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Biomedical subjects

A L Muir

Publications and source records attributed to A L Muir.

At least 91 records · Page 5Linked to original sources
PubMed1983

Failure in labelling of red blood cells with 99mTc: interaction between intravenous cannulae and stannous pyrophosphate.

The effect of different methods of stannous pyrophosphate (SnPYP) administration on a modified in vivo technique for labelling red blood cells (RBCs) with 99mTc has been studied. Retention of 99mTc in the bloodstream was measured and parallel in vitro RBC labelling experiments were performed. After administration of SnPYP or a mixture of SnPYP and heparin via the metal needles of intravenous cannulae, the mean 30-min retentions of 99mTc were 96.8% (SD 8.6) and 95.3% (SD 12.4) respectively and the mean in vitro labelling efficiencies were 86.9% (SD 5.0) and 81.9% (SD 18.2) respectively. When the SnPYP was administered via teflon cannulae, the mean 30-min retention of 99mTc was 40.0% (SD 16.7) and the in vitro labelling efficiency was 18.7% (SD 27.0). Reduced RBC labelling and rapid clearance of 99mTc from the bloodstream were not explained by adsorption of stannous ion or pyrophosphate onto the teflon cannulae or retention of SnPYP in the cannulae. When labelling RBCs with 99mTc it is important that SnPYP is not injected via a teflon cannula.

Erythrocytes↗
PubMed1983

A study of cold cardioplegic myocardial protection in rats: an experimental model using the uptake of technetium 99m pyrophosphate and enzyme activity as parameters of injury.

This study compares the use of St Thomas' cardioplegia and cold saline cardioplegia at 4 degrees C for protection against global myocardial ischaemia in a model of heterotopic cardiac transplantation in rats of isogeneic strain. The parameters of myocardial injury applied were the uptake of Technetium 99m pyrophosphate (Tc 99m Pyp) in the transplanted heart and the measurement of serum total creatine kinase (CK) and creatine kinase MB (CK:MB) isoenzyme activity. The findings indicate that St Thomas' cardioplegic solution confers improved myocardial protection compared with normal saline as judged by statistically significant differences between: (a) the uptake of Tc 99m Pyp between the two solutions at 30 min storage: and (b) the peak total serum creatine kinase enzyme activity at 90 min storage. Excellent correlation was present between the uptake of Tc 99m Pyp and peak total serum creatine kinase activity. Further application of this model is described.

Animals↗
PubMed1983

Can right ventricular performance be assessed by equilibrium radionuclide ventriculography?

Although right ventricular function may be examined by following the passage (first pass) of a bolus of radionuclide through the right heart before it reaches the left heart, the counts detected with conventional gamma cameras in such a short time interval are low; moreover, repeated determinations would result in an unacceptable radiation burden to the patient. We have modified the gated equilibrium blood pool method to allow repeated assessment of the right ventricular ejection fraction (RVEF) and have compared the results with the first-pass method in 43 patients. Good agreement was obtained between the two methods (r = 0.91, p less than 0.001). The mean difference between the two methods was 0.04 with an intra-observer variation for the equilibrium studies of 0.03 and an inter-observer difference of 0.04. The mean difference in RVEF for seven patients studied on two separate occasions 30 minutes apart was only 0.02. In four patients the mean RVEF measured at rest was 0.44 +/- 0.05 (SEM) and after exercise it was 0.48 +/- 0.06. After infusion of isoprenaline at 1 microgram/min the mean rose to 0.64 +/- 0.04 (p less than 0.02) and after infusion of a new beta 1-sympathomimetic agent, prenalterol, at doses of 1 and 2 mg it was 0.56 +/- 0.02 (p less than 0.02) and 0.59 +/- 0.03 (p less than 0.01) respectively, where the significance levels are relative to the resting values. In nine patients with good ventricular function the vasodilator nifedipine caused right and left ventricular ejection fractions to increase by the same amount; while in six patients with severe impairment of left ventricular function due to ischaemic heart disease the RVEF increased from 0.58 +/- 0.03 to 0.73 +/- 0.03 (p less than 0.01) after 2 mg of prenalterol, but the left ventricular ejection fraction increased only from 0.22 +/- 0.04 to 0.26 +/- 0.04. We conclude that repeated estimation of right ventricular performance is possible by equilibrium radionuclide ventriculography.

Adrenergic beta-Agonists↗
PubMed1983

Assessment by radionuclide angiography of right and left ventricular function in chronic bronchitis and emphysema.

Non-invasive measurements of right and left ventricular ejection fraction (RVEF, LVEF) by multiple-gated equilibrium radionuclide ventriculography were performed in 18 control subjects, 16 patients with angina pectoris, and 45 patients with hypoxic chronic bronchitis and emphysema. The mean RVEF in the control subjects was 0.62 +/- 0.09 (SD), which was not significantly different from the mean RVEF in the patients with angina (0.60 +/- 0.09), but was significantly higher (p less than 0.01) than the mean value in patients with chronic bronchitis and emphysema (0.45 +/- 0.11). LVEF was not significantly different in the groups studied. There was a significant correlation between LVEF and RVEF only in patients with chronic bronchitis and emphysema (p less than 0.001). Those patients with chronic bronchitis and emphysema who had clinical evidence of cor pulmonale at the time of the study had significantly lower values of RVEF and LVEF (p less than 0.001) than patients with no previous cor pulmonale or those who had had cor pulmonale in the past. There was a significant correlation between RVEF and arterial oxygen (p less than 0.01) and carbon dioxide tensions (p less than 0.05). Reduced RVEF in patients with chronic bronchitis and emphysema may be an early indicator of the development of cor pulmonale and may be useful as a non-invasive method of assessing the effects of therapeutic interventions.

Adult↗
PubMed1983

Sample collection and processing for the assay of plasma renin activity. A comparison of anticoagulants and inhibitors.

Plasma renin activity was measured in samples collected in lithium heparin, sodium heparin, and ethylenediaminetetraacetate. The samples were incubated under two widely used sets of conditions to generate angiotensin I, and the results were compared. Under certain incubation conditions, the absence of ethylenediaminetetraacetate from the sample tube produced low plasma renin activity values. This was obviated by using an alternative incubation medium and was not, therefore, due to direct inhibition of renin by heparin. These lower values were not seen in samples from patients receiving captopril. This suggests that the discrepant values were due to some angiotensin I conversion to angiotensin II and lower homologues in the incubates. Sodium heparin samples compared closely with lithium heparin samples, indicating that the presence of lithium is not significant. These results show that, provided the incubation conditions are suitably modified, samples collected into lithium or sodium heparin can be used for measurement of plasma renin activity.

Captopril↗
PubMed1983

Management of hypertension--a study of hospital outpatient practice.

In this third report on the management of hypertension by general practitioners and hospital physicians we review hospital outpatient practice in a representative sample of 90 new patients and 436 returning patients attending the clinics of three Edinburgh hospitals. Seventyeight per cent of the new patients were seen by a consultant or senior registrar. An unacceptable number of deficiencies was found in clinical assessment and these are discussed. Consultants are shown to be more conservative than junior hospital doctors in their treatment of hypertension.

Adult↗
PubMed1982

Abnormal left ventricular function in hyperthyroidism: evidence for a possible reversible cardiomyopathy.

We assessed the effects of exercise and beta-adrenoceptor blockade on left ventricular ejection fraction (LVEF) measured by radionuclide ventriculography in nine patients with uncomplicated hyperthyroidism. Patients were studied in both the hyperthyroid and euthyroid states. The hyperthyroid state was characterized by a high LVEF at rest but--paradoxically--by a significant fall (P less than 0.01) in LVEF during exercise. At the same workload and at the same heart rate, patients had a restoration of the normal rise in LVEF during exercise when they were euthyroid. The LVEF was greater during exercise (P less than 0.02) when the patients were euthyroid than when they were hyperthyroid. Pretreatment with propranolol caused similar reductions in resting LVEF in the hyperthyroid and euthyroid states; the drug attenuated the rise in LVEF during exercise when the patients were euthyroid, but did not influence the exercise-induced reduction in LVEF in hyperthyroidism. The abnormal left ventricular function observed during exercise in hyperthyroidism suggests a reversible functional cardiomyopathy, independent of beta-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones.

Adult↗
PubMed1982

Left ventricular function in hypothyroidism. Responses to exercise and beta adrenoceptor blockade.

The effects of exercise and beta adrenoceptor blockade on left ventricular function were assessed in eight patients with hypothyroidism before and during thyroxine replacement treatment. Left ventricular ejection fraction, measured by radionuclide ventriculography, was reduced in hypothyroid patients at rest and on exercise. The rise in ejection fraction with exercise was, however, similar in both groups. Pretreatment with intravenous propranolol reduced the ejection fraction at rest 9% in both hypothyroid and euthyroid patients and reduced the rise on exercise. Directional changes in a second index of myocardial contractility based on the shape of the ventricular volume curve paralleled the changes in the ejection fraction. Left ventricular function is therefore reversibly depressed by thyroid hormone deficiency but responses to exercise and beta adrenoceptor blockade are normal. There is no evidence of altered adrenergic sensitivity in the control of myocardial contractility in hypothyroidism.

Adult↗
PubMed1982

Effect of exercise and isoprenaline on left ventricular ejection fraction in patients with angina pectoris as assessed by radionuclide angiography.

The effect of supine leg exercise and an infusion of isoprenaline (2 micrograms/min) have been compared in 9 patients with angina pectoris and 8 normal control subjects. Left ventricular ejection fraction was measured by radionuclide angiography using the gated blood pool technique. The normal subjects increased their ejection fraction from 0.57 +/- 0.02 at rest to 0.71 +/- 0.02 during exercise, and 0.76 +/- 0.03 during isoprenaline infusion. In patients with angina pectoris, the resting ejection fraction of 0.47 +/- 0.04 decreased to 0.35 +/- 0.04 during exercise but increased to 0.63 +/- 0.06 during isoprenaline infusion. Our results suggest that the changes in ejection fraction probably depend on the changes in left ventricular segmental wall motion. When dyskinesia is increased, as with exercise, the ejection fraction declines, but when dyskinesia is unaffected or improved, as with isoprenaline, the ejection fraction increases.

Adult↗
PubMed1982

Effective penetration of the lung periphery using radioactive aerosols: concise communication.

Radioactive microspheres could offer several advantages over gases in the investigation of pulmonary ventilation. Monodisperse microspheres of human serum albumin have been produced using a spinning-disc generator, and kits were prepared for subsequent labelling with technetium-99m. The average labeling efficiency was 88% and unlabeled Tc-99m was removed before aerosol delivery. A simple system was constructed to nebulize and deliver dry monodisperse microspheres. The ventilation images obtained were compared quantitatively with the corresponding krypton-81m images, subdividing the lung regions into inner, central, and peripheral zones. No significant difference was found in the proportions of the total counts for any lung region. There was good agreement between the distributions of microspheres obtained on separate days (r = 0.97, p less than 0.0001), An "aerosol penetration index" was defined as the ratio of the peripheral to the inner counts for the microspheres normalized by the corresponding ratio for krypton-81m. The mean value of this index for 16 normal subjects was 0.98 +/- 0.23 (s.d.), indicating that the microspheres had achieved penetration of the lung periphery. For patients with chronic obstructive lung disease, more localized defects were observed with the microspheres than with krypton-81m. The mean penetration index for this group was only 0.69 +/- 0.21 (s.d.). This was significantly different from the value for normal subjects (p less than 0.002).

Humans↗
PubMed1981

Pulmonary hypertension and fenfluramine.

Pulmonary hypertension developed in two women who had been taking fenfluramine for over eight months for weight reduction. On withdrawing the drug symptoms and electrocardiographic evidence of pulmonary hypertension disappeared in both cases. In one patient, however, the evidence recurred after rechallenge with fenfluramine.These findings are strong evidence that fenfluramine may cause pulmonary hypertension. Hence any patient taking the drug should report immediately any deterioration in exercise tolerance.

Adult↗
PubMed1981

An index of valvular regurgitation from a radionuclide bolus.

Mitral and aortic regurgitation was assessed from analysis of activity-time curves from right and left ventricles following the intravenous bolus injection of 99Tcm-labelled human serum albumin. The differences in the initial arrival times and the mean transit times for the ventricles were combined to provide an index of regurgitation. The mean index for 18 patients with good ventricular function and no regurgitation was -0.07 +/- 0.55 (SD) seconds. This was not significantly different from the mean value of 0.39 +/- 1.22 s obtained for 9 patients with left ventricular failure but no regurgitation. The indices for 16 patients with mitral or aortic regurgitation agreed well with the severity as assessed by contrast angiography. The mean indices for the mild, moderate and severe regurgitation groups were 2.62 +/- 1.13 s, 5.30 +/- 3.05 s and 10.15 +/- 3.62 s respectively.

Aortic Valve Insufficiency↗