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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phasic and tonic motor neurons of crustaceans differ strikingly in their junctional synaptic physiology. Tonic neurons generally produce small excitatory postsynaptic potentials (EPSPs) that facilitate strongly as stimulation frequency is increased, and normally show no synaptic depression. In contrast, phasic neurons produce relatively large EPSPs with weak frequency facilitation and pronounced depression. We addressed the hypothesis that mitochondrial function is an important determinant of the features of synaptic transmission in these neurons. Mitochondrial fluorescence was measured with confocal microscopy in phasic and tonic axons and terminals of abdominal and leg muscles after exposure to supravital mitochondrial fluorochromes, rhodamine-123 (Rh123) and 4-diethylaminostyryl-N-methylpyridinium iodide (4-Di-2-Asp). Mitochondria of tonic axons and neuromuscular junctions had significantly higher mean Rh123 and 4-Di-2-Asp fluorescence than in phasic neurons, indicating more accumulation of the fluorochromes. Mitochondrial membrane potential, which is responsible for Rh123 uptake and is related to mitochondrial oxidative activity (the production of ATP by oxidation of metabolic substrates), is likely higher in tonic axons. Electron microscopy showed that tonic axons contain approximately fivefold more mitochondria per microm2 cross-sectional area than phasic axons. Neuromuscular junctions of tonic axons also have a much higher mitochondrial content than those of phasic axons. We tested the hypothesis that synaptic fatigue resistance is dependent on mitochondrial function in crayfish motor axons. Impairment of mitochondrial function by uncouplers of oxidative phosphorylation, dinitrophenol or carbonyl cyanide m-chlorophenylhydrazone, or by the electron transport inhibitor sodium azide, led to marked synaptic depression of a tonic axon and accelerated depression of a phasic axon during maintained stimulation. Iodoacetate, an inhibitor of glycolysis, and chloramphenicol, a mitochondrial protein synthesis inhibitor, had no significant effects on either mitochondrial fluorescence or synaptic depression in tonic or phasic axons. Collectively, the results provide evidence that mitochondrial oxidative metabolism is important for sustaining synaptic transmission during maintained stimulation of tonic and phasic motor neurons. Tonic neurons have a higher mitochondrial content and greater oxidative activity; these features are correlated with their greater resistance to synaptic depression. Conversely, phasic neurons have a lower mitochondrial content, less oxidative activity, and greater synaptic fatigability.
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PMID:Synaptic physiology and mitochondrial function in crayfish tonic and phasic motor neurons. 924 80

Postpartum thyroiditis (PPT) occurs in 5%-9% of unselected postpartum women; hyperthyroidism and hypothyroidism develop, the latter being permanent, in up to 25 %-30% of women. PPT is strongly associated with antithyroid peroxidase (anti-TPO) antibodies, but 50% of anti-TPO positive women do not develop thyroid dysfunction. Symptom analysis has shown that lack of energy and irritability were the most frequent hyperthyroid symptoms whereas lack of energy, aches and pains, poor memory, dry skin, and cold intolerance were the significant hypothyroid features. Some of these symptoms were more frequently observed than in antibody-negative controls even when these patients were euthyroid and in anti-TPOAb positive women who did not develop PPT at all. The diagnosis of PPT is based on the observation of abnormal thyroid function tests in a postpartum anti-TPOAb-positive woman: transient hyperthyroidism occurs at 14 weeks and hypothyroidism at 19 weeks postpartum. Diffuse or multifocal hypoechogenicity of the thyroid is seen on echography and a thyroid destructive process is evidenced by an increase in serum thyroglobulin and urinary iodine excretion. In addition to the 25%-30% of women who develop permanent hypothyroidism at 3 years, recent data indicate that 50% of women who have developed PPT will be hypothyroid 7-9 years later. The long-term risk is only 5% for those anti-TPOAb positive women not developing thyroid dysfunction postpartum. The risk of recurrent PPT is 70% if previous PPT was experienced and 25% if the patient was euthyroid after the first pregnancy.
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PMID:Clinical manifestations of postpartum thyroid disease. 1044 15

Sterilization can influence the mechanical properties of elastic ligatures used for mandibulomaxillary immobilization. The aim of this study was to compare different sterilization protocols (ethylene oxide, autoclave, irradiation, plasma sterilization, povidone-iodine for 24 hours and 70% isopropyl alcohol for 24 hours) of three elastomers (natural rubber, silicone rubber, and polyurethane). Three mechanical variables were assessed in a testing machine: breaking strength, tensile strength and tensile strength after a 24-hour load (material fatigue). Natural rubber was most susceptible to mechanical alteration by sterilization and lost 46% of its breaking strength and 43% of its tensile strength after autoclaving. Polyurethane was more resistant (multiple comparison, Tukey-Kramer), but polyurethane ligatures stuck together after autoclaving. The protocols for low-temperature sterilization, ethylene oxide, irradiation, and plasma were superior to autoclaving and the disinfecting solutions. These data suggest that polyurethane sterilized with ethylene oxide is the material of choice.
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PMID:Sterilization of elastic ligatures for intraoperative mandibulomaxillary immobilization. 1092 55

The effect that three different radiopacifying agents, two of them inorganic (BaSO4, ZrO2) and one organic (an iodine containing monomer, IHQM) have on the static and dynamic mechanical properties of acrylic bone cements was studied. Compressive and tensile strength, fracture toughness and fatigue crack propagation were evaluated. The effect of the inorganic fillers depends on their size and morphology. In relation to the radiolucent cement, the addition of zirconium dioxide improved significantly the tensile strength, the fracture toughness and the fatigue crack propagation resistance. In contrast, the addition of barium sulphate produced a decrease of the tensile strength, but did not affect the fracture toughness and improved the crack propagation resistance. When the iodine containing monomer was used, although the tensile strength and the fracture toughness increased, the fatigue crack propagation resistance remained as low as it was for the radiolucent cement.
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PMID:Mechanical performance of acrylic bone cements containing different radiopacifying agents. 1195 58

Reactions to oral contraceptive therapy tend to be maximal during the first few months of use. They include nausea or epigastric discomfort, malaise, dizziness, nervousness, fatigue, weakness, leg cramps, headache, and depression. The estrogenic component is thought to be the cause. There may also be a psychogenic basis reflecting apprehension. Breast tenderness is an occasional complaint and intermenstrual spotting or breakthrough bleeding is often reported. Increasing dosage has reduced this symptom. Dysmenorrhea prior to treatment may be improved but occasionally it is aggravated. Drug-induced amenorrhea presents a double problem in that failure to resume medication 7 days after completion of a cycle results in a risk of conception. Episodes of severe uterine bleeding in patients discontinuing use after several months or years have been reported. Other side effects include a skin reaction resembling acne, pruritus, hirsutism, thinning of scalp hair, increased skin pigmentation, and weight gain or loss. Serious vascular complications and hepatic dysfunction have been shown and deviation of thyroid function may be shown by increase of serum protein-bound iodine (PBI). Clinical signs of hyperthyroidism have not been described. Oral contraception is associated with elevated plasma cortisol (hydrocortisone) levels and decreased urinary levels of 17-hydroxycorticosteroids (17-OCHS). Suppression of ovarian activity by oral contraceptives is rapidly reversible. Fear of carcinogenesis has caused much alarm but no proof as of the present time. Safety of long term use will require additional years of experience.
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PMID:Side-effects and possible complications of oral contraceptive drugs. 1225 41

Table salt can now be fortified with iodine and iron without interaction and without loss of potency. According to Levente Diosady, professor of Food Engineering at the University of Toronto, the amounts of the two micronutrients available to the human body have been significantly reduced when the two interacted. In the new technology, the iodine is covered with a dextrin (a water soluble starch) capsule that serves as a physical barrier to the iron. Micronutrient Initiative (an international secretariat based at IDRC that works to eliminate health problems resulting from iron, iodine, and vitamin A deficiencies) and IDRC supported the development of the technology. The efficiency of absorption of the two micronutrients in the new double fortified salt in the human body is being tested at the Hospital for Sick Children in Toronto. Later testing will be conducted by University of Ghana scientists in IDRC-funded trials that will focus on women and their families in areas of Ghana where these deficiencies are endemic. Iodine is part of thyroid hormone, which contributes to brain development in the fetus and regulates human metabolism; iodine deficiency is the most frequent cause of preventable mental retardation. Related disorders include lethargy, physical disabilities, goiter, stillbirth, and neonatal death. Iron deficiency, the most common nutritional problem in the world (particularly among women, infants, and children), is associated with anemia, fatigue, learning problems, pregnancy complications, premature births, and maternal mortality. The two deficiencies together affect more than one-third of the world's population. Approximately 1.6 billion people, in more than 100 countries, live in areas where iodine is not available in sufficient amounts; those most at risk include about one-third of China's population. It is also a severe problem in the Himalayas, the Andes, India, and West Africa.
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PMID:Micronutrient deficiencies. Reports from the field -- Africa. 1229 Mar 27

Fatigue-induced microdamage in bone contributes to stress and fragility fractures and acts as a stimulus for bone remodelling. Detecting such microdamage is difficult as pre-existing microdamage sustained in vivo must be differentiated from artefactual damage incurred during specimen preparation. This was addressed by bulk staining specimens in alcohol-soluble basic fuchsin dye, but cutting and grinding them in an aqueous medium. Nonetheless, some artefactual cracks are partially stained and careful observation under transmitted light, or epifluorescence microscopy, is required. Fuchsin lodges in cracks, but is not site-specific. Cracks are discontinuities in the calcium-rich bone matrix and chelating agents, which bind calcium, can selectively label them. Oxytetracycline, alizarin complexone, calcein, calcein blue and xylenol orange all selectively bind microcracks and, as they fluoresce at different wavelengths and colours, can be used in sequence to label microcrack growth. New agents that only fluoresce when involved in a chelate are currently being developed--fluorescent photoinduced electron transfer (PET) sensors. Such agents enable microdamage to be quantified and crack growth to be measured and are useful histological tools in providing data for modelling the material behaviour of bone. However, a non-invasive method is needed to measure microdamage in patients. Micro-CT is being studied and initial work with iodine dyes linked to a chelating group has shown some promise. In the long term, it is hoped that repeated measurements can be made at critical sites and microdamage accumulation monitored. Quantification of microdamage, together with bone mass measurements, will help in predicting and preventing bone fracture failure in patients with osteoporosis.
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PMID:Detecting microdamage in bone. 1292 17

Often patients in whom there is little to suggest myxedema or cretinism have subclinical hypothyroidism. Once the condition is suspected, it can be diagnosed by determination of protein-bound iodine and, if the PBI is low, by response to therapy with thyroid hormone. Patients in the following categories should have protein-bound iodine determination: Those having (1) a history of previous treatment for hypothyroidism; (2) suboptimal development in children; (3) ovarian dysfunction, infertility, habitual abortion or unusual menopausal disorders; (4) symptoms of malaise and debility, such as undue fatigue, somnolence, mental asthenia and anxiety; (5) unexplained anemia; (6) colloid goiter, adenomatous goiter and cancer of the thyroid gland. If hypothyroidism is diagnosed, administration of thyroid hormone in increasing amounts, as determined by serial serum PBI tests, should be carried out indefinitely. Instruction of the patient is essential.
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PMID:Subclinical hypothyroidism. Recognition and treatment. 1398 2

In total hip replacement, fixation of a prosthesis is in most cases obtained by the application of methacrylic bone cements. Most of the commercially available bone cements contain barium sulphate or zirconium dioxide as radiopacifier. As is shown in the literature, the presence of these inorganic particles can be unfavourable in terms of mechanical and biological properties. Here, we describe a new type of bone cement, where X-ray contrast is obtained via the introduction of an iodine-containing methacrylate copolymer; a copolymer of methylmethacrylate and 2-[4-iodobenzoyl]-oxo-ethylmethacrylate (4-IEMA) is added to the powder component of the cement. The properties of the new I-containing bone cement (I-cement) are compared to those of a commercially available bone cement, with barium sulphate as radiopacifier (B-cement). The composition of the I-cement is adjusted such that similar handling properties and radiopacity as for the commercial cement are obtained. In view of the mechanical properties, it can be stated that the intrinsic mechanical behaviour of the I-cement, as revealed from compression tests, is superior to that of B-cement. Concerning the fatigue behaviour it can be concluded that, though B-cement has a slightly higher fatigue crack propagation resistance than I-cement, the fatigue life of vacuum-mixed I-cement is significantly better than that of B-cement. This is explained by the presence of BaSO4 clumps in the commercial cement; these act as crack initiation sites. The mechanical properties (especially fatigue resistance) of the new I-cement warrant its further development toward clinical application.
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PMID:Mechanical behaviour of a new acrylic radiopaque iodine-containing bone cement. 1475 52

Thyroid dysfunction is extremely common in women and has unique consequences related to menstrual cyclicity and reproduction. Even minimal hypothyroidism can increase rates of miscarriage and fetal death and may also have adverse effects on later cognitive development of the offspring. Hyperthyroidism during pregnancy may also have adverse consequences. Accordingly, thyrotropin (TSH) determination is warranted for all women planning pregnancy or those already pregnant. Replacement doses should be carefully monitored throughout pregnancy because the increased renal iodine loss and estrogen-induced rise in thyroxine-binding globulin (TBG) often result in a higher dose requirement. Although thyroid abnormalities are part of the standard differential diagnosis of menstrual disorders, recent studies indicate that these are relatively infrequent causes. Nonetheless, TSH is still required as part of the laboratory evaluation of women with abnormal cycles. The incidence of postpartum thyroiditis is high--6%-8% in various studies. A TSH should be performed in all postpartum patients who are depressed, who complain of unusual fatigue or anxiety or have any of the classical symptoms of hyperthyroidism or hypothyroidism. Practitioners providing health care for women should be alert to thyroid disorders as possible etiological factors in nonspecific symptoms such as fatigue and depression. However, most women with these symptoms are euthyroid; replacement therapy for them is not indicated. The long-standing dogma of thyroidology that replacement with levothyroxine alone is satisfactory for all hypothyroid patients has recently been questioned but results of trials are inconclusive. Nonetheless, satisfactory regimens can be found for the vast majority of patients.
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PMID:Thyroid dysfunction and women's reproductive health. 1567


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