行检测，结合常规病理结果总结不同组织的光谱特征。结果 胆囊正常、炎性和癌组织具有不同的FT-IR光谱表现，1550cm^-1处的酰胺Ⅱ带在癌组织中显得较弱，峰形低平，而在正常组织中则较强，峰形高尖。1080cm^-1处核酸的吸收谱带在癌组织中较强，I1080／I1550的比值在正常组织中为0．62，癌组织中为0．87。正常组织中1450cm^-1处的峰多强于1400cm^-1处，而在癌组织中则相反。结论 胆囊正常、炎性和癌组织的FT-UR谱图不同，主要表现为组织中蛋白质、核酸和磷脂等含量与结构的改变，FT-IR有望成为胆道疾病临床诊断的一种新手段。     

Cardiac metabolism: A technical spectrum of modalities including positron emission tomography,single-photon emission computed tomography,and magnetic resonance spectroscopy

Noninvasive techniques for the assessment of cardiac metabolism are important for the detection of potentially salvageable tissue in jeopardized areas of the myocardium. The correct identification of hibernating and stunned myocardium in patients with severely depressed cardiac function can have vital therapeutic consequences for the patient. Changes in myocardial fatty acid and glucose metabolism during acute and prolonged ischemia can be traced by positron-emitting or gamma-emitting radiopharmaceuticals. Alternatively,³¹P-labeled magnetic resonance spectroscopy can be used for the assessment of high-energy phosphate metabolism. It is not yet clear which modality will emerge as the most useful in the clinical setting. Positron emission tomography (PET) that uses combinations of flow tracers and metabolic tracers offers unique opportunities for quantification and high-resolution static and rapid dynamic studies. Currently, assessment of glucose metabolism with¹⁸F-fluorodeoxyglucose is regarded as the gold standard for myocardial viability and prediction of improvement of impaired contractile function after revascularization. However, preserved oxidative metabolism may be required for potential functional improvement, and therefore assessment of residual oxidative metabolism by¹¹C-labeled acetate PET may prove to be more accurate than¹⁸F-fluorodeoxyglucose PET, which reflects both anaerobic and oxidative metabolism. Moreover, because fatty acids are metabolized only aerobically, they are excellent candidates for the clinical assessment of myocardial viability and prediction of functional improvement after revascularization. Especially derivatives of fatty acids that are not metabolized but accumulate in the myocyte are attractive for myocardial imaging. Examples are¹²³I-beta-methyl-p-iodophenyl pentadecanoic acid and 15-(o-¹²³I-phenyl)-pentadecanoic acid. These tracers can be detected by planar scintigraphy and single-photon emission computed tomography, which are more economical and widely available than PET. In addition, 511 keV collimators have been developed recently, making the detection of positron emitters by planar scintigraphy and single-photon emission computed tomography feasible. The experience with³¹P-labeled magnetic resonance spectroscopy in humans is still limited. With current magnetic resonance spectroscopic techniques, insufficient spatial resolution is achieved for clinical purposes, but the possibility of serial measurements to monitor rapid changes of phosphate-containing molecules in time makes magnetic resonance spectroscopy very valuable for the research of myocardial metabolism.