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Biomedical subjects

J F Nunn

Publications and source records attributed to J F Nunn.

At least 73 records · Page 4Linked to original sources
PubMed1984

A reassessment of the validity of the iso-shunt graph.

The iso-shunt diagram was introduced in 1973 to simplify the selection of the optimal inspired oxygen concentration in patients undergoing intensive therapy. A further study of 25 patients in a District General Hospital showed that plots of arterial PO2 against inspired oxygen concentration closely follow predicted iso-shunt lines. There was no significant difference in calculated mean values for shunt with inspired oxygen concentrations between 30 and 100%. Results are compared with other studies and it is suggested that some reported discrepancies may be explained by the reduced response of many polarographic electrodes when measuring high values for arterial PO2.

Adult↗
PubMed1984

A model lung with the capacity for simulated spontaneous breathing.

A model lung is described which can be ventilated artificially but which also has the capacity to breathe spontaneously at pre-determined rate and depth. It appears particularly suitable for studying the performance of ventilators which interact with the patient, including those with the facility for triggering, synchronization and mandatory minute ventilation. An additional facility is the blocking of a simulated spontaneous inspiration during an artificial inflation (" Hering -Breuer reflex").

Electronics↗
PubMed1984

Bronchiolectasis caused by positive end-expiratory pressure.

Bronchiolectasis in patients with respiratory failure who are ventilated artificially with positive end-expiratory pressure (PEEP) appears to be associated with increased physiologic dead space. We found that the survival rate of 40 patients ventilated with PEEP was not significantly different from that of a control series of patients not receiving PEEP. Pulmonary function values, including the dead-space/tidal-volume ratio, returned to normal for the five PEEP patients in whom these variables were measured.

Adolescent↗
PubMed1984

Differential sensory and motor blockade after spinal cocaine in the rat and marmoset.

Various concentrations of local anaesthetic agents have been injected into the rat and marmoset via a chronically implanted cannula in the subarachnoid space. In the rat, cocaine at a concentration of 0.125% produced analgesia without motor blockade whereas higher concentrations produced motor blockade in some animals. No clear differentiation could be shown with any concentrations of lignocaine or bupivacaine. In the marmoset, 0.125% cocaine resulted in sensory block in four out of five marmosets without motor blockade, whereas 0.25% cocaine produced motor block in two out of four marmosets. It would appear that differential blockade of sensory function without motor loss can be achieved by cocaine. New local anaesthetics based on cocaine or similar chemical structures would seem potentially valuable.

Analgesia↗
PubMed1983

Effects of chronic exposure to nitrous oxide on methionine synthase activity.

Hepatic methionine synthase activity has been determined in rats continuously exposed (24 h day-1 and 7 day week-1) to concentrations of nitrous oxide ranging from 500 to 50 000 p.p.m. for periods ranging from 24 h to 28 days. The inactivation of this enzyme was dependent upon both time and concentration of nitrous oxide exposure, but there was no statistical evidence that exposure continuing beyond 48 h increased the effect. However, the dose-response curve for 24 h was significantly different from the curve for pooled data from exposures lasting 2-28 days. These latter data indicated no significant effect with 450 p.p.m. and an ED50 of 5400 p.p.m. Significant inhibition was detected at 1000 p.p.m. These results suggest that the limit of exposure of 25 p.p.m. recommended by the American National Institute of Occupational Safety & Health may be unduly restrictive.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1983

No effect of hyperbaric oxygen on methionine synthetase activity in rats.

Nitrous oxide is the only anesthetic gas or vapor known to inactivate the vitamin B12 cofactor of the enzyme methionine synthetase. However, there are conflicting reports on whether oxygen at one atmosphere has any effect. The authors found that the hepatic methionine synthetase activity of Sprague-Dawley rats was unchanged after 4 h exposure to two atmospheres of oxygen.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1983

Inhalational anaesthesia in developing countries. Part II. Review of existing apparatus.

We have reviewed the availability of apparatus which permits the maximum use to be made of available supplies and services in developing countries. In particular we have stressed the use of electrically operated air compressors and oxygen concentrators to drive sophisticated anaesthetic apparatus which is not dependent on supplies of compressed gases in cylinders.

Adult↗
PubMed1983

Studies on the haemopoietic toxicity of nitrous oxide in man.

Nitrous oxide inactivates vitamin B12 and in man can produce a megaloblastic anaemia. Haematological and biochemical changes were studied in nine surgical patients ventilated with 70% N2O for up to 24 h and in three control patients. There was a rise in the numbers of hypersegmented neutrophils in peripheral blood following N2O. Serial bone marrow aspirates showed gross megaloblastic change after 24 h of N2O which had reverted to normoblastic but dyserythropoietic haemopoiesis by 1 week. Giant forms of early myeloid precursors were also seen after 24 h ventilation with N2O but by 1 week abnormalities were evident in more mature cells, metamyelocytes and segmented neutrophils. Megaloblastosis was associated with abnormal dU suppression which showed a correction pattern similar to that seen in vitamin B12 deficiency. Administration of N2O was also associated with a progressive rise in serum folate and fall in serum methionine levels. No similar patterns were seen in the three control patients.

Anesthesia, General↗
PubMed1982

Bronchiolectasis-a complication of artificial ventilation.

Pulmonary barotrauma associated with artificial ventilation is recognised clinically as pneumothorax, pneumo-mediastinum, or subcutaneous emphysema. Eleven patients who died in the intensive therapy unit after artificial ventilation were found at necropsy to have pronounced bronchiolectasis, which was associated with a greatly increased physiological dead space during life. The condition was best predicted by the maximum level of positive end expiratory pressure and the duration of application of positive end expiratory pressure. The clinical course of the lesion in survivors is not known. Further detailed studies are needed, but it is suggested that high levels of positive end expiratory pressure should be used with caution.

Adolescent↗
PubMed1982

Serum methionine and hepatic enzyme activity in anaesthetists exposed to nitrous oxide.

Normal serum concentrations of methionine, leucine, isoleucine and valine have been found in 10 anaesthetists using nitrous oxide under their regular working conditions without scavenging of patients' exhaled gas. Mean inhaled concentrations of nitrous oxide ranged from 150 to 400 p.p.m. The results indicate either that there was no significant inhibition of methionine synthase (attributable to oxidation of vitamin B12 by nitrous oxide) or that methionine concentrations were maintained by dietary intake or by the alternative betaine pathway of methylation of homocysteine. In either case, anaesthetists working under these conditions should not be at risk from reduced methionine concentrations. We also report normal serum activities of aspartate transaminase and gamma glutamyl transpeptidase.

Adult↗
PubMed1982

Nitrous oxide decreases motility of human neutrophils in vitro.

The effect of 80 per cent nitrous oxide on motility of human neutrophils obtained from six volunteers was studied in vitro. In every case, random migration through the pores of 3 micrometer-millipore filter paper, was reduced (mean value 16 per cent). Chemotaxis toward casein also was reduced in every case (mean value 22 per cent). These results contrast with a previous study in which mean rates of migration were found to increase following exposure to 2 per cent halothane.

Cell Movement↗