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Y Stirling

Publications and source records attributed to Y Stirling.

70 records · Page 4Linked to original sources
PubMed1978

Automation of two-stage factor VIII assay.

Two automated methods for two-stage factor VIII assays have been compared with one another, and evaluated in practice. The Depex method records the clotting time when an electric circuit is completed by the formation of a fibrin thread across a hook-type electrode; the Electra method is based on an optical density technique of clot detection. The two methods gave comparable results for measured levels of factor VIII when haemophilic or "normal" plasmas were assayed. Results from the two methods in practice also suggest that both are valid at low and "normal" factor VIII levels. The Electra method is also probably suitable for assays of concentrates; however, the Depex method appears to give falsely high values in these circumstances, and experimental findings suggest that the reason may be that increased viscosity due to the high fibrinogen levels in factor VIII concentrates causes premature closure of the circuit between the two ends of the Depex electrode. The main advantage of the Depex method is that, provided 3 or 4 machines are available, a given number of assays can be completed more quickly than on Electra. The main advantages of Electra are that it is probably subject to less laboratory error than Depex, and that it is suitable for assaying concentrates as well as haemophilic and "normal" plasmas.

Automation↗
PubMed1977

Haemostatic, lipid, and blood-pressure profiles of women on oral contraceptives containing 50 microgram or 30 microgram oestrogen.

In 15 women on oral contraceptives containing 30 microgram oestrogen, mean values for factors II, VII, and X, fibrinogen, fibrinolytic activity, antithrombin III, cholesterol, and fasting triglycerides were intermediate between values for 63 women on preparations containing 50 microgram oestrogen and those for 243 premenopausal women not on oral contraceptives. Mean blood-pressure levels, however, were higher in women on 30 microgram than in those on 50 microgram preparations. In 28 women on 50 microgram preparations containing 3 mg or 4 mg norethisterone, mean values of factor VII, fibrinogen, fibrinolytic activity, cholesterol, fasting triglycerides, and systolic blood-pressure were higher than in 15 women whose preparations contained only 1 mg of norethisterone. A less consistent picture was found in women on 30 microgram oestrogen preparations containing either 250 microgram (10 women) or 150 microgram (5 women) d-norgestrel. It is concluded that 30 microgram oestrogen preparations probably result in smaller hemostatic and lipid changes than 50 microgram preparations but that they may have a blood-pressure-raising effect attributable to the particular progestagen, d-norgestrel, used in 30 microgram preparations. The safety of these 30 microgram oestrogen preparations may thus depend partly on the balance between these two sets of effects. It is also concluded that norethisterone may have effects similar to those attributed to oestrogens.

Adult↗
PubMed1977

Changes in haemostatic system after application of a tourniquet.

In 35 patients undergoing routine orthopaedic operations in which occlusive tourniquets were used there was a pronounced rise in fibrinolytic activity in the systemic circulation which lasted for at least 15 minutes after the release of the tourniquet; this response was seen after operations on both arms and legs. In contrast there was no increase in fibrinolytic activity in the systemic circulation associated with venous occlusion. Neither the application of a tourniquet nor venous occlusion resulted in changes in factors V or VIII, fibrinogen, or platelet-count. The application of a completely occlusive tourniquet might be a simple form of prophylaxis against deep-vein thrombosis and would avoid the disadvantages of using heparin.

Adult↗
PubMed1976

Four heparin preparations: anti-Xa potentiating effect of heparin after subcutaneous injection.

Four different heparin preparations--sodium and calcium salts of the same batch of heparin (mean molecular weight 15,000), low molecular weight sodium heparin (mean m.w. 9,000) and high molecular weight sodium heparin (mean m.w. 22,000) were injected subcutaneously on different days each into 6 healthy young volunteers in a randomized trial. Plasma heparin levels were measured using the anti-Xa assay at 1 hour, 3-4 hours and 6-7 hours after the injection. The highest anti-Xa potentiating effect was obtained after the injection of the low molecular weight sodium heparin (mean 0.381 i.u./ml) at 3-4 hours after the injection. With sodium heparin (m.w. 15,000) the highest values (0.135 i.u./ml) were found at 1 hour. Significantly lower anti-Xa potentiating effect was obtained 1 hour after the injection of calcium heparin and in particular after the injection of high molecular weight heparin (mean values 0.072 i. u./ml and 0.043 i. u./ml respectively). Both these preparations showed an increase from 1 hour after injection to 3-4 hours after injection (mean values 0.082 i. u./ml and 0.057 i. u./ml at 3-4 hours after injection). These results indicate that the salt and the molecular weight of the preparation may strongly influence the degree of anticoagulation achieved after subcutaneous injection.

Calcium↗
PubMed1976

Factor V in an industrial population.

Factor-V levels have been measured in a random sample of 626 men and 307 women working in a variety of occupations in North West London. The method is an automated one-stage assay using the same batch of freeze-dried thromboplastin, all results being expressed in terms of the same freeze-dried standard plasma; it has been shown that only one dilution of test plasma is necessary. Factor-V levels are significantly higher when venepuncture is difficult than when it is satisfactory, the mean levels being about 130% and 117% respectively. Factor-V levels are approximately normally distributed; they are similar in men and women and in blacks and whites, and increase significantly with age at the rate of about 0.6% per annum. Factor-V levels are not affected by oral contraceptives or the menopause, and there are no differences according to blood group or secretor status.

Adult↗
PubMed1976

An epidemiological study of the haemostatic and other effects of oral contraceptives.

Factors V, VII and VIII (each determined by biological assay), fibrinogen, platelet count and adhesiveness, and fibrinolytic activity were measured in 234 white pre-menopausal women, of whom 57 (24%) were on oral contraceptives and 177 (76%) were not. Cholesterol, triglyceride and blood pressure levels were also recorded. In 20 of the women on oral contraceptives, and in an age-matched group of 20 who were not, prothrombin, factor X, antithrombin III and alpha 2-macroglobulin levels were determined, and factors VII and VIII were also measured immunologically. For the majority of the variables studied, the differences between those using and not using oral contraceptives were greater in younger than older women; in the case of factor VII (biological assay) and fibrinogen, the differences between the regression slopes on age were statistically significant, and mean values were substantially higher in those on oral contraceptives. There was also a significant difference between regression slopes on age for cholesterol. Mean levels of prothrombin, factors VII (immunological assay) and X, triglycerides and blood pressure were significantly higher, and mean levels of antithrombin III significantly lower, in those on oral contraceptives compared with those not. Overall, fibrinolytic activity was significantly higher in the women on oral contraceptives; this difference was, however, almost entirely due to the greatly increased fibrinolytic activity of the non-smokers on oral contraceptives, activity in the smokers on oral contraceptives being similar to that of the women not on these preparations. There were no significant differences in mean platelet count or adhesiveness, or in haemoglobin, packed cell volume, uric acid and blood sugar levels. Among the women on oral contraceptives, there was a significant negative correlation between factor VIII and fibrinolytic activity; this was largely due to five women all of blood groups A and B, in whom, besides high factor-VIII levels and poor fibrinolytic activity, other variables (e.g. fibrinogen) were raised in a direction that might be expected to favour thrombogenesis. It is possible that it is those women whose fibrinolytic activity does not increase in order to compensate for the effects of oral contraceptives on clotting factors, lipids and blood pressure, who are at special risk of thromboembolic episodes. The differential effects of oral contraceptives by age must be borne in mind in evaluating the effects of these preparations on the haemostatic and lipid systems.

Age Factors↗
PubMed1975

Plasma heparin levels after low dose subcutaneous heparin in patients undergoing hip replacement.

Plasma heparin levels were measured at 2 and 8 h after 5000 iu of heparin subcutaneously in 43 patients awaiting total hip replacement. At 2 h, 37 patients had plasma levels between 0.05 and 0.15 iu/ml, three patients had more than 0.2 iu/ml, and three had only trace levels. At 8 h, most patients had less than 0.1 iu/ml, and six patients had no detectable plasma heparin. There were no correlations between plasma heparin levels and age, sex, body weight or use of analgesics. Patients with high 2 h plasma heparin levels may bleed at operation, whereas those with very low plasma heparin concentrations may be at risk of post-operative venous thrombosis; it may therefore sometimes be necessary to monitor plasma heparin levels in order to determine the optimal regime in individual cases.

Adult↗