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

Fatigue, that cardinal symptom of heart failure, expresses muscle deconditioning and is becoming the main complaint of our patients. Dyspnoea also is, at least partially, a consequence of muscle deconditioning; however, the wide use of diuretics which reduce water and salt retention has improved the "pump" function an therefore dyspnoea. The "muscle deconditioning" syndrome in heart failure has two causes: reduction of the nutritive blood flow in skeletal muscle, and specific alteration of mitochondrial oxidative metabolism. The syndrome appears only after a lasting reduction of physical activities. Its anatomical substrate is a mild muscular fibrosis and, mainly, reduced area of oxidative mitochondrial cristae. It remains for approximately three months, which accounts for the delayed improvement of exercise tolerance under vasodilatator treatment with angiotensin-converting enzyme inhibitors. This syndrome explains the success of retraining techniques which, in ou opinion, should become part of our therapeutic armamentarium.
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PMID:[The syndrome of "muscle deconditioning" in chronic cardiac insufficiency]. 250 99

It has been known for some time that surface integrity has an effect on the fatigue life of metals and "brittle" polymers. In cardiovascular applications of polymeric materials, emphasis is placed on elastomers having extended flexure lifetimes (i.e., fatigue life). The effect of surface integrity on the performance properties of Biomer (Ethicon, Inc, Somerville, NJ) a segmented polyurethane used in many blood contacting devices, is being investigated using uniaxial tensile tests in air at room temperature, and biaxial fatigue tests in deionized water at body temperature. Tensile tests were done using ASTM-D-882: Standard Test Methods for Tensile Properties of Thin Plastic Sheeting. No significant differences were noted in the stress-strain curves for specimens with various surface finishes. Fatigue tests were performed using an apparatus developed to allow for the exposure of thin-sheet polymer specimens to fluid at body temperature, while being biaxially strained. Because no standard test method was available, a test protocol was developed with reference to ASTM-D-671-78: Standard Test Methods for the Flexural Fatigue of Plastics by Constant Amplitude of Force. Stress versus life cycle data for specimens with differing surface finishes are being collected. Results to date suggest fatigue life of thin flexing membranes will decrease with increasing order of surface roughness, and fatigue properties are more sensitive to effects of changes in surface integrity than tensile properties measured by monotonic loading.
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PMID:Effects of surface integrity on the fatigue life of thin flexing membranes. 259 64

We assessed the effect of pressure support ventilation (PSV) on breathing patterns and the work of breathing in 10 postoperative patients. Minute ventilation (VE) increased by 8% with 5 cm H2O PSV and 10% with 10 cm H2O PSV compared to 0 cm H2O PSV. The increase in VE was achieved by increased mean inspiratory flow (24% with 5 cm H2O PSV and 67% with 10 cm H2O PSV) and a decrease in duty cycle (13% with 5 cm H2O PSV and 39% with 10 cm H2O PSV). The decrease in duty cycle along with a decrease in respiratory frequency allowed a greater expiratory time including a rest period for the respiratory muscles, which might minimize the risk of muscle fatigue. Furthermore, the inspiratory work added by the ventilator was near zero with 5 cm H2O PSV and 10 cm H2O PSV. Oxygen consumption also decreased significantly with 5 cm H2O PSV. We conclude that PSV improves the breathing patterns and minimizes the work of breathing spontaneously via a ventilator.
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PMID:Effect of pressure support ventilation on breathing patterns and respiratory work. 260 36

Class I inlays were produced according to the direct method using six white light-cured composite, one inlay material and one veneer acrylic. They were subjected to extraoral heat treatment at 125 degrees C for 150 s. In addition, heat-cured inlays were produced according to the indirect method. In all cases heat treatment resulted in a considerable increase in transverse strength and modulus of elasticity as well as a material specific decrease in the specimen volume between 0.15% and 1.05%, and it facilitated finishing. With one exception heat-treated and heat-cured inlays could be inserted without open margins; even 5000 threshold load cycles of 500 N failed to cause marginal defects. However, these inlays also had no open margins when inserted without previous heat treatment. While in the case of four materials this resulted in no measurable reduction in fatigue strength, it reduced this value to a maximum of 100 N in three materials. Swelling of the polymeric inlays due to high water absorption resulted in extensive enamel cracks with one of the materials tested.
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PMID:[Risks and benefits of polymeric inlays]. 263 4

Persistent inability to tolerate discontinuation from mechanical ventilation is frequently encountered in patients recovering from acute respiratory failure. We studied the ability of inspiratory pressure support, a new mode of ventilatory assistance, to promote a nonfatiguing respiratory muscle activity in eight patients unsuccessful at weaning from mechanical ventilation. During spontaneous breathing, seven of the eight patients demonstrated electromyographic signs of incipient diaphragmatic fatigue. During ventilation with pressure support at increasing levels, the work of breathing gradually decreased (p less than 0.02) as well as the oxygen consumption of the respiratory muscles (p less than 0.01), and electrical signs suggestive of diaphragmatic fatigue were no longer present. In addition, intrinsic positive end-expiratory pressure was progressively reduced. For each patient an optimal level of pressure support was found (as much as 20 cm H2O), identified as the lowest level maintaining diaphragmatic activity without fatigue. Above this level, diaphragmatic activity was further reduced and untoward effects such as hyperinflation and apnea occurred. When electrical diaphragmatic fatigue occurred, the activity of the sternocleidomastoid muscle was markedly increased, whereas it was minimal when the optimal level was reached. We conclude that in patients demonstrating difficulties in weaning from the ventilator: (1) pressure support ventilation can assist spontaneous breathing and avoid diaphragmatic fatigue (pressure support allows adjustment of the work of each breath to provide an optimal muscle load); (2) clinical monitoring of sternocleidomastoid muscle activity allows the required level of pressure support to be determined to prevent fatigue.
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PMID:Inspiratory pressure support prevents diaphragmatic fatigue during weaning from mechanical ventilation. 267 10

Muscular fatigue is of critical importance to performance and as such has been the subject of numerous investigations. However, a clear cause remains elusive. Although many factors have been identified, this review deals only with those which occur distal to the neuromuscular junction. Factors discussed include: energy supply (ATP/creatine phosphate, glycogen, oxygen, and free fatty acids); the accumulation of metabolites (lactate/hydrogen ions, calcium, ammonium, electrolyte and water shifts); and, the special case of eccentric work. The results of many studies using various methodologies are examined. Peripheral fatigue appears to be a complex series of interactions with variable influence on the development of fatigue depending upon the nature of the work performed.
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PMID:Biochemical aspects of peripheral muscle fatigue. A review. 264 71

The purpose of this study was to compare the bond strengths of dental amalgam cores and dental alloy-glass ionomer cores that were luted to cast gold crowns with glass ionomer cement. Seventy-two human extracted molars were sectioned horizontally and four regular thread mate system pins were inserted into a flat pulpal floor. The teeth were restored with amalgam or alloy-glass ionomer admixture and prepared for crown preparations. Castings were produced with type III gold and cemented to the cores with Fuji type I glass ionomer cement. Thirty-six of the specimens were subjected to thermal fatigue by cycling between 4 and 50 degrees C for periods of 1, 5 and 10 weeks. The remainder of the specimens were retained in deionized water at 37 degrees C. Bond strengths of the cores, in tension, were measured with a universal testing machine. The alloy-glass ionomer cores exhibited higher bond strengths than the amalgam cores for virtually all time periods, particularly the thermocycled samples. The alloy-glass ionomer cores exclusively displayed core fractures and pin/tooth insufficiencies while the amalgam cores failed because of a deterioration of the glass ionomer luting cement.
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PMID:A comparative study of the bond strengths of amalgam and alloy-glass ionomer cores. 266 11

To assess the prevalence and severity of premenstrual symptoms in adolescents, we administered the Premenstrual Assessment Form, a 95-item instrument previously validated in adults. Adolescent females (n = 207) at a suburban-based adolescent health service completed the form. Subjects had a mean age of 17.6 years, 89% were white, 59% were in high school, 28% were in college. Almost all subjects reported at least one premenstrual change of minimal (96%) or moderate (89%) severity, while many reported changes they considered severe (59%) or extreme (43%). The most commonly reported changes in physical condition were general discomfort and water retention symptoms, fatigue, and autonomic physical changes. The most commonly reported changes in mood and behavior included impaired social function, depressive changes, and impulsive behavior. These changes matched almost exactly those previously reported in adults and were most severe in those adolescents who reported having dysmenorrhea and were not on an oral contraceptive. We believe that clinicians and researchers who evaluate and treat adolescents should view the physical and emotional complaints of teenagers in the context of our findings.
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PMID:Premenstrual symptoms in adolescents. 268 Nov 6

The triathlon is an endurance contest in which contestants must compete in 3 consecutive events, usually swimming, cycling and running. Success in a triathlon depends upon the ability of the triathlete to perform each of the sequential events at optimal pace without creating fatigue that will hinder performance in the next event. The successful triathlete must, therefore, have highly developed oxygen transport and utilisation systems as well as the ability to efficiently produce a high energy output for prolonged periods without creating metabolic acidosis. Accordingly, mean VO2max values for groups of triathletes during treadmill running have been reported to range from 52.4 to 72 ml/kg/min in men; 58.7 to 65.9 ml/kg/min in women. VO2max values during cycle ergometry were 3 to 6% less than treadmill running values; tethered swimming maximums 13 to 18% less. Predictable and well-known adaptations occur in the cardiovascular systems of triathletes. Structural adaptations of the heart that have been documented in triathletes include increased left ventricular cavity size or wall thickness, or both. Morphological characteristics of the triathlete's heart appear to be unrelated to success in triathlon races. Following the acute stress of triathlon competition, alterations in both systolic and diastolic function have been observed. Heart muscle fatigue is the most likely reason for these changes, since there is a rapid return to normal with rest. Like the cardiovascular system, the musculoskeletal system responds to triathlon training. Peripheral adaptations occur that lead to increased muscle respiratory capacity and to modifications in substrate utilisation. The musculoskeletal system is the site of most injuries to triathletes, and non-traumatic overuse injuries account for 80 to 85% of the musculoskeletal injuries. Maintenance of fluid and electrolyte balance is of primary importance for the triathlete both in day-to-day training and during races. Water may be an adequate replacement fluid for short distance triathlons, but some combination of carbohydrate, electrolyte and fluid replacement is necessary for longer races. Although the physiological bases for success in a triathlon are not well understood at present, the ability to maintain minimal alterations in the homeostasis of cardiovascular, haemodynamic, thermal, metabolic, and musculoskeletal functions are of obvious importance.
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PMID:Applied physiology of a triathlon. 269 16

The desynchronisation of an athlete's physiological and psychological cycles has adverse effects on his/her performance. The primary cause of dysrhythmia in an athlete is jet-lag, which is a rapid displacement across the earth's time zones and is often experienced while competing in international events and in continental leagues. General symptoms which arise from dysynchronization include malaise, appetite loss, tiredness during the day and disturbed sleep. The specific symptoms resulting from jet-lag are characterised as phase shifts in physiological and psychological cycles. These phase shifts occur in body temperature, ability to mobilise energy substrates, excretion of water and metabolites, arousal levels, sleep/wake cycles and reaction time. The severity of these adverse effects and therefore the time required for resynchronization depends on the ability to preset the bodily rhythms prior to flying, the number of time zones crossed, the direction of flight, the type of individual (introvert/extrovert), age, social interaction and activity, diet plan and prescribed use of chronobiotic drugs.
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PMID:Jet-lag and human performance. 269 17


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