Dynamic Function Tests

The changes in base-line hormone secretion are useful for interpretation of drug effects, it is often advisable to include dynamic function tests based on stimulation of pituitary hormone secretion, or of gonadal and adrenal hormone secretion. Examples for pituitary testing have been mentioned above and secretion. Typical pituitary function tests are the TRH test for TSH secretion, the LHRH test for secretion of FSH and LH, and the mono iodo-tyrosine (MIT) test for prolactin secretion. Synthetic CRF may be injected to stimulate secretion of corticotropin (ACTH), more frequently the injection of corticotropin is used to stimulate the adrenal directly. At the target organ level, similar 

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Measurement of thyroid hormone concentrations in the serum has become an important final step in the endocrine safety pharmacology procedures (Capen 1992, O Connor et al. 2002). Basal concentrations are measured in serum samples in the morning before treatment (to avoid artefacts by the in diurnal fluctuation of thyroid hormone concentrations). In contrast to the rise in TSH after a test injection of TRH (dynamic function test), there is no pronounced rise after TRH stimulation. However, in specific situations, the secretion of thyroid hormones may be stimulated by the injection of a biosynthetic TSH preparation. 

Rheometric Scientific markets several devices designed for characterizing viscoelastic fluids. These instmments measure the response of a Hquid to sinusoidal oscillatory motion to determine dynamic viscosity as well as storage and loss moduH. The Rheometric Scientific line includes a fluids spectrometer (RFS-II), a dynamic spectrometer (RDS-7700 series II), and a mechanical spectrometer (RMS-800). The fluids spectrometer is designed for fairly low viscosity materials. The dynamic spectrometer can be used to test soHds, melts, and Hquids at frequencies from 10 to 500 rad/s and as a function of strain ampHtude and temperature. It is a stripped down version of the extremely versatile mechanical spectrometer, which is both a dynamic viscometer and a dynamic mechanical testing device. The RMS-800 can carry out measurements under rotational shear, oscillatory shear, torsional motion, and tension compression, as well as normal stress measurements. Step strain, creep, and creep recovery modes are also available. It is used on a wide range of materials, including adhesives, pastes, mbber, and plastics. 

Experiments on recovery of dynamic functions after the application of large strain amplitude perturbation were performed to understand the modulus recovery kinetics. To determine the recovery kinetics, samples underwent the following test sequences (a) frequency sweep, (b) strain sweep, (c) relaxation time of 2 min, (d) frequency sweep, (e) strain sweep, (f) relaxation time of 2 min, (g) frequency sweep, and (h) strain sweep [50]. Figure 7 shows the comparative subsequent strain sweep results performed immediately after a relaxation time of... 

In Figure 21.8, a softening temperature for the polystyrene endblock is shown as a function of endblock molecular weight (ranging from about 6000 to 30000). The softening temperature is characterized as the onset of test specimen creep (in a small-strain dynamic mechanical test in tensile mode), the creep point occurring when strain extension becomes considerable in order to maintain the appropriate stress level to continue the test. This softening temperature lies below the measured Tg, and it is an indication of the... 

Dynamic mechanical tests have been widely applied in the viscoelastic analysis of polymers and other materials. The reason for this has been the technical simplicity of the method and the low tensions and deformations used. The response of materials to dynamic perturbation fields provides information concerning the moduli and the compliances for storage and loss. Dynamic properties are of considerable interest when they are analyzed as a function of both frequency and temperature. They permit the evaluation of the energy dissipated per cycle and also provide information concerning the structure of the material, phase transitions, chemical reactions, and other technical properties, such as fatigue or the resistance to impact. Of particular relevance are the applications in the field of the isolation of vibrations in mechanical engineering. The dynamic measurements are a... 

Figure 6. Energy absorption as a function of composition. (a) from hysteresis, (b) average of pendulum and dynamic mechanical tests.

Winter (Winter and Chambon, 1986, Winter, 1987) also described an isothermal dynamic relaxation test to measure the gel point. He noted that the gel point coincides with a power-law relationship between the relaxation modulus (G) and relaxation time (t) G = St ", where S and n are constants. An isothermal step strain test measures the relaxation modulus as a function of time after an instantaneously applied strain. The gel time can be measured as the point at which the profile of the relaxation modulus can be expressed by this power law. This model is equivalent to tan <5 being independent of frequency. 

Typically, in dynamic oscillatory testing, a sinusoidal (oscillatory) small-amplitude stress is applied to the sample and the mechanical response measured as functions of both oscillatory frequency and, in some instances, temperature. 

The clinical biochemistry laboratory is commonly called upon to establish if there is excessive hormone secretion. Simple screening test.s to eliminate other diagnoses are followed by more complicated dynamic tests. If a pituitary tumour is suspected, it is important to establish the extent of damage to other pituitary functions. The combined anterior pituitary function test (Fig. 3) is used here. TRH. GnRH and insulin are given from separate. syringes. All hormones are measured at 0, 30 and 60 min, and cortisol and GH additionally at... 

As mentioned earlier, the DMTA technique measures molecular motion in adhesives, and not heat changes as with DSC. Many adhesives exhibit time-dependent, reversible viscoelastic properties in deformation. Hence a viscoelactic material can be characterized by measuring its elastic modulus as a function of temperature. The modulus depends both on the method and the time of measurement. Dynamic mechanical tests are characterized by application of a small stress in a time-varying periodic or sinusoidal fashion. For viscoelastic materials when a sinusoidal deformation is applied, the stress is not in phase with displacement. A complex tensile modulus E ) or shear modulus (G ) can be obtained ... 

Alternative valve operability testing, such as dynamic vibration testing, will be used if it is shown to assure the functional ability of the valve system adequately. These alternate methods, if used, will be completely described in the FSAR. 

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