Disturbances in the cerebral perfusion of human immune deficiency virus-1 seropositive asymptomatic subjects: a quantitative tomography study of 18 cases.

Quantitative measurements of cerebral blood flow (CBF) by xenon-133 (133Xe) tomography, together with magnetic resonance imaging (MRI), electroencephalography (EEG), psychometric tests, and laboratory analyses were performed on 18 human immunodeficiency virus 1 (HIV-1) seropositive asymptomatic subjects. Abnormalities of cerebral perfusion were observed in 16 cases (88%). These abnormalities were particularly frequent in the frontal regions (77% of cases). MRI demonstrated leucoencephalopathy in only two cases. EEG showed only induced diffuse abnormalities in two cases. Psychometric tests showed restricted moderate disturbances in 55% of patients. These disturbances mostly concerned those sectors involved in cognitive functions and memorization. These results indicate that quantitative measurements of CBF by 133Xe-SPECT is capable of detecting abnormalities of cerebral perfusion at a very early stage (Phase II) of HIV-1 infection. These abnormalities are indications of disturbances resulting from unidentified metabolic or vascular lesions. This technique appears to be superior to MRI at this stage of the disease's development. It could provide objective information leading to earlier treatment, and prove useful in evaluating potential antiviral chemotherapy.

Cerebral blood flow in schizophrenia.

The regional cerebral blood flow of 27 young (mean age 24 years) schizophrenic patients was measured using the intravenous 133Xe method. The results were compared with those obtained from a group of age- and sex-matched control subjects. The main findings of the study were as follows: (a) the gray matter mean values of cerebral blood flow for both hemispheres were slightly but significantly lower in the schizophrenic group, and the statistical variance was significantly greater in the patients than in the control group; (b) the mean value for each hemisphere was found to be significantly lower for the right hemisphere; (c) the physiological hyperfrontal patterns of cerebral blood flow were identical in patients and controls; (d) visual hallucinations were associated with a reduction of regional cerebral blood flow in the temporo-occipital regions; and (e) antipsychotic medication did not appear to influence gray matter cerebral blood flow.

Cerebral blood flow in systemic lupus erythematosus with and without central nervous system involvement.

Regional cerebral blood flow (rCBF) was studied by the intravenous 133Xe method in 38 patients with systemic lupus erythematosus (SLE); 21 patients had neuropsychiatric manifestations (N+) and 17 did not (N-). Twelve of the N+ patients had had neuropsychiatric episodes less than one year before measurement of CBF ("recent" N+), while seven patients in this group had had episodes over a year before measurement ("old" N+). The results were compared with those obtained from a group of 27 age-matched normal healthy subjects. It was found that, in most of the N+ and N- patients, rCBF was evenly distributed bilaterally, but there was a "patchwork" of high/normal and low flow areas. This disturbance of rCBF distribution was significantly greater in "recent" N+ patients than in "old" N- patients, but was not a function of the potential evolution of systemic lupus erythematosus. It was also found that there was a reduction in the physiological high frontal rCBF in the "old" N+ patients. No correlation could be found between rCBF, the topography of the neuropsychological lesions, other neurological investigations or the glucocorticoid dosage and treatment schedules.

Cerebral blood flow in normal pressure hydrocephalus.

A xenon-133 method was used to measure cerebral blood flow (CBF) before and after cerebrospinal fluid (CSF) removal in patients with normal pressure hydrocephalus (NPH). Preliminary results suggested that shunting should be performed on patients whose CBF increased after CSF removal. There was a significant increase in CBF in patients with NPH, which was confirmed by the favorable outcome of 88% of patients shunted. The majority of patients with senile and presenile dementia showed a decrease or no change in CBF after CSF removal. It is suggested that although changes in CBF and clinical symptoms of NPH may have the same cause, i.e., changes in the cerebral intraparenchymal pressure, there is no simple direct relation between these two events. The mechanism underlying the loss of autoregulation observed in NPH is also discussed.

[Study of the cerebral blood flow by intravenous injection of xenon-133 in thalamic and juxtathalamic lesions]. / Etude du débit sanguin cérébral par injection intra-veineuse de xénon 133 lors de lésions thalamiques et juxta-thalamiques.

Sixteen patients with subcortical vascular lesions of one hemisphere, (7 left, including 4 aphasics and 9 right, 4 of which had a left neglect syndrome) and 4 controls without noticeable cerebral pathology underwent cerebral blood flow (CBF) measurements with intra-venous Xe 133, both at rest and during activation. The latter consisted of listening to a text together with eye opening and was considered non specific. At rest, a non significant CBF lowering on the side of the lesion was found in most patients, mainly in right brain damaged ones. Hypoperfusion areas (HA) were noted, predominantly in parieto-temporal cortex in right lesions, and in lower and middle frontal areas as well in left lesions. HA persisted during activation on both sides, except on the right side in left damaged patients. Activation resulted in a bilateral and roughly symmetrical mean CBF increase, which was not significant in left lesions nor in controls, but was significant (p less than .05) in right brain damaged patients without neglect syndrome. Conversely, patients with right lesions resulting in left neglect exhibited conspicuous mean CBF asymmetry during activation with depression on the right side. Right-left difference in mean CBF was significantly higher in this group than in right sided lesions without neglect (p less than .05). These facts are consistent with an activation imbalance between hemispheres as the mechanism of unilateral neglect syndromes, and support the view that right subcortical pathways and especially the thalamus, play a part in the activation of both cerebral hemispheres.

Hyperfrontal pattern of human cerebral circulation. Variations with age and atherosclerotic state.

The phenomenon of relative hyperperfusion of the frontal areas of the cerebral cortex (hyperfrontal flow distribution) was analyzed in 84 patients between 13 and 78 years of age. Fifty-two patients (group 1) had histories of vascular disease or vascular risk factors, and 32 (group 2) did not. Regional cerebral blood flow was measured by an atraumatic xenon Xe 133 method. The mean hemispheric gray-matter flow was found to decrease similarly with age in the two groups. Other findings were as follows: (1) the level of flow within the frontal region was not homogeneous in young adults; (2) in group 1, the frontal hyperperfusion decreased progressively with age, disappearing during the fifth and sixth decades according to a specific topographic pattern; (3) in group 2, hyperperfusion persisted into old age; and (4) hyperperfusion appeared more persistent with age in women than in men.

Analysis of reproducibility and sensitivity of atraumatic measurements of regional cerebral blood flow in cerebrovascular diseases.

We tested the reproducibility of consecutive measurements of regional cerebral blood flow (rCBF) made in 13 areas of each hemisphere in patients with cerebrovascular diseases by the atraumatic 133Xe intravenous injection method. The data were analysed by a two-compartment model similar to that used in the Obrist inhalation method. Four parameters derived from the model were tested: Fg (flow of the fast-clearing compartment), FF and W (respectively fractional flow and relative tissue weight of the same compartment), ISI (initial slope index as defined by Risberg et al.). No significant variation was found in these four parameters between two consecutive rest measurements for all the areas studied and whatever the time interval between the measurements. The variances of the differences of Fg and ISI between the two measurements were found to be similar to those found in normal healthy subjects. The variances of FF and, consequently, W were greater than the values determined in healthy volunteers. An attempt to improve the quality of the results, by correcting them for the effects of PaCO2 changes between the measurements, resulted on the contrary in a general increase of the variances of the differences, showing the inadequacy of the correction coefficients used for healthy subjects at least for a proportion of the patients with cerebrovascular diseases. Sensitivity, tested by activation (hand work), shows a positive answer for FG but no significant change in ISI in any area. These findings demonstrate that in cases of cerebrovascular diseases the raw data (uncorrected for the changes in PaCO2) are the most reliable data but the meaning of the values found for FF and W must be regarded with caution since they may be affected by the "slippage" phenomenon. It is suggested that the ISI should only be used when there is evidence of a failure of the compartmental model, but only as a rough estimation of the flow level because of its lack of sensitivity.

Is there an active mechanism limiting the influence of the sympathetic system on the cerebral vascular bed? Evidence for vasomotor escape from sympathetic stimulation in the rabbit.

The influence of the cervical sympathetic chain on cerebral circulation in the rabbit was studied by means of 3 complementary techniques. Two dynamic techniques involving chronically implanted probes were used: blood flow in the caudate nucleus (CN) was measured by thermal clearance; tissue PO2 and PCO2 in the same structure were measured by mass spectrometry. Other variables measured continuously and simultaneously included arterial blood pressure (BP), PaO2 and PaCO2. The third technique was a tissue sampling method based on the Fick principle and using 14C1 ethanol as tracer. Blood flow in 7 regions was measured at stable BP, PaO2 and PaCO2. Stimulation of the sympathetic chain at 15 Hz induced mean maximal decreases in CN blood flow of 23.9% (thermal clearance) and 24.4% (ethanol technique). Mean decrease of PO2 in the CN at 15 Hz was 16.6%. Significant falls in blood flow were observed with the ethanol technique in all 7 structures measured. During prolonged stimulation (greater than 1 min) CN blood flow and PO2 were found to escape towards the baseline level, which was sometimes even exceeded during the stimulation (blood flow). Stimulation frequency had only a very moderate influence on the rate of escape, and no evidence of a metabolic mechanism was found, although injection of barbiturate decreased the escape. These results are discussed with respect to the conflicting evidence on the effects of sympathetic stimulation in the brain, and to possible mechanisms for the escape phenomenon.

Measurement of regional cerebral blood flow by intravenous injection of Xe133.

Clearance of Xenon 133 following intravenous injection has been used to perform atraumatic measurements of regional cerebral blood flow (rCBF). rCBF was computed by a two-compartmental analysis of the clearance curves associated with a correction for Xenon recirculation based on the end-tidal tracer concentration. Direct comparison was made between the results of this method and those obtained from the reference intracarotid method. A systematic analysis has shown that the results of the non-invasive method depend on the part of the clearance curves chosen for computation of rCBF. The best concordance with the intra-carotid method was found when the analysed part of the curve was situated between 3 and 11 min. after the beginning of the injection. Under these conditions, the differences between the results from the two methods did not exceed 10% of the flow values even for low flows. Such precision makes the atraumatic measurements of rCBF by intravenous injection of Xenon valuable for clinical applications.

[Action of vaso-active drugs on gasz of cerebral tissue. Experimental study by mass spectrometry (author's transl)]. / Effets de drogues vaso-actives sur les gaz tissulaires cérébraux. (Etude expérimentale par spectrométrie de masse).

The authors describe a method for measuring cerebral tissue respiration by mass spectrometry. The first applications concern the action of vaso-active drugs on intracerebral PCO2 and PO2. The information gained with this method may prove of value in elucidating the mechanisms of drug action and the regulatory mechanisms of cerebral blood flow. Further prospects of experimentation offered by the method are mentioned.