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Biomedical subjects

H Mamo

Publications and source records attributed to H Mamo.

At least 19 recordsLinked to original sources
PubMed1990

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.

Adult↗
PubMed1988

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.

Adult↗
PubMed1987

[Study of the cerebral blood flow by intravenous injection of xenon-133 in thalamic and juxtathalamic lesions].

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.

Adult↗
PubMed1979

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.

Anesthesia, General↗
PubMed1979

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.

Cerebrovascular Circulation↗
PubMed1978

[Action of vaso-active drugs on gasz of cerebral tissue. Experimental study by mass spectrometry (author's transl)].

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.

Animals↗
PubMed1977

Quantitative multiregional blood flow measurements during cervical sympathetic stimulation.

The ethanol tissue sampling method for rCBF measurement was used to obtain information on the effects of cervical sympathetic stimulation in 8 cerebral structures in the non-anaesthetized rabbit. Sympathetic stimulation induced flow decreases of 12-29% according to structure, confirming the capability of this nerve to significantly reduce rCBF. Furthermore, a regional differentiation of cerebral structures into an 'anterior' group (mean decrease 22%) and a 'posterior' group (mean decrease 12%) with different reactivity to stimulation was established, thus confirming previous work in this laboratory with a local thermoclearance technique, and histochemical studies on sympathetic innervation to cerebral arteries and arterioles. These results provide strong evidence of the functional nature of the sympathetic nervous system in CBF regulation. The complementary nature of the ethanol technique (quantitative, multiregional measurement) and the local thermoclearance technique (continuous, semiquantitative measurements in 2-3 regions), and the absence of anaesthesia and significant trauma, means that combination of these two techniques offers considerable advantages in research on dynamic phenomena of the kind studied here.

Anesthesia↗
PubMed1977

Pharmacological evidence in vitro and in vivo for functional beta1 receptors in the cerebral circulation.

Blood flow in the caudate nucleus was measured by the thermoclearance technique in non-anesthetized rabbits, accompanied by recording of electrocorticogram, systemic blood pressure, and Pao2 and Paco2 (mass spectrometry). Isoprenaline increased caudate nucleus blood flow and reduced systemic blood pressure. The beta2-receptor agonist, terbutaline, on the other hand, had only peripheral effects. The caudate nucleus flow response was selectively blocked by the beta1-receptor antagonist, practolol, whereas propranolol inhibited all effects of both agonists. Isoprenaline dilated isolated pieces of the tributary artery (middle cerebral) tested in cats, the effect being inhibited not only by propranolol but also by practolol. The results offer further evidence for the view that the beta-receptors in the cerebral vascular bed are of the beta1-type.

Animals↗
PubMed1975

Neurogenic influence on local cerebral blood flow. Effect of catecholamines or sympathetic stimulation as correlated with the sympathetic innervation.

Local cerebral flow was measured continuously in conscious rabbits (thermoclearance technique), and PaO2 and PaCO2 were recorded by mass spectrometry. Though inhalation of CO2 increased flow in caudate nucleus and lateral geniculate body, catecholamines only had effect on caudate nucleus where isoproterenol enhanced and epinephrine and norepinephrine reduced flow. Reduction by electrical stimulation of the neck sympathetic trunk was particularly evident in the caudate. Blood flow increased markedly in both regions after preganglionic conduction blockade. The effects were correlated with a significantly lower degree of sympathetic arteriolar innervation (fluorescence histochemistry) in the lateral geniculate body compared with the caudate nucleus.

Animals↗