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Biomedical subjects

N Langford

Publications and source records attributed to N Langford.

8 recordsLinked to original sources
PubMed2006

Application of a quantum cascade laser for time-resolved, in situ probing of CH4/H2 and C2H2/H2 gas mixtures during microwave plasma enhanced chemical vapor deposition of diamond.

First illustrations of the utility of pulsed quantum cascade lasers for in situ probing of the chemistry prevailing in microwave plasma activated hydrocarbon/Ar/H2 gas mixtures used for diamond thin film growth are reported. CH4 and C2H2 molecules, and their interconversion, have been monitored by line-of-sight single pass absorption methods, as a function of process conditions (e.g., choice of input hydrocarbon (CH4 or C2H2), hydrocarbon mole fraction, total gas pressure, and applied microwave power). The observed trends can be rationalized, qualitatively, within the framework of the previously reported modeling of the gas-phase chemistry prevailing in hot filament activated hydrocarbon/H2 gas mixtures (Ashfold et al. Phys. Chem. Chem. Phys. 2001, 3, 3471). Column densities of vibrationally excited C2H2(v5=1) molecules at low input carbon fractions are shown to be far higher than expected on the basis of local thermodynamic equilibrium. The presence of vibrationally excited C2H2 molecules (C2H2(double dagger)) can be attributed to the exothermicity of the C2H3 + H <==> C2H2 + H2 elementary reaction within the overall multistep CH4 --> C2H2 conversion. Diagnostic methods that sample just C2H2(v=0) molecules thus run the risk of underestimating total C2H2 column densities in hydrocarbon/H2 mixtures operated under conditions where the production rate of C2H2(double dagger) molecules exceeds their vibrational relaxation (and thermal equilibration) rates.

Journal Article↗
PubMed2004

Is postural tremor size controlled by interstitial potassium concentration in muscle?

OBJECTIVES: To determine whether factors associated with postural tremor operate by altering muscle interstitial K(+). METHODS: An experimental approach was used to investigate the effects of procedures designed to increase or decrease interstitial K(+). Postural physiological tremor was measured by conventional means. Brief periods of ischaemic muscle activity were used to increase muscle interstitial K(+). Infusion of the beta(2) agonist terbutaline was used to decrease plasma (and interstitial) K(+). Blood samples were taken for the determination of plasma K(+). RESULTS: Ischaemia rapidly reduced tremor size, but only when the muscle was active. The beta(2) agonist produced a slow and progressive rise in tremor size that was almost exactly mirrored by a slow and progressive decrease in plasma K(+). CONCLUSIONS: Ischaemic reduction of postural tremor has been attributed to effects on muscle spindles or an unexplained effect on muscle. This study showed that ischaemia did not reduce tremor size unless there was accompanying muscular activity. An accumulation of K(+) in the interstitium of the ischaemic active muscle may blunt the response of the muscle and reduce its fusion frequency, so that the force output becomes less pulsatile and tremor size decreases. When a beta(2) agonist is infused, the rise in tremor mirrors the resultant decrease in plasma K(+). Decreased plasma K(+) reduces interstitial K(+) concentration and may produce greater muscular force fluctuation (more tremor). Many other factors that affect postural tremor size may exert their effect by altering plasma K(+) concentration, thereby changing the concentration of K(+) in the interstitial fluid.

Adrenergic beta-Agonists↗
PubMed2003

Fast, real-time spectrometer based on a pulsed quantum-cascade laser.

We describe a mid-infrared spectrometer that is based on the combination of a multiple-pass absorption cell and a submicrosecond pulsed quantum-cascade laser. The spectrometer is capable of both making sensitive measurements and providing a real-time display of the spectral fingerprint of molecular vapors. For a cell with a path length of 9.6 m, dilution measurements made of the nu9 band transitions of 1,1-difluoroethylene indicate a sensitivity of 500 parts in 10(9), corresponding to a fractional absorbance of 4 x 10(-4).

Journal Article↗
PubMed2003

The impact of therapeutic doses of paracetamol on serum total antioxidant capacity.

INTRODUCTION: A link between regular paracetamol intake and asthma in adults has recently been postulated. Detoxification of paracetamol may deplete stores of glutathione, which is one of the major antioxidants present in the lung. A reduced source of glutathione in the lung may lead to increased oxidative damage to the epithelium and hence increased frequency and severity of asthma attacks in susceptible individuals. AIM OF STUDY: This study aimed to determine whether regular intake of maximum therapeutic doses of paracetamol reduced serum antioxidant capacity in healthy volunteers. METHODS: Fifteen young healthy volunteers (nine men, six women, mean age 21.3 years, range 19-32) took maximum therapeutic doses of paracetamol (1 g four times a day) for 14 days. On days 0 and 14 blood samples were taken at baseline and hourly for a period of 4 h following ingestion of 1 g paracetamol. Single venous blood samples were collected 1 h after ingestion of 1 g paracetamol on days 4, 7 and 10. Blood samples were analysed for serum paracetamol concentration and total antioxidant capacity. RESULTS: Mean total antioxidant capacity was significantly reduced over the 3-h post-dosing on both days 0 and 14 (P < 0.01). The results from days 4, 7 and 10 showed a trend towards reduced antioxidant activity over time. On day 14 values were consistently lower compared with the corresponding times on day 0 (P < 0.01 at 0, 1, 3 and 4 h, P < 0.05 at 2 h). CONCLUSIONS: Chronic ingestion of maximum therapeutic doses of paracetamol depletes serum antioxidant capacity in healthy volunteers in as few as 14 days, possibly by a reduction in glutathione. This may have implications for analgesic use in asthmatic individuals. Further studies are now required to assess the impact of paracetamol on antioxidant defences in the lung.

Acetaminophen↗
PubMed2000

Use of the stable isotope (106)Cd for studying dietary cadmium absorption in humans.

Hydroponically grown wheat was intrinsically labelled with the stable isotope 106cadmium (106Cd) and the flour made into a porridge. The abundance of the isotope in the porridge was approximately 30 times the natural abundance, but the total level of Cd in the porridge was 0.03 mg/kg fresh weight, which was the same as expected in a normal diet. Cadmium measurements were made using inductively coupled plasma-mass spectrometry (ICP-MS). The porridge was eaten at breakfast by adult and infant volunteers. Bulked faecal collections were analysed for unabsorbed Cd. Initial results suggest that the apparent absorption of Cd may be higher than 5% as commonly quoted, but longer faecal collection times may be necessary to confirm this.

Adult↗
PubMed1999

Toxicity of mercury.

A ruling by the European Union heralds the demise of those useful clinical instruments, the mercury thermometer and the mercury sphygmomanometer. The new laws have been passed because of worries about mercury poisoning. Yet you can drink metallic mercury and come to no harm. What does it all mean? There are three forms of mercury from a toxicological point of view: inorganic mercury salts; organic mercury compounds; and metallic mercury. Inorganic mercury salts are water soluble, irritate the gut, and cause severe kidney damage. Organic mercury compounds, which are fat soluble, can cross the blood brain barrier and cause neurological damage. Mercury metal poses two dangers. It can be vaporised: the vapour pressure at room temperature is about 100 times the safe amount, so poisoning can occur if mercury metal is spilled into crevices or cracks in the floorboards. Dentists are occasionally poisoned this way. Mercury easily crosses into the brain, and causes tremor, depression, and behavioural disturbances. A second danger from metallic mercury is that it is biotransformed into organic mercury, by bacteria at the bottom of lakes. This can be passed along the food chain and eventually to man. It was this process that led to the Japanese tragedy at Minimata Bay in the late 1950s when over 800 people were poisoned. It is the need to reduce mercury contamination of the environment which should encourage us to cut the usage of metallic mercury. However, much more metallic mercury is spilled as waste by the chemical industry than is dropped on the floor in the clinic.

Animals↗
PubMed1975

Collision behavior of young drivers. Impact of the change in the age of majority.

A comparison of the number of collisions experienced by young male drivers in London, Ontario, before and after the reduction in the legal age for drinking and purchasing alcoholic beverages from 21 to 18, indicated that the change in the law led to an increase in the collision involvement of young drivers.

Accidents, Traffic↗