Whole body hyperthermia may produce vasodialation, nausea, and altered cognitive function. Animal research has identified brain regions that have important roles in thermoregulation. However, differences in both the cognitive and sweating abilities of humans and animals implicate the need for human research. Positron emission tomography (PET) was used to identify brain regions with altered activity during systemic hyperthermia. Human subjects were studied under cool (control) conditions and during steady-state hyperthermia induced by means of a liquid-conditioned suit perfused with hot water. PET images were obtained by injecting [(18)F]fluorodeoxyglucose, waiting 20 min for brain uptake, and then scanning for 10 min. Heating was associated with a 23% increase in resting metabolic rate. Significant increases in cerebral metabolic rate occurred in the hypothalamus, thalamus, corpus callosum, cingulate gyrus, and cerebellum. In contrast, significant decreases occurred in the caudate, putamen, insula, and posterior cingulum. These results are important for understanding the mechanisms responsible for altered cognitive and systemic responses during hyperthermia. Novel regions (e.g., lateral cerebellum) with possible thermoregulatory roles were identified.
Objective: To determine the effect of two iodine-containing contrast agents used for coronary angiography on subsequent thyroid hormone concentrations. Methods: We prospectively studied thyroid function in 56 patients, with no previous history of thyroid disease and normal findings on thyroid examinations, who underwent nonemergent cardiac catheterization. Thyroid hormone concentrations were assessed at baseline and at day 1 and day 7 after administration of a radiographic iodinated contrast agent (Renografin or Omnipaque). Results: Use of Omnipaque and Renografin was not associated with significant changes in thyroid-stimulating hormone, total thyroxine, triiodothyronine resin uptake, free thyroxine index, or total triiodothyronine. Three patients had slightly increased thyroid-stimulating hormone concentrations at 7 days after angiography. Conclusion: Administration of iodinated contrast agents for cardiac catheterization does not result in hyperthyroidism in patients with previously normal findings on thyroid examination.
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