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

A 35-year-old man affected with pulmonary sarcoidosis had a 12-year history of fatigue and pain in the limbs, with normal neurological examination, except for diffusely absent deep tendon reflexes. Muscle biopsy samples showed multiple noncaseating granulomas, most prominent around the intramuscular nerves, with predominance of CD4+ cells. Intramuscular nerve bundles surrounded by granulomas were immunolabelled with laminin alpha1, alpha2, beta1 and gamma1 chain, and collagen IV. Sural nerve biopsy samples were normal. This patient showed a unique histopathological pattern of sarcoid neuromyopathy characterized by distribution of granulomas or infiltrating cells around intramuscular nerve fibers. The clinical picture, restricted to nonspecific symptoms of fatigue and myalgia, and loss of deep tendon reflexes, correlated well with the selective localization of sarcoid lesions in contiguity with the intramuscular nerves. To our knowledge, this peculiar clinico-pathological correlation has not been reported previously.
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PMID:Sarcoid neuromyopathy with selective involvement of the intramuscular nerves. 956 24

As with many chronic diseases that express themselves late in life, osteoporosis is distinctly multifactorial, both in etiology and pathophysiology. Osteoporotic fractures occur because of a combination of injury and intrinsic bony fragility. Injury comes most often from a combination of falls, falling to the side, poor postural reflexes that fail to protect bony parts from impact, and reduced soft-tissue padding over bony prominences. The bony fragility itself is a composite of geometry, low mass density, severance of microarchitectural connections in trabecular structures, and altered bone material quality. The latter is primarily the result of accumulated fatigue damage, but reduced collagen cross-links and other intrinsic material defects may play a role as well. Reduced bone mass, in turn, is the result of varying combinations of gonadal hormone deficiency, inadequate intakes of calcium and vitamin D, decreased physical activity, comorbidity, and the effects of drugs used to treat various unrelated medical conditions. Finally, the often poor outcome from hip fracture in the elderly is partly due to associated protein-calorie malnutrition. An adequate preventive program for osteoporotic fracture must address as many of these factors as possible and be as multifaceted as the disease is multifactorial.
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PMID:Pathophysiology of osteoporosis. 966 37

We undertook the following study to quantitatively assess the changes in porcine bioprosthetic heart valve (PBHV) fiber architecture to increasing levels of fatigue damage using an in vitro accelerated test model. PBHVs were subjected to 0-500 million test cycles at 16 Hz, and small-angle light scattering (SALS) was used to quantify the gross fiber structure of the cusps. The degree of gross fiber alignment remained essentially constant from 0 to 500 million cycles over the entire cusp. Increasing fiber orientation randomness, indicative of local damage, was observed only in the vicinity of the nodulus of Arantii after 50 million cycles. The SALS data from the damaged regions suggested shearing between fiber layers, which may be part of the failure process and accelerates valve failure. Histological analysis revealed a relatively intact gross fiber structure with the collagen fiber crimp remaining, although delamination and de-registration of the crimp was also observed. Accelerated tested PBHVs also demonstrated a pronounced 'sagging', which began at the earliest cycle number tested (1.4 million cycles) and whose rate decreased logarithmically with cycle number. Results of this study suggest that PBHV cusps can alter their shape without any visually apparent material yielding or fiber failure under continual cyclic loading. Further, while most of the 4 mmHg pressure fixed PBHV's gross fiber architecture remains unchanged after 500 million cycles of accelerated testing, localized accumulated fiber damage can occur on a sub-visual structural level as early as 50 million cycles.
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PMID:Effects of accelerated testing on porcine bioprosthetic heart valve fiber architecture. 969 1

Bioprosthetic heart valve (BPHV) degeneration, characterized by extracellular matrix deterioration, remodeling, and calcification, is an important clinical problem accounting for thousands of surgeries annually. Here we report for the first time, in a series of in vitro accelerated fatigue studies (5-500 million cycles) with glutaraldehyde fixed porcine aortic valve bioprostheses, that the mechanical function of cardiac valve cusps caused progressive damage to the molecular structure of type I collagen as assessed by Fourier transform IR spectroscopy (FTIR). The cyclic fatigue caused a progressive loss of helicity of the bioprosthetic cuspal collagen, which was evident from FTIR spectral changes in the amide I carbonyl stretching region. Furthermore, cardiac valve fatigue in these studies also led to loss of glycosaminoglycans (GAGs) from the cuspal extracellular matrix. The GAG levels in glutaraldehyde crosslinked porcine aortic valve cusps were 65.2 +/- 8.66 microg uronic acid/10 mg of dry weight for control and 7.91 +/- 1.1 microg uronic acid/10 mg of dry weight for 10-300 million cycled cusps. Together, these molecular changes contribute to a significant gradual decrease in cuspal bending strength as documented in a biomechanical bending assay measuring three point deformation. We conclude that fatigue-induced damage to type I collagen and loss of GAGs are major contributing factors to material degeneration in bioprosthetic cardiac valve deterioration.
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PMID:Mechanisms of bioprosthetic heart valve failure: fatigue causes collagen denaturation and glycosaminoglycan loss. 1035 34

Bioprosthetic heart valves fail as the result of two simultaneous processes: structural deterioration and calcification. Leaflet deterioration and perforation have been correlated with regions of highest stress in the tissue. The failures have long been assumed to be due to simple mechanical fatigue of the collagen fibre architecture; however, we have hypothesized that local stresses-and particularly dynamic stresses-accelerate local proteolysis, leading to tissue failure. This study addresses that hypothesis. Using a novel, custom-built microtensile culture system, strips of bovine pericardium were subjected to static and dynamic loads while being exposed to solutions of microbial collagenase or trypsin (a non-specific proteolytic enzyme). The time to extend to 30% strain (defined here as time to failure) was recorded. After failure, the percentage of collagen solubilized was calculated based on the amount of hydroxyproline present in solution. All data were analyzed by analysis of variance (ANOVA). In collagenase, exposure to static load significantly decreased the time to failure (P < 0.002) due to increased mean rate of collagen solubilization. Importantly, specimens exposed to collagenase and dynamic load failed faster than those exposed to collagenase under the same average static load (P = 0.02). In trypsin, by contrast, static load never led to failure and produced only minimal degradation. Under dynamic load, however, specimens exposed to collagenase, trypsin, and even Tris/CaCl2 buffer solution, all failed. Only samples exposed to Hanks' physiological solution did not fail. Failure of the specimens exposed to trypsin and Tris/CaCl2 suggests that the non-collagenous components and the calcium-dependent proteolytic enzymes present in pericardial tissue may play roles in the pathogenesis of bioprosthetic heart valve degeneration.
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PMID:Mechanical loading of bovine pericardium accelerates enzymatic degradation. 1038 30

Hypertension is a cardiovascular risk factor classically attributed to a reduction in the calibre and/or number of small arteries and arterioles resulting in increased peripheral vascular resistance. The definition of blood pressure as a product of total peripheral resistance (TPR) and cardiac output, however, does not take into account the fluctuation of blood pressure and flow during the cardiac cycle, with systolic and diastolic blood pressure representing the extremes of pulse pressure fluctuations. Diastolic blood pressure is closer to mean blood pressure (and therefore to TPR) than systolic blood pressure, and as such has been used as a marker for the diagnosis of hypertension. However, this approach has no rational basis and was challenged by the Framingham Heart Study which demonstrated that systolic rather than diastolic blood pressure is a better risk marker for stroke and coronary artery disease in subjects aged 45 years and older. This view has subsequently been confirmed by several epidemiological and interventional studies. Systolic blood pressure is closely associated with pulse pressure and is determined by the pattern of left ventricular ejection, arterial stiffness and timing of arterial wave reflections, i.e. the geometrical and viscoelastic properties of large conduit arteries. In humans, with ageing and hypertension, the arteries stiffen as a result of progressive degeneration of the arterial media, increased collagen and calcium content, and dilation and hypertrophy of large arteries and the aorta. Thus, the increase in systolic blood pressure (as a result of arterial damage) increases the fatigue of arterial walls and accelerates arterial damage, producing a self-perpetuating cycle.
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PMID:Influence of arterial pulse and reflective waves on systolic blood pressure and cardiac function. 1046 60

A 79-year-old woman, who had had no history of trauma, tuberculosis, or collagen diseases, was referred for examination of general fatigue and shortness of breath on exertion. Physical examination revealed engorged neck veins, hepatomegaly, and ascites with abdominal distention. On chest x-ray the cardiac shadow was slightly enlarged and bilateral pleural effusion was present. An electrocardiogram showed low voltage of the QRS complex. Computed tomographic scans revealed two lumens in the remarkably dilated ascending aorta and the severely thickened pericardium. Cardiac catheterization showed elevated right atrial pressure and elevated right and left ventricular end-diastolic pressures, in addition to a pressure record of early diastolic dip and end-systolic plateau in the right ventricle. Aortography demonstrated aortic dissection localized to the ascending aorta. On the basis of these findings, the diagnosis of chronic ascending aortic dissection complicated with constrictive pericarditis was made. After subtotal pericardiectomy, graft replacement of the ascending aorta and proximal aortic arch was performed with successful results. Her postoperative recovery was uneventful. Histological studies of the pericardium showed fibrosis and marked infiltration of the inflammatory cells. No findings of specific pericarditis such as tuberculosis or collagen diseases were detected.
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PMID:Constrictive pericarditis following hemopericardium due to ascending aortic dissection: A case report. 1050 55

Circumferential extension is a direct measure of the preservation of functional collagen crimp in the fibrosal layer of aortic valve leaflets. The aim of this study was to determine whether the elastic properties of zero-pressure, glutaraldehyde-fixed leaflets are changed by mechanical fatigue. Nine Medtronic Freestyle bioprostheses were subjected to 200x10(6) cycles of accelerated fatigue and then biaxially tested to quantify the elastic properties of the leaflets. At physiological load (60 Nm(-1)) the radial extensibility was approximately halved relative to controls (P<10(-4)); there were also lesser reductions in the circumferential extensions (P<.01). The pulsatile regurgitant volume showed no change relative to the control leaflets. The natural corrugations of the fibrosal layer were flattened by the fatigue cycling, but this was not related to an increase in the radial size of the leaflets. Valve competency was maintained.
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PMID:Fatigue-induced changes to the biaxial mechanical properties of glutaraldehyde-fixed porcine aortic valve leaflets. 1066 Jan 93

Between January 1989 and June 1998, we operated on 45 patients for sulcus vergeture. The studied population encompassed 38 women (84%) and 7 men (16%). The median age was 36 (range 12 to 71 years). The surgical technique is based on a concept of Cornut and Bouchayer according to which the dissection of the epithelium adherent to the deep subepithelial plane improves the vocal fold vibration. Dissection is performed with a single-pulsed carbon dioxide laser at 2 to 3 W with a pulse duration of 0.1 second. We use the Super-pulse microwave. The Acuspot micromanipulator provides a spot size of 250 microm at 350-mm focal length. When the vocal fold is atrophic, surgery is completed with a bovine or autologous collagen injection; the median injected quantity is 0.3 mL (range 0.1 to 0.4 mL). The epithelial microflap is redraped with fibrin glue. Voice therapy is indispensable for correcting the associated hyperkinetic dysphonia. The median postoperative follow-up period is 5 months (range 1 to 18 months). In terms of median values, the maximum phonation time improved from 9 to 13 seconds, the phonation quotient improved from 296.5 to 228.5 mL/s, and the spectral analysis distribution improved by 1 class. Stroboscopic examination reveals an improvement of the vibratory symmetry, amplitude, and wave. Subjectively, the patients describe an improved ability for vocal effort and the regression or disappearance of vocal fatigue. Although the timbre is improved, the voice often remains breathy and hoarse.
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PMID:Microsurgery of sulcus vergeture with carbon dioxide laser and injectable collagen. 1068 64

The incidence of fractures increases with age. This is partly due to extraosseous factors and partly to the increased fragility of the bone material itself. Ageing adversely affects the "quality" of human bone material, its elastic and ultimate properties. The hypothesis here is that these effects are caused by factors such as architectural changes, compositional changes, physicochemical changes, changes at the micromechanical level, and the degree of prior in vivo microdamage. Examination of the extent of the secondary osteonal area, the porosity level, the calcium content, the mineral/wet weight fraction, the dry density, the condition of the collagen and its content in mature x-links, the elasticity of osteonal and interstitial lamellae at the microscopic level and the numerical- and surface-density of the in vivo fatigue microcracks has been undertaken. The findings show that some factors simply affect the stiffness and the strength of bone, while others soley affect its toughness. We discuss the implications of these findings in the context of the composite nature of the ageing bone material matrix.
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PMID:Ageing human bone: factors affecting its biomechanical properties and the role of collagen. 1126


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