Functional Physiological Tests

The purpose of this section is to summarize those procedures carried out on patients which depend upon certain physiological aspects of thyroid function including the interrelationship of the thyroid gland with the hypothalamus and the anterior pituitary glands. The TSH stimulation and the Ts suppression tests are only briefly discussed, mainly for historical reasons, as both are becoming redundant because of more recent developments such as TSH and T3 assays, and the diagnostic use of thyrotropin releasing hormone. 

The TSH stimulation is primarily a test of thyroid reserve and has three main applications (1) to identify those patients with minor impairment in thyroid function where the conventional thyroid function tests produce normal results (2) to determine whether or not a patient, who is receiving thyroid therapy for presumed idiopathic myxedema, requires this therapy (3) to distinguish between idiopathic (primary) myxedema from hypothyroidism secondary to pituitary disease. 

Normally there is a brisk increase both in the thyroid uptake of and in serum levels of total T4 following intramuscular TSH injection. If doses of 10 USP units of TSH are given on three consecutive days, a normal subject will respond with a rise in serum total T4 of at least 3 /ug/100 ml from baseline level, blood being taken 8 hours after the last injection. The 24-hour thyroidal uptake should increase by 2- to 3-fold or by an absolute increment of 15-20 of the dose compared with the initial 24-hour uptake. Care must be taken if using this i-dose schedule in elderly patients or where ischemic heart disease is present. 

There is definitely an overlap in responses obtained in normd subjects and those obtained in patients with partial thyroid deficiency, even if the number of injections of TSH is reduced. However, failure of the thyroid uptake and total T4 to increase after TSH is strong evidence of primary thyroid disease. In the patients receiving thyroid hormone therapy, a significant response to TSH fairly conclusively excludes underlying thyroid failure unless the patient has been taking this therapy in full doses for many years. The test is probably most useful in distinguishing idiopathic thyroid failure from secondary or pituitary hypothyroidism. 

A single estimation of serum TSH which is so convenient, has replaced the TSH stimulation test which was inconvenient and sometimes dangerous for the patient. A definitely elevated level of serum TSH, e.g., in excess of 30 /xU/ml, is very convincing evidence of impairment of thyroid reserve (H4, 18). A finding of a normal TSH with a definitely lowered FTI and T3 concentration in the serum, in a clinically hypothyroid patient, is good evidence for pituitary disease. Also see Sections 4.1.1 or 4.1.2 for further discussion on the usefulness of the TSH assay. 

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This work needs to be completed by performing more behavioral tests and also electro-physiological assays to test synthetic and natural blends as well as isolated compounds. We know that non-congenerous HCs can be detected by ant antennae (see Chapter 10 for a review) so it should be possible, since the chemicals are available, to perform similar sensory physiology tests on pectines, which seem to have a function in the detection of contact chemicals (G. and B 2001) or other chemosensory sensitive parts of the scorpion body. In conclusion this chemical ecology work is only preliminary, but it appears to point in the same direction as behavioral studies by our American colleagues. 

Humans have energy production limits. Because thCTe are limits to anaerobic capacity and duration, most activity involves aerobic oxidation. Maximum aerobic power is a function of maximum oxygen uptake. Physiological tests on treadmills or bicycle ergometers determine the maximum aerobic capacity. The maximum aerobic edacity varies with physical conditioning for an individual. One expression for an individual activity level is a percent of maximum aerobic capacity. 

Nonspecific physiological measures. Less reliable than the tests above, physiological tests, such as pulmonary function tests, only... 

I have mentioned the decalcification of the bones from middle age onwards and the decline in renal function in old age, but there are many other ways in which an old person is at a disadvantage compared with a younger one. Physiological tests show that men at the age of 70 are capable of only about the same muscular work as they were when they were ten years old, and strength continues to decline during the next three decades. At 70 years the efficiency of the... 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

The invertebrate phyla are often neglected in ecotoxicological testing protocols. A token invertebrate species such as the copepod Daphnia may be used to evaluate the effects on extremely diverse phyla. This neglects the diversity of biochemical and physiological functions that may render different phyla vulnerable to different classes of compound at different stages of their life cycles. 

MULTIPLE CHEMICAL SENSITIVITY An acquired disorder characterized by recurrent symptoms, referable to multiple organ systems, occurring in response to many chemically-unrelated compounds at doses far below those established in the general population to cause harmful effects. No single widely accepted test of physiologic function can be shown to coiTelate with symptoms. 

It is generally true that if a toxin kills a particular species by one mechanism it will kill other species in the same phyllum by the same mechanism. However mechanisms of lethality cannot necessarily be expected to cross phylla. Such considerations of zoology should play a role in assessing toxicity especially where the species used to test for toxicity is the prey-species. In such a situation one would expect rapid lethality and a toxin targeted to a fundamental physiological function of that species. 

The Lung Clinical Physiology and Pulmonary Function Tests, Year Book, Chicago, 2nd ed., 1962. 

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