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In these cases drugs for erectile dysfunction ppt buy forzest in united states online, the divergenceless of J is equivalent to the law of conservation of current that is often invoked when analyzing electrical circuits erectile dysfunction treatment pumps discount 20mg forzest with amex. Finally erectile dysfunction pump surgery buy discount forzest, the relationship between the electric field and the gradient erectile dysfunction quizlet cheap forzest 20mg amex, of the potential is E = -. This task is not easy, because g is generally a macroscopic parameter (an "effective conductivity") that represents the electrical properties of the tissue averaged over many cells. The effective conductivity can vary with direction, can be complex (contain real and imaginary parts), and can depend on the temporal and spatial frequencies. Before discussing the conductivity of tissue, consider one of the simplest and most easily understood volume conductors: saline. The electrical conductivity of saline arises from the motion of free ions in response to a steady electric field, and is on the order of 1 S/m. Besides conductivity, another property of saline is its electrical permittivity, (S sec/m). This property is related to the dielectric constant, (dimensionless), by = 0, where 0 is the permittivity of free space, 8. Dielectric properties arise from bound charge that is displaced by the electric field, creating a dipole. They can also arise if the applied electric field aligns molecular dipoles (such as the dipole moments of water molecules) that are normally oriented randomly. The movement of free charge produces conductivity, whereas stationary dipoles produce permittivity. In steady state, the distinction between the two is clear, but at higher frequencies the concepts merge. In such a case, we can combine the electrical properties into a complex conductivity, g: g = g + i, (21. The real part of g accounts for the movement of charge in phase with the electric field; the imaginary part accounts for out-of-phase motion. Both the real and the imaginary parts of the complex conductivity may depend on the frequency. This violation is the only exception we will make to our general rule of a quasistatic potential. The saline surrounding the cells constitutes the interstitial space (conductivity e), while the conducting fluid inside the cells constitutes the intracellular space (conductivity i). One additional parameter - the intracellular volume fraction, f (dimensionless) - indicates how tightly the cells are packed together. In these cases, it is easier to specify the surface-to-volume ratio of the tissue (the ratio of the membrane surface area to tissue volume). We can define operationally the effective conductivity, g, of a cell suspension by the following process (Figure 21. Deriving an expression for the effective conductivity of a suspension of spheres in terms of microscopic parameters is an old and interesting problem in electromagnetic theory [Cole, 1968]. The net effect of the cells is to decrease the conductivity of the solution (the decrease can be substantial for tightly packed cells). At high frequencies, C shunts current across the membrane, so that the effective conductivity of the tissue is: g = 2(1 - f)e + (1 + 2f)i. The increase in the phase at about 300 kHz is sometimes called the "beta dispersion. Henceforth, we must speak of the longitudinal effective conductivity parallel to the cylindrical fibers, gL, and the transverse effective conductivity perpendicular to the fibers, gT. If our coordinate axes lie along the principle directions of this matrix (invariably, the directions parallel to and perpendicular to the fibers), then the off-diagonal terms of the matrix are zero. If, however, we choose our coordinate axes differently, or if the fibers curve so that the direction parallel to the fibers varies over space, we have to deal with tensor properties, including off-diagonal components. When the electric field is applied perpendicular to the fiber direction, a suspension of fibers is similar to the suspension of cells described above (in Figure 21. The expression for the effective transverse conductivity of a suspension of cylindrical cells, of radius a and intracellular conductivity i, placed in a solution of conductivity e, with intracellular volume fraction f, is [Cole, 1968] gT = (1 - f)e + (1 + f)i e, (1 + f)e + (1 - f)i (21. When an electric field is applied parallel to the fiber direction, a new behavior arises that is fundamentally different from that observed for a suspension of spherical cells. Surprisingly, the effective longitudinal conductivity of a suspension of fibers depends on the length L of the tissue sample used for the measurement. To understand this dependence, we must consider one-dimensional cable theory [Plonsey, 1969].

Eccentric - a contraction in which a muscle lengthens while continuing to maintain tension [Gowitzke et al erectile dysfunction quran order discount forzest on line. Kroemer [1991] prefers the term zocor impotence generic forzest 20mg, isovelocity erectile dysfunction emotional order genuine forzest, to describe this type of muscle exertion erectile dysfunction protocol video discount forzest 20mg online. Isoinertial - a static or dynamic muscle contraction where the external load is held constant [Kroemer, 1983]. The ability of a muscle to develop tension depends on the type of muscle contraction. Per unit of muscle, the greatest tension can be generated eccentrically, less can be developed isometrically, and the least can be generated concentrically. These differences in tension-generating capacity are so great that the type of contraction being strength-tested requires specification. Additionally, strength is partially determined by the ability of the nervous system to cause more motor units to fire synchronously. As one trains, practices an activity, or learns test expectations, strength can increase. Each muscle has a moment arm length, which is the length of a line normal to the muscle passing through the joint center. Optimal tension is developed when a muscle is pulling at a 90 angle to the bony segment. Active tension decreases when a muscle is either lengthened or shortened relative to its resting length. However, applying a precontraction stretch, or slightly lengthening a muscle and the series elastic component (connective tissue), prior to a contraction causes a greater amount of total tension to Measurement of Neuromuscular Performance Capacities 76-11 be developed [Soderberg, 1992]. When a multijoint muscle simultaneously shortens at all joints it crosses, further effective tension development is prevented. For example, when the hamstrings are tested as knee flexors with the hip extended, less tension can be developed than when the hamstrings are tested with the hip flexed. Therefore, when testing the strength of multijoint muscles, the position of all involved joints must be considered. With concentric muscle contractions, the least tension is developed at the highest velocity of movement and vice versa. When the external load equals the maximal force that the muscle can exert, the velocity of shortening reaches zero and the muscle contracts isometrically. During eccentric contractions, the highest tension can be achieved at the highest velocity of movement [Komi, 1973]. The longer the contraction time, the greater the force development up to the point of maximum tension. Slower contraction leads to greater force production because more time is allowed for the tension produced in contractile elements to be transferred through the noncontractile components to the tendon. Tension in the tendon will reach the maximum tension developed by the contractile tissues only if the active contraction process is of adequate (even up to 300 msec) duration [Sukop and Nelson, 1974]. Subject effort or motivation, gender, age, fatigue, time of day, temperature, occupation, and dominance can also affect force or torque production capacity. Important additional considerations may be changes in muscle function as a result of pain, overstretching, immobilization, trauma, paralytic disorders, neurologic conditions, and muscle transfers. In each of these cases interval scaled grading criteria are operationally defined. However, a distinct advantage of using instruments to measure strength is that quantifiable units can be obtained. Deciding whether to measure force (a translational quantity) or torque (a rotational quantity) is an important issue in testing strength. Even when the functional units of interest produce rotational motion, force measurement at some point along the moment arm is common. This is due to the evolution from manual muscle tests to the use of objective measurements where a force sensor replaces the human examiner sense of force resisted or generated. If d is the distance from the point of rotation to the point of force measurement and the force vector is tangent to the arc of motion, then T = Fd (76. Torque can be measured directly if the strength-testing device has an axis of rotation that can be aligned with the anatomical axis of rotation and a torque sensor is used, as in many isokinetic test devices. Thus, for neuromuscular systems producing rotational motion, torque measures make the most sense and are preferred.

It is clear that in addition to the moduli varying along the length and over all four aspects of the femur impotent rage definition discount 20 mg forzest with amex, the anisotropy varies as well impotence losartan potassium buy cheap forzest 20 mg online, reflecting the response of the femur to the manner of loading erectile dysfunction 27 purchase forzest us. There is independent experimental evidence to support this calculation of isotropy based on the ultrasonic data erectile dysfunction in the young purchase forzest 20 mg amex. As% for Various Types of Hard Tissues and Apatites Experiments (specimen type) Van Buskirk et al. It is interesting to note that haversian bones, whether human or bovine, have both their compressive and shear anisotropy factors considerably lower than the respective values for plexiform bone. Thus, not only is plexiform bone both stiffer and more rigid than haversian bone, it is also more anisotropic. These two scalar anisotropy quantities also provide a means of assessing whether there is the possibility either of systematic errors in the measurements or artifacts in the modeling of the elastic properties of hard tissues. This is determined when the values of Ac (%) and/or As (%) are much greater than the close range of lower values obtained by calculations on a variety of different ultrasonic measurements (Table 47. He followed this later [1969] with an attempt to take into account the orientation of the Ap crystallites using a model proposed by Cox [1952] for fiberreinforced composites. The failure of all these early models could be traced to the fact that they were based only on considerations of material properties. This is comparable to trying to determine the properties of an Eiffel Tower built using a composite material by simply modeling the composite material properties without considering void spaces and the interconnectivity of the structure [Lakes, 1993]. This consideration of hierarchical organization clearly must be introduced into the modeling. Katz in a number of papers [1971b, 1976] and meeting presentations put forth the hypothesis that haversian bone should be modeled as a hierarchical composite, eventually adapting a hollow fiber composite model by Hashin and Rosen [1964]. Bonfield and Grynpas [1977] used extensional (longitudinal) ultrasonic wave propagation in both wet and dry bovine femoral cortical bone specimens oriented at angles of 5, 10, 20, 40, 50, 70, 80, and 85 with respect to the long bone axis. Katz [1980, 1981], applying his hierarchical material-structure composite model, showed that the data in Figure 47. This early attempt at hierarchical micromechanical modeling is now being extended with more sophisticated modeling using either finite-element micromechanical computations [Hogan, 1992] or homogenization theory [Crolet et al. Further improvements will come by including more definitive information on the structural organization of collagen and Ap at the molecular-ultrastructural level [Wagner and Weiner, 1992; Weiner and Traub, 1989]. Each curve represents a different lamellar configuration within a single osteon, with longitudinal fibers; A, 64%; B, 57%; C, 50%; D, 37%; and the rest of the fibers assumed horizontal. The behavior of an anisotropic linear viscoelastic material may be described by using the Boltzmann superposition integral as a constitutive equation: t - ij (t) = Cijkl (t -) d kl d d (47. This tensor has 36 independent elements for the lowest symmetry case and 12 nonzero independent elements for an orthotropic solid. Again, as for linear elasticity, a reduced notation is used, that is, 11 1, 22 2, 33 3, 23 4, 31 5, and 12 6. Solv ing them simultaneously for [d 2]/d and [d 3]/d and and substituting these values in Equation 47. As in the linear elastic case, the inverse form of the Boltzmann integral can be used; this would constitute the compliance formulation. Usually, data are presented by a graph of the storage modulus along with a graph of tan, both against frequency. For a more complete development of the values of E and E, as well as for the derivation of other viscoelastic technical moduli, see Lakes and Katz [1974]; for a similar development of the shear storage and loss moduli, see Cowin [1989]. There have been a number of early studies of the viscoelastic properties of various long bones [Sedlin, 1965; Smith and Keiper, 1965; Lugassy, 1968; Black and Korostoff, 1973; Laird and Kingsbury, 1973]. However, none of these was performed over a wide enough range of frequency (or time) to completely define the viscoelastic properties measured, for example, creep or stress relaxation. Thus it is not possible to mathematically transform one property into any other to compare results of three different experiments on different bones [Lakes and Katz, 1974]. In the first experiments over an extended frequency range, the biaxial viscoelastic as well as uniaxial viscoelastic properties of wet cortical human and bovine femoral bone were measured using both dynamic and stress relaxation techniques over eight decades of frequency (time) [Lakes et al.

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Laboratory study can be planned intelligently only on the basis of clinical information erectile dysfunction pill brands buy cheap forzest on-line. However erectile dysfunction 50 purchase forzest 20mg amex, a central goal of neurology is the prevention of disease erectile dysfunction doctors in tulsa purchase cheap forzest, because the brain changes induced by many neurologic diseases are irreversible erectile dysfunction clinics discount forzest 20 mg on line. In the prevention of neurologic disease, the clinical method in itself is inadequate; of necessity, one therefore resorts to two other approaches, namely, the use of genetic information and laboratory screening tests. There is no doubt that some clinicians are more adept than others at solving difficult clinical problems. Their talent is not intuitive, as sometimes is presumed, but is attributable to having paid close attention to the details of their experience with many diseases and having catalogued them for future reference. The unusual case is recorded in memory and can be resurrected when another one like it is encountered. Long experience also teaches one to not immediately accept the obvious explanation. There are a growing number of diseases, some medical and others surgical, for which specific therapy is now available; through advances in neuroscience, their number is steadily increasing. Matters pertaining to these therapies and to the dosages, timing, and manner of administration of particular drugs are considered in later chapters in relation to the description of individual diseases. There are, in addition, many diseases in which neurologic function can be restored to a varying degree by appropriate rehabilitation measures or by the judicious use of therapeutic agents that have not been fully validated. Claims for the effectiveness of a particular therapy, based on statistical analysis of large-scale clinical studies, must be treated circumspectly. Was the study well conceived, was there rigid adherence to the criteria for randomization and admission of cases into the study, were the statistical methods standardized, were the controls truly comparable It has been our experience, based on participation in a number of such multicenter trials, that the original claims must always be accepted with caution. This is in part true because small albeit statistically significant effects may be of little consequence when applied to an individual patient. Since newly proposed therapeutic agents are sometimes risky and expensive, it is often prudent to wait until further studies confirm the benefits that have been claimed for them or expose flaws in the design or fundamental assumptions of the original trial. Even when no effective treatment is possible, neurologic diagnosis is more than an intellectual pastime. The first step in the scientific study of a disease process is its identification in the living patient. Until this is achieved, it is impossible to apply adequately the "master method of controlled experiment. In closing this introductory chapter, a comment regarding the extraordinary burden of diseases of the nervous system throughout the world and in the United States should be made. It is not just that conditions such as brain and spinal cord trauma, stroke, epilepsy, mental retardation, mental diseases, and dementia are ubiquitous and account for the majority of illness, second only in some parts of the world to infectious disease, but that these are highly disabling and often chronic in nature, altering in a fundamental way the lives of the affected individuals. Furthermore, more so than in other fields, the promise of cure or amelioration by new techniques such as molecular biology and genetic therapy has excited vast interest, for which reason aspects of the current scientific insights are included in appropriate sections. Special laboratory examinations then do no more than corroborate the clinical impression. However, it happens more often that the nature of the disease is not discerned by "case study" alone; the diagnostic possibilities may be reduced to two or three, but the correct one is uncertain. Under these circumstances, one resorts to the ancillary examinations described below. The aim of the neurologist is to arrive at a final diagnosis by artful analysis of the clinical data aided by the least number of laboratory procedures. A few decades ago the only laboratory procedures available to the neurologist were lumbar puncture and examination of a sample of cerebrospinal fluid, radiology of the skull and spinal column, contrast myelography, pneumoencephalography, and electroencephalography. Some of these new methods are so impressive that there is a temptation to substitute them for a careful, detailed history and physical examination. Use of the laboratory in this way should be avoided; it certainly does not guarantee a diagnosis. Quite often in modern practice, ancillary testing reveals abnormalities that are of no significance to the problem at hand. The physician should therefore always keep in mind the primacy of the clinical method and judge the relevance and significance of each laboratory datum only in the context of clinical findings. Hence the neurologist must be familiar with all laboratory procedures relevant to neurologic disease, their reliability, and their hazards.