S'UMMARY 1. The circulatory effects of artificial hyperventilation with air and low oxygen mixtures were studied in rabbits anaesthetized with chloraloseurethane and given decamethonium iodide. The role of vagal afferents in the response to hypoxia was also assessed in spontaneously breathing unanaesthetized and anaesthetized animals.2. In the anaesthetized rabbit artificial hyperventilation inhibited all the changes in autonomic activity to the heart and peripheral circulation resulting from stimulation of the arterial chemoreceptors, and also reduced vagal efferent tone. In animals with section of the carotid sinus and aortic nerves the changes in autonomic activity observed during hypoxia and hyperventilation were much smaller than in normal animals and affected only cardiac autonomic activity.3. The effects of hyperventilation during hypoxia were mediated chiefly through vagal afferents rather than through the effects of hypocapnia. In the absence of changes in autonomic activity (e.g. during artificial hyperventilation with air) the circulatory effects were small and less clearly related to afferent vagal activity.4. In the spontaneously breathing anaesthetized and unanaesthetized rabbit vagal afferent activity resulting from the respiratory response to hypoxia inhibits sympatho-adrenal activity in the same way as during hypoxia with artificial hyperventilation.5. The importance of the vagal afferent input in the rabbit is discussed
The effect of dexamethasone on the accumulation of iothalamate and 99mTc pertechnetate in cerebral tumors was investigated in 6 patients over a five-month period. Patients were examined by x-ray (transmission) computed tomography (CT) and by radionuclide (emission) computed tomography (RCT) prior to and during a course of dexamethasone therapy. Stenosis diminished the degree of accumulation of both agents but did not change the boundaries of their distribution.
Fifty patients with radiographic evidence of an acute scaphoid fracture were studied prospectively. Technetium bone scans were performed on all patients soon after injury in an attempt to detect fractures at risk of non-union or avascular necrosis. In three patients the scan showed a focal area of decreased radionuclide concentration in the region of the proximal pole of scaphoid implying avascularity, and each developed the radiographic signs of avascular necrosis. Two of these patients, each with a displaced fracture, developed non-union. Acute fractures of the scaphoid with evidence of avascularity on bone scan are at high risk of developing non-union.
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