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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explore the pathophysiology of respiratory failure in an experimental pneumonia, a Pasteurella haemolytica broth culture was injected intratracheally into 12 calves, which were then studied over a period of 10 h. Measurements were made of inspired minute ventilation (VE), ventilatory pattern [inspiratory time (TI), expiratory time (TE), respiratory rate (RR) and tidal volume (VT)], transdiaphragmatic pressure (Pdi), occlusion pressure at the airway opening 100 milliseconds after onset of inspiration (Pawo100ms), arterial blood gas tensions and pH and recorded diaphragmatic electromyogram (EMGdi) and rectal temperature (Tr). On and after the third hour after inoculation, the animals varied in respect of clinical signs, Tr, RR, VE, Pawo100ms/EMGdi, and arterial gases and pH. In benign cases, diminished alertness, laboured respiration and fall of arterial oxygen pressure (PaO2) worsened up to 7 h after inoculation, but then progressively improved, VE being maintained at approximately 150% baseline throughout the study (10 h). Neither arterial carbon dioxide pressure (PaCO2) nor pH was altered. Moderate cases resembled benign cases in respect of laboured respiration, VE, PaO2 and PaCO2; however, pH was at first maintained at preinoculation levels, but declined thereafter. In severe cases, the animals were drowsy between hours 3 and 7, and became comatose between hours 8 and 10; in contrast to both benign and moderate cases: (1) RR was reduced by hour 5, (2) there was no trend towards recovery of PaO2 and pH, (3) VE, Pdi, Pawo100ms and Pawo100ms/EMGdi were severely decreased, and (4) PaCO2 increased. These results suggest that pneumonia does not alter ventilatory neuromuscular pump function in calves, unless concomitant cardiovascular collapse occurs. It is not clear whether fatal ventilatory failure is caused mainly by deterioration in ventilatory muscle fibre processes or structures, altered central nervous system adjustment of ventilatory timing, or cardiovascular dysfunction. However, inspiratory pressures fall when excitation to the diaphragm is still growing, which suggests peripheral respiratory muscle fatigue.
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PMID:The relation of ventilatory failure to pulmonary, respiratory muscle and central nervous system disturbances in calves with an experimentally produced pneumonia. 892 32

We observed, after 38 months of follow-up, the rupture of the metallic shell of a Harris-Galante cup implanted in a dysplastic acetabulum augmented with a femoral head autograft. Bone ingrowth was extended to 53% of the porous surface, but only in the areas in contact with the true acetabulum. No bone ingrowth was identified in the fiber mesh in contact with the autograft. The graft was necrotic on histologic examination and showed collapse radiographically. These last conditions were responsible for shear stress in the part of the cup that was in contact with the graft-acetabulum junction. These stresses were involved in the fatigue rupture mechanism identified on microscopic examination of rupture surfaces. We observed metallic structure anomalies in the failed cup by comparing with another Harris-Galante cup considered as a reference: larger alpha elements, reduction of the titanium equiaxial structure. These defects could be related to uncontrolled temperature during the sintering process utilized for fiber mesh fixation. These structural anomalies, by reducing the metallic fatigue strength, potentiated the deleterious effect of partial bone ingrowth and graft collapse.
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PMID:[Fatigue rupture of a Harris-Galante shell in contact with an autograft of the femur head. Analysis of bone, mechanical and metallurgical factors]. 896 97

Impulsive stress in repeated shock waves administered during extracorporeal shock-wave lithotripsy (ESWL) causes injury to kidney tissue. In a study of the mechanical input of ESWL, the effects of focused shock waves on thin planar polymeric membranes immersed in a variety of tissue-mimicking fluids have been examined. A direct mechanism of failure by shock compression and an indirect mechanism by bubble collapse have been observed. Thin membranes are easily damaged by bubble collapse. After propagating through cavitation-free acoustically heterogeneous media (liquids mixed with hollow glass spheres, and tissue) shock waves cause membranes to fail in fatigue by a shearing mechanism. As is characteristic of dynamic fatigue, the failure stress increases with strain rate, determined by the amplitude and rise time of the attenuated shock wave. Shocks with large amplitude and short rise time (i.e., in uniform media) cause no damage. Thus the inhomogeneity of tissue is likely to contribute to injury in ESWL. A definition of dose is proposed which yields a criterion for damage based on measurable shock wave properties.
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PMID:In vitro study of the mechanical effects of shock-wave lithotripsy. 933 Apr 54

The cross section radiographs and histology of nine bone grafts were examined to determine whether grafts are durable enough to support a total knee implant when the load is shared by host bone, graft bone, and a stemmed component. All cases had cemented total knee arthroplasties with stemmed components adjacent to bulk grafts. The cases included autografts and allografts, which had been in situ for an average of 41 months (range, 20-62 months). Seven of the grafts were retrieved postmortem from three patients (four knees), and two were retrieved at revision surgery from one patient. The allografts all were intact, but had not revascularized. The autografts were viable bone. New bone was being laid down on the dead graft bone at the periphery of the allografts. No change in the bone to cement interface, no graft collapse, no development of radiolucent lines, and no component loosening occurred in these cases. The promising clinical results of bone grafts in total knee arthroplasties were confirmed by the examination of these grafts at the cellular level. Using stemmed components in bone grafted knee reconstructions may have increased graft durability and protected the grafts from fatigue failure.
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PMID:The Ranawat Award. Histology of nine structural bone grafts used in total knee arthroplasty. 941 16

Obstructive sleep apnea (OSA) is a potentially life-threatening sleep disorder that is estimated to affect 20 million Americans. OSA is characterized by repeated collapse of the upper airway during sleep, which produces breathing pauses and interruption of the sleep cycle. Symptoms include heavy snoring, many nighttime arousals, sleep deprivation, chronic fatigue and a variety of cardiovascular diseases. While many treatments are advocated for OSA, oral devices have been shown to be effective. Dental technicians and dentists may be involved in the construction of oral appliances for patients with OSA. In this article, a synopsis of various treatment modalities is presented, and the construction of two appliances is described and illustrated.
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PMID:Custom devices for sleep apnea treatment. 951 77

Many bones within the axial and appendicular skeleton are subjected to repetitive, cyclic loading during the course of ordinary daily activities. If this repetitive loading is of sufficient magnitude or duration, fatigue failure of the bone tissue may result. In clinical orthopedics, trabecular fatigue fractures are observed as compressive stress fractures in the proximal femur, vertebrae, calcaneus and tibia, and are often preceded by buckling and bending of microstructural elements. However, the relative importance of bone density and architecture in the etiology of these fractures is poorly understood. The aim of the study was to investigate failure mechanisms of 3D trabecular bone using micro-computed tomography (microCT). Because of its nondestructive nature, microCT represents an ideal approach for performing not only static measurements of bone architecture but also dynamic measurements of failure initiation and propagation as well as damage accumulation. For the purpose of the study, a novel micro-compression device was devised to measure loaded trabecular bone specimens directly in a micro-tomographic system. The measurement window in the device was made of a radiolucent, highly stiff plastic to enable X-rays to penetrate the material. The micro-compressor has an outer diameter of 19 mm and a total length of 65 mm. The internal load chamber fits wet or dry bone specimens with maximal diameters of 9 mm and maximal lengths of 22 mm. For the actual measurement, first, the unloaded bone is measured in the microCT. Second, a load-displacement curve is recorded where the load is measured with an integrated mini-button load cell and the displacement is computed directly from the microCT scout-view. For each load case, a 3D snap-shot of the structure under load is taken providing 34 microm nominal resolution. Initial measurements included specimens from bovine tibiae and whale spine to investigate the influence of the structure type on the failure mechanism. In a rod-like type of architecture as seen in the whale spine, structural failure was described by an initial buckling and bending of structural elements followed by a collapse of the overloaded trabeculae. In the more plate-like bovine tibial architecture, buckling and bending could not be observed. Failure rather seemed to occur instantaneously. In conclusion, micro-compression in combination with 3D microCT allows visualization of failure initiation and propagation and monitoring of damage accumulation in a nondestructive way. We expect these findings to improve our understanding of the relative importance of density, architecture and load in the etiology of spontaneous fractures of the hip and the spine. Eventually, this improved understanding may lead to more successful approaches to the prevention of age-related fractures.
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PMID:Micro-compression: a novel technique for the nondestructive assessment of local bone failure. 1010 Sep 46

The authors discuss the significance of interbody fusion for early and long term stability of the lumbar spine. They stress that the aim of the modern spinal instrumentation is to promote bone healing and not to replace fusion. Without fusion every stabilization device will fail in fatigue. The biomechanics of different types of spinal fusion and biomechanical conditions at fusion site are discussed. A history of lumbar interbody fusion including threaded implants (cages) is presented. Interbody cages combine positive properties of tricortical bone graft: the strength of cortical to the bone with improved incorporation properties of cancellous bone. In contrast bone graft their biomechanical performance is far better: they increase strength and stability of osteosynthesis, do not go collapse and resorption, prevent from decrease in disc space height and kyphotic angulation of the fused motion segment, require less bone to achieve fusion. They can be used solely without support of any stabilization system. Preliminary experience in fusion with interbody threaded implants suggest significant efficacy of this method.
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PMID:[Lumbar interbody fusion. Biomechanical significance for the spine]. 1046 37

Obstructive sleep apnea is a significant medical problem affecting up to 4 percent of middle-aged adults. The most common complaints are loud snoring, disrupted sleep and excessive daytime sleepiness. Patients with apnea suffer from fragmented sleep and may develop cardiovascular abnormalities because of the repetitive cycles of snoring, airway collapse and arousal. Although most patients are overweight and have a short, thick neck, some are of normal weight but have a small, receding jaw. Because many patients are not aware of their heavy snoring and nocturnal arousals, obstructive sleep apnea may remain undiagnosed; therefore, it is helpful to question the bedroom partner of a patient with chronic sleepiness and fatigue. Polysomnography in a sleep laboratory is the gold standard for confirming the diagnosis of obstructive sleep apnea; however, the test is expensive and not widely available. Home sleep studies are less costly but not as diagnostically accurate. Treatments include weight loss, nasal continuous positive airway pressure and dental devices that modify the position of the tongue or jaw. Upper airway and jaw surgical procedures may also be appropriate in selected patients, but invasiveness and expense restrict their use.
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PMID:Obstructive sleep apnea. 1059 19

Isolated iliac artery aneurysm threatening to rupture is a rare condition with a poor prognosis if not dealt with by the physician in a brisk and effective manner. Symptoms from an iliac aneurysm can masquerade as a range of symptoms from neighbouring organs or be almost asymptomatic before rupturing. A case of a 81 year old man, with symptoms of dizziness, fatigue and light lower abdominal pain, who developed sudden cardiovascular collapse, is presented.
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PMID:[Rupture of an isolated iliac aneurysm]. 1068 Apr 75

1. The effects of diabetes on the electrical and contractile function of skeletal muscle are variable, depending on muscle fibre type distribution. The muscles of the upper airway have a characteristic fibre distribution that differs from previously studied muscles, but the effects of diabetes on upper airway muscle function are unknown. Normally, contraction of upper airway muscles, such as the sternohyoids, dilates and/or stabilizes the upper airway, thereby preventing its collapse. Diabetes is associated with obstructive sleep apnoea in which there is collapse of the upper airway due to failure of the upper airway musculature to maintain airway patency. Therefore, the purpose of the present study was to determine the effects of diabetes on the electrical and contractile characteristics of upper airway muscle. 2. Rats were treated with vehicle (sodium citrate buffer; pH 4.5) or with streptozotocin to induce diabetes, confirmed by the presence of hyperglycaemia, and the contractile and electrical properties of the sternohyoid were compared in these two groups. Isometric contractile properties and membrane potentials were determined in isolated sternohyoid muscles in physiological saline solution at 25 degrees C. 3. Streptozotocin had no effect on sternohyoid muscle fatigue, the tension-frequency relationship or membrane potentials, but did increase contraction time, half-relaxation time, twitch tension and tetanic tension. 4. Streptozotocin-induced diabetes has no effect on sternohyoid muscle fatigue or the tension-frequency relationship, but does reduce contractile kinetics and increases force generation. These effects are not due to changes in resting membrane potential. These data are evidence that the association of sleep apnoea and diabetes is not due to effects on upper airway muscle contractile properties.
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PMID:Contractile and electrical properties of sternohyoid muscle in streptozotocin diabetic rats. 1120 73


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