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26.07.2014

Definition fatigue failure, tinnitus causes natural cures - Try Out

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Fatigue is sometimes referred to as asthenia, tiredness, lack of energy, weakness, and exhaustion.
The causes of fatigue in an individual patient are often multiple, with many interrelated factors.
In patients without cancer who present with fatigue, the final diagnosis is psychological (eg, depression, anxiety, and other psychological disorders) in almost 75% of patients.
Low red blood cell count related to advanced cancer or chemotherapy has been associated with fatigue, and its treatment results in improvement of fatigue and quality of life in these patients. Administration of chemotherapy and radiotherapy for malignancy causes a specific fatigue syndrome. Comorbid conditions not necessarily related to cancer, such as renal failure and congestive heart failure, may coexist and contribute to the problem.
The fourth category in Table 1 is the most relevant for both clinical management and clinical trials in fatigue. In addition to the assessment of the intensity of fatigue, the clinical assessment of these patients requires clinicians to determine the impact of all factors on the presence of fatigue. To treat fatigue optimally, it is vital to identify and prioritize the different underlying factors in the individual patient.
In patients with cancer treatment–related fatigue, it is important to exclude specific causes, such as hypothyroidism, hypogonadism, and anemia, and to consider other potential adverse effects of treatment.
Psychosocial interventions, such as CBT, have been found to be effective in improving cancer-related fatigue in cancer patients receiving treatment. The flexural fatigue test is used to characterize the fatigue life of HMA at intermediate pavement operating temperatures. The basic flexural fatigue test subjects a HMA beam to repeated flexural bending in a controlled atmosphere (Figure 1). In HMA pavements, fatigue cracking occurs when repeated traffic loads ultimately cause sufficient damage in a flexible pavement to result in fatigue cracking (Figure 2).
The concept of a fatigue life centers around the universal idea that most materials undergo a gradual deterioration under repeated loads that are much smaller than the ultimate strength of the material.
A classic fatigue crack starts at the bottom of a HMA pavement layer (or structure) and grows towards the surface.
Work on NCHRP Project 9-38, Endurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible Pavements, is underway to identify the existence of a fatigue endurance limit and measure it for selected HMA mixtures. The flexural fatigue test is performed by placing a beam of HMA in repetitive four point loading at a specified strain level. In recent years fatigue testing has been conducted using both constant stress or constant strain load applications.
The decision on when to terminate a flexural fatigue test depends on the test mode and purpose.
Beam fatigue testing is performed at intermediate temperatures, usually 68°F (20°C), because fatigue cracking is thought to be a primary HMA distress at these intermediate temperatures. The beam fatigue test provides a measure of the fatigue life and fatigue energy of HMA pavements. To gain an understanding of the fatigue behaviour of hollow section joints and the available methods of design.
Hollow sections (circular, square and rectangular) are used in many applications subjected to fatigue loading, e.g. The various Ds-N methods are based on experiments resulting in Ds-N graphs with a defined stress range Ds on the vertical axis and the number of cycles N to a specified failure criterion on the horizontal axis. Initially it was thought that if a geometric (or so-called hot spot) peak stress range is used which takes the global geometry and the loading into account, the fatigue behaviour of all types of joints could be related to one basic Sr-N line. Since the fatigue behaviour depends on the thickness, the maximum geometric or hot spot stress range has to be determined for the chord and the brace considering different thicknesses.
The fatigue life is generally specified as the number of cycles N for stress or strain of a specified character that a given joint sustains before failure of a specified nature occurs. Usually, a crack through the wall is adopted as the failure criterion for hollow section joints, which corresponds to about 80% of the total fatigue life of a joint. For thicknesses below 4 mm no guidance is given, since the fatigue behaviour may be adversely affected by the welding imperfections at the root of the weld. For random or variable amplitude loading with stresses exceeding the Ds, at 5 ? 106 certain interaction effects may appear with the result that smaller stress ranges can have an influence on the fatigue life. As shown in Figure 5, the fatigue test results of hollow section joints for N = 103 are still in line with the Ds-N curves given. The number of cycles to failure N for both brace and chord is obtained from the Ds-N line for the appropriate wall thickness. In the previous section it has been shown that the geometric (peak) stress range largely determines the fatigue life.
This funding may be explained by the fact that the static strength depends on the same geometrical parameters which influence the geometric stress and also that the incremental load capacity of the joint between initial localized yielding and failure has some relation to the stress gradient.


For hollow section joints, the same partial safety factors apply for the stress range as for other structures loaded in fatigue.
The secondary bending moments in lattice girders have to be incorporated in the fatigue analysis. Fatigue is also commonly associated with cancer treatment and occurs in up to 90% of patients undergoing chemotherapy. In terminally ill patients with advanced cancer, treatment of anemia may not resolve fatigue adequately because of the multifactorial nature of its etiology.
Autonomic failure has also been documented in patients with severe chronic fatigue syndrome. The pattern of fatigue reported by patients with cancer who receive myelosuppressive chemotherapy is cyclical. Combined therapy with the two modalities appears to cause worse fatigue than does either modality given alone.
In addition, commonly used medications, such as opioids and hypnotics, may cause sedation and fatigue. There is agreement that self-assessment should be the “gold standard.” Because of the complex nature of the symptoms of fatigue, an effort to identify a set of diagnostic criteria similar to those for depression has been attempted. Visual analog scales, numerical scales, the Brief Fatigue Inventory (BFI), and the Piper Fatigue Self-Report Scale have been validated. There is substantial evidence that corticosteroids can reduce fatigue and other symptoms in cancer patients. Psychostimulants (eg, methylphenidate, 5 to 10 mg in the morning and at noon or 5 mg as needed) may be useful in treating fatigue in patients with advanced cancer.
Based on a preliminary study that found significant improvement of cancer-related fatigue with a dose of 2,000 mg extract of ground root of American ginseng (Panax quinquefolius), Barton et al recently completed a double-blind trial of 2,000 mg of American ginseng vs placebo for 8 weeks in 364 fatigued cancer survivors. A recent randomized controlled trial by Montogomery et al found that the benefits of CBT on cancer-related fatigue lasted long after the CBT was finished. This characterization is useful because it provides estimates of HMA pavement layer fatigue life under repeated traffic loading.
A number of factors can influence a pavement’s ability to withstand fatigue, including pavement structure (thin pavements or those that do not have strong underlying layers are more likely to show fatigue cracking than thicker pavements or those with a strong support structure), age of the pavement, and the materials used in construction. The flexural fatigue test is essentially a research test and is not used in specifications.
In these lectures it is shown that the peak stress ranges determine the fatigue life of a particular connection to a large extent. Using the Ds-N curve for geometric or hot spot stress, the number of cycles to failure can be determined. The fatigue life of welded hollow section joints is related to both crack initiation and crack propagation.
The lowest number of cycles in brace or chord determines the fatigue strength of the joint. As fatigue is a quite different phenomenon from static strength, one could expect poor correlation between the test results and the Ds -N line. Moreover, different studies of fatigue and asthenia have looked at different outcomes, ranging from physical performance to the purely subjective sensation. When injected into a rested subject, blood from a fatigued subject has produced manifestations of fatigue.
The metabolic abnormalities involved in the production of cachexia and the loss of muscle mass resulting from progressive cachexia may cause profound weakness and fatigue.
Although the association between fatigue and autonomic dysfunction has not been established in cancer patients, it should be suspected in patients with severe postural hypotension or other signs of autonomic failure. Fatigue has been noted to decrease in the first 2 weeks after localized treatment for breast cancer but then to increase as radiation therapy persists into week 4. This syndromal approach has been useful to assess the presence or absence of the clinical syndrome of fatigue.
In a well designed pavement, strains in the pavement are low enough so that fatigue is not a problem.
Because of the testing equipment complexity and long testing times, the flexural fatigue test is primarily a research test and is not a standard test in Superpave mix design or quality assurance testing.
The flexural fatigue test is used to investigate fatigue as it relates to HMA construction materials.
More recent studies seem to suggest that at low levels of strain (around 70 microstrain), HMA mixtures have, in effect, an infinite fatigue life. For the constant strain mode, failure is more difficult to define because in order to keep the strain constant the applied stress is continually reduced, which results in a beam that never really breaks. For example, for basic steel, the fatigue limit for constant amplitude loading might be of the order of 2 ? 106 cycles, whereas for welded connections with high peak stresses it will be about 107 cycles. The fatigue limit for variable amplitude loading is given for all welded connections including hollow section joints at 108 cycles.


In general, in the case of low cycle fatigue, the stress range concept is not valid and the fatigue strength is determined more by strain range.
These extended Ds-N curves can be used; but a brittle failure check should be carried out to determine the critical crack depth. If the fatigue strength were to be based on nominal stress ranges, then on the one hand it would be simpler for the designer, but on the other hand, an atlas would be required to cover all cases [10]. In most patients, the etiology of fatigue or dyspnea is multifactorial, with many contributing interrelated abnormalities. The host production of cytokines in response to the tumor can also have a direct fatigue-inducing effect.
However, many abnormalities described in Figure 1 are capable of causing profound fatigue in the absence of significant weight loss. Patients with an adjustment disorder or a major depressive disorder can have fatigue as their most prevalent symptom. Fatigue tends to worsen with subsequent cycles of chemotherapy, which suggests a cumulative dose-related toxic effect.
However, when pavements are under-designed strains are sufficiently high to cause fatigue failures under repeated loads.
Therefore, in constant strain mode, failure is normally defined as the point at which the load or stiffness reaches some predetermined value; most typically 50 percent of the original value. The fatigue behaviour of fillet welded specimens is sometimes related by factors to that of butt welded specimens. However, for fatigue design the peak stress range is the governing parameter and secondary bending moments influence the peak stress (range).
In one study of patients with advanced cancer, fatigue was found to be significantly correlated with the intensity of dyspnea. Muscular or neuromuscular junction abnormalities are a possible cause of chemotherapy- or radiotherapy-induced fatigue. Compared with women who have no history of cancer, former patients with breast cancer who had received adjuvant chemotherapy reported more fatigue and worse quality of life due to this symptom. It is impossible to be certain whether one of these identified problems is a major contributor to fatigue or simply a coexisting problem in a given patient. The results of this study showed that there was no significant improvement in fatigue in the methylphenidate group compared with the placebo group. These failures ultimately result in fatigue cracking which will cause disintegration of the pavement if not maintained in time. For this reason the fatigue behaviour of hollow section joints is generally treated in a different way to that, for example, for welded connections between plates. Therefore, it is of great importance to measure the intensity of fatigue and the patient’s performance before and after treating any contributing factor.
In a recent double-blind placebo controlled study of 84 advanced cancer patients with fatigue, oral dexamethasone at a standard dose of 8 mg daily for 2 weeks was associated with significant improvement in cancer-related fatigue. There was also no significant benefit from methylphenidate plus a nursing telephone intervention on cancer-related fatigue. Counseling (more specifically, cognitive-behavioral therapy [CBT]) for stress management, depression, and anxiety may reduce distress and fatigue as well as improve mood.
The number of loading cycles to failure can then give an estimate of a particular HMA mixture’s fatigue life.
Hence, it may take several days to several weeks to develop sufficient fatigue data to allow analysis of a given mixture. If the level of fatigue does not improve after correction of these abnormalities, it is clear then that further treatment will not result in improvement in the future. A 148-patient study by Moraska et al also found no significant improvement in cancer-related fatigue with long-acting methylphenidate compared with placebo.
Another important value that can be obtained from the beam fatigue test is the dissipated energy of the specimen.
Similar to the previous studies of Bruera et al and Moraska et al, fatigue improved among patients treated with modafinil but there was no significant difference between the active and placebo treatments.
Note that beyond a certain point the plot is essentially horizontal – indicating an infinite fatigue life. Based on these results, future studies of psychostimulants should be focused on a specific patient group, such as fatigued patients with depression or drowsiness.



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