Regional cerebral blood flow was measured by means of an autoradiographic technique in unanaesthetized, unrestrained cats during wakefulness, slow wave sleep (S‐SW), and rapid eye movement sleep (S‐REM). The electrocorticogram, electro‐oculogram, and electromyogram from the posterior neck muscles were continuously recorded. All operative procedures were completed at least four days prior to the experiment. Arterial blood samples were obtained immediately prior to the regional cerebral blood flow determination and analysed for PCO2, PO2, pH, and haematocrit. There were no significant differences in these parameters among the three groups. During S‐REM there was a significant increase in flow in all twenty‐five regions measured which varied from 62 per cent in the cerebellar white matter and sensory‐motor cortex to 173 per cent in the cochlear nuclei. During S‐SW a significant increase in flow occurred in only ten of the twenty‐five regions, and these changes were smaller in magnitude, varying from 26 per cent in the association cortex to 68 per cent in the superior olive. It is postulated that local changes in cerebral metabolism account for the regional cerebral blood flow changes demonstrated.

A new scintigraphic count-based method for measuring absolute left ventricular volumes is presented. It is a fast and simple technique that allows geometrical assumptions to be avoided and is free of radiation attenuation corrections. This method requires the acquisition of an image of the left ventricle in the right anterior oblique projection and the collection of gated blood pool images in the left anterior oblique projection. To assess the accuracy of the method scintigraphic stroke volumes were compared with those derived from thermodilution measurements during cardiac catheterization in 20 subjects, and to assess its precision the technique was applied to phantom data of known radionuclide volumes. Excellent correlations were found between the scintigraphic and both the thermodilution (r = .98) and phantom data (r = .99). The reproducibility (r = .97) of results was investigated by repeating data acquisition and analysis for 15 subjects on two different days, and the interobserver variability (r = .97) of the method was studied by having two computer operators calculate volumes for the same patient data for 20 randomly selected studies. Circulation 70, No. 4, 672-680, 1984. SEVERAL METHODS have been reported for estimating left ventricular volumes with the use of scintigraphic data and all of these come under the general categories of geometric or count-based methods. Geometric methods such as the Dodge-Sandler approximation1' 2 are convenient in that they do not require any information in addition to gated equilibrium data in one view, but have the disadvantage of not taking into account the variety of shapes of the ventricular chamber.3 Also, these geometric techniques are not particularly well suited to the analysis of scintigraphic data since the resolution of the boundaries of the ventricular walls is poorer than for contrast angiocardiographic chambers,9 "0 while others require removal, processing, and counting of blood samples after the gated equilibrium studies.9-Means of correcting for attenuation by placing a source within the patient's esophogus have been implemented,'2 but may not gain wide acceptance because of the inconvenience to the patient. Aside from the additional time and effort on the part of technologists that these methods require, they can yield inaccurate results in children and in obese patients, as evidenced by the wide range of average attenuation coefficients obtained by these methods.'2The

Studies in dogs have indicated that after the injection of thyrotropin (TSH) there is an enhanced release into thyroid venous blood of inorganic iodine in addition to the expected secretion of hormonal iodine (1, 2). Plasma iodide that has been newly accumulated by the thyroid iodide "trap" and still exists in the gland in inorganic form (transported iodide) does not appear to be the major source of the iodide released after TSH stimulation. The published data [reviewed in (3) ] suggest that the iodide so released is produced within the gland and is derived from deiodination of glandular organic compounds.However, a release of transported iodide into thyroid venous blood after TSH administration also has been demonstrated by studies in which organic binding of iodide was blocked (4, 5). The mechanism for the release of transported iodide and its relationship to the generation and release of iodide produced within the gland from organic precursors remain unresolved. It has been suggested (5) that the effect of TSH upon the release of transported iodide may be a consequence of the formation of iodide from glandular organic stores.The purpose of this report is to present data that provide more precise characterization of the effect of TSH upon glandular iodide release and of the * Submitted for publication October 22, 1965; accepted January 25, 1966. Supported by research grants A-2585 and A-5589 from the National Institute of Arthritis and Metabolic Diseases.Presented in part at the Forty- relationship of iodide derived from intraglandular organic stores to that newly accumulated from the circulation. Experiments were performed in which these two sources of glandular iodide were individually labeled in the same animal with different radioiodine isotopes whose flux between thyroid and circulation was estimated from differences between the radioiodide concentrations of arterial and thyroid venous plasma. Related studies on the acute effect of TSH on unidirectional (blood to thyroid) radioiodide clearance and on the sensitivity of iodide release to exogenous TSH stimulation are also reported. MethodsPentobarbital-anesthetized male mongrel dogs, weighing 30 to 50 pounds, were used in all experiments. The inferior thyroid vein of one lobe was cannulated, and continuous serial samples of thyroid venous blood were obtained by methods previously reported (1). The duration of each sampling period was usually 4 to 6 minutes; this was reduced to 2 to 3 minutes in the clearance experiments. Femoral arterial blood was drawn at the midpoint of each venous sample. Intravenous injections were given through a femoral vein cannula.Radioactivity measurements were made with a scintillation well counter and spectrometer. All samples were counted at a final volume of 1.0 ml. Separate 'I and 'I standards were made from suitable dilutions of the same isotope solutions administered to the animals. The activity present at each of two different energy levels was determined for each plasma sample and isotope standard with spectrometer wi...

No abstract