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Biomedical subjects

W Stone

Publications and source records attributed to W Stone.

At least 37 records · Page 2Linked to original sources
PubMed1990

Quantitative risk assessment of polychlorodibenzofurans (PCDFs) released in PCB fires: use of high-resolution gas chromatography.

The toxicity of polychlorodibenzofurans (PCDFs), produced during incineration and in accidental fires involving polychlorinated biphenyls (PCBs), is generally assessed in terms of total concentration or more recently in terms of the group concentrations of the tetra-, penta- and hexachloro-isomers. This approach fails to account for the great differences in potency of the relatively few toxic congeners and isomers present in the sample. A quantitative risk assessment of PCDF mixtures must not only be based on the concentrations of the toxic components but also account for the relative potency of each congener in a form which permits summation of the toxicities of the individual contributors. This paper outlines a method by which the concentration of each of the toxic components, determined by high-resolution congener-specific gas chromatographic analysis, may be converted to equivalent toxic concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Summation of the resulting values permits the overall toxicity of the sample to be expressed in terms of an equivalent toxic weight of TCDD per unit weight of sample (ng TCDD/g) in the case of fly ash or an equivalent toxic weight of TCDD per unit area (ng TCDD/m2) for soot deposit.

Benzofurans↗
PubMed1990

Exercise capacity of untrained spinal cord injured individuals and the relationship of peak oxygen uptake to level of injury.

Twenty spinal cord injured individuals were tested for maximal oxygen uptake (VO2 peak using a hysteresis brake wheelchair ergometer. The subjects were divided into 4 groups as follows: (a) quadriplegics (4 subjects); (b) untrained female paraplegics (5 subjects); (c) untrained male paraplegics (7 subjects); and (d) trained male paraplegics (4 subjects). The VO2 peak were analysed by a one way ANOVA and Fisher's LSD multiple comparisons. The F-ratio (50.93) was significant (p = less than 0.0001). Fisher's LSD post hoc multiple comparisons found the following differences: (a) quadriplegics were significantly lower than the untrained paraplegic females, untrained paraplegic males and trained paraplegic males; (b) untrained females were significantly lower than the untrained male paraplegics, and trained paraplegic males; (c) untrained paraplegic males were significantly lower than the trained male paraplegics. A Spearman Rho correlation was calculated using injury level and VO2 max for all the untrained SCI individuals. The correlation was 0.68 and had a significance level of 0.0019. The present study combined with the known research literature gives strong evidence that VO2 peak in the untrained SCI is highly related to level of injury.

Exercise Test↗
PubMed1988

Doctors and alcohol screening--the gap between attitudes and action.

The failure of doctors to identify patients who drink to excess has been attributed to inadequate education, negative attitudes towards problem drinkers and pessimism about treatment. As part of an early intervention programme at the York District Hospital, doctors were given brief alcohol education and encouraged to screen patients for alcohol problems. At subsequent evaluation doctors were well-informed about the nature and extent of alcohol problems and had positive attitudes to screening patients. Their performance did not reflect their views, however, with only 29 per cent of patients being screened. It is suggested that it is not unfavourable attitudes towards alcohol problems but doctors' perception of their role which determines their treatment of problem drinkers.

Alcoholism↗
PubMed1984

Pharmacology, electrophysiology, and pharmacokinetics of mexiletine.

Mexiletine is a class I antiarrhythmic agent that is active after both oral and intravenous administration and similar in structure and activity to lidocaine. It decreases phase O maximal rate of depolarization (Vmax) by fast sodium channel blockade. The marked rate dependence of Vmax depression may explain mexiletine's lack of effect on normal conduction and its efficacy against ventricular tachyarrhythmias. Mexiletine significantly decreases the relative refractory period in His-Purkinje fibers without changing the sinus rate or atrioventricular and His-Purkinje conduction times. Action potential duration is usually shortened. Mexiletine may aggravate preexisting impairment of impulse generation and conduction. Uptake and distribution of mexiletine are rapid, systemic bioavailability is about 90%, and tissue distribution is extensive. Mexiletine is primarily metabolized in the liver; 10% to 15% is excreted unchanged in the urine. Elimination half-life is 9 to 11 hours after intravenous or oral administration. Microsomal enzyme induction shortens mexiletine's elimination half-life, whereas hepatic disease and acute myocardial infarction prolong it. Renal disease has little effect, although hemodialysis increases mexiletine clearance. Plasma concentrations from 0.75 to 2.0 mg/L are usually associated with a desirable therapeutic response.

Absorption↗
PubMed1984

Control of cage lighting by locomotor activity through feedback circuits.

This paper describes an electronic device through which environmental lighting conditions are linked to locomotor activity thus allowing only the photosensitive portions of a nocturnal rodents phase-response-curve to be exposed to light. In the past, this type of lighting schedule has been difficult, if not impossible, to present with an exogenously controlled lighting system due to the phase shifting ability of the rodent's circadian system. The feedback lighting system is made from components which can be purchased at most electronics outlets for less than $100.

Animals↗
PubMed1975

Clinical use of NISR 440 polycarbonate membrane for hemodialysis.

1. In order to accredit the NISR440 Polycarbonate Membrane for clinical studies, the following was accomplished and/or established: a. Casting and synthesis were increased from the laboratory level to production scale. b. Quality control of permeabilities and physical properties was within +/- 5%, from membrane lot to lot and within the same roll. c. The target properties of the Artificial Kidney Program (NIH) were reached(7): 1) Middle M. W. solute permeability of marked molecules was established by 3 different laboratories and averaged: Vitamin B12 - 296 x Cuprophan¿; Inulin 3.6 x Cuprophan¿; Bacitracin 2.94 x Cuprophan¿. 2) Low M. W. species permeabilities were approximately the same as Cuprophan¿, to avoid a depletion syndrome. 3) Hydraulic permeability was essentially the same as Cuprophan¿ (UF rate 1.25 to 2.0 x Cuprophan¿) to avoid dehydration and hypotension. 4) Burst strength was 1.5 to 2.0 x Cuprophan¿. d. Toxicology studies were all negative in spot and in serial lot testing. e. Non-thrombogenicity tests (Lindholm test) were up to 36.6% better than Cuprophan¿. f. No protein adsorption was found. g. The membrane could be produced in the wet and dry state with the same permeability and physical properties. 2. In an earlier clinical study at USC, it was established that: a. There were no toxic effects manifested in patients in 25 episodic studies. b. Clearances forlow M. W. solutes and hydraulic permeabilities were, as targeted, approximately the same as Cuprophan¿. c. In 4 1/2 mos of a double blind study of 6 patients, no significant toxic effects were noted for either the patients on Cuprophan¿ or NISR 440 Polycarbonate Membrane. Two patients had an increase of hematocrit. 3. The ability to heat seal the membrane in the periphery and in channels through many layers, combined with its relative rigidity when wet, make possible clinical hemodialyzer designs approximately the size of a package of cigarettes and inexpensive to produce.

Adult↗