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Cognitive activity leads to an increased regional cerebral blood flow (rCBF) and energy metabolism in both cerebral hemispheres. In order to assess the reliability of rCBF-SPECT measurements in hemispheric dominance (Broca's area) speech activation SPECT studies were performed in nine patients. Patients (men, n = 6; women, n = 3, mean age: 33.8 +/- 13.8 years) with diagnosis of epilepsy (n = 7) and AVM (n = 2) participated in the preoperative study. Two SPECT studies were performed in each case, one in rest, and one during speech activation. 740 MBq of 99mTc-HMPAO/ECD was injected and stereo TCD monitoring was performed during the three minutes of speech activation. The acquisition was performed by a dual-head ADAC Solus Epic Atlas SPECT camera (ADAC Laboratories, Milpitas, USA). RCBF SPECT measurements were analyzed visually and by a special region-of-interest (ROI) program. The hemispheric dominance profiles were established on the basis of the respective blood flow velocity values obtained by fTCD and cortical hyperperfusion measured by SPECT. The neuropsychological test battery, used in the present study, was developed in our institute. The results of rCBF-SPECT studies highly correlated with the lateralization of hemispheric dominance measured by fTCD. There was a significant increase of rCBF in the inferior posterior frontal cortex (Broca's area, p0.0003). The non-invasive speech activation rCBF-SPECT measurement is a highly reliable and useful method in the determination of hemispheric dominance. SPECT studies are especially useful in cases where the performance of fTCD measurements are impossible due to the lack of temporal bone window or occlusive cerebral arterial disease.

Regional inhomogeneity of cerebrovascular CO2-sensitivity as well as its changes at three different levels of standardized haemorrhagic hypotension were studied in ten distinct brain and spinal cord regions of anesthetized, ventilated cats. Regional cerebral blood flow was measured with radiolabelled microspheres in hypocapnic, normocapnic, and hypercapnic conditions, and CO2-responsiveness was determined from the equation of the slopes of the best fit regression lines to the obtained flow values. It was concluded that in normotensive, normoxic cats response of the cerebral and spinal vessels to PaCO2 alterations can be assigned to four major categories. The CO2-responsiveness of a brain region is not solely determined by the rate of its basal steady state blood flow: CO2-reactivity of the hypothalamus was significantly different from that of any other investigated regions with almost identical steady state flow values. Vulnerability of the cerebrovascular CO2-sensitivity during hypotension was different from region to region, with the vessels of the pons-medulla oblongata region being the most sensitive to haemorrhage. Reduced regional cerebral and spinal CO2-responsiveness during haemorrhage is not a consequence of a reduced L-arginine supply for nitric oxide generation since administration of an excess amount of the precursor L-arginine failed to restore the haemorrhage-induced reduction of regional CO2-sensitivity at the 60 mm Hg mean arterial pressure level.

Local blood flow of the hypothalamus (HBF) was measured by the hydrogen clearance method in anaesthetized dogs. The average value for HBF in normal controls was 0.64 +/- 0.05 ml/g/min, which compares favourably with values available in the literature. During haemorrhagic hypotension induced by a modified Wiggers method there occurred a marked reduction of HBF to 52% of the initial control value at a mean arterial blood pressure (MABP) of 55--60 mm Hg and to 44% at 35--40 mm Hg. Prevention of concomitant extracellular acidosis by infusion of sodium bicarbonate solution during the hypotensive period resulted in a significantly smaller decrease in HBF as compared to an untreated control group, and a significant protection of HBF was also found at 55--60 mm Hg MABP in the bicarbonate treated group, but not in controls treated with physiologic saline. Hypothalamic tissue hypoxia was inevitable in untreated bled animals due to insufficient circulatory transport, while evidence suggested that the metabolism might have remained unaltered in the group protected against acidosis during haemorrhage. Analysis of the control of local hypothalamic blood flow revealed a significant correlation (r = 0.7026, p less than 0.001) between HBF and arterial blood pH in severe hypotension which is outside the autoregulatory blood pressure domain.

The reflex changes of local hepatic blood flow (HBF) were studied in anaesthetized dogs. An increase of HBF following the acidification of duodenal mucosa and the injection of glucose solution into the intestinal lumen was demonstrated. An attempt was made to cast light on the underlying mechanism which may govern the above mentioned local circulatory reflexes in the liver, by investigating the effect of bilateral vagotomy and of the local anaesthesia of duodenal mucosa. The importance of these hepatic circulatory reflexes from the point of view of surgical indications and the clinical treatment is discussed.