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Biomedical subjects

S C Nichols

Publications and source records attributed to S C Nichols.

9 recordsLinked to original sources
PubMed1998

Static posture tests for the assessment of postural instability after virtual environment use.

The aim of this experiment was to measure the effect of immersion in a virtual environment (VE) on postural stability and examine the relationship between postural stability and self-reported simulator sickness. Forty healthy subjects were exposed to 20 min of immersion in an interactive VE with restricted user movement. The VE was viewed on a head mounted display (HMD) and the subject remained standing throughout the immersion period. Two static postures, normal stance and tandem romberg, were recorded before immersion, immediately after immersion and again at 10 min postimmersion. Performance in each posture was simultaneously measured by recording time that the posture could be maintained and mm path length of body sway over a 30-s period. The results demonstrated differences in the sensitivity of postural stability measurement techniques and variations in inter- and intraindividual responses to measures. Sway magnetometry measured a significant increase in postural instability in normal stance after VE immersion. None of the other measures were sensitive to this change. Postimmersion reports of simulator sickness symptoms indicate that the VE stimulus was provocative and correlation was found between reports of simulator sickness and balance-related symptoms. However, no association between self-reported symptoms and performance measures of postural instability was found.

Adolescent↗
PubMed1994

The S-oxidative degradation of a novel corticosteroid tipredane (INN). Part II--Detailed investigations into the primary S-oxidation of tipredane using achiral oxidants.

The C-17 dithioketal moiety of the corticosteroid tipredane (INN,I) has been shown to undergo site and stereoselective S-oxidations with a range of achiral oxidants. S-Oxidation was favoured on the methylthio substitutent (beta-plane) in preference to the ethylthio substituent (alpha-plane) in a ratio of 1.8-3.5:1. S-Oxidation on both substituents appeared to be stereoselective yielding an approximate ratio of 4:1 and 1:3.5-6 for the S-:R-methyl and ethylsulphoxide diastereoisomers, (II and VI) respectively. The preferred sites for S-oxidation have been explained in terms of the preferred rotamers of the C-17 substituents and the steric factors imposed on the attack of the oxidant on the lone pair of electrons at each sulphur atom. Optimized HPLC conditions using a Hypersil ODS column and an acetonitrile-0.025 M NH4OAc pH 7.2 gradient at 26 degrees C were developed to prevent degradation of the ethylsulphoxide diastereoisomers (VI) occurring during chromatographic analysis, via elimination of ethylsulphenic acid to yield the corresponding C-17 vinylmethylthio derivative (VII).

Administration, Topical↗
PubMed1992

The S-oxidative degradation of a novel corticosteroid tipredane (INN). Part I: Preliminary investigations into the hydrogen peroxide S-oxidation of tipredane.

The C-17 dithioketal moiety of the corticosteroid tipredane (INN, I) has been shown to undergo peroxide oxidation yielding an array of sulphoxide epimers. All epimers have been isolated and characterized by spectroscopic techniques. Oxidation of the C-17 beta methylthio-substituent appeared to occur exclusively giving a 4:1 ratio of the S:R configuration at the sulphoxide moiety. Both methylthiosulphoxide epimers (V) have been shown to be susceptible to thermolysis yielding the monoethylthio- derivative (VI) via elimination of methylsulphenic acid. As expected from stereochemical considerations at the C-17 position the S epimer has been found to be more susceptible than its corresponding R epimer towards thermolysis. The monomethylthiosulphoxide epimers (III) were produced in a 1:1 ratio, indicating that they were formed from the oxidation of the corresponding monomethylthio- derivative (VII). This probably arose from the elimination of ethylsulphenic acid from the alpha-ethylthiosulphoxide (VIII).

Administration, Topical↗
PubMed1983

Microcalorimetry studies of energy changes during the growth of Klebsiella aerogenes in simple salts/carbon-limited media: growth in the presence of glucose and alpha-methyl-D-glucoside.

The power-time profile and the derived thermal parameters obtained during the growth of glucose-adapted cells of K. aerogenes in glucose-limited medium containing added alpha-methyl-D-glucoside (alpha-MG) are markedly different from those obtained during growth in glucose alone. The power-time profile changes in a regular manner with increasing concentrations of alpha-MG; the rate constants for exponential growth and heat output decrease linearly. Yield and enthalpy data indicate that alpha-MG is not metabolized, and this is not supported by the data for carbon dioxide production. The increase in the total cell volume which occurs as a result of growth in the presence of alpha-MG indicates that this carbon source is possibly stored. The power-time profile and thermal parameters for alpha-MG trained cells, grown with alpha-MG limitation and in mixed carbon-limited media are reported. In mixed media catabolic repression occurs.

Calorimetry↗
PubMed1981

Microcalorimetry studies of energy changes during the growth of Klebsiella aerogenes in simple salts/glucose media. 3. The effect of growth temperature on energy conversion.

Calorimetric and growth data are reported for the growth of K. aerogenes in glucose-limited media over the temperature range 25 degrees to 42 degrees C. Rate constants for heat output, CO2 evolution and biomass production are maximal at 37 degrees C; the rate constant for heat output is greater than that for biomass production at growth temperatures less than 37 degrees C. Changes in the power-time profile indicate that different metabolic processes occur at the different temperatures even when aerobic conditions prevail. An energy budget has been established for each temperature, stored and waste energy are constant below 40 degrees C; at higher temperatures the stored energy decreases and the waste energy increases. The energy used for biosynthesis delta HB is maximal at 37 degrees C, and is probably dependent on the growth rate.

Calorimetry↗
PubMed1980

Microcalorimetry studies of energy changes during the growth of Klebsiella aerogenes in simple salt/glucose media. 2. Enthalpy of aerobic growth.

Power-time traces for cells of K. aerogenes growing aerobically in batch culture with glucose limitation are reported and the results discussed with the corresponding mass balance data. Enthalpy values during the consumption of glucose and production of cellular material are calculated during growth in glucose (concentration range 0.56-5.4 mmol dm-3). The efficiency of caloric conversion and energy requirements during growth are considered by two methods. The measured enthalpy (delta hgluc) is significantly lower than the theoretical value, (delta Hox). The difference in the values is considered o be a measure of the enthalpy of growth (delta HB) and accounts for 5-15% of the initial substrate energy present.

Aerobiosis↗
PubMed1979

Microcalorimetry studies of energy changes during the growth of Klebsiella aerogenes in simple salts/glucose media. 1 Establishment of standard conditions.

The shape of the thermogram and the total heat output of aerobically growing cultures of Klebsiella aerogenes depend on the nature and state of the inoculum, the composition of the growth medium, aeration in the fermentor and in the calorimeter, and the pump rate of the culture through the microcalorimeter cell. Standard conditions of growth and heat measurement have been established which give reproducible thermograms and total heat output. Experimental results using different glucose concentrations are reported and the enthalpy changes for the consumption of glucose and the production of cells have been calculated.

Calorimetry↗