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Biomedical subjects

I Prohovnik

Publications and source records attributed to I Prohovnik.

At least 91 records · Page 5Linked to original sources
PubMed1988

Scopolamine reduces frontal cortex perfusion.

While the cognitive deficits of Alzheimer's disease are considered related to a cholinergic deficit, no attempt has yet been made to test the hypothesis that the characteristic regional cerebral blood flow (rCBF) pattern of Alzheimer's disease may also relate to such a deficit. We therefore measured rCBF using the [133Xe] inhalation technique in 15 young normal subjects before and after induction of reversible cholinergic blockade with scopolamine at doses of 6.1 and 7.3 micrograms/kg i.v. Significant cognitive impairment was observed at both doses, while rCBF changes occurred only at the higher dose. Global CBF was significantly reduced 25 min after scopolamine. The pattern of regional change in CBF was not similar to Alzheimer's disease. Rather than a focal parietotemporal deficit as seen in Alzheimer's disease, we observed a predominantly frontal reduction in flow of about 20%. These results suggest that the frontal but not the parietotemporal deficits seen in several dementing conditions may be related to cholinergic dysfunction.

Acetylcholine↗
PubMed1988

Rapid monitoring of intraoperative cerebral blood flow using 133Xe.

This study examined the feasibility of rapid rCBF monitoring using 133Xe as a tracer during operative procedures. We compared the initial slope index derived from two bicompartmental and one monocompartmental physiological models. The single-compartment model requires only 3 min of monitoring, whereas the bicompartmental models, thought to be more reliable, require 11 min of clearance. Data were collected from 26 patients undergoing carotid endarterectomy. Approximately 20 mCi of 133Xe in saline was injected i.v. for up to five measurements per patient, for a total of 117 measurements. The robustness of the regression for the three parameters (r = 0.781-0.99, p less than 0.0001) suggests that the three parameters are closely related. This is supported by similarity of the slopes of the regression lines (between 0.944 and 1.25) and the mean +/- SD of the three rCBF models (24.9-27.5 +/- 12.0-14.3 ml 100 g-1 min-1). Similar results were obtained for individual detectors, despite the expected higher variability. For intraoperative use in surgical procedures in which physiological conditions may change rapidly and i.v. injections of tracer must be used, a rCBF index that quickly and accurately reflects flow conditions is useful. Our data suggest that the single-compartmental Wyper index may be used to provide information about cerebral perfusion that is as accurate and robust as bicompartmental models, but requires only one-quarter of the data collection time.

Cerebrovascular Circulation↗
PubMed1988

Reduced hypercapnic vasoreactivity in moyamoya disease.

We measured cerebral perfusion at rest and in response to CO2 in eight patients with moyamoya disease (MMD), using the 133xenon inhalation method to determine the effect of large-vessel occlusive disease on vasoreactivity. We studied three other groups for comparison, including four with bilateral internal carotid artery occlusions (BICAO), 11 with unilateral carotid occlusion (UICAO), and six with unilateral middle cerebral artery stem occlusion (UMCAO). Resting flows appeared to correlate with the severity of occlusive disease overall. Normocapnic perfusion was lowest in the group with BICAO and decreased in proportion to the degree of contralateral stenosis in the group with UICAO. Hypercapnic perfusion correlated with the apparent adequacy of angiographic collaterals. Reactivity was lowest in the MMD group (0.79%/mm Hg) whose collateral supply was limited to leptomeningeal anastomosis from the posterior cerebral artery, but highest in the patients with BICAO (2.72%/mm Hg), each of whom showed excellent posterior communicating artery flow. The clinical course of the MMD group was compatible with the syndrome of perfusion insufficiency with repeated ischemic attacks or a saltatory progression of an ischemic deficit; CT showed infarction in the borderzone territory. These results suggest that a severely reduced hypercapnic response may help to identify patients with ischemic syndromes due to perfusion failure in the borderzones, as in MMD.

Adult↗
PubMed1988

Cerebral perfusion as a diagnostic marker of early Alzheimer's disease.

Clinical diagnosis of Alzheimer's disease (AD) is not fully satisfactory, and laboratory markers of this disease are not yet established. We report substantial regional Cerebral Blood Flow (rCBF) abnormalities in patients with documented early stages of the disease, when differential diagnosis is most critical. Thirty-six patients with carefully documented clinical diagnosis of early AD (mean disease duration, 3.25 +/- 1.80 years) and 12 elderly healthy controls participated in rCBF studies using the 133Xe inhalation method. Whole-brain perfusion was significantly (p less than 0.001) lower in the AD group, and a characteristic perfusion deficit was consistently found in temporoparietal cortex of the AD patients. Discriminant analyses demonstrated over 90% correct classification of the two groups. Two subgroups of patients with mildest disease manifestations were equally well discriminated. The similarity of these findings to those in late stages, which have been validated neuropathologically, offers indirect confirmation of validity and specificity. These results suggest that rCBF procedures may provide an accurate and sensitive laboratory marker for early AD.

Aged↗
PubMed1988

133Xe blood flow monitoring during arteriovenous malformation resection: a case of intraoperative hyperperfusion with subsequent brain swelling.

Measurement of regional cerebral blood flow (rCBF) using the i.v. 133Xe technique was carried out during resection of a right temporooccipital arteriovenous malformation (AVM) with ipsilateral middle and posterior cerebral arterial supply. Intraoperatively, a rCBF detector was in place over the right frontotemporal area, about 5 to 6 cm from the border of the AVM. Anesthesia was 0.75% isoflurane in oxygen and nitrous oxide. After dural exposure, the rCBF was 27 ml/100 g/min at a pCO2 of 29 mm Hg and a mean arterial pressure (MAP) of 90 mm Hg. The pCO2 was then elevated to 40 mm Hg, and the rCBF was increased to 55 ml/100 g/min at a MAP of 83 mm Hg. After AVM removal, the rCBF rose to 50 ml/100 g/min at a pCO2 of 27 mm Hg and a MAP of 75 mm Hg. The pCO2 was elevated to 33 mm Hg and the rCBF increased to 86 ml/100 g/min at a MAP of 97 mm Hg. During skin closure, the rCBF was 94 ml/100 g/min at a pCO2 of 26 mm Hg and a MAP of 97 mm Hg. The patient was neurologically normal postoperatively except for a mild, new visual field defect. After 2 to 3 days, the patient gradually developed lethargy, confusion, and nausea with relatively normal blood pressure. An angiogram revealed residual enlargement of the posterior cerebral artery feeding vessel. Computed tomography showed edema extending from the area of AVM resection as far as the frontal region, producing a significant midline shift anteriorly. Intraoperative rCBF monitoring revealed significant hyperperfusion after AVM resection, which was associated with signs and symptoms of the normal perfusion pressure breakthrough syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Seizure threshold in electroconvulsive therapy. Effects of sex, age, electrode placement, and number of treatments.

In a random-assignment trial to unilateral right and bilateral electrode placements, electroconvulsive therapy (ECT) stimulus intensity was titrated to just above seizure threshold for each of 52 depressed patients. Seizure threshold was quantified in units of charge. There was a 12-fold range in the minimum electrical intensity necessary to produce seizure. Sex, age, electrode placement, and the cumulative number of treatments were each associated with seizure threshold. Bilateral ECT had both a higher initial seizure threshold and a greater cumulative increase in seizure threshold compared with unilateral ECT. Clinical and research implications are discussed with respect to dosing strategies in ECT.

Adult↗
PubMed1985

Case report of lateralized affective states immediately after ECT.

Dysphoric states were observed in a patient immediately after right unilateral and bilateral ECT, while euphoric states followed left unilateral ECT, suggesting that disruption of lateralized neural mechanisms may have been involved in the pathophysiology of the affective states.

Adult↗
PubMed1983

Anticonvulsant and antidepressant properties of electroconvulsive therapy: a proposed mechanism of action.

The efficacy of electroconvulsive therapy (ECT) in the treatment of affective disorders is well established. Despite its clinical utility, there is no generally accepted theory regarding its mode of action. Several lines of evidence indicate that ECT has significant anticonvulsant properties and results in decreased neural metabolic activity. We suggest that these effects are due to enhanced gamma-aminobutyric acid (GABA) transmission and that localized suppression of neural metabolic activity is associated with therapeutic response to ECT. An implication of this view is that ECT may be a useful adjunctive treatment in intractable epilepsy.

Animals↗
PubMed1983

Cortical processing of visual and tactile stimuli studied by non-invasive rCBF measurements.

Blood flow determinations were made in 32 cortical regions of normal subjects during processing of visual and tactile stimuli. One experiment involved eight subjects who were studied during three conditions of visual stimulation achieved by a Spiral-After-Effect (SAE) apparatus: 1. looking at a stationary spiral, 2. a rotating spiral, and 3. performing the SAE test. Average cortical flow increases during these conditions compared to resting were 5%, 7% and 12% respectively. Local activation was seen in occipital, parietal, temporal, and frontal regions. The magnitude and spread of local flow increases were related to task complexity. In another experiment ten subjects were studied during rest and tactile stimulation of the right hand, left hand, and both. The subjects were instructed either to ignore the stimulation (sensation) or to pay attention to it. Sensation was accompanied by parietal and prefrontal flow increases contralateral to side of stimulation. Attention to the right hand mainly enhanced right hemisphere flow, in the same areas as during sensation. Attention to the left hand was associated with large, diffuse flow increases in both hemispheres. The results support recent proposals of right hemisphere dominance for functions related to attention.

Adult↗
PubMed1982

Regional cerebral blood flow and verbal memory after chronic exposure to organic solvents.

Regional cerebral blood flow (rCBF; 133Xe-inhalation method) was investigated in 32 industrial workers (age: 51 +/- 9 years) who had been exposed to organic solvents during an average of 24.5 years. The measurements were made at rest and during learning of associated word pairs. The resting flow level was 17% lower than expected for normal subjects of similar age and the activation-induced changes of rCBF during the test lacked the frontal activation normally seen. Significant correlations between age, length of exposure, and rCBF level were found. In order to control for the age factor, results were also calculated from two subgroups of similar age but with very different levels of exposure (13 and 31 years of average exposure). The two groups differed only slightly in resting rCBF. A marked difference was, however, seen during activation, with significant post-central flow increases recorded in the lower-exposed group only. The results indicate the potential of the rCBF method for elucidating functional cortical changes related to neurotoxic effects of organic solvents.

Aging↗
PubMed1981

rCBF measurements by 133Xe inhalation: recent methodological advances.

Some recent methodological improvements of the 133Xe-inhalation method for determination of the rCBF are reviewed. Improvements of the classical (Obrist) method of analysis involving routines for correction of background, remaining activity and contamination from 133Xe in the air passages are described. Advantages and limitations of the ISI as compared to the bi-exponential flow parameters are discussed as well as different ways to determine technical quality and reliability of the flow calculations. Finally, a new method of curve analysis based on Fourier transforms is described. This method allows use of the full curve from start of 133Xe breathing and offers improved methods for correction of influence from air passages and arteries. Its advantages in terms of greater sensitivity and validity are discussed.

Cerebrovascular Circulation↗