Showing papers by "George Davey Smith published in 1984"

Sympathoadrenal responses to anaesthesia and surgery

Abstract: Nociceptive surgical stimulation is accompanied by increased hypothalamopituitary activity which is generally referred to as the stress response to injury. This is manifest by a release of trophic hormones from the hypothalamus which in turn stimulate release of ACTH, TSH, GH, FSH, luteinizing hormone and prolactin in addition to ADH from the pituitary. Consequently, there is increased secretion of cortisol and thyroxine with suppression of insulin and increase in blood sugar concentrations. These responses may be partly attenuated by large doses of opioid analgesic drugs and some local anaesthetic techniques used during general anaesthesia. These endocrine changes have recently been reviewed elsewhere (Kaufman 1982, 1984; Weatherill and Spence, 1984). In addition, increased hypothalamic activity induced by nociceptive stimulation is accompanied by increased traffic in sympathetic efferent tracts. This is manifest by the well known signs which are conventionally used to diagnose unduly light levels of anaesthesia — notably dilatation of the pupils, sweating, tachycardia and hypertension. Thus measurements of heart rate, arterial pressure and skin resistance have been used as indirect indices of the level of sympathetic activity to assess both the efficacy of premedication and depth of anaesthesia. Increased sympathetic tone involves augmented release of noradrenaline by presynaptic sympathetic fibres and also increased secretion of catecholamines from the adrenal medulla. Thus attempts have been made for a number of years to assess sympathetic activity \"directly\" by measurement of plasma catecholamine concentrations. Until recently, assays were not available with sufficient sensitivity to measure resting concentrations of plasma catecholamines. However, with the advent of radioenzymatic assay (REA) and, over the past 5-6 years, high pressure liquid chromatography (HPLC) techniques for measurement of catecholamines in plasma, there has been a large

The lower oesophageal sphincter and anaesthesia

Abstract: Since Fyke, Code and Schlegel (1956) first demonstrated the existence of a high pressure zone at the lower end of the oesophagus, there has been increasing interest shown in this structure by anaesthetists. This area is termed the lower oesophageal sphincter (LOS) and is the major barrier preventing regurgitation of acid gastric contents into the oesophagus. This is of considerable concern to anaesthetists, as any regurgitated material may be aspirated into the lungs and produce the acid aspiration (Mendelson's) syndrome. It is of vital importance, therefore, that anaesthetists are aware of the effect of the drugs which they use on the LOS. Regurgitation and subsequent aspiration of gastric contents remains a major cause of morbidity and mortality in clinical anaesthesia. The overall mortality from aspiration has changed little over the past 20 years in the U.K. (Edwards et al., 1956; Lunn and Mushin, 1982). In every published study on deaths attributable to anaesthesia, there have been reports of fatalities resulting from vomiting or regurgitation and subsequent aspiration (Harrison, 1978; HoviViander, 1980). The occurrence of regurgitation has been estimated at 14-26% using older techniques of anaesthesia with ether, cyclopropane and uncuffed endotracheal tubes (Culver, Makel and Beecher, 1951; Berson and Adriani, 1954). Of these 7-16% had evidence of aspiration as judged by the appearance of tracer dye in the trachea at laryngoscopy and bronchoscopy. Using contemporary anaesthetic techniques and the same methodology it was shown in 1970 that the frequency of regurgitation had decreased to 7.8% and of this number, 8.6% of patients had aspirated (Blitt et al., 1970).

Pharmacokinetics and analgesic effect of slow-release oral morphine sulphate in volunteers

Abstract: Sustained-release oral morphine sulphate (MST) 20 mg was administered to 11 healthy volunteers. Mean peak plasma morphine concentration was 14.8 ng ml, and occurred at a mean time of 142.5 min after ingestion. Analgesia by an ischaemic forearm pain test increased to a maximum 40 min after the calculated peak plasma concentration of morphine had been achieved, and remained greater than control values as plasma morphine concentration decayed. However, there was not a significant correlation between analgesia and plasma morphine concentration. This may result from delay in brain penetration by morphine. The mean systemic availability of morphine in the first 7 h after administration of MST was 18.3%

Non-parenteral postoperative analgesia. A comparison of sublingual buprenorphine and morphine sulphate (slow release) tablets.

Abstract: Summary Sixty-nine patients undergoing upper and lower abdominal surgery were studied after operation to compare the analgesic effects of sublingual buprenorphine (0.4 mg) and slow release morphine sulphate tablets (MST, 20 mg) given 6 hourly in a double-blind, double-dummy trial. Both MST and buprenorphine produced satisfactory postoperative analgesia but the linear analogue pain scores were significantly lower on the second post operative day with MST.

Plasma catecholamine concentrations. The effects of infiltration with local analgesics and vasoconstrictors during nasal operations.

Abstract: Summary Plasma catecholamine concentrations were measured in 19 patients allocated randomly to receive submucous infiltration with 4 ml of either 0.5% lignocaine with adrenaline 1:200 000 or prilocaine 0.5% with octapressin 0.03 iu per ml. Venous blood samples were obtained before and at 2, 5, and 10 minutes following infiltration. Plasma adrenaline increased from 0.35 to 1.72 p mol/ml at 2 minutes infiltration with the former solution whilst there was little change in plasma noradrenaline concentration. No similar peak in adrenaline concentration occurred after infiltration with prilocaine/octapressin solutions but with both solutions there was a small increase in plasma noradrenaline and adrenaline concentrations 10 minutes after infiltration, at the time of surgical stimulation.

The silicon effect in the tempering of martensite in steels

Abstract: Etude du troisieme stade de revenu d'un acier contenant 0,75% poids C-1,4% poids Si. Apres un revenu d'une heure a 380 C on observe que les atomes de Si sont rejetes de la cementite en cours de croissance vers la matrice de ferrite pour former une atmosphere enrichie en Si autour des particules. La concentration en Si dans la zone de segregation atteint 12%. Il semble que la region riche en Si constitue une barriere cinetique pour la croissance ulterieure de la cementite et que la diffusion du silicium au-dela de l'interface controle les processus de croissance et de grossissement

In situ ion milling of field ion specimens using a liquid metal ion source

Abstract: A controlled ion milling procedure is described which permits a feature of interest, such as a grain boundary to be brought towards the imaging region at the apex of a field ion specimen.

The fim100 - performance of a commercial atom probe system

Abstract: La sonde a atomes VG Scientific FIM 100 permet de fournir des impulsions a l'echantillon soit par tension electrique soit par laser. Description des proprietes de transmission et de resolution en masse du systeme; presentation de resultats preliminaires sur Alnico 5 et sur la martensite Fe-Ni-C

Barrier pressure and muscle relaxants. Comparison of the effects of pancuronium and vecuronium on the lower oesophageal sphincter.

Abstract: The effects of pancuronium and vecuronium on the lower oesophageal sphincter pressure were studied in 24 healthy patients anaesthetised with 0.5% halothane in nitrous oxide and oxygen. Following pancuronium 0.1 mg/kg intravenously, there was a significant increase in barrier pressure from a control value of 2.0 (SEM 0.14) kPa to 3.0 (SEM 0.27) kPa 1 minute after injection (p less than 0.05). This increase was sustained throughout the 15 minute period of recording and was accompanied by a significant increase in heart rate (p less than 0.001). Following administration of vecuronium 0.1 mg/kg intravenously there was an initial modest, though not significant increase in barrier pressure. This increase was significant (p less than 0.05) at 15 minutes. There were no cardiovascular changes following vecuronium.

Observations on the microstructure and magnetization of alnico permanent magnets

Abstract: Etude sur Alnico 5 et Alnico 7 par microscopie ionique a emission de champ, microsonde atomique et microscopie electronique a haute tension Determination precise de la composition et de la morphologie des phases A partir des resultats, on montre que les variations d'aimantation se font par mouvement des parois de Bloch

Atom Probe Analysis of Native Oxides and the Thermal Oxide/Silicon Interface.

Abstract: The Pulsed Laser Atom Probe has been used to determine for the first time the stoichiometry of both the native oxide on Si and of the SiO2/Si interface.

AGEING OF Fe-Ni-C MARTENSITE

Abstract: We report a collaborative study of the early stages of ageing of high-carbon Fe-Ni-C martensite, using the combined techniques of atom probe field-ion microscopy (FIM) and high-resolution transmission electron microscopy (TEM). The material used in this investigation was an Fe-15wt%Ni-1wt%C alloy, with Ms temperature below -35°C. The alloy was examined in both the unaged condition and after ageing at 20°C for times up to 2000 hours. Both FIM and TEM micrographs revealed a very fine scale modulated microstructure. Atom probe microanalyses revealed carbon-rich bands containing up to 11at%C. This work provides a positive characterization of the chemical changes that occur during the so-called "zeroth" stage of tempering or ageing - i.e. preceding transition carbide formation.

Surface structure and composition changes on platinum - rhodium alloy catalysts

Abstract: Platinum-rhodium gauze catalysts used in the manufacture of nitric acid undergo an extensive surface reconstruction process. This has been investigated using a miniature catalytic reactor, FIM atom probe, electron microscopy and X-ray techniques. A mechanism involving vapour transport is proposed to explain the main features of the variation in catalyst behaviour with operating conditions.