Search

1. The primary objective of this study was to examine in man, how induced changes in global cerebral blood flow (gCBF) affected a regional cerebral blood flow (rCBF) increase resulting from a neural activation task (opening of eyes). A secondary objective was to quantify how such induced changes in gCBF were distributed between representative regions of either predominantly grey matter or white matter. 2. Positron emission tomography with intravenous infusion of H2(15)O, was used to measure gCBF in six normal males. Concomitant measures of rCBF were obtained in three different regions of interest (ROI): a representative area of predominantly grey matter, a representative area of predominantly white matter and an area of visual cortex. 3. Cerebral blood flow was altered by establishing steady-state changes in PCO2 at a near constant ventilation of approximately 30 l min-1. The mean PET,CO2 (+/- S.D.) levels (mmHg) that resulted were: low, 21.8 +/- 1.8; normal, 39.8 +/- 1.0, and high, 54.8 +/- 1.2. The normal and high levels were obtained by adding appropriate amounts of CO2 to the inspirate. The corresponding mean gCBF levels across all six subjects with eyes closed were: low, 24.2 +/- 4.6; normal, 37.2 +/- 3.9 and high, 66.8 +/- 7.6 ml min-1 dl-1. 4. Blood flow in grey matter (insular cortex) and white matter (centrum semiovale) at normal levels of PCO2 averaged 56.8 +/- 10.1 and 20.3 +/- 3.4 ml min dl-1 respectively. As PCO2 rose, the increase in rCBF to grey matter was approximately three times greater than that to white matter. 5. An activation state of eyes open in a brightly lit room was compared to a baseline state of eyes closed in a darkened room at the three levels of PCO2 (and hence at three levels of gCBF). Over the whole gCBF range a significant (P = 0.028) effect of increasing rCBF in the visual cortex ROI was found in response to opening the eyes; the effect of this activation on rCBF was not significantly dependent (P = 0.34) on the PCO2 (and hence gCBF) level. The effect of the activation on the rCBF was apparently 'additive' to the rise of rCBF associated with PCO2-related gCBF increase. 6. The results confirm the need to normalize for changes in gCBF during studies of rCBF in response to an activation protocol. They also provide support for the use of an 'additive' model to achieve such normalization provided that other cortical areas behave in a similar manner to that of the visual cortex.

1. Positron emission tomographic (PET) imaging of regional cerebral blood flow (rCBF), using a new 3-dimensional technique of data collection, was used to identify areas of neuronal activation associated with volitional inspiration and separately with volitional expiration in five normal male subjects. A comparison of the activated areas was also undertaken to isolate regions specific for one or other active task. 2. Scans were performed during intravenous infusion of H2(15)O under conditions of (a) volitional inspiration with passive expiration, (b) passive inspiration with volitional expiration and (c) passive inspiration with passive expiration. Four measurements in these three conditions were performed in each subject. Breathing pattern was well matched between conditions. 3. Regional increases in brain blood flow, due to increased neural activity associated with either active inspiration or active expiration, were derived using a pixel by pixel comparison of images obtained during the volitional and passive ventilation phases. Data were pooled from all runs in all subjects and were then processed to detect statistically significant (P < 0.05) increases in rCBF comparing active inspiration with passive inspiration and active expiration with passive expiration. 4. During active inspiration significant increases in rCBF were found bilaterally in the primary motor cortex dorsally just lateral to the vertex, in the supplementary motor area, in the right lateral pre-motor cortex and in the left ventrolateral thalamus. 5. In active expiration significant increases in rCBF were found in the right and left primary motor cortices dorsally just lateral to the vertex, the right and left primary motor cortices more ventrolaterally, the supplementary motor area, the right lateral pre-motor cortex, the ventrolateral thalamus bilaterally, and the cerebellum. 6. Using this modified and more sensitive PET technique, these findings essentially replicate those for volitional inspiration obtained in a previous study. For volitional expiration the areas activated are more extensive, but overlap with those involved in volitional inspiration. 7. The technique used has been successful in demonstrating the regions of the brain involved in the generation of volitional breathing, and probably in the volitional modulation of automatic breathing patterns such as would be required for the production of speech.

Single photon emission computed tomography (SPECT) scanning with 99TcHMPAO (Ceretec) was used to demonstrate regional cerebral blood flow (rCBF) in sixteen patients with hemodynamically significant unilateral carotid stenosis. All patients were demonstrated by cerebral computed tomography to be without cerebral infarction. When dysautoregulation was induced by intravenous acetazolamide, eight patients demonstrated a perfusion defect ipsilateral to carotid stenosis. Repeat SPECT scanning with dysautoregulation following carotid endarterectomy showed improved or normal cerebral perfusion in seven of these patients. The results suggest that a hemodynamic mechanism for cerebral ischemic events, including transient ischemic attacks (TIA) may be more common than previously suspected. Carotid disobliteration usually improves ipsilateral cerebrovascular reserve in patients with a preoperative perfusion defect.

Cerebral perfusion through stenosed internal carotid arteries is usually maintained by autoregulation. However, flow reserve may be reduced, suggesting hemodynamically significant stenosis, and such reduction should be improved by carotid endarterectomy. This concept was studied in 20 subjects with unilateral internal carotid artery stenosis (major stenosis greater than or equal to 70%, minor stenosis less than or equal to 50%). Thirteen had experienced recent transient ischemic attacks and seven had no definite focal symptoms. Subjects underwent Tc-HMPAO cerebral SPECT during acetazolamide dysautoregulation before and after internal carotid endarterectomy. Nine (45%) had perfusion defects that improved after surgery, suggesting surgery had improved cerebral flow reserve. Seven had defects that did not improve after surgery. Four had worsened or new defects after surgery, suggesting perioperative infarcts. The relatively large proportion of patients with improved cerebral blood flow reserve after surgery suggests that this technique may have a significant role to play in assessing which patients might benefit from carotid endarterectomy.