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Biomedical subjects

A L Muir

Publications and source records attributed to A L Muir.

At least 73 records · Page 4Linked to original sources
PubMed1985

Right ventricular performance during exercise in chronic obstructive pulmonary disease. The effects of oxygen.

Radionuclide ventriculography allows non-invasive assessment of right ventricular performance. This study has confirmed that there is a modest reduction in right ventricular ejection fraction (RVEF) in patients with chronic obstructive pulmonary disease (COPD), as compared to normal subjects. However, occult right ventricular dysfunction also becomes apparent in these patients during exercise. The change in RVEF during exercise is related to the corresponding fall in arterial oxygen saturation in patients with COPD. Oxygen improves the response of the right ventricle to exercise, although the mechanism remains unclear. Long-term oxygen therapy, in patients with respiratory failure, does not appear to have any significant effect on RVEF.

Adult↗
PubMed1985

Effects of felodipine on resistance and capacitance vessels in patients with essential hypertension.

The acute cardiovascular effects of oral felodipine (0.05 mg/kg and 0.1 mg/kg) were studied using radionuclide methods in 14 hypertensive patients. Eight were previously untreated and 6 had been treated with atenolol 100mg daily for a least 1 month. The maximal effects were observed 60 minutes after the first oral dose and no greater effect was observed with the higher dose. Felodipine caused a reduction in systemic vascular resistance, with a fall in blood pressure and an increase in cardiac output and left ventricular ejection fraction. Those responses were presumably mediated by the reduction in afterload, as they were not modified by pretreatment with atenolol. There were no changes in venous capacitance and the overall pattern of response was similar to that noted with hydralazine. Thus, in hypertensive subjects felodipine acts as a potent arteriolar vasodilator. The results suggest the drug may be an effective means of controlling hypertension, particularly when given in combination with other antihypertensive therapy.

Adult↗
PubMed1985

Felodipine can replace minoxidil in the treatment of refractory hypertension.

In a group of 15 men with severe hypertension in a double-blind crossover trial, the new calcium antagonist felodipine has been shown to lower blood pressure as effectively as minoxidil when used in combination with a beta-blocker and a loop diuretic. Felodipine was well tolerated and may have a role in the management of severe hypertension.

Aged↗
PubMed1985

Left ventricular performance in subclinical hypothyroidism.

Normal plasma thyroid hormones with elevation of thyrotrophin levels in asymptomatic patients is known as subclinical hypothyroidism. Radionuclide angiography was used to study left ventricular function in 10 such patients before and after establishment of normal thyrotrophin levels with thyroxine. Resting left ventricular ejection fraction was similar in both states but exercise left ventricular ejection fraction was less in the subclinical hypothyroid (61 +/- 3 per cent) compared with the euthyroid (68 +/- 3 per cent; p less than 0.025) state. Sodium nitroprusside caused similar increases in resting cardiac output but in subclinical hypothyroidism this resulted from a large increase in heart rate (26 +/- 4 beats/min) and reduction in stroke volume (11 +/- 4 per cent) whereas in the euthyroid state, the heart rate increment was less (14 +/- beats/min) and stroke volume was unchanged. Analysis of left ventricular pressure-volume relationships at end-systole during exercise showed a steeper pressure-volume slope in the euthyroid compared with the subclinical hypothyroid state (p less than 0.05). Subtle impairment of left ventricular function is detectable in subclinical hypothyroidism and may justify use of hormone replacement.

Adult↗
PubMed1984

Ventricular performance and prognosis after primary ventricular fibrillation complicating acute myocardial infarction.

To examine the relationship between early arrhythmias, infarct size and prognosis, we compared 22 consecutive patients surviving acute myocardial infarction (AMI) and primary ventricular fibrillation (VF) with a control population after AMI uncomplicated by primary VF. Left ventricular ejection fraction (EF) was measured by radionuclide ventriculography before discharge from hospital. Mean EF was significantly reduced below normal following AMI with or without primary VF (normal 0.57 +/- 0.05, mean +/- SD; P less than 0.01). Mean EF was lower among patients who survived primary VF than among those with infarction uncomplicated by primary arrhythmia (0.33 +/- 0.12 v. 0.46 +/- 0.07; P less than 0.01). There were striking differences in EF between those patients with anterior and those with inferior infarction. Mean EF for those surviving primary VF after transmural anterior infarction (0.23 +/- 0.06) was lower than those who had primary VF after transmural inferior infarction (0.43 +/- 0.06; P less than 0.01). Normal left ventricular function was seen in four individuals who developed no further complications. Recurrent primary ventricular arrhythmia was seen only in those individuals subsequently shown to have reduced EF. Low EF (less than 0.35) was seen in 12 patients with primary VF in the context of anterior infarction, five developed breakthrough ventricular arrhythmias despite therapy and in a limited follow-up period, three have died.

Adult↗
PubMed1984

Left ventricular function and the distribution of pulmonary and total blood volume in hypertensive and normotensive man.

Using radionuclide methods the relationship between total and central blood volume and left ventricular function was studied in 12 patients with untreated essential hypertension and contrasted with the findings in eight normotensive subjects. The principal findings were of an increased stroke volume and end-diastolic volume with an increase in the ratio of pulmonary to total blood volume in the hypertensive patients. Left ventricular ejection fraction was similar in both groups but end-systolic volume was increased presumably in response to the increased afterload of the ventricle. The increased pulmonary blood volume may be secondary to altered left ventricular mechanics and not a primary determinant of cardiac function.

Adult↗
PubMed1984

Contribution of prostaglandins to the systemic and renal vascular response to frusemide in normal man.

In eight normotensive male volunteers indomethacin decreased both the peak urine flow rate and total sodium excreted within 1 h of an intravenous dose of frusemide. Resting effective renal plasma flow and glomerular filtration rate were unchanged by indomethacin, but the increase in both parameters after frusemide was inhibited. The early increase in plasma renin activity after frusemide was inhibited by indomethacin. Indomethacin decreased urinary excretion of PGE by 80% and the increase after frusemide was abolished. The urinary excretion of a metabolite of systemic PGI2 was unaltered in the 40-60 min period following frusemide. The early haemodynamic effects of frusemide are likely to be prostaglandin mediated, but there was no evidence of any change in systemic PGI2 synthesis after frusemide.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

Myocardial infarction related to coronary artery bypass graft surgery.

Fifty consecutive patients undergoing coronary artery bypass grafting for chronic stable angina were assessed by serial electrocardiography, preoperative and postoperative myocardial scanning with technetium-99m pyrophosphate, gated radionuclide ventriculography, and serial measurement of creatine kinase, aspartate aminotransferase, urea stable lactic dehydrogenase, and creatine kinase isoenzyme (MB) to assess the incidence of perioperative myocardial infarction and identify the most appropriate diagnostic techniques. The correlation between myocardial scanning and the measurement of peak enzyme and isoenzyme activity was excellent in the diagnosis of perioperative infarction, although electrocardiography proved less helpful. There appeared to be no advantage in measuring creatine kinase MB rather than the more routinely measured enzymes. There were two deaths and evidence of myocardial infarction in five other patients, an incidence of 14%. Perioperative infarction was associated with a significant reduction in resting ejection fraction in two cases. In those patients without evidence of perioperative infarction the mean increase in ejection fraction of 7.8% was statistically significant.

Adult↗
PubMed1984

Myocardial infarction related to valve replacement surgery.

Fifty consecutive patients, 25 undergoing aortic valve replacement and 25 mitral valve replacement, were studied by serial electrocardiography, preoperative and postoperative technetium-99m pyrophosphate radionuclide scanning, and serial measurement of enzymes (creatine kinase, aspartate aminotransferase, urea stable lactic dehydrogenase) and the MB isoenzyme of creatine kinase to define the incidence of preoperative myocardial infarction and to identify the most appropriate diagnostic techniques. The use of myocardial scanning and measurement of peak enzyme activity proved to be accurate indicators of myocardial infarction, but the electrocardiogram was of limited value. The measurement of creatine kinase MB isoenzyme had no diagnostic advantage over that of the other enzymes. There were two deaths in the series, one due to acute pancreatitis after aortic valve replacement and the other due to myocardial injury after mitral valve replacement. There were four non-fatal myocardial infarctions after aortic valve replacement, giving an incidence of 16%, and none after mitral valve replacement, giving an incidence of 4%.

Adolescent↗
PubMed1984

Leukocyte kinetics in the human lung: role of exercise and catecholamines.

In six normal supine subjects epinephrine infusion produced a greater leukocytosis with smaller changes in heart rate and blood pressure than did norepinephrine or isoproterenol. Upright exercise in those subjects produced a greater leukocytosis than supine exercise at the same work load. To determine the lung's participation in these events, indium-labeled neutrophils (PMN) were given to four of the subjects. We found that 20-25% were retained in the first pass through the lung when compared with technetium-labeled erythrocytes. The number of labeled PMN in the lung gradually decreased and the number in the spleen and the liver increased. Exercise and catecholamine infusion caused an acceleration in the release of labeled cells from the lung, an increase in both labeled and unlabeled cells in the peripheral blood, and an increase in the number of labeled cells in the liver and spleen. This suggests that increased perfusion of low-flow areas in the lung may contribute to the increased leukocytosis seen in association with both exercise and catecholamine infusion.

Blood Pressure↗
PubMed1984

Long-term effects of cold cardioplegic myocardial protection in the rat.

The long-term histologic effects of the use of two cold cardioplegic solutions (St. Thomas' and saline) were studied and compared in a model of heterotopic cardiac transplantation in rats of isogeneic strain. After cold cardioplegic arrest, hearts were stored for varying times ("minimal," 30, or 90 minutes) in one of the solution prior to transplantation, giving a total of six groups (five animals in each group). Early assessment of myocardial injury 48 hours after transplantation was by the uptake of technetium 99m pyrophosphate and by measurement of serum creatine kinase activity. Late assessment of myocardial injury at 3 months after transplantation was by quantitative histologic examination. The findings indicated that significant myocardial fibrosis occurred in hearts stored in both solutions for the longest storage period (90 minutes) and that St. Thomas' cardioplegic formula conferred better myocardial protection after 90 minutes' storage than did cold saline, as judged by the degree of histologic injury at 3 months (p less than 0.025). Significant correlation was found between long-term histologic changes at 3 months and the uptake of technetium 99m pyrophosphate (p less than 0.001) and serum creatine kinase activity (p less than 0.05) assessed at 48 hours. Uptake of technetium 99m pyrophosphate and increased serum creatine kinase activity was demonstrated 48 hours after injury in animals having no detectable histologic injury at 3 months. These observations indicate that there may be technetium 99m pyrophosphate uptake and enzyme release from reversibly damaged myocardial cells.

Animals↗
PubMed1983

Effects of pirbuterol and sodium nitroprusside on pulmonary haemodynamics in hypoxic cor pulmonale.

The acute haemodynamic effects of oral pirbuterol (a beta-agonist) were contrasted with those of sodium nitroprusside, a vasodilator, in six patients with hypoxic chronic bronchitis and emphysema. Sodium nitroprusside (1-5 mg/kg intravenously) reduced mean pulmonary arterial pressure and total pulmonary vascular resistance significantly (p less than 0.01) without change in cardiac output or right ventricular ejection fraction, measured by radionuclide ventriculography. Oral pirbuterol (22.5 mg) produced a greater reduction in total pulmonary vascular resistance than sodium nitroprusside, largely as a result of increasing cardiac output. Right ventricular ejection fraction also increased significantly after pirbuterol (p less than 0.01). Pirbuterol in a lower dosage (15 mg by mouth) in six further patients with hypoxic chronic bronchitis and emphysema produced similar changes in total pulmonary vascular resistance and right ventricular ejection fraction. Nine of the patients who were studied acutely thereafter received pirbuterol 15 mg thrice daily for six weeks, which produced a significant fall in systolic pulmonary arterial pressure and a rise in right ventricular ejection fraction (p less than 0.01), without a significant fall in arterial oxygen tension. Pirbuterol acts as a vasodilator on the pulmonary circulation in these patients and may in addition improve right ventricular performance by an inotropic action.

Adrenergic beta-Agonists↗