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Biomedical subjects

W Good

Publications and source records attributed to W Good.

At least 19 recordsLinked to original sources
PubMed1989

NMR relaxation of water in hydrogel polymers: a model for tissue.

The NMR relaxation rates of a class of hydrated polymers (hydrogels) have been investigated over a wide range of frequencies (0.01 to 60 MHz) and compositions. The gels comprise long chains of polytetramethylene oxide diol crosslinked by copolymers of dimethylacrylamide and methylmethacrylate. The longitudinal relaxation rate dispersion curves of these materials are very similar to those shown by human tissues and they can be altered in flexible fashion by changing the polymer content. By substitution of the water by deuterium oxide, the contribution of intermolecular cross-relaxation effects has been shown to account for two-thirds the total water relaxation rate. With their close similarity to tissue relaxation behavior, hydrogels of differing compositions are particularly well-suited to MRI phantoms and test objects.

Hydrogel, Polyethylene Glycol Dimethacrylate↗
PubMed1985

Influence of site of drug delivery on the systemic availability of metoprolol: comparison of intragastric infusion and 14/190 Oros administration.

The influence of the site of drug delivery on the systemic availability of metoprolol has been evaluated by measuring plasma drug concentrations in six healthy volunteers after administration of a continuous 13.5 h intragastric infusion and a 14/190 Oros controlled-release dosage form, on two separate occasions. The same total amount of drug was administered at the same rate on both occasions but the Oros system moved through the gut whereas the site of the infusion was constant. The differences between treatments were confined largely to the period 6-15 h after dosing when lower plasma concentrations were obtained after administration of the Oros system. The levels after 20 h were higher for Oros, however, reflecting its longer duration of drug release. The amount of drug reaching the circulation was 19.8% less for the Oros preparation compared with intragastric infusion but this was not due to incomplete release since the residual amounts of drug in three systems recovered from faeces corresponded to less than 12% of the administered dose. Analysis of the plasma profiles by the Wagner-Nelson method indicated a reasonable agreement between in vitro release and in vivo absorption. The appearance of drug in plasma was delayed for both treatments, and for Oros the apparent absorption rate slowed 6 h after dosing. Plasma profiles after 14/190 metoprolol Oros were consistent with prolonged in vivo delivery and absorption from the gut. The absorption process, however, was associated with some reduction both in the rate, after 6 h, and in the total amount reaching the circulation.

Adult↗
PubMed1985

Comparison of single-dose pharmacokinetic and pharmacodynamic properties of two metoprolol Oros systems with different initial zero-order release rates.

Plasma concentrations and haemodynamic effects at rest and during exercise have been measured in six healthy volunteers after single oral dosing with two Oros drug delivery systems containing 190 mg metoprolol fumarate but with initial release rates of 14 and 19 mg/h, respectively. Sub-maximal exercise heart rates were attenuated by both Oros systems throughout most of the 30 h study period but no significant differences were detected between the 14/190 and 19/190 forms. Resting pulse rates and blood pressure were similarly affected by the Oros preparations. Approximately the same amount of drug reached the circulation from the Oros systems, but the 19/190 form produced higher peak concentrations at earlier times after dosing. At 24 h higher plasma concentrations were observed for the 14/190 preparation, reflecting its longer duration of drug release. There was no apparent advantage of one form over the other as regards haemodynamic response. The reduced peak plasma concentration with 14/190 Oros may, however, be an advantage in terms of tolerability.

Adult↗
PubMed1985

Oros controlled-release formulations of metoprolol: an approach to the development of a system for once daily administration.

A combined biopharmaceutical and haemodynamic approach to the development of a metoprolol Oros controlled-release delivery system for once daily administration is reported. Two studies, each involving 18 healthy volunteers, were performed in which twice daily administration of 100 mg conventional metoprolol tartrate tablets was compared with once daily administration of Oros systems containing 190 mg metoprolol fumarate but with different drug release rates. Plasma drug concentrations and beta-adrenoceptor blocking effects were measured over 24 h on days 1 and 5 of each treatment, and pre-dose in the interval between the main study days. The results of the first study with a 19 mg/h Oros system indicated that this rate was too rapid to provide the required response under steady-state dosing conditions. Theoretical calculations based on a one-compartment pharmacokinetic model and input functions for hypothetical Oros systems were then performed to define the optimal release rate for a once daily preparation. The results of the second study confirmed that a 14 mg/h system possessed the required characteristics in that it maintained more uniform beta-adrenoceptor blockade throughout 24 h, and produced pre-dosing plasma concentrations and haemodynamic effects which were identical to those for the conventional tablet twice daily regimen.

Adolescent↗
PubMed1985

Central herniation revealed by focal decrease in blood flow without elevation of intracranial pressure: a case report.

Until recently, in standard hospital settings the tissue blood supply could be inferred only from indirect measures such as assessment of the clinical signs and intracranial pressure (ICP) monitoring. This critical parameter can now be imaged directly with stable xenon-enhanced computed tomographic (CT) imaging. The procedure requires only an additional 10 minutes after a standard head study, yet it provides potentially vital information about tissue perfusion. We describe here a patient in whom a frontal lobe hematoma produced a direct mass effect, causing an element of central herniation with relative sparing of lateral and posterior cortical regions. Although the ICP recordings remained unchanged, symptoms of brain stem compression became apparent. Xenon/CT cerebral blood flow (CBF) mapping demonstrated a flow decrease mainly within the left frontal lobe and throughout central ganglionic structures. After removal of the left frontal hematoma, both clinical status and local and central flow improved. Because the xenon/CT method combines direct anatomical information with blood flow information in one examination, it may be a valuable clinical tool in providing a better understanding of pathophysiology in patients with head injuries and other mass lesions.

Adult↗
PubMed1979

Water relations of fetal development.

Normal pregnancy is accompanied by a remarkable increase in total body water, due partly to the growth and development of the conceptus and partly to water retention by the mother. An evaluation of the changes in body water during pregnancy suggests that they could very largely be brought about by the hydrostatic element of osmotic water regulation and are mainly under fetal, rather than maternal control. The results also suggest that pathological disorders of water in pregnancy are essentially secondary, and not primary manifestations of disease.

Amniotic Fluid↗
PubMed1979

Biochemical changes of normal pregnancy and puerperium in Lagos, Nigeria.

A cross-sectional study is presented of biochemical changes in the third trimester of normal pregnancy and puerperium during the wet season in the tropical climate of Lagos, Nigeria. These changes are less marked in first than in subsequent pregnancies, and although qualitatively similar, in some respects they differ from those observed in the temperate climatic zone. The indications are that quantitative differences may exist which could be relevant to the management of pregnancy in the tropics.

Adult↗
PubMed1978

Water relations of early embryogenesis.

Attention is drawn to the changes in maternal serum osmolality that accompany ovulation, fertilization and early embryogenesis, and the possible significance of those changes is discussed in relation to the sequence of development. From these considerations it is tentatively concluded that maternal hydration influences all stages of early development, and that transient derangement of maternal body fluid regulation could, therefore, be a significant factor in the aetiology of fetal malformations.

Congenital Abnormalities↗
PubMed1978

Water relations of the ovarian cycle.

This study reports the likely pattern of change in serum osmolality during the normal ovarian cycle, together with that which occurs during ovulation-induction by gonadotrophin. The variation in serum osmolality is attributed to the action of oestrogen on venous distensibility, and the effect of that response on the osmotic equilibrium between intra- and extravascular fluid. Although the action of gonadotrophin is mediated by the products of follicular theca and granulosa cells, the physiological response is ultimately affected by water. Both ovulation and menstruation may therefore depend on achieving a critical water content of follicular fluid and endometrial tissue.

Blood↗
PubMed1977

Correlations of sialomucins and IgA in the maternal serum of primiparous and multiparous subjects at delivery.

Attention is drawn to correlations between placental coefficients and maternal serum levels of IgA at delivery in primiparae and multiparae. These correlations associate maternal serum IgA with gestational performance and appear to discriminate between groups which differ in that respect. Similar correlations exist between the placental coefficient and maternal serum seromucoid, with group discrimination preserved in primiparae, but not multiparae. Direct correlations between serum seromucoid and IgA in maternal serum can be attributed to their mutual dependence on the size and state of the feto-maternal interface, and may provide a means of detecting placental insufficiency in multigravidae.

Female↗
PubMed1976

Plasma solute concentrations during gonadotrophin-induced ovulation.

The effects of ovulation induction on some plasma solute concentrations were investigated serially in eleven women, nine of whom conceived in that cycle. Increasing oestrogen output during the follicular phase was associated with decreasing levels of osmolality, urea, total protein and the albumin free protein fraction. Smaller decreases in the concentrations of sodium, potassium, chloride, carbon dioxide combining power (CO2CP) and albumin were not statistically significant. The luteal phase was marked by a rise in osmolality and a fall in CO2CP but no other significant changes. Levels of osmolality, sodium and potassium fell in early pregnancy when oestrogen output was further increased. These results appear consistent with an oestrogen induced expansion of the extracellular fluid compartment by retention of water in excess of solute, which might also account for the similar changes in pregnancy.

Blood Proteins↗
PubMed1976

Haematological changes during ovulation-induction by gonadotrophins.

The oestrogen response to ovulation-induction by gonadotrophins initiates a preovulation rise in total leucocytes and promotes fluid retention. In consequence of the latter, cyclic changes occur in blood haemoglobin and the haematocrit. The level of oestrone excretion in the follicular phase of induced cycles indicates that multiple follicular development probably occurs, and this also appears to affect the luteal phase. It seems likely, therefore, that the data present a rather exaggerated picture of the situation which obtains in normal menstrual cycles.

Blood↗
PubMed1975

Maternal serum sialomucins during pregnancy and postpartum in patients with pre-eclampsia.

The seromucoid fraction of maternal serum glycoproteins is increased in pre-eclampsia and the rise, which is proportional to the severity of the disease, may reflect progressive placental deterioration with increasing trophoblast fragmentation and deportation. The pulmonary lysis of deported trophoblast effects the local release of fetal antigens and thromboplastin in the lungs. The former, which are immunologically inert because they are complexed with maternal serum seromucoid, are released into the peripheral circulation, while the local coagulation hazard presented by the latter is countered by intensified fibrinolytic activity, the products of which are also released into the peripheral circulation. In severe pre-eclampsia the peripheral circulation contains a considerable excess of physically similar proteins derived from the seromucoid fraction and fibrin degradation products, and the conditions which then obtain in the renal glomerulus favour the physical process of coacervation. In that event the mechanism of the origin and development of the renal lesion can be described in purely physical terms.

Antigens↗