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 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

There is a close epidemiological association between obesity and elevated blood pressure for all age groups, although not every obese individual becomes hypertensive. In populations without age-related increases in body weight, an elevation of blood pressure with age is not seen. Mechanisms included in the development of hypertension in obesity are hyperinsulinemia, insulin induced sodium retention and increased sympathetic tone. Overnutrition with over intake of sodium and lack of physical exercise contribute to the metabolic syndrome of obesity. Thus, weight reduction by decreased energy uptake and increased physical exercise is recommended in the treatment of hypertension in obese patients. The resulting fall in insulin levels may lead to decreased sodium absorption in the kidney. Although treatment of obesity by weight loss decreases blood pressure substantially, a minority of patients do not respond to the weight loss. Blood pressure generally decreases before normal weight is achieved. Salt intake reduction does not appear to explain why weight reduction lowers blood pressure. Reduced levels of plasma renin activity, serum aldosterone levels, catecholamine levels and serum insulin levels may be involved in the blood pressure lowering associated with weight loss. Since the risk of cardiovascular disease in the hypertensive patient is not only determined by the blood pressure, an overall treatment which aims at reduction of other risk factors such as glucose intolerance and hyperlipoproteinemia is advocated. Thus, in any obese hypertensive patient normalization of excess body weight and increased physical activity appears to be the first and most important step of any rational therapeutic strategy.
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PMID:Obesity and hypertension: epidemiology, mechanisms, treatment. 636 45

During the past 20 years there have been great developments in the scientific understanding of the role of nutrition in health and physical performance. Epidemiological and physiological studies have provided evidence that certain forms of dietary behaviour may be linked with an increased risk of developing disorders such as high blood pressure, coronary artery disease and some cancers. This has resulted in dietary recommendations that are intended to reduce the incidence of these disorders in the community. The science of nutrition in relation to sports performance has progressed from empirical studies investigating the effects of dietary manipulations, such as restriction and supplementation, to the direct investigation of the physiological basis of the specific nutritional demands of hard physical exercise. This review is based on the premise that it is "what comes out' rather than "what goes in', which provides the clues to ideal nutrition for athletic performance. Various aspects of the physical demands of athletic exercise are viewed as stresses that induce specific biochemical, and hence nutritional, strains in the athlete. Training is the predominant demand in the athletic lifestyle. This is characterised by acute bouts of high power output. During one hour of hard training an athlete may expend 30% of his or her total 24-hour energy output. These high power outputs have important implications for energy substrate and water requirements. Carbohydrate, specifically muscle glycogen, is an obligatory fuel for the high power outputs demanded by athletic sports. Muscle glycogen is a limiting factor in hard exercise because it is held in limited amounts, utilised rapidly by intense exercise, and fatigue occurs when it is depleted to low levels in the active muscles. Liver glycogen may also be exhausted by hard exercise and low blood glucose contributes to fatigue. High sweat rates are demanded during severe exercise and large water deficits commensurate with energy expenditure are incurred during extended periods of hard training and competition. Salt, potassium, and magnesium are lost in nutritionally significant amounts in the sweat, but vitamins and trace elements are not. Adaptive mechanisms protect athletes against electrolyte depletion. Iron loss in sweat may contribute to the iron deficiency seen in some endurance runners. Protein is degraded and amino acids are oxidised during physical exercise. Protein is also retained during muscle building training. Recent investigations indicate that the minimal protein requirements of athletes may be substantially higher than those for sedentary persons.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Nutrition and sports performance. 639 Jun 9

Loosening remains an impediment to the long-term success of total hip replacements despite numerous improvements in the materials used. In cemented prostheses, fatigue and fracture of bone cement have been implicated in the failure of these devices. A new material, self-reinforced composite poly(methyl methacrylate). (SRC-PMMA), has been developed. SRC-PMMA is formed by a novel processing method that will be described. The composite consists of high strength, highly oriented PMMA fibers embedded in a matrix of PMMA. Using a woven form of SRC-PMMA, an in vitro physical and mechanical evaluation was performed to assess the feasibility of its use in an orthopedic prosthesis. Three different weaves of SRC-PMMA were evaluated in bending and fracture toughness in air, after immersion for 30 days in 37 degrees C saline, and after gamma irradiation followed by immersion. Bending modulus and strength were decreased by gamma irradiation followed by saline immersion. The effect of saline immersion alone on bending strength and modulus was negligible. Saline immersion and gamma irradiation followed by saline immersion was shown to have little or no effect on the fracture toughness of woven SRC-PMMA. Differences in the fracture processes of the different weaves were found and can be related to the differing orientation of fibers to the fracture toughness pre-crack. Optimally incorporated SRC-PMMA absorbs the same amount of water as bone cement. Comparison to previous and current work with bone cement controls shows that SRC-PMMA is a material equal to or better than bone cement in all tests performed. It deserves further consideration as a candidate biomaterial.
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PMID:Bending and fracture toughness of woven self-reinforced composite poly(methyl methacrylate). 929 60

This study investigated the effects of cyclic bending stress levels and testing in simulated physiological solutions or air on the integrity of plasma-sprayed hydroxylapatite (HA) coatings of two different crystallinities. Hydroxylapatite-coated commercially pure (CP) Ti rods were evaluated by immersion testing in Hank's Balanced Salt Solution (HBSS) and by rotating bending in air and HBSS. Static immersion testing of nonstressed specimens resulted in significant microcracking of coating surfaces after 42 days. Specimens cyclically tested at bending stresses above the yield strength of Ti experienced low cycle fatigue failure of the Ti substrates prior to spallation of the HA coatings. Coatings tested at 1 x 10(6) cycles with interface bending stresses of 180 MPa displayed increased surface microcracking, but no bulk coating spallation. Coatings cycled in HBSS displayed greater amounts of microcracking and surface alteration than samples cycled in air. There was no apparent relation between HA crystallinity and mechanical integrity under cyclic bending stresses.
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PMID:Effects of cyclic bending and physiological solution on plasma-sprayed hydroxylapatite coatings of varying crystallinity. 1042 80

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

The purpose of this descriptive study was to determine the perceptions of activity and vocational status in women with cardiac illness. A convenience sample of 20 women with the diagnosis of coronary heart disease or hypertrophic cardiomyopathy participated. Subjects underwent an audiotaped interview, using a semistructured interview guide, which was then transcribed into the Ethnograph software program (Qualis Research Associates, Salt Lake City, UT). Transcripts were analyzed for common themes via content analysis. There were four themes identified for activity: variable activity patterns, fatigue, guilt, and depression. There were four themes identified for vocational status: desire to work, social aspects of work, unpaid work, and struggle to maintain the status quo. In conclusion, the themes of fatigue, guilt over unmet activity expectations, and the common occurrence of unpaid work validated prior research findings. The themes of variable patterns of activity management, feelings of depression about lowered activity levels, the desire to return to a prior vocation, the importance of the social nature of work, and the struggle to balance both home and work roles were new findings.
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PMID:Perceptions of activity and vocational status in women with cardiac illness. 1289 74

Fatigue of hand and forearm muscle groups can limit task performance by astronauts wearing space suits. Countermeasures to delay fatigue would therefore be useful to the space program. N-acetylcysteine (NAC) has been shown to inhibit fatigue during other tasks so we tested its effects during handgrip exercise. Volunteers practiced isometric handgrip maneuvers until performance was reproducible over three successive sessions (baseline). Performance then was retested after ingesting NAC (150 mg.kg(-1)) or saline. Drug administration increased NAC and cysteine blood levels (P < 0.001). Performance of sustained maximal efforts was unaffected. During repetitive submaximal efforts, NAC delayed fatigue (130% baseline) and inhibited glutathione oxidation. Saline did not alter glutathione status or performance of sustained maneuvers; repetitive task performance was increased by 15% (P < 0.05), a placebo effect. These data indicate that NAC supports glutathione homeostasis in exercising humans and may delay muscle fatigue during repetitive handgrip exercise. Our findings support oxidative stress as a causal factor in human muscle fatigue and argue for larger translational studies to define NAC effects on human performance.
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PMID:Effects of N-acetylcysteine on glutathione oxidation and fatigue during handgrip exercise. 1602 22

The functional activity of the urethral sphincters during cavernosus muscles' contraction at coitus has been poorly addressed in the literature. We investigated the hypothesis that cavernosus muscles' contraction affects reflex contraction of the urethral sphincters to guard against semen reflux into the urinary bladder or urine leakage from the bladder during orgasm and ejaculation. The electromyographic (EMG) response of the external (EUS) and internal (IUS) urethral sphincters to ischio- (ICM) and bulbo- (BCM) cavernosus muscle stimulation was studied in 15 healthy volunteers (9 men, 6 women, age 39.3 +/- 8.2 SD years). An electrode was applied to each of ICM and BCM (stimulating electrodes) and the 2 urethral sphincters (recording electrodes). The test was repeated after individual anesthetization of the urethral sphincters and the 2 cavernosus muscles, and after using saline instead of lidocaine. Upon stimulation of each of the 2 cavernosus muscles, the EUS and IUS recorded increased EMG activity. Repeated cavernosus muscles' stimulation evoked the urethral sphincteric response without fatigue. The urethral sphincters did not respond to stimulation of the anesthetized cavernosus muscles nor did the anesthetized urethral sphincters respond to cavernosus muscle stimulation. Saline infiltration instead of lidocaine did not affect the urethral sphincteric response to cavernosal muscle stimulation. Results were reproducible. Cavernosus muscles' contraction is suggested to effect EUS and IUS contraction. This action seems to be reflex and mediated through the 'cavernoso-urethral reflex.' Urethral sphincters contraction upon cavernosus muscles contraction during sexual intercourse presumably prevents urine leak from the urinary bladder to urethra, prevents retrograde ejaculation, and propels ejaculate from the posterior to the penile urethra. The cavernoso-urethral reflex can act a diagnostic tool in the investigations of patients with ejaculatory disorders.
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PMID:Urethral sphincters response to cavernosus muscles stimulation with identification of cavernoso-urethral reflex. 1608 61

Breast implant strength and durability is presently an important topic in biomaterials science. Research studies are being conducted to determine the mechanisms and rates of failure in order to assess the in vivo performance of breast implants. Fatigue life is a measure of breast implant durability since fatigue failure is a potential in vivo failure mechanism. This study describes the characterization of the fracture surface morphology of breast implant shell regions that have failed due to cyclic fatigue. Saline breast implants were fatigue tested to failure using a laboratory apparatus in which flat plates cyclically compressed the implants. The implants were unimplanted control devices of both textured and smooth saline implants. The failure surfaces of the fatigued shells were examined using scanning electron microscopy (SEM). The morphological features of the failure surfaces are described for implants with short and long fatigue lifetimes. The details of both the inside and outside surfaces of the shell at the failure location are described. Two different modes of failure were observed in both the textured and smooth shells. These modes depend on the magnitude of the cyclic load and corresponding number of fatigue cycles at failure. The first mode is a tear in the shell of about 18 mm in length, and the second mode is a pinhole approximately 1 mm in diameter. Details of the surface morphology for these two types of failure modes and shell thickness data are presented herein. There was no significant change in the crosslink density of the shell as a result of fatigue.
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PMID:Scanning electron microscope fractography of induced fatigue-damaged saline breast implants. 1656 47

Endovascular stents made of the superelastic nickel-titanium alloy Nitinol are subjected in service to tens of millions of loading cycles and even "single-event" overloads, both of which can potentially result in fracture and/or complete failure of the device. A fracture-mechanics-based methodology can provide a means to quantify relevant material parameters critical to the design against such failures. However, there is a dearth of relevant experimental data in the literature on such fracture-mechanics-based approaches to fatigue in Nitinol; furthermore, that which does exist invariably pertains to product forms that are not appropriate for stent manufacture, e.g., bulk Nitinol bar and strip. Consequently, the current work is focused on characterizing in vitro both subcritical and critical crack growth (fatigue-crack growth and R-curve fracture toughness) behavior in thin-walled ( approximately 400microm thick) Nitinol tubing similar to that used for medical device manufacture (following shape-setting procedures to flatten the material), with a resultant austenite finish temperature of A(f) approximately 25-30 degrees C, identical to self-expanding Nitinol stents. Fatigue-crack growth behavior, measured in Hanks' Balanced Saline Solution over a wide spectrum of growth rates (down to 10(-10)m/cycle) and at a range of positive load ratios (R=0.1-0.7), revealed significantly higher fatigue thresholds than had been previously reported for bulk Nitinol material. In addition, we examine the critical effect of test frequency, as most fatigue experiments on Nitinol have been performed at 30Hz or above, despite the fact that this is far in excess of the frequency of physiological loading. Finally, the fracture toughness properties are characterized in thin-section Nitinol and show marked crack-resistance (R-curve) behavior with a dependence on crack-growth angle (with respect to the tube drawing axis); additionally, measured toughnesses are found to be lower than has been previously reported for bulk Nitinol.
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PMID:In vitro fatigue-crack growth and fracture toughness behavior of thin-walled superelastic Nitinol tube for endovascular stents: A basis for defining the effect of crack-like defects. 1703 45


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