PubMed Health⌕ Search

Biomedical subjects

P Dawson

Publications and source records attributed to P Dawson.

At least 19 recordsLinked to original sources
PubMed1992

Contrast media-induced effects on blood rheology and their importance in angiography.

Factors which alter blood viscosity may have important consequences during angiography. The differential effects of various concentrations of five different radiocontrast media on the viscosity characteristics of erythrocyte-plasma suspensions were made over a range of applied shear rates. The results showed that, at both high and low shear rates, the rate of change of viscosity with contrast concentration differs markedly between the various types of contrast media. The conventional ionic monomers caused most disturbance to blood viscosity. The monoionic dimer hexabrix was least disturbing to the viscometric characteristics of blood, and the newer non-ionic monomers were intermediate in their effects. Significant effects on blood viscosity may be caused by radiocontrast agents during a number of in vivo angiographic situations, in particular: early after contrast bolus injection into large vessels, in the microcirculation after selective injections, and during angioplasty procedures.

Adult↗
PubMed1992

Thrombin-soaked embolization coils: the effect on whole blood clotting time.

Embolization coils are well established as embolic agents for the treatment of various conditions. Several authors have commented on the increased 'thrombogenicity' of coils following soaking in thrombin solutions. We have carried out an in vitro study, carefully measuring the effect on whole blood clotting time (WBCT), of soaking coils in thrombin solutions of different concentrations (100, 200, 400, 1000 U/ml). Untreated steel coils are shown to have clot promoting activity (CPA) in vitro, reducing WBCT from 14.85 min to 5.53 min. Passing the coils down a saline-filled catheter slightly reduces their CPA, but not significantly (p = 0.21). With thrombin concentrations above 100 U/ml, a significant reduction in WBCT is recorded, but although there is a trend of increasing CPA with increasing thrombin concentration from 200-1000 U/ml, a plateau in WBCT is seen, and the difference is not significant. It therefore appears that the clot promoting activity of embolic coils is significantly increased by soaking them in a relatively weak thrombin solution. The use of such a solution (e.g. 200 U/ml) in vivo would have obvious value in limiting the potential systemic effects of thrombin.

Blood Coagulation↗
PubMed1992

Brave biopsy.

Explore the source record for details and available documents.

Biopsy↗
PubMed1992

Propofol induction for laryngeal mask airway insertion: dose requirement and cardiorespiratory effects.

The dosage, haemodynamic and respiratory effects of propofol for laryngeal mask airway (LMA) insertion were investigated. Fifty patients (ASA I-II) were randomly assigned one of four induction doses of propofol (1.5-2.5 mg/kg) delivered over 30 seconds and the first attempt at LMA insertion was made at 90 seconds. The LMA was inserted at 90 seconds in 35 patients and by 300 seconds in 13 others (mean plasma concentration at 90 seconds was 7.7 mcg/ml (no delay) versus 5.2 mcg/ml (insertion delayed), P < 0.01). Insertion was less successful after 1.5 mcg/kg (failed at 90 seconds in 6 of 12 patients), but did not vary with the other doses. Additional propofol (0.5 mg/kg/30s) was required in 22 patients for LMA insertion or to prevent movement, resulting in propofol concentrations at 120-180 seconds above 7 mcg/ml. Respiratory effects were minor, but MAP decreased by 18 +/- 1.4 mmHg at 90 seconds. Cardiovascular effects did not differ significantly between dosage groups or with the use of additional propofol.

Adult↗
PubMed1991

Thromboembolic phenomena in clinical angiography: role of materials and technique.

Interactions between blood and iodinated contrast agents and syringes and catheters are discussed with regard to clot formation and thromboembolic phenomena in angiography. Syringe and catheter materials are, to varying extents, contact activators of coagulation, whereas contrast agents inhibit coagulation and platelet aggregation. Current understanding of these phenomena is surveyed, and the implications for clinical angiographic technique are discussed.

Angiography↗
PubMed1991

Embolic problems in angiography.

All contrast agents, including the non-ionic variety, are anticoagulant and have antiplatelet effects. There is absolutely no evidence from any source, in vitro or in vivo, that non-ionic contrast agents have any "prothrombotic" or "procoagulant" or "thrombogenic" potential, as has been suggested in some quarters. They simply have a lesser anticoagulant effect than do the ionic agents old or new, which is entirely predictable and in line with their generally greater inertness and biocompatibility. Although there may still be scope for greater understanding of structure-toxicity relationships in contrast agent design, currently it is believed that it would be impossible to restore a stronger anticoagulant effect to a non-ionic contrast agent without simultaneously restoring other aspects of toxicity. The angiographer who calls for more anticoagulant contrast agents is calling for more toxic contrast agents. It has been our clinical experience, and that of many others throughout Europe, that there has been no increase in clinically apparent thromboembolic phenomena since the introduction of non-ionic agents. Furthermore, it has been our experimental experience that, although contrast agents of all kinds play a role (inhibitory) in thromboembolism, the role of other materials used by the angiographer are of greater importance. Thus, the materials of and, indeed, the method of preparation of, the catheters and guidewires used has a great bearing on the phenomenon. Heparinization of the patient should surely be beneficial in some cases, but there is, surprisingly, no firm consensus or data on this and the individual requirements of patients vary, necessitating some method of monitoring and control.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography↗
PubMed1991

Effects of strength training on lactate threshold and endurance performance.

To determine the effects of 12 wk of strength training on lactate threshold (LT) and endurance performance, 18 healthy untrained males between 25 and 34 yr of age were randomly assigned to either strength training (N = 10) or control (N = 8) groups. Despite no changes in treadmill VO2max or cycle peak VO2, a 33 +/- 5% increase (P less than 0.001) in cycling time to exhaustion at 75% of peak VO2 was observed following training. No significant changes in cycling time were observed in the control group. There were significant reductions in plasma lactate concentration at all relative exercise intensities ranging between 55 and 75% of peak VO2 training. The improved endurance performance was associated with a 12% increase in LT (r = 0.78, P less than 0.001). The strength training program resulted in significant improvements (P less than 0.001) of 31 +/- 5% and 35 +/- 7% in isokinetic peak torque values for leg extension and flexion, respectively, at a velocity of 30 degrees.s-1. There were also significant increases in 1-RM values of 30 +/- 4% (P less than 0.001) for leg extension, 52 +/- 6% (P less than 0.001) for leg flexion, and 20 +/- 4% (P less than 0.001) for the bench press. These findings indicate that strength training improves cycle endurance performance independently of changes in VO2max. This improved performance appears to be related to increases in LT and leg strength.

Adult↗