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Increasingly small animals have been seen as models for humans with highly compliant medicine 3x a day cheap flexeril uk, relatively oblong chests medicine 123 flexeril 15 mg on line, as in children medicine 0829085 best flexeril 15 mg. A lateral decubitus, or a dorsal position, but supported by a "V" shaped cradle may be used to overcome this, but the former influences the distances between compression surfaces and the latter may limit lateral movement of the chest wall. In series of experiments animals may be used as their own controls, with a few minutes between one technique followed by another. However, care should be taken in extrapolating this data to humans for the same reasons . Animal models may provide increased insights, but may also give rise to confusion. Although the "cardiac" pump theory (Kouwenhoven) and the "thoracic" pump theory (Criley) have been promoted as one-or-the-other mechanism, it has gradually become accepted over time that depending on the physiology of the patient the blood flow may be caused by either or both, perhaps alternating or time sensitive. The main line of adjuvants is presented in the order of their initial publication. Cardiopulmonary Resuscitation 18-7 Compressions are supplemented by ventilations in a ratio of 15 compression to 2 ventilations of about 800 ml (one caregiver), and this respiratory pause should be shorter than 6 sec. This group, noting airway pressures of 60 to 110 cm H2 O, found more than a 100% improvement over baseline values for carotid flow, while working in humans. The cause of the detrimental effect may be that open alveoli become severely overdistended, and that the pulmonary capillary bed becomes underperfused. While demonstrating improvement in cerebral blood flow, at unspecified pressures, by improving the arterial to venous pressure gradient, as well as improving cardiac filling, the technique was not deemed useful due to extensive abdominal trauma. The improvements were suggested to (a) increase intrathoracic pressure (decrease in pressure loss due to movement of the flaccid diaphragm and abdominal wall), (b) increase functional arterial resistance, and (c) redistribute blood volume to compartments above the diaphragm out of the abdominal compartment due to the flaccid nature of the diaphragm . No original research papers have appeared on this specific topic in more than 10 years. The mechanism for coughing is clear: the diaphragm contracts strongly after a deep breath. With the upper airway partially obstructed forceful contraction will compress the air in the lungs and create equal pressure change on all intrathoracic structures. Blood, not compressible, will move out of the highpressure area to low-pressure areas. To achieve effective forward flow some (at least one) anatomical or functional valves and resistance differences are required. A similar functional valvular obstruction at the level of the diaphragm is unproven, with retrograde flow being limited by the peripheral capillary beds and arteriolar resistance. Some hospitals routinely describe it in patient information folders and have the nursing staff issue instructions on the technique prior to procedures. A 50% compression duration (compression: relaxation ratio of 1), was introduced as standard and still is advocated. Caregiver skills evaluation has demonstrated that at higher frequencies, that is, compression rates greater than 120 cpm, the compression: relaxation ratios almost always approach 1. Later, other studies, typically in conjunction with much higher compression rates or increased force of compression (see Section 18. The concept rests on basic physiological principles directly relating to intrathoracic pressure changes influencing venous return. With intermittent positive-pressure ventilation (mouth-to-mouth or using a respirator), intrathoracic pressure is predominantly positive, reducing venous return by interfering with the pressure gradient. The negative airway pressure creates an artificially normal negative segment in the pressure curve, in theory recreating a pressure cycle similar to that seen under spontaneous breathing. The technique has fallen into disuse due to extensive ventilation to perfusion mismatch (shunting) in the lung and severe atelectasis. However, a variation on this concept, in the form of a transient occlusion of the airway during decompression of the chest is currently under clinical investigation (see Section 18. Conceptually, it will decrease the arterial inflow into the lower extremities by increasing the peripheral resistance and decrease the venous pool in the legs by compression of the superficial and deep veins. This should generate a small, one-time, fluid challenge to the central circulation, known as autotransfusion and decrease the systemic vascular bed size. The autotransfusion has been suggested to be in the order of 8 to 12 ml/kg body weight. Studies in humans have not been able to demonstrate improved outcome, perhaps due to the involved nature of application. This model, based on a pure "thoracic" pump concept, has not been demonstrated to improve outcome in humans, and has been associated with pulmonary complications attributed to high airway pressures. The mechanism for improvement has been thought to be counterpulsation in the aorta and increased venous loading of the thoracic cavity, as demonstrated by increased antegrade flow in the vena cava inferior , and typically involves at least three well-trained caregivers. Rates of up to 150 compression per minute (100 compressions per minute is currently advised, see Table 18. When modeling from the cardiac pump theory, as long as the compression allows the mitral valve to close, and allows for sufficient filling time, artificial cardiac output will be determined by left ventricular end-diastolic volume. Modeled from the thoracic pump theory, the benefit may be due to the overall increase in the percentage of time actually allotted to compression. Using a mechanical compression device, exact massage depths could be reproduced at any given frequency or compression duration. This preliminary study demonstrated a small improvement in initial outcome, with better perfusion gradients. However, time needed to apply the vest, as well as its bulkiness have limited its general use. This is due to its independence from changes in thoracic compliance, myocardial stiffness, and ventilation parameters. Conceptually, the simultaneous compression of chest and abdomen should create an improvement in the pressure rise, due to coupling of the thoracic and abdominal cavities (thoracic pump theory). Initial investigations seem to support improved pressure gradients, but as improved outcome has not been demonstrated, little recent work has been presented. Initial reports of significant improvement of outcome have been challenged by others who were unable to find improvements . Insertion time is less than 30 sec, and as little as 10 sec may be required in trained hands. Early human work, in the prehospital setting, in patients with failed basic and advanced life support, demonstrated good clinical parameters, although one cardiac rupture was noted . The name, pGz, refers to a periodic fractional part of the acceleration of gravity, applied along the head to foot or "Z "-axis. It has been demonstrated to produce blood flow and ventilation proportional to the amplitude and frequency of the force applied. Using radiolabeled microspheres injected into the circulation, preferential flow to vital organs, including the splanchic microcirculation, could be detected. Conceptually, this model is independent of the "cardiac" or "thoracic" pump theories, although the "thoracic" (volume) aspect does play a role. This procedure involves utilizing a valvular device in combination with a facemask or attached to the endotracheal tube.
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He has no close friends and lives with his mother symptoms 1974 cheap flexeril 15 mg online, with whom there is some degree of conflict medicine dispenser flexeril 15 mg online. His communication and socializing skills are moderately handicapped given that symptoms 0f pneumonia buy flexeril 15 mg low cost, because of his memory impairment, he is unable to maintain a topic of conversation. He relies upon his mother to prepare the meals, and it seems that he would be unable to live in the community without such live-in support and supervision. Yet in spite of the large amount of spare time, there is little evidence of a well-developed avocational programme in lieu of work. Even though, following hospital discharge, they live in the community, they are dependent upon such emotional and practical supports as are provided by family. Although it is difficult to compare individual cases with group studies, there is a suggestion in group studies examining other neurological conditions of sudden onset, such as stroke and traumatic brain injury, that many of these people may in fact have less disruption of their social roles than those with pure amnesia, in terms of occupational activity, interpersonal relationships and independent living skills. This is in spite of the additional multiple neuropsychological and motor-sensory disabilities frequently experienced by the stroke and traumatic brain injury groups. It is counter-intuitive that people with fairly circumscribed memory disorders should experience lifestyles that are so extremely disrupted. He stoutly maintains that note-taking and diary keeping are crutches that would prevent him from improving" (Kaushall et al. Considering the model of Kendall & Terry (1996) presented earlier, however, the severity and nature of the impairment was only one factor contributing to outcome and psychosocial adjustment. A consideration of "person" factors (including the personality structure of the individual and the emotional responses to the situation) is necessary to understand the psychosocial effects of acquired memory disorders. A literal interpretation of the elevated scales can be misleading, however, because of the preponderance of items that would likely be endorsed by persons with neurological conditions (see also Alfano et al. Items such as, "There is something wrong with my mind", rather than being indicative of psychiatric abnormality, represent an accurate interpretation of the effects of the impairments these individuals experience. Similar observations have been made about other instruments, such as the Symptom Checklist (Woessner & Caplan, 1995) and the Eysenck Personality Questionnaire (Tate, submitted). The quantity of responses was low and additionally qualitative analysis indicated obsessional tendencies, as well as themes of deterioration and decay. The authors suggested that, whereas the latter may reflect a damaged sense of self as a result of his illness, the former may represent either "a lifelong personality pattern. Hence, if the data are to be interpreted as showing pathology of his personality structure, this is secondary to the amnesic syndrome. To these standardized results can be added the clinical observations made about H. It is also noted that his adjustment to all changes in relationships and circumstances has been smooth (Corkin, 1984), although whether this reflects maturity or is a function of his adynamia is a moot point. To date, personality change from the premorbid state has not been examined in people with amnesia. Although the traumatic brain-injured group is one for which changes in personality are commonly reported, very few studies with that group have used standardized measures of personality, including ratings taken of the premorbid state soon after onset of injury. Employing the Eysenck Personality Questionnaire-Revised (Eysenck & Eysenck, 1991), Tate (submitted) found more extensive changes between premorbid and 6 month posttrauma ratings: significant decrease in Extraversion and increases in Neuroticism and Criminality, as well as Psychoticism at 12 months posttrauma. These data are interpreted as being changes in personality structure that are a direct consequence of the injury. One of these pertains to the effect of the memory disorder on the development of personality over time. What is the effect of an individual being unable to incorporate and integrate new information and life experiences into the existing personality structure? They hypothesized that, if individuals with amnesia predominantly draw upon immediate memory as a reference point for their personality structure, then they will likely experience fluctuations in emotional states in response to changes in everyday events. By contrast, if they draw upon remote memories, then a much more stable profile will likely emerge. Their own data point to the latter alternative, but clearly this depends upon the nature of the memory disorder. This left him with the most severe episodic memory impairment reported to date, such that he is described as living in "a moment with no past to anchor it and no future to look ahead to" (Wearing, 1988, cited in Wilson & Wearing, 1995, p. With such devastating losses of personal knowledge, in addition to the inability to retain and build upon new memories, one can only speculate that his memory disorder must cut across his very sense of self. Articulate individuals, such as the psychologist Malcolm Meltzer (1983), who writes about the effect of his own (albeit comparatively less severe) memory disorder on his psyche, had such an experience: I felt to some extent that I had lost some of my identity. This was not total or extreme, but there were some questions in my mind about beliefs, values and purposes in life. In addition, I felt I had lost some of my cultural background when I had difficulty remembering some of the customs, traditions and beliefs of the groups to which I belonged. Emotional Status There is a substantial literature on the emotional distress encountered in other groups with acquired neurological conditions, such as stroke and traumatic brain injury, with anxiety and depression, in particular, commonly reported. The data are generally given a straightforward interpretation as being indirect consequences of the neurological event. Rather, he "maintains a steadfastly optimistic, and sometimes unrealistic, view of his own life and progress" (p. The authors suggest three hypotheses to account for the test scores: first, that S. A second hypothesis pertains to the presence of psychological denial as a protective mechanism to shield himself from the full knowledge of his situation. To these possibilities needs to be added the method by which data are gathered, namely self-report instruments. Hermann (1982, cited in Schacter, 1991) observed that completing a self-report instrument is itself a memory task, and this could be a reason why memory-disordered individuals fail to reliably endorse items on checklists such as the Everyday Memory Questionnaire (Sunderland et al. The hypothesis is not only of theoretical importance but is also clinically relevant because it impacts upon management. Ben-Yishay, 2000; Prigatano, 2000) maintain that awareness and insight are requisites for successful rehabilitation. Those with the so-called "pure amnesias" from circumscribed temporal and diencephalic lesions do not have problems with insight. Although their temporal lobe group rated their memory performances worst of any group, nonetheless the frontal and diencephalic (mostly Korsakoff) groups endorsed significantly more severe responses than the normal control group. This would imply that these people have shallow and superficial emotional responses to many situations, not just to their own altered life circumstances, but also that their close relationships may be lacking in warmth, sensitivity and spontaneity. A Psychosocial Study of a Person with Amnesia-the Whole Picture Background the foregoing cases provide incomplete data from one or other psychosocial perspective: social functioning is well described in case N. The following case of a person (who has requested that she be identified as Michelle), reported by Tate et al. The data are particularly instructive in that ratings on standardized personality instruments regarding her premorbid status were obtained from her father soon after the injury, and then compared with postinjury ratings at 6 and 12 months postinjury.
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Single crystal alumina can be made by feeding fine alumina powders onto the surface of a seed crystal which is slowly withdrawn from an electric arc or oxy-hydrogen flame as the fused powder builds up medicine glossary 15 mg flexeril free shipping. Single crystals of alumina up to symptoms strep throat discount flexeril generic 10 cm in diameter have been grown by this method [Park and Lakes medications made from plants 15mg flexeril, 1992]. Generally, the smaller the grains, the lower the porosity and the higher the strength [Park and Lakes, 1992]. Aluminum oxide has been used in the area of orthopaedics for more than 25 years [Hench, 1991]. Single crystal alumina has been used in orthopaedics and dental surgery for almost 20 years. This high hardness permits its use as an abrasive (emery) and as bearings for watch movements [Park and Lakes, 1992]. The high hardness is accompanied by low friction and wear and inertness to the in vivo environment. These properties make alumina an ideal material for use in joint replacements [Park and Lakes, 1992]. Aluminum oxide implants in bones of rhesus monkeys have shown no signs of rejection or toxicity for 350 days [Graves et al. However, the key for success of any implant, besides the correct surgical implantation, is the highest possible quality control during fabrication of the material and the production of the implant [Hench, 1991]. Zirconia has a high melting temperature (Tm = 2953 K) and chemical stability with a = 5. It undergoes a large volume change during phase changes at high temperature in pure form; therefore, a dopant oxide such as Y2 O3 is used to stabilize the high temperature (cubic) phase. We have used 6 mole% Y2 O3 as dopant to make zirconia for implantation in bone [Hentrich et al. Zirconia produced in this manner is referred to as partially stabilized zirconia [Drennan and Steele, 1991]. However, the physical properties of zirconia are somewhat inferior to that of alumina (Table 39. High density zirconia oxide showed excellent compatibility with autogenous rhesus monkey bone and was completely nonreactive to the body environment for the duration of the 350 day study [Hentrich et al. Zirconia has shown excellent biocompatibility and good wear and friction when combined with ultra-high molecular weight polyethylene [Kumar et al. Among these, only pyrolitic carbon is widely utilized for implant fabrication; it is normally used as a surface coating. Although the techniques of coating with diamond have the potential to revolutionize medical device manufacturing, it is not yet commercially available [Park and Lakes, 1992]. The crystalline structure of carbon, as used in implants, is similar to the graphite structure shown in Figure 39. The planar hexagonal arrays are formed by strong covalent bonds in which one of the valence electrons or atoms is free to move, resulting in high but anisotropic electric conductivity. Since the bonding between the layers is stronger than the van der Waals force, it has been suggested that the layers are cross-linked. However, the remarkable lubricating property of graphite cannot be attained unless the cross-links are eliminated [Park and Lakes, 1992]. The poorly crystalline carbons are thought to contain unassociated or unoriented carbon atoms. However, if the crystallites are randomly dispersed, the aggregate becomes isotropic [Park and Lakes, 1992]. The mechanical properties of carbon, especially pyrolitic carbon, are largely dependent on its density, as shown in Figure 39. The increased mechanical properties are directly related to increased 39-6 Biomedical Engineering Fundamentals (a) (b) 0. Graphite and glassy carbon have a much lower mechanical strength than pyrolitic carbon (Table 39. The strength of pyrolitic carbon is quite high compared to graphite and glassy carbon. Again, this is due to the fewer number of flaws and unassociated carbons in the aggregate. A composite carbon which is reinforced with carbon fiber has been considered for making implants. Compatibility of pyrolitic carbon-coated devices with blood have resulted in extensive use of these devices for repairing diseased heart valves and blood vessels [Park and Lakes, 1992]. Pyrolitic carbons can be deposited onto finished implants from hydrocarbon gas in a fluidized bed at a controlled temperature and pressure. The anisotropy, density, crystallite size and structure of the deposited carbon can be controlled by temperature, composition of the fluidized gas, the bed geometry, and the residence time (velocity) of the gas molecules in the bed. It is also possible to introduce various elements into the fluidized gas and co-deposit them with carbon. Usually silicon (10 to 20 w/o) is co-deposited (or alloyed) to increase hardness for applications requiring resistance to abrasion, such as heart valve discs. Recently, success was achieved in depositing pyrolitic carbon onto the surfaces of blood vessel implants made of polymers. The deposited carbon has excellent compatibility with blood and is thin enough not to interfere with the flexibility of the grafts [Park and Lakes, 1992]. The vitreous or glassy carbon is made by controlled pyrolysis of polymers such as phenolformaldehyde, Rayon (cellulose), and polyacrylnitrite at a high temperature in a controlled environment. This process is particularly useful for making carbon fibers and textiles which can be used alone or as components of composites. Almost all bioresorbable ceramics except Biocoral and Plaster of Paris (calcium sulfate dihydrate) are variations of calcium phosphate (Table 39. Examples of resorbable ceramics are aluminum calcium phosphate, coralline, Plaster of Paris, hydroxyapatite, and tricalcium phosphate (Table 39. This material has been synthesized and used for manufacturing various forms of implants, as well as for solid or porous coatings on other implants (Table 39. Calcium phosphate can be crystallized into salts such as hydroxyapatite and -whitlockite depending on the Ca: P ratio, presence of water, impurities, and temperature. In a wet environment and at lower temperatures (<900 C), it is more likely that hydroxyl- or hydroxyapatite will form, while in a dry atmosphere and at a higher temperature, -whitlockite will be formed [Park and Lakes 1992]. Both forms are very tissue compatible and are used as bone substitutes in a granular form or a solid block. The apatite form of calcium phosphate is considered to be closely related to the mineral phase of bone and teeth. For filling space vacated by bone screws, donor bone, excised tumors, and diseased bone loss 4. The atomic structure of hydroxyapatite projected down the c-axis onto the basal plane is shown in Figure 39. Note that the hydroxyl ions lie on the corners of the projected basal plane and they occur at equidistant intervals (3.
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Might one patient understand the significance of a picture of an elephant medications vs medicine order discount flexeril, while not understanding the verbal label "elephant" symptoms 16 dpo buy generic flexeril 15mg online, and another patient understand the verbal label and not the picture? What are the implications for the distinction between semantic and episodic memory? Might a patient understand a word or recognize an object in one context but not another? Subordinate Information It is a common clinical observation that semantically impaired patients may classify a word or picture correctly in terms of broad taxonomic category treatment zone tonbridge buy flexeril with american express, yet have difficulty discriminating between category exemplars (Warrington, 1975; Warrington & Shallice, 1984; Hodges et al. A patient may state that a rabbit is an animal but not know how it differs from a dog or horse, and will make coordinate category errors in naming. Nevertheless, for all animal words she selected an animal picture and for all food words a food picture, suggesting knowledge of word meaning sufficient to enable superordinate category classification. This apparently greater vulnerability to disruption of subordinate categories has been interpreted by some (Warrington, 1975; Shallice, 1988) as favouring a hierarchical model of semantic memory. In the influential hierarchical network model of Collins & Quillian (1969), it would be assumed that lower levels of the hierarchical tree, representing information about properties or attributes, are most vulnerable to disruption and are damaged first, the higher, superordinate level the last to be lost. Findings from a longitudinal study of naming errors in a semantic dementia patient (Hodges et al. Over repeated testing sessions, the patient made progressively fewer coordinate category responses. According to the model, access from a lower to higher level of the hierarchy requires traversing intervening levels. Knowledge that a robin is an animal is accessed through the intermediate level "bird". A robin should not be correctly classified as an animal if it cannot first be classified as a bird. Yet, patients with semantic disorder do classify robins as animals, without knowing that they are birds. According to Rapp & Caramazza, if some of those features are lost, then the remaining impoverished information will be better able to support broad. Impoverished feature knowledge may be sufficient to differentiate an animal from a vegetable, but not a dog from a cat. Similarly, Tyler & Moss (1998), using a semantic priming and verification task in a longitudinal study of a patient with semantic dementia, found no support for the view that property information is affected before higher level, category information. Far from having general or broad conceptual understanding, their semantic knowledge appeared to have become limited to the particular, to their own specific experience of the world. Nevertheless, those same patients who demonstrate narrowed, personalized conceptual understanding, showed the usual pattern of errors on naming tasks. We would argue, in line with Rapp & Caramazza, that superordinate category information is not inherently less vulnerable to disruption in a degraded semantic memory system. However, the severely impoverished information available is sufficient to allow a horse to be recognized as an animal (as opposed to a food or an article of clothing), but not sufficient to allow it to be distinguished from a dog. Category Specificity In 1984 Warrington & Shallice described four patients recovering from herpes simplex encephalitis who showed a disproportionate impairment in their ability to recognize living things and food compared to inanimate objects. A similar pattern of findings has been reported in other postencephalitic patients (Pietrini et al. Opponents have argued that category dissociations arise artefactually, as a result of differences in the frequency, familiarity and visual complexity (Stewart et al. Picture stimuli of inanimate objects are typically high-familiarity items, whereas those of animals are low in familiarity. Members of biological categories are often more visually similar than those of man-made categories. Indeed, normal superiority for man-made artefacts has been demonstrated by some authors (Capitani et al. It is certainly the case that some apparent category dissociations disappear when factors such as frequency and familiarity are controlled. Superior rather than inferior performance for biological categories has been demonstrated in some patients (Warrington & McCarthy, 1983, 1987; Sacchett & Humphreys, 1992) and an identical set of test materials has been shown to elicit opposing patterns of performance in different patients (Hillis & Caramazza, 1991). A further compelling argument comes from the consistency between pattern of deficit and location of brain lesions (Gainotti et al. Inferior knowledge of biological categories has invariably been reported in patients with temporal lobe damage, whereas inferior performance for inanimate objects is associated with extensive damage to the frontoparietal lobes of the left hemisphere and occurs in conjunction with global or nonfluent aphasia. Sensory Attributes of Meaning the term "category specificity" is in a sense a misnomer. It conveys the impression of exclusive involvement of one category and absolute sparing of another, which is rarely the case. A salient view, advanced by Warrington & McCarthy (1987) and Warrington & Shallice (1984), is that category dissociations result from differences in the properties that define a concept, reflecting differences in the sensory processing channels through which information was initially acquired. The conceptual distinction between two inanimate objects, such as a glass and a vase, derives largely from their different functions. Conversely, animals and foods are distinguished predominantly on the basis of sensory properties such as colour, shape, texture, taste and smell. That is, biological categories are weighted towards sensory properties and inanimate objects towards functional properties. A disruption to knowledge about sensory attributes would result in a disproportionately severe impairment for animals compared to household objects, whereas disruption to knowledge about functional attributes would have the opposite effect. This distinction between sensory and functional aspects of knowledge accounts for the otherwise anomalous finding that patients with impaired biological category knowledge typically show relatively preserved knowledge of the biological category of body parts and impaired knowledge of the nonbiological categories of musical instruments and precious stones. Functional properties are salient conceptual attributes of body parts, and sensory properties of musical instruments and precious stones. Although not all authors have framed distinctions in precisely the same terms, distinctions drawn between perceptual and functional (Sartori & Job, 1988), visual and verbal (Silveri & Gainotti, 1988) and perceptual and associative (Chertkow et al. It avoids the seemingly phrenological notion that different categories are stored in separate parts of the brain. The link between perceptual/sensory attributes and the anterior temporal lobes is consistent with the established role of the ventral pathways in the processing of visual information and for object recognition (Mishkin et al. It has been speculated that the anterior regions of the inferior temporal cortex may be involved in networks at the interface between perception and language (Breedin et al. The link between functional information and the language areas of the left hemisphere is consonant with the more abstract nature of function information, which may be more closely allied with language. The argument is that distinct domains of knowledge have developed as an adaptation to evolutionary pressures, which have resulted in allocation of distinct neural networks to the processing of each knowledge domain. On this account, category-specific deficits should selectively impair all information pertaining to the affected domain, while sparing all information pertaining to other knowledge domains.
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The principle of summation may be applied either in time or in space or in a combination of both treatment trichomoniasis order flexeril. The main kinds of summation are listed below: (a) One-point spatial summation: In this kind of summation coil elements medicine omeprazole 20mg flexeril 15mg amex, carrying current in the desired direction medications contraindicated in pregnancy order flexeril discount, are placed in various locations around the head in such a configuration to create high electric field intensity in a specific deep brain region, which is simultaneously a high percent of the maximal electric field at the brain cortex. If, for example, we know the path of a certain axonal bundle, a coil shall be designed in a configuration that will produce significant electric field at several points along the bundle. This configuration may enable induction of an action potential in this bundle, while minimizing the activation of other brain regions. In such a case, the coil may be stimulated consecutively, so that at each time period only a certain element or a group of elements are activated. This way, in the desired deep brain region will be induced a significant electric field at all time periods while in more cortical regions a significant field will be induced mainly at certain periods when proximate coil elements are activated. This will enable stimulation of the deep brain structure while minimizing stimulation of other brain regions and specifically of cortical regions. Minimization of radial components: Coil construction is meant to minimize wire elements carrying current components which are nontangential to the skull. Electrical field intensity in the tissue to be stimulated and the rate of decrease of electrical field as a function of distance from the coil depend on the orientation of the coil elements relative to the tissue surface. It has been shown that coil elements which are nontangential to the surface induce accumulation of surface charge, which leads to cancellation of the perpendicular component of the induced field at all points within the tissue, and reduction of the electrical field in all other directions. At each specific point, the produced electric field is affected by the lengths of the nontangential components, and their distances from this point. Thus, the length of coil elements which are not tangential to the brain tissue surface should be minimized. Furthermore, the nontangential coil elements should be as small as possible and placed as far as possible from the deep region to be activated. Remote location of return paths: the wires leading currents in a direction opposite to the preferred direction (the return paths) should be located far from the base and the desired brain region. In other cases part of the return paths may be adjacent to a different region in the head which is distant from the desired brain region. Since the return paths are far from the main base, it is possible to screen all, or part of their field, by inserting a shield around them or between them and the base. The shield is comprised of a material with high magnetic permeability, capable of inhibiting or diverting a magnetic field, such as mu metal, iron, or steel core. Alternatively the shield is comprised of a metal with high conductivity which can cause electric currents or charge accumulation that may oppose the effect produced by the return portions. Other brain regions are also associated with reward circuits, such as the ventral tegmental area, amygdala, and medial prefrontal, cingulate, and orbitofrontal cortices [Breiter and Rosen, 1999; Kalivas and Nakamura, 1999]. Moreover, neuronal fibers connecting the medial prefrontal, cingulate, or orbitofrontal cortex with the nucleus accumbens may have an important role in reward and motivation [Jentsch and Taylor, 1999; Volkow and Fowler, 2000]. The nucleus accumbens is also connected to the amygdala and the ventral tegmental area. Therefore, activation of these brain regions may affect neuronal circuits mediating reward and motivation. In rats and monkeys and even in humans, electrical stimulation of the median forebrain bundle is rewarding, and when a stimulating electrode is inserted into various parts of that bundle (including the ventral tegmental area, the median prefrontal cortex and the nucleus accumbens septi), compulsive self-stimulation can be obtained [Milner, 1991; Jacques, 1999]. The new coil (termed the Hesed coil) is designed to stimulate effectively deeper brain regions without increasing the electrical field intensity in the superficial cortical regions. Numeric simulations and phantom measurements of the total electrical field produced by the Hesed coil inside a homogeneous spherical volume conductor are presented and compared with results from a circular coil in different orientations and from the double-cone coil. The drop of the electrical field in the brain as a function of the distance from the new coil is much slower compared with previous coils. It is hoped that such a coil can Transcranial Magnetic Stimulation 37-7 stimulate deeper regions such as the nucleus accumbens and the fibers connecting the medial prefrontal or cingulate cortex with the nucleus accumbens. Activation of these fibers may induce reward, and chronic treatment may have antidepressant properties or serve as a new strategy against drug addiction. The head was modeled as a spherical homogeneous volume conductor with a radius of 7 cm. The induced and electrostatic field at a specific point inside the spherical volume were computed for several coil configurations, using the method presented by Eaton , and the total electric fields in the x, y, and z directions were calculated. The vector potential A and scalar potential can be expanded in terms of spherical harmonic functions up to N order. R is the radius vector to the point inside the sphere where the field is computed, and r is the vector to the differential coil element on which the integration is performed. The convergence rate depends on the distance from coil elements and on coil configuration, and in general, is faster for more remote points. For the new coil design, the convergence rate was faster than for the circular coil. The distance between the noninsulated edges of the two wires of the probe was 14 mm. Voltage measured divided by the distance between the wire edges gives the induced electrical field figure. Stimulation was delivered using the Magstim Model 200 stimulator at 100% power level. The coils were placed on the glass surface and the electrical field was measured in numerous points within the saline solution. The presence of an electrostatic field not only reduces the total field at any point, but also leads to significant reduction in the percentage of the total field in depth, relative to total field at the surface. Moreover, both the total field and the percentage relative to the surface at any specific point depend on its distance from the nontangential coil elements. The basic concept of the new coil design is to generate summation of the electrical field in depth by inducing electrical fields at different locations around the surface of the head, all of which have a common direction. Such an approach increased the percentage of electrical field induced in depth, relative to the field in the surface regions. In addition, because a radial component had a dramatic effect on the percentage of the electrical field in depth, an effort was made to minimize the overall length of nontangential coil elements, and to locate them as distant as possible from the deep region to be activated. Calculations for several coil configurations were made and the optimal configuration (termed the Hesed coil) was compared with standard circular coils and with the double-cone coil. We compare simulation results of field distribution of the Hesed coil design (Figure 37. This desired direction is the anteroposterior direction in the example shown in Figure 37. For each strip there is a return path wire having current component at the opposite direction (z direction), located 5 cm above the head. These return paths are located at the top edges of four fans to remove the currents flowing through them away from the deep regions of the head. These loci were chosen to remove the return paths as much as possible from the deep brain region to be activated most effectively. The only wires with currents that have radial components are those connecting the strips that are attached to the head with their return paths, along the sides of the fans.
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Although it was absent in our patient symptoms liver disease buy flexeril 15mg without prescription, peripheral nerve involvement is present in most cases symptoms 6dpiui discount 15mg flexeril overnight delivery. Brain fludeoxyglucose F 18 positron emission tomography hypometabolism in magnetic resonance imaging-negative x-linked adrenoleukodystrophy treatment 11mm kidney stone purchase 15 mg flexeril visa. Four years ago, he noted bilateral lower extremity numbness below the knee, particularly in his shins. At the time he also had a right transcarpal ligament release at an outside institution for a diagnosis of carpal tunnel syndrome. One year ago, he began tripping over his feet due to ankle weakness, resulting in falls on several occasions. Concurrently, he complained of burning in the hands more than in the feet, and treatment with gabapentin and a topical Lidoderm patch was started. Six months ago, he started having bilateral hand weakness with trouble opening jars or manipulating buttons. At the same time, he developed near-syncope and was found to have orthostatic hypotension, and treatment with midodrine was started. A Foley catheter was placed 1 year ago because of urinary retention and bilateral hydronephrosis, attributed at the time to benign prostatic hypertrophy. His medical history included bilateral cataract surgery at 75 years but was otherwise negative. His general examination showed a drop of 20 mm Hg in his systolic blood pressure when standing without an increase in pulse rate. He had loss of sensation to pinprick up to the knees and midforearms bilaterally and vibratory sensation loss in his toes and fingertips. His reflexes were absent except for those for the biceps and brachioradialis, which were diminished. His dysautonomia included constipation, erectile dysfunction, orthostatic hypotension, and urinary retention. His weight loss could be related to a systemic condition that resulted in neuropathy or could be part of the dysautonomia, which may cause early satiety from reduced gastric emptying. Most polyneuropathies have some involvement of the autonomic system, but when autonomic signs are prominent as in this patient, the differential diagnosis is narrower. For example, this patient denied any toxic exposures and did not have risk factors or clinical findings suggestive of infectious disorders. Anti-Hu neuropathy is primarily a sensory neuropathy and does not result in motor weakness. Screening for other etiologies such as metabolic and autoimmune disease is necessary because neuropathy may be the only manifestation of the disease. A chest X-ray and skeletal survey were also done to rule out myeloma, and results were negative. In these 3 diagnoses, autonomic neuropathy tends to occur relatively early in the course of the disease and results in sexual impotence in men, gastrointestinal motility problems, and bladder retention. Other causes of hereditary amyloid neuropathy are ruled out because of the clinical features. The procedure is easy to perform and is a safe and less invasive alternative to a nerve biopsy, but the sensitivity of 72% is relatively low. If results of genetic testing are negative, one can then proceed with a sural nerve and muscle biopsy. In this patient, the presence of prominent dysautonomia and the chronicity of the symptoms narrowed the diagnosis. After acquired causes of chronic polyneuropathy and autonomic neuropathy were ruled out, the most likely diagnosis was amyloid polyneuropathy. His parents may have died before developing severe symptoms, or genetic anticipation may have occurred. Carpal tunnel syndrome is often an early feature and may be the only clinical manifestation. It should be noted that not all amyloid disorders are associated with a peripheral neuropathy. For example, peripheral neuropathy is not seen in reactive (secondary) amyloidosis or in most of the inherited amyloidoses characterized by renal, hepatic, or cardiac deposition. This procedure is typically reserved for patients with polyneuropathy restricted to the lower extremities or with autonomic neuropathy alone. These patients should be younger than 60 years, should have disease duration of less than 5 years, and should not have significant cardiac or renal dysfunction. Utility of subcutaneous fat aspiration for the diagnosis of systemic amyloidosis (immunoglobulin light chain). Utility of subcutaneous fat aspiration for diagnosing amyloidosis in patients with isolated peripheral neuropathy. Familial carpal tunnel syndrome due to amyloidogenic transthyretin His114 variant. Biochemical characteristics of variant transthyretins causing hereditary leptomeningeal amyloidosis. The course and prognostic factors of familial amyloid polyneuropathy after liver transplantation. Long-term results of liver transplantation in familial amyloidotic polyneuropathy type I. He had been complaining of generalized asthenia, numbness, and tingling involving the soles of both feet for the last year. He had a history of chronic renal failure due to type 2 diabetes, for which he was on maintenance hemodialysis. He had hypertension and hyperlipidemia, treated respectively with propranolol and simvastatin. General examination was normal, heart rate was 80 bpm, and orthostatism was not observed. Neurologic examination revealed mild ataxic gait with negative Romberg sign; right mild ptosis, which did not fluctuate after 60 sec- onds of upward gaze; equally sized pupils, briskly reacting to light and accommodation; full range and no clinical evidence of extraocular movement fatigability. Medical Research Council strength score was 4/5 in distal muscles of upper and lower limbs, with the exception of 1/5 score in wrist and finger extensors (extensor carpi ulnaris and radialis, extensor digitorum, extensor indicis); there was no evidence of fatigability. Sensory examination showed increased thermo-nociceptive and vibration threshold at distal lower limbs bilaterally. What is the differential diagnosis suggested by the clinical history and neurologic examination? Numbness of the lateral dorsum of the hand (including thumb and proximal phalanges of index, middle, and ring fingers), associated with wrist and finger drop, is the common presentation of the Saturday night palsy, due to focal compression of the radial nerve at the spiral groove. Subacute wrist drop, beginning with deep pain and followed by weakness, could be due to a limited form of brachial plexitis (Parsonage-Turner syndrome) or peripheral nerve vasculitis (mononeuritis multiplex). In our case, the negative family history and late disease onset argued against this diagnosis.
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Thus medications breastfeeding order flexeril 15 mg fast delivery, there are at least two major tribological dimensions involved - one concerning the nature of the synovial fluid and the other having to symptoms in dogs purchase flexeril discount do with the properties of articular cartilage itself treatment hypothyroidism best order for flexeril. Changes in either the synovial fluid or cartilage could conceivably lead to increased wear or damage (or friction) as shown in Figure 50. A simplified model or illustration of possible connections between osteoarthritis and tribology is offered in Figure 50. There are other pathways to the disease, pathways which may include genetic factors. In some cases, the body makes an unsuccessful attempt at repair, and bone growth may occur at the periphery of contact. This softer, degraded cartilage does not possess the wear-resistance of the original. It has been shown previously that treatment of cartilage with collagenase-3 increases wear significantly, thus supporting the idea of enzyme release as a factor in osteoarthritis. Thus, there exists a feedback process in which the occurrence of cartilage wear can lead to even more damage. Degradative enzymes can also be released by trauma, shock, or injury to the joint. Ultimately, as the cartilage is progressively thinned and bony growth occurs, a condition of osteoarthritis or degenerative joint disease may exist. Joint Lubrication Joint friction Cartilage repair Synthesis of biochemical constituents Triboprocesses Cartilage wear Wear particles Inflammation Softening and degradation of cartilage Enzyme release Trauma, shock, injury Other pathways? However, the inclusion of tribological processes in one set of pathways to osteoarthrosis would not seem strange or unusual. A specific example of a different tribological dimension to the problem of synovial joint lubrication. In an excellent study of the effect of crystals on the wear of articular cartilage, they carried out in vitro tests using cylindrical cartilage subchondral bone plugs obtained from equine fetlock joints in sliding contact against a stainless steel plate. Concentration of cartilage wear debris in the fluid was determined by analyzing for inorganic sulphate derived from the proteoglycans present. Several interesting findings were made, one of them being that the presence of the crystals roughly doubled cartilage wear. This is an important contribution which should be read by anyone seriously contemplating research on the tribology of articular cartilage. The careful attention to detail and potential problems, as well as the precise description of the biochemical procedures and diverse experimental techniques used, set a high standard. Synovial joints are undoubtedly the most sophisticated and complex tribological systems that exist or will ever exist. It will require a great deal more research - possibly very different approaches - before we even begin to understand the processes involved. Some general comments and specific suggestions are offered - not for the purpose of criticizing any particular study but hopefully to provide ideas which may be helpful in further research as well as in the re-interpretation of some past research. A glance at any number of the published papers on synovial joint lubrication will reveal such terms and phrases as "lubricating ability," "lubricity," "lubricating properties," "lubricating component," and many others, all undefined. We also 50-18 Biomedical Engineering Fundamentals see terms like "boundary lubricant," "lubricating glycoprotein," or "lubricin. Saying that a fluid is a "good" lubricant does not distinguish between friction and wear. And assuming that friction and wear are correlated and go together is the first pitfall in any tribological study. It cannot be overemphasized that friction and wear are different, though sometimes related, phenomena. For example, in a brief and early review article by Wright and Dowson , it was stated that "Digestion of hyaluronate does not alter the boundary lubrication," referring to the work of Radin, Swann, and Weisser . However, hyaluronic acid - shown earlier not to be responsible for friction-reduction - did reduce cartilage wear. Thus, it is important to make the distinction between friction-reduction and wear-reduction. It is suggested that operational definitions be used in place of vague "lubricating ability," etc. Sliding contact combinations in in vitro studies have consisted of (1) cartilage-on-cartilage, (2) cartilage-on-some other surface. The cartilage-on-cartilage combination is of course the most realistic and yet most complex contact system. But variations in shape or macroscopic geometry, microtopography, and the nature of contact present problems in carrying out well-controlled experiments. There is also the added problem of acquiring suitable specimens which are large enough and reasonably uniform. The next combination - cartilage-on-another material - allows for better control of contact, with the more elastic, deformable cartilage loaded against a well-defined hard surface. This contact configuration can provide useful tribological information on effects of changes in biochemical environment. It also could parallel the situation in a partial joint replacement in which healthy cartilage is in contact with a metal alloy. The third combination, which appears in some of the literature on synovial joint lubrication, does not involve any articular cartilage at all. For example, Jay made friction measurements using a latex-covered stainless steel stud in oscillating contact against polished glass . And in a recent paper on the action of a surface-active phospholipid as the "lubricating component of lubricin," Schwarz and Hills carried out friction measurements using two optically flat quartz plates in sliding contact . In another study, a standard four-ball machine using alloy steel balls was used to examine the "lubricating ability" of synovial fluid constituents. With a glass sphere sliding against a glass flat, almost anything will reduce friction - including a wide variety of chemicals, biochemicals, semi-solids, and fluids. In addition, a few studies used synovial fluids from patients suffering from either osteoarthritis or rheumatoid arthritis. The general comment made here is that the use of synovial fluids - whether derived from human or animal sources and whether "healthy" or "abnormal" - is important in in vitro studies of synovial joint lubrication. The documented behavior of synovial fluid in producing low friction and wear with articular cartilage sets a reference standard and demonstrates that useful information can indeed come from in vitro tests. Studies that are based on adding synovial fluid constituents to a reference fluid. But if significant interactions between compounds exist, then such an approach may require an extensive program of tests. It should also be mentioned that in the view of the present author, the use of a pure undissolved constituent of synovial fluid, either derived or synthetic, in a sliding contact test is not only irrelevant but may be misleading. This is basic in any study of lubrication and particularly in the case of boundary lubrication where major effects on wear or friction can be brought on by minor, seemingly trivial, changes in chemistry. It is noted that there is a proliferation of mathematical modeling papers stressing rheology and the mechanics of deformation, flow, and fluid pressures developed in the cartilage model. One recent example is the paper "The Role of Interstitial Fluid Pressurization and Surface Properties on the Boundary Friction of Articular Cartilage" by Ateshian et al. This study, a genuine contribution, grew out of the early work by Mow and connects also with the "weeping lubrication" model of McCutchen.
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Based on extensive spike-train analysis of neural recordings in vivo medicine the 1975 purchase genuine flexeril on-line, the network connectivity differs from the Richter model in several essential ways medicine to stop vomiting purchase flexeril 15mg with amex. The model has been shown to medicine everyday therapy cheap flexeril 15mg with visa mimick the normal and abnormal respiratory neural waveforms including the inspiratory ramp, inspiratory and expiratory off-switches, as well as apnea and apneusis. In neonatal rats, certain conditional bursting pacemaker neurons have recently been identified in a region of the ventrolateral medulla referred to as the pre-Botzinger complex [Smith et al. During the postnatal developmental stage there may be progressive transformation from pacemaker to network oscillation with possibly some form of hybrid operation in the transition period [Smith, 1994]. Another property of nonlinear oscillators is that they may be entrained by (or phase-locked to) other oscillators that are coupled to them. The respiratory rhythm has been shown to be entrained by a variety of oscillatory inputs including locomotion, mechanical ventilation, blood gas oscillation, and musical rhythm. A third property of nonlinear oscillators is that the limit-cycle trajectory may bifurcate and become quasiperiodic or chaotic when the system is perturbed by nonlinear feedback or other oscillatory sources. The resting respiratory rhythm is highly rhythmic in vagotomized animals but may become chaotic in normal humans [Donaldson, 1992] and vagi-intact animals [Sammon and Bruce, 1991] especially when lung volume is reduced [Sammon et al. The significance of nonlinear variations in respiratory pattern is discussed in a recent review [Bruce, 1996]. One approach to understanding respiratory control is therefore to discover the innate control objective that fits the observed behavior of the controller. Rohrer  was among the first to recognize that respiratory frequency at rest may be chosen by the controller to minimize the work rate of breathing, a notion that was subsequently advanced by Otis and colleagues . Similarly, the optimization principle has also been applied to the prediction of airway caliber and dead space volume [Widdicombe and Nadel, 1963] as well as end-expiratory lung volume and respiratory duty cycle [Yamashiro et al. This may explain the observed variability of breathing pattern which is generally more pronounced at rest than during hyperpnea or ventilatory loading. It thus appears that the controller is charged with two opposing objectives: to meet the metabolic demand by performing the work of breathing, and to conserve energy by minimizing the work. In a hierarchical model of respiratory control, metabolic needs take priority over energetic needs. A potential drawback of such a hierarchical system is that it is nonrobust to perturbations. Changes in ventilatory load, for example, would disrupt the ventilatory command from the feedforward signal. This is at variance with the experimental observation of a load compensation response of the controller which protects ventilation against perturbations of the mechanical plant at rest and during exercise [Poon et al. Furthermore, if the prime objective of the controller were indeed to meet the metabolic demand. Poon [1983a, 1987] proposed that an optimal controller might counterbalance the metabolic needs versus energetic needs of the body, and the resulting compromise would determine the ventilatory response. The ventilatory optimization model [Poon, 1983a, b, 1987b] has several interesting implications. First, it provides a unified and coherent framework for describing the control of ventilation and control of breathing pattern with a common optimization criterion. Second, it offers a parsimonious explanation of exercise hyperpnea and ventilatory load compensation responses, without the need to invoke any putative exercise stimulus and load compensation stimulus. Energetics of breathing is only one of many constraints that conflict with the metabolic cause of respiration. Another is the sensation of dyspnea which may be a limiting factor at high ventilatory levels [Oku et al. In addition, the ventilatory apparatus may also be constrained by other factors such as behavioral and postural interference, which may further tip the balance of the optimization equation. It has been suggested that the periodic breathing pattern at extremely high altitudes may represent an optimal response for the conservation of chemical and mechanical costs of hypoxic ventilation [Ghazanshahi and Khoo, 1993]. A more accurate representation of the control signal is Pmus (t) which drives the respiratory pump. The model of Poon and coworkers  assumes a compound optimization criterion, Equation 11. The optimal Pmus (t) output is found by minimization of J subjects to the constraints set by the chemical and mechanical plants, Equation 11. Because Pmus (t) is generally a continuous time function with sharp phase transitions, this amounts to solving a difficult dynamic nonlinear optimal control problem with piecewise smooth trajectories. Poon and colleagues  have shown that the dynamic optimization model predicts closely the Pmus (t) trajectories under various conditions of ventilatory loading as well as respiratory muscle fatigue and weakness (Figure 11. In addition, the model also accurately predicts the ventilatory and breathing pattern responses to combinations of chemical and exercise stimulation and ventilatory loading [Poon et al. There is increasing evidence that the respiratory system is an adaptive control system [Poon, 1992a]. The first is that in order to adapt to changes, the system signals must be constantly fluctuating or persistently exciting. This should be readily satisfied by the respiratory system which is inherently oscillatory [Yamamoto, 1962] and chaotic [Donaldson, 1992; Sammon and Bruce, 1992]. Another requirement is that the system must be able to learn and then memorize the changes in the environment. Similar short and long-term memories have been identified recently in brain stem cardiorespiratory-related region in vitro [Zhou et al. It has been shown that learning and memory in the brain are sufficient to achieve an optimal behavior characterized by the chemoreflex response and isocapnic exercise response [Poon, 1991]. In other words, the controller gain may be adaptively increased or decreased depending on the coupling between the cause and effect of respiration. During exercise, ventilatory neural output and chemical feedback are strongly negatively correlated (since Spco2 has a large negative value) so that the controller learns to increase its gain, G0, in proportion to metabolic load. Respiratory short- and long-term potentiation have been variously reported as indicated above. The possibility of synaptic depression was recently demonstrated in the nucleus tractus solitarius of the medulla [Zhou et al. However, experimental and simulation data are presently lacking for verification of this conjecture. The classical chemostat model is useful in describing chemoreflex responses but may be too simplistic to explain the variety of system responses to exercise input and mechanical disturbances. This remarkable ability of the respiratory neural network is interesting from both biologic and engineering standpoints. Understanding how it works may shed light on not only the wisdom of the body [Cannon, 1932] but also on the design of novel intelligent control systems with improved speed, accuracy and economy.
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A gradient in the partition stiffness similar to symptoms lyme disease buy discount flexeril online that in the cochlea medications you cant take with grapefruit flexeril 15mg overnight delivery, gives beautiful traveling waves in both experimental and mathematical models symptoms jaundice cheap flexeril online mastercard. With this simplification the governing equations are similar to those for an electrical transmission line and for the long wavelength response of an elastic tube containing fluid. Often K is represented in the form of a single degree-of-freedom oscillator: K = k + id - m2 in which k is the static stiffness, d is the damping, and m is the mass density: m = P h b (63. A good approximation is to treat the pectinate zone of the basilar membrane as transverse beams with simply supported edges, for which k= 10Eh 3 cf b5 (63. Thus for the moderate changes in the geometry along the cochlea as in the cat, h decreasing by a factor of 2, cf decreasing by a factor of 12, b increasing by a factor of 5, the stiffness k from Equation 63. Thus it is the bending stiffness of the basilar membrane pectinate zone and not the tension which governs the frequency response of the cochlea. The result is traveling waves for which the amplitude of the basilar membrane displacement builds to a maximum and then rapidly diminishes. The parameters of K are adjusted to obtain agreement with measurements of the dynamic response in the cochlea. Often all the material of the organ of Corti is assumed to be rigidly attached to the basilar membrane so that h is relatively large and the effect of mass m is large. Then the maximum response is near the in vacua resonance of the partition given by 2 = bk h (63. We note that there is interest in utilizing the principles in an analog model built on a silicon chip, because of the high performance of the actual cochlea. Watts  reports on the first model with an electrical analog of 2-D fluid in the scali. An interesting observation is that the transmission line hardware models are sensitive to failure of one component, while the 2-D model is not. Analysis of 2-D and 3-D fluid motion without the a priori assumption of long or short wavelengths and for physical values of all parameters is discussed by Steele . The first of two major benefits derived from the 2-D model is the allowance of short wavelength behavior, that is, the variation in fluid displacement and pressure in the duct height direction. Localized fluid motion near the elastic partition generally occurs near the point of maximum amplitude and the exact value of A becomes immaterial. The second major benefit of a 2-D model is the admission of a stiffness-dominated elastic partition. The two benefits together address all the objections the 1-D model discussed previously. Two-dimensional models start with the Navier-Stokes and continuity equations governing the fluid motion, and an anisotropic plate equation governing the elastic partition motion. This is an exact solution for constant properties and is a good approximation Cochlear Mechanics 63-7 when the properties vary slowly along the partition. For physiological values of the parameters, the wave number for a given frequency is small at the stapes and becomes large. This provides a uniformly valid solution for the entire region of interest without an a prior assumption of the wave form. For a physically realistic model, the mass of the membrane can be neglected and K written as: K = k(1 + i) (63. The actual duct is tapered, so H = H (x) and additional terms must be added to Equation 63. The best verification of the mathematical model and calculation procedure comes from comparison with measurements in experimental models for which the parameters are known. Zhou and coworkers  provide the first life-sized experimental model, designed to be similar to the human cochlea, but with fluid viscosity 28 times that of water to facilitate optical imaging. The solution by direct numerical means is computationally intensive, and was first carried out by Raftenberg , who reports a portion of his results for the fluid motion around the organ of Corti. However, the fluid is not included and only a restricted segment of the cochlea considered. The fluid is also not included in the finite element calculations of Zhang and colleagues . A "large finite element method," which combines asymptotic and numerical methods for shell analysis, can be 63-8 10 15 kHz 6 kHz 3 kHz 6 4 2 0 0 10 20 1. As shown by Taber and Steele , the 3-D Cochlear Mechanics 63-9 fluid motion has a significant effect on the pressure distribution. This is confirmed by the measurements by Olson  for the pressure at different depths in the cochlea, that show a substantial increase near the partition. First the basilar membrane and fluid provide the correct place for a given frequency (a purely mechanical "first filter"). Subsequently, the micromechanics and electrochemistry in the organ of Corti, with possible neural interactions, perform a further sharpening (a physiologically vulnerable "second filter"). A hint that the two-filter concept had difficulties was in the measurements of Rhode , who found significant nonlinear behavior of the basilar membrane in the region of the maximum amplitude at moderate amplitudes of tone intensity. Passive models cannot explain this, since the usual mechanical nonlinearities are significant only at very high intensities, that is, at the threshold of pain. Russell and Sellick  made the first in vivo mammalian intracellular hair cell recordings and found that the cells are as sharply tuned as the nerve fibers. Subsequently, improved measurement techniques in several laboratories found that the basilar membrane is actually as sharply tuned as the hair cells and the nerve fibers. No passive cochlear model, even with physically unreasonable parameters, has yielded amplitude and phase response similar to such measurements. Measurements in a damaged or dead cochlea show a response similar to that of a passive model. Further evidence for an active process comes from Kemp , who discovered that sound pulses into the ear caused echoes coming from the cochlea at delay times corresponding to the travel time to the place for the frequency and back. Spontaneous emission of sound energy from the cochlea has now been measured in the external ear canal in all vertebrates [Probst, 1990]. Some of the emissions can be related to the hearing disability of tinnitus (ringing in the ear). The conclusion drawn from these discoveries is that normal hearing involves an active process in which the energy of the input sound is greatly enhanced. A widely accepted concept is that spontaneous emission of sound energy occurs when the local amplifiers are not functioning properly and enter some sort of limit cycle [Zweig and Shera, 1995]. However, there remains doubt about the nature of this process [Allen and Neely (1992), Hudspeth (1989), Nobili and coworkers (1998)]. Nevertheless, it was surprising when Brownell and colleagues  found that the outer hair cells have electromotility: the cell expands and contracts in an oscillating electric field, either extra- or intracellular. The electromotility exists at frequencies far higher than possible for normal contractile mechanisms [Ashmore, 1987]. It has not been determined if the electromotility can operate to the 200 kHz used by high frequency mammals.
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Demonstrate skill in anterior segment surgery including eyelid medications ending in pam cheap 15mg flexeril with visa, conjunctival medicine 035 15 mg flexeril fast delivery, scleral medicine 802 generic flexeril 15 mg amex, and corneal procedures, with emphasis on corneal protective procedures (eg, tarsorrhaphy), 2. The fellow should actively participate in the postoperative management in the majority of grafts where they are part of the surgical team. Describe the basics of ophthalmic optics, including how the following affect the optics of the eye: ** a. Describe basic refraction techniques using trial lenses or phoropter for basic refractive errors, including: a. Describe the optical principles of common refractive surgery diagnostic tools, including: a. Describe the following topographic maps using different scales (ie, absolute, normalized, adjustable): a. Describe normal corneal topographic patterns, as well as topographic signs of keratoconus and ectasia. Describe elevation topography maps and their importance in screening refractive surgery candidates. Describe the complications of high myopia, high hyperopia, and pathologies related to high astigmatism. Define the clinical stages of keratoconus and forme fruste keratoconus using clinical and topographic tests. List current refractive procedures, their mechanisms of action, indications, and limitations, including: a. Describe the principles and different types (ie, linear, rotational, pendular) of mechanical microkeratomes, including their characteristics, indications, risks, and possible complications. Describe the role of femtosecond technology in refractive surgery, including advantages and limitations of flap creation with a femtosecond laser. Describe different techniques of keratoplasty and their relation with refractive surgery. Perform objective and subjective refraction, including cross cylinder and Worth 4-dot test. Prescribe spectacles for at least 20 patients with simple refractive errors (eg, myopia, hyperopia, regular astigmatism). Perform refraction on patients with extreme errors of refraction (eg, 5 patients with hyperopia over 8. Recognize signs of ectatic disorders and/or candidates at risk for an unsatisfactory refractive surgery outcome, and rule out poor-quality tests (eg, artifacts, alignment, and corneal exposure issues). Interpret an aberration map and evaluate its significance in the refractive defect of a patient, as well as the need to treat or not. Validate a manual refraction as a real refractive defect of a patient, comparing results with keratometers, aberrometers, and topography. Describe various types of refractive defects, and define the possible corrective solutions for each one. Describe basic diagnostic tools used in refractive surgery, including topography, pachymetry, and biometry; and interpret results. Describe more complex types of refractive errors, including postoperative refractive errors following cataract surgery, keratoplasty, refractive surgeries, ectatic conditions, and irregular astigmatism. Explain basics of wavefront analysis, including ray tracing and dynamic skiascopy, and graphical representation of wavefront errors, including corneal and entire eye high-order aberration maps, point-spread function, and modulation-transfer function. Use different topographic maps and scales for different purposes (eg, screening, postoperative evaluation, detection of complications). Describe corneal biomechanics, including biomechanical responses to keratorefractive surgery, corneal healing after excimer laser procedures, corneal hysteresis, and corneal resistance factor. Describe the mechanism of action, indications, advantages, and potential complications of mitomycin C application in surface ablation. Describe the affect of corneal crosslinking on the biomechanical properties of the cornea, including its indications and how it can be combined with other refractive surgery procedures. Perform refraction techniques using trial lenses or phoropter for basic and more complex cases, including: a. Apply the basics of optics and optical principles of refraction and retinoscopy in the clinical setting, including higher order aberrations. Gather accurate information essential for preoperative evaluation of patients seeking refractive surgery, including: a. Use the keratometer to make corneal measurements in more complex patients (eg, prior corneal surgery or corneal disease), and correlate results with corneal topography maps, visual acuity, and quality of vision. Assist in developing patient care management plans for simple refractive errors (eg, myopia, hyperopia, regular astigmatism), and define the risks and benefits for each procedure. Describe and diagnose various types of refractive problems, including irregular astigmatism, and identify the best solution for each. Describe the most complex types of refractive errors, including postoperative refractive errors, postkeratoplasty, and refractive surgery. Describe the most advanced optics and optical principles of refraction and retinoscopy, including higher-order aberrations. List the indications for and interpret preoperative and postoperative diagnostic testing, including: a. Formulate informed diagnostic and therapeutic decisions based on patient information, current scientific evidence, clinical judgment, and patient expectations. Describe accommodative and nonaccommodative treatments of presbyopia, including: a. Develop patient care management plans for more complex cases (eg, mixed and irregular astigmatism, irregular corneas, combined refractive surgery procedures). Describe the basics of topography-guided, wavefront-guided, and optimized ablations as compared to standard ablations. Perform the most advanced objective and subjective refraction techniques using trial lenses or the phoropter, including: a. Contact lens refraction for more complex refractive errors, including modification and refinement of subjective manifest refractive error b. Utilize the most advanced optics and optical principles for refraction and retinoscopy, including higher order aberrations. Utilize the keratometer for detection of subtle or complex advanced corneal refractive errors. Fit contact lenses in patients with irregular corneas, irregular astigmatism, and following refractive surgery. Assist in advanced refractive surgeries, including topography-guided ablation, wavefrontguided ablation, and combined refractive surgeries. Encourage patients to actively participate in their own care by providing disease and treatment information, and counsel patients on how to prevent postoperative injury. Correct refractive error after surgeries, such as penetrating keratoplasty, deep anterior lamellar keratoplasty, and radial keratotomy. Formulate informed diagnostic and therapeutic decisions based on patient information, current scientific evidence, and clinical judgment: a. Collect data, analyze refractive outcomes, and develop personal nomograms based on data. Develop refractive surgery management plans in the context of other conditions (eg, dry eyes, herpes, keratoconus, postkeratoplasty, glaucoma, retinal disease, amblyopia).