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Biomedical subjects

R W Russell

Publications and source records attributed to R W Russell.

At least 127 records · Page 7Linked to original sources
PubMed1976

Cerebrovascular carbon dioxide reactivity and conductance in patients awake and under general anesthesia.

Paired cerebral blood flow measurements at two levels of arterial carbon dioxide (CO2) tension were made in 36 awake patients and 85 patients under general anesthesia to measure the percent change in flow per mm Hg change in PaCO2 (CO2 reactivity). CO2 reactivity was significantly greater in the generally anesthetized (5.96) than in the awake group (3.65). In both groups, a linear correlation was found between mean percent CO2 reactivity and conductance (the reciprocal of resistance), up to a level of conductance of 0.85 in awake and 0.95 in unconscious patients. When the CO2 reactivity of 18 awake patients and 59 unconscious patients was compared with that of respective control groups, only 11 patients were found to have abnormal CO2 reactivities for their conductance levels.

Anesthesia, General↗
PubMed1975

How does blood-pressure cause stroke?

In chronic hypertension the specific arterial lesions responsible for brain damage affect the small resistance arteries. The pathological characteristics of these lesions (notably the presence of microaneurysms, intramural fibrin, and lipid) and the location of lesions within the brain all suggest that they arise from mechanical distension, which destroys the integrity of the vessel and allows plasma insudation into the wall (lipohyalinosis), finally leading to occlusion or rupture. The process in analogous to the breakdown in vascular resistance and permeability which occurs in acute hypertension.

Blood Pressure↗
PubMed1975

Cerebral blood flow in dementia.

Twenty-four patients of comparable age, blood pressure, and degree of dementia were classified by an "Ischemic Score" based on clinical features into "multi-infarct" and "primary degenerative" dementia. Regional cerebral blood flow (CBF) was measured by the intracarotid xenon 133 method. Both groups showed a decreased proportion of rapidly clearing brain tissue (largely gray matter). Cerebral blood flow per 100 gm brain per minute was normal in the primary degenerative group but low in the multi-infarct group. This suggests the blood flow is adequate for metabolic needs of the brain in patients with primary degenerative dementia but inadequate for those with multi-infarct dementia. There was no correlation between degree of dementia and CBF in the primary degenerative group but an inverse relationship existed in the multi-infarct group. Reactivity of blood vessels to reduction of arterial carbon dioxide pressure was normal in both groups.

Aged↗
PubMed1975

No-reflow phenomenon in the cerebral circulation of the gerbil.

The no-reflow phenomenon has been produced in the cerebral hemispheres of the gerbil by 30 minutes of bilateral carotid artery occlusion. The no-reflow phenomenon was found to develop in relation to the fall in blood pressure which occurred on release of bilateral carotid clips. Metaraminol tartrate intravenously prevented the fall of blood pressure and significantly reduced the occurrence of the no-reflow phenomenon. Metaraminol tartrate, however, did not alter the morbidity or mortality of carotid artery occlusion for 30 minutes. There is thus no support from these experiments for the view that the no-relow phenomenon plays an important functional role in the reversibility of the effects of severe cerebral ischaemia.

Animals↗
PubMed1975

Ischaemic swelling of cerebral hemisphere in the gerbil.

Ligation of the common carotid artery in the gerbil was found to be associated with an increase in wet weight, volume, and area of the ipsilateral cerebral hemisphere. True swelling and oedema of the hemisphere occurs. This evidence suggests that it is reasonable to continue to use the gerbil as an animal model of the oedema that many accompany cerebral infarction.

Animals↗
PubMed1975

Pregastric esterase in milk sham fed to adult jersey steers.

Pregastric esterase activity was detected in reconstituted nonfat milk sham fed from a nipple pail to two 4-yr-old rumen-fistualted steers. Lipolytic activity, determined in a medium containing 5% tri-n-butyrin, averaged 8.6 plus or minus .4 lipase units. Further assays, in which activitiy was measured by free fatty acids released from a condensed milk substrate, averaged 166.9 plus or minus 9.2 mumol. These values are higher than those noted for young calves, indicating that secretion of pregastric esterase may persist in cattle beyond calfhood. Esterase activity in one of the steers fed whole milk until he was 2 yr of age showed no marked residual effect of earlier intake of milk fat.

Age Factors↗
PubMed1975

Experimental tests of hypotheses about neurochemical mechanisms underlying behavioral tolerance to the anticholinesterase, diisopropyl fluorophosphate.

Neurochemical and psychopharmacological studies of rats were designed to examine four hypotheses which have been proposed to account for the development of behavioral tolerance to the anticholinesterase, diisopropyl fluorophosphate (DFP). The fact that the activity of the enzymes, adenosine triphosphatase, alkaline phosphatase and cytochrome oxidase, did not change concomitantly with behavioral measures during chronic treatment with DFP suggests that nonspecific metabolic changes are unlikely mechanisms of behavioral tolerance. Similarly, a lack of change in choline acetylase activity coupled with constantly high acetylcholine levels (140%) and low cholinesterase activity (28.5%) tends to eliminate end-product inhibition of acetylcholine synthesis as a primary mechanism of tolerance to DFP. Alpha-Methyl-p-tyrosine in doses to 150 mg/kg affected the behaviors of control and DFP-treated rats to a comparable degree, offering no support for the hypothesis that a redundant adrenergic system may replace the cholinergic system during the development of tolerance to DFP. In contrast to these various negative findings, pilocarpine was less effective in suppressing the responding of rats tolerant to DFP than that of control subjects. This confirms other evidence indicating that a decreased sensitivity of cholinergic (muscarinic) receptors is one mechanism underlying the development of tolerance to DFP.

Acetylcholine↗
PubMed1974

Effect of changes in cerebral blood flow on proportion of high and low flow tissue in the brain.

Regional cerebral blood flow was measured by injection of (133)Xenon into the internal carotid artery in 11 patients with cerebrovascular disease. All patients were studied under general anaesthesia, first at normocapnia and then at hypocapnia. The 15 minute isotope clearance curves were analysed by computer by two-compartmental analysis and regional changes in flow and the proportions of fast and slow clearing tissue obtained at two levels of arterial CO(2) tension. Hypocapnia caused a fall in blood flow which was consistently accompanied by a decrease in the proportion of fast clearing tissue. Regional changes were not significantly different from the hemisphere mean changes. There was no correlation between changes in blood flow through grey matter and the proportion of fast clearing tissue on a hemisphere mean basis, but on regional analysis the data from 10 out of the 11 patients showed that in areas where blood flow through grey matter changed most the proportion of fast clearing tissue changed least and vice versa. A hypothesis has been proposed to explain this phenomenon.

Adult↗