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Biomedical subjects

R M Farrell

Publications and source records attributed to R M Farrell.

7 recordsLinked to original sources
PubMed2001

Novel glucocorticoid antedrugs possessing a 17beta-(gamma-lactone) ring.

The chemical synthesis and structure-activity relationships of a novel series of 17beta-glucocorticoid butyrolactones possessing either a 16alpha,17alpha-isopropylidene or -butylidene group are described. The sulfur-linked gamma-lactone group was incorporated onto the 17beta-position of the androstane nucleus via Barton ester decarboxylation and trapping the generated 17-radical with butyrolactone disulfides. The glucocorticoid butyrolactones were hydrolyzed in human plasma by the enzyme paraoxonase to the respective hydroxy acids, which were very weak glucocorticoid agonists. The rate of hydrolysis in plasma was very rapid (t1/2 = 4-5 min) in the case of lactones possessing a sulfur atom in the alpha-position of the butyrolactone group, whereas carbon-linked lactones were stable in plasma. 16alpha,17alpha-Butylidenes were more potent glucocorticoid agonists than the corresponding isopropylidene derivatives. Similarly, 1,4-dien-3-ones were more potent than the corresponding 4-en-3-ones. The butyrolactones linked to the steroidal nucleus via the beta-position were more potent glucocorticoid agonists than those linked through the alpha-position of the lactone. The most potent compounds were also shown to be stable in human lung S9 fraction, showed much lower systemic effects than budesonide in the thymus involution test, and possessed topical antiinflammatory activity in the rat ear edema model.

Administration, Topical↗
PubMed1992

Brain adaptation to chronic hypobaric hypoxia in rats.

Rats were exposed to hypobaric hypoxia (0.5 atm) for up to 3 wk. Hypoxic rats failed to gain weight but maintained normal brain water and ion content. Blood hematocrit was increased by 48% to a level of 71% after 3 wk of hypoxia compared with littermate controls. Brain blood flow was increased by an average of 38% in rats exposed to 15 min of 10% normobaric oxygen and by 23% after 3 h but was not different from normobaric normoxic rats after 3 wk of hypoxia. Sucrose space, as a measure of brain plasma volume, was not changed under any hypoxic conditions. The mean brain microvessel density was increased by 76% in the frontopolar cerebral cortex, 46% in the frontal motor cortex, 54% in the frontal sensory cortex, 65% in the parietal motor cortex, 68% in the parietal sensory cortex, 68% in the hippocampal CA1 region, 57% in the hippocampal CA3 region, 26% in the striatum, and 56% in the cerebellum. The results indicate that hypoxia elicits three main responses that affect brain oxygen availability. The acute effect of hypoxia is an increase in regional blood flow, which returns to control levels on continued hypoxic exposure. Longer-term effects of continued moderate hypoxic exposure are erythropoiesis and a decrease in intercapillary distance as a result of angiogenesis. The rise in hematocrit and the increase in microvessel density together increase oxygen availability to the brain to within normal limits, although this does not imply that tissue PO2 is restored to normal.

Adaptation, Physiological↗
PubMed1992

Differential features for a neural network based anesthesia alarm system.

We have developed a neural network based alarm system that identifies 19 specific faults in the anesthesia breathing circuit, such as "Inspiratory Hose Leak," or "Y-Piece Disconnection." CO2, pressure, and expired flow waveforms, along with ventilator settings, were sampled by a personal computer. Fifty-two features, such as "maximum CO2" or "minimum pressure", were extracted from each breath, converted to "differential" features, normalized, and used as the inputs of a three layered feed-forward neural network. The network was trained, using backward error propagation with momentum, to classify each breath as normal or containing one of 19 faults. To collect the neutral network training set, seven dogs were anesthetized and ventilated using controlled ventilation. Each of 19 faults were created over a range of ventilator settings and fresh gas flows. The neural network correctly identified 83.1% of 550 events presented to it during testing. These preliminary results are an encouraging example of neural network applications in the field of clinical monitoring.

Anesthesia, Closed-Circuit↗