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Biomedical subjects

J W Clark

Publications and source records attributed to J W Clark.

At least 181 records · Page 10Linked to original sources
PubMed1979

Effect of androgen on growth hormone secretion and growth in boys with short stature.

The response of plasma growth hormone (GH) to insulin-induced hypoglycaemia (IIH) and arginine infusion (AI) was studied in 22 young males (ages 8 to 17 years) with short atature and absent or delayed sexual maturation, before and after androgen administration. During initial evaluation, 5 patients had blunted GH response to IIH, 12 responded subnormally to AI and 4 failed to respond normally to either stimulus. These same studies were repeated in each patient following androgen administration. The source of androgen was as follows: a) 5 days of testosterone propionate (25 mg intramuscularly daily) in 20 patients. b) Methyltestosterone, 10 mg t.i.d. orally for four days in the other 2 subjects. In almost every case, androgen administration resulted in raising the levels of fasting GH and enhancement of the GH responses to IIH and AI was observed. Patients manifesting subnormal GH responses to these stimuli before androgen consistently demonstrated a normal response when challenged with identical stimuli during androgen administration. Growth velocities during the year following these studies were significantly increased in most instances and the growth spurts correlated well with the progression of sexual maturation. Sustained improvement in the GH responses to IIH and AI were uniformly observed in 3 patients when repetitive studies were performed 8 to 12 months later during spontaneous advancing sexual development. The results indicate that brief androgen administration can be helpful in delineating the cause of growth retardation in boys with short stature and delayed sexual maturation, particularly when the diagnosis of isolated growth hormone deficiency is suspected. They also offer prognostic value in determining growth potential in this same group of young males.

Administration, Oral↗
PubMed1978

Experience with a Fourier method for determining the extracellular potential fields of excitable cells with cylindrical geometry.

In this chapter, well-known solutions that utilize a Fourier transform method for determining the extracellular, volume-conductor potential distribution surrounding elongated excitable cells of cylindrical geometry are reformulated as a discrete Fourier transform (DFT) problem, which subsequently permits the volume-conductor problem to be viewed as an equivalent linear-filtering problem. This DFT formulation is fast and computationally efficient. In addition, it lends itself to the application of some rather well-known techniques in linear systems theory (e.g., the DFT for convolution and least mean-square (Wiener) filtering for optimal prediction of a signal in random noise). Two specific examples are employed to demonstrate the utility of this discrete Fourier method: (1) the single, isolated, active nerve fiber in an essentially infinite volume conductor and (2) the isolated, active nerve trunk in a similar type of extracellular medium. In each of these, our DFT method is employed to obtain both the classical "forward" and "inverse" potential solutions for each volume conductor problem. In the case where the single, active nerve fiber is the bioelectric source in the volume conductor, simulated action-potential data from an invertebrate giant axon is utilized, and potentials at various points in the extracellular medium are calculated. The calculated potential distributions in axial distance z, at various radial distances r, are consistent with well-known experimental fact. When the active nerve trunk acts as the bioelectric source, the DFT method provides calculated potential distributions that are fairly consistent with experimental data under a variety of experimental conditions. For example, in these experiments, a special, isolated frog spinal cord preparation is used that permits separate or combined stimulation of the motor and sensory nerve fiber components of the attached sciatic nerve trunk. By manipulating the stimulus intensity applied to the motor (ventral) or appropriate sensory (dorsal) roots of the spinal cord, a variety of multiphasic extracellular volume-conductor potentials can be recorded from the sciatic nerve. The excellent agreement of model-generated and experimental data, regardless of the complexity of surface potential waveform, tends to validate the modeling assumptions and offer encouragement that this computationally efficient DFT method may be usefully employed in volume-conductor problems where both the bioelectric source, and the surrounding volume conductor, are of a much more complicated nature.

Action Potentials↗
PubMed1977

Contributions of computed tomography in the staging and management of malignant lymphoma.

Pretreatment staging is considered essential in the management of patients with malignant lymphoma, particularly nodular sclerosing Hodgkin disease. The results of CT examination of 33 patients with malignant lymphoma are correlated with the results of lymphangiography, nuclide images of the liver and spleen, gallium citrate57 images of lymphoid tissue, and nuclide bone images. CT is least effective in the early clinical stages of malignant lymphoma because normal or minimally enlarged nodes are difficult to detect; CT is probably reliable enough to replace lymphangiography of gallium57 imaging in patients with advanced disease.

Humans↗
PubMed1976

Computed tomography of the abdomen: initial experience.

Computed tomography has provided a new dimension in the roentgenologic evaluation of the abdomen. Normal structures not visible on conventional examinations are clearly identified. Abnormalities are recognized by their alterations in anatomic form or by their effect on tissue absorption values. Our early experience suggests that in the abdomen computed tomography will be most valuable in detecting lesions in those sites least accessible to conventional roentgenographic methods such as the liver, spleen, pancreas and retroperitoneum.

Adult↗
PubMed1974

Synergistic effect of pactamycin and sparsomycin on Mycoplasma-induced lethal toxicity of mice.

Pactamycin and sparsomycin, antitumor drugs which act synergistically with endotoxins, also potentiate the lethal toxicity of mice by Mycoplasma fermentans, strain K10. Sparsomycin (50 mug/20 g mouse, injected intraperitoneally 1 h after various doses of M. fermentans) exerted a minimal degree of synergism with few extra deaths, but with prolonged appearance of nonlethal disease. Pactamycin (75 mug in the same protocol) increased susceptibility to Mycoplasma-induced lethal toxicity approximately 1,000-fold. The optimal response was noted when pactamycin was administered in the period between 6 h before and 3 h after the administration of 10(8) colony-forming units of viable mycoplasmas. Doses of 12.5, 25, or 50 mug increased severity of signs, but only 75 mug/mouse produced synergism of the lethal effect. Methylprednisolone partially negated the synergism when injected simultaneously with the pactamycin 1 h after the cells. The lethal synergistic effect occurred with four species of Mycoplasma in addition to M. fermentans.

Animals↗