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Biomedical subjects

A L Muir

Publications and source records attributed to A L Muir.

At least 109 records · Page 6Linked to original sources
PubMed1981

The effects of intravenous prenalterol on ventricular performance, as assessed by radionuclide ventriculography, in patients with ischaemic heart disease.

1 We have observed the effects of intravenous prenalterol (1 mg and 2 mg) on ventricular performance, assessed by radionuclide ventriculography, in nine patients with ischaemic heart disease with varying degrees of impairment of ventricular performance. In seven of these patients the effects of prenalterol were compared with those of isoprenaline infused at 1 microgram/min. 2 Prenalterol caused no significant increase in heart rate, but systolic blood pressure increased by 26% (P less than 0.002). In contrast, isoprenaline caused heart rate to increase by 22% (P less than 0.02) and diastolic blood pressure to fall by 9% (P less than 0.01). 3 Left ventricular ejection fraction (LVEF) increased with both drugs, but the increase was greater with isoprenaline, as was the fall in the ratio mean ejection time: left ventricular ejection time, which is an index of improved ventricular performance. 4 Because of the increased heart rate and stroke volume produced by isoprenaline, cardiac output increased 45% above control values (P less than 0.001), but the increase in cardiac output after prenalterol did not reach statistical significance. 5 In three patients with very poor ventricular function (LVEF less than 0.30) prenalterol had little effect on ejection fraction, and caused increased regional ventricular dyskinesia. 6 The increase in systolic blood pressure, and therefore cardiac afterload brought about by prenalterol may limit ventricular response. The response might be enhanced by the addition of vasodilator therapy.

Blood Pressure↗
PubMed1981

Radionuclide determined pulmonary blood volume in ischaemic heart disease.

Most measurements of pulmonary blood volume have been based on the Stewart-Hamilton dye dilution principle and have required direct catheterisation of the cardiac chambers. Alternatively a precordial counter may be used to detect the composite right and left heart curves after an intravenous injection of radionuclide. We investigated the use of a gamma camera/computer system to determine the radionuclide dilution curves from individual cardiac chambers. Pulmonary transit time and pulmonary blood volume were measured in nine normal subjects, eight patients with angina pectoris but without heart failure, and 13 patients with ischaemic heart disease and left ventricular failure. Patients with heart failure had significantly greater (p less than 0.001) pulmonary blood volumes and pulmonary transit times than normal subjects or patients without heart failure. Reproducibility measurements of pulmonary blood volume, determined in 12 subjects, gave a coefficient of variation of 2.6%. The effect of posture on pulmonary blood volume was determined in six subjects lying supine and tilted at a 45 degree angle. A reduction in pulmonary blood volume in the tilted position was observed in each subject (p less than 0.005). This simple non-invasive measurement should allow more detailed assessment of physiological or pharmacological changes of the pulmonary vascular bed.

Blood Volume↗
PubMed1980

The influence of ectopic heart beats in gated ventricular blood-pool studies.

Direct data collection from ventricular blood-pool studies were stored in frame mode in a computer and by means of a modified tape recorder, the blood-pool image and ECG were recorded on tape. At the end of the study the tape data were replayed into the computer. The ECG signal was passed through a trigger circuit that detected the R wave which was sampled by the computer once every msec. Contractions outside of the desired range could be rejected along with the subsequent contraction. Of seven patients whose calculated ejection fractions were changed by more than 0.03, all had frequent (one in 20) ectopic contractions. The distorted ventricular volume curves were effectively restructured by the constraining procedure, changing the end-systolic volume and EF. Computer modeling showed a linear relationship between the percent of ectopic contractions and the underestimate of ejection fraction. One ectopic beat in ten led to a 5% underestimate of EF.

Cardiac Complexes, Premature↗
PubMed1980

Prognostic value of radionuclide ventriculography after myocardial infarction.

We have studied 50 consecutive patients who had sustained their first myocardial infarction. Using the noninvasive technique of radionuclide ventriculography, ventricular performance, as assessed by left ventricular ejection fraction (EF), was measured at rest just before discharge from hospital when patients were well and free from cardiac failure and then at one and four months after infarction, at rest and during submaximal supine exercise. Left ventricular ejection fraction was below normal in 42 patients (normal range 0.43-0.71). Mean EF for those patients recovering from inferior infarction was 0.43 +/- 0.09 (mean +/- 1 S.D.), whereas for those who had sustained anterior infarction mean EF was significantly lower, 0.33 +/- 0.13 (p less than 0.01). EF was significantly reduced (p less than 0.01) in those patients whose early progress was complicated either by serious arrhythmia or left ventricular failure. There was only poor correlation between EF and radiographically determined heart size but global left ventricular performance correlated well with the presence of abnormalities of regional wall movement. Over the first four months low EF failed to improve in seven patients with areas of dyskinesis (EF less tha 0.30) and despite diuretic therapy five suffered further episodes of cardiac failure. Excluding those with dyskinesis there were 18 patients who were unable to increase EF on exercise on month after infarction. Of these four already had symptoms of angina but a further 10 patients developed angina in the subsequent three months. Poor left ventricular performance is common after anterior myocardial infarction, complicated in the acute phase by serious arrhythmia or left ventricular failure. Patients with persistently low EF had an increased risk of further episodes of cardiac failure, whereas a fall in EF on exercise was associated with subsequent angina.

Adult↗
PubMed1979

An evaluation of six kits of technetium 99m human serum albumin injection for cardiac blood pool imaging.

We have investigated the suitability of five different commercially available kits which provide human serum albumin (HSA) labelled with technetium 99m (99mTc) for cardiac blood pool imaging. Four of these products were one-step processes using stannous chloride as the reducing agent; the fifth was based on an electrolytic reduction. In addition, we also assessed our own modification of the electrolytic method. We measured the radiochemical purity by precipitation with trichloroacetic acid and by gel filtration on a Biogel P4 column. In addition, we measured the clearance of radioactivity from the blood at frequent time intervals after intravenous injection. Each product was assessed in separate groups of six patients. The labelling efficiency of the one-step kits varied between 73 and 93% compared with 94 and 98% for the electrolytically labelled albumin. The blood clearance for all one-step kits was significantly faster than that obtained for the radiopharmaceuticals prepared by the electrolytic method. We conclude that HSA labelled with 99mTc by the electrolytic method is to be preferred.

Cardiac Volume↗
PubMed1979

A rotating transducer real-time scanner for ultrasonic examination of the heart and abdomen.

A mechanical real-time ultrasonic scanner utilizing a rotating transducer head has been successfully applied clinically to visualize the heart and abdomen. The design features of this scanner are discussed. The small dimensions and the 90 degree field of view of the sealed oil-filled transducer head optimize visualization of the heart avoiding bone and lung. The single point of entry aspect of this scanner results in a good field of view from any point on the abdominal surface. For example, in upper abdominal studies the liver and kidney can be readily viewed. Rapid and thorough searching of the abdomen is easily carried out and good quality selected sections can be captured by optimizing frame rate and angle of view. In obstetrical applications the complete mature fetus can be visualized using the alternative large 180 degree field of view.

Abdomen↗
PubMed1977

Simplified method of determining left ventricular ejection fraction from a radionuclide bolus.

A method which does not require an online computer has been developed to measure left ventircular ejection fraction from a bolus of 99mTc-pertechnetate. The passage of the bolus through the cardiac chambers was imaged using a gamma camera and recorded on video tape. On replay a region of interest corresponding to the left ventricle was selected directly at the gamma camera console. Counts detected in this region were analysed in 30ms intervals. The data were corrected for the contribution from extra-cardiac activity and were then digitally filtered to remove statistical noise. Ejection fractions measured in 13 patients by this technique agreed well with those determined by contrast ventriculography (r=0.97, P less than 0.001).

Cardiac Output↗
PubMed1977

The assessment of left ventricular ejection fraction in patients with ischaemic heart disease by contrast ventriculography and nuclear angiography.

1. In 18 patients with ischaemic heart disease left ventricular ejection fraction, measured by two different nuclear angiographic methods, has been compared with ejection fraction measured by single-plane contrast angiography. 2. The first nuclear angiographic technique involves detection of variation in the radio-activity from the left ventricle during the initial passage of a bolus of 99Tcm-labelled human serum albumin injected intravenously; the second is our own modification of a "gated" method, which accumulates the radioactivity detected during the continuing recirculation of the plasma bound radioisotope, so presenting an "averaged" ventricular volume curve. 3. Ejection fraction, measured by the "bolus" method, is lower than that measured either by contrast ventriculography or by the "gated" method. This may be due to a damping effect. 4. Ejection fraction measured by the "gated" method is well correlated with that measured by contrast ventriculography (r = 0-89). 5. Our modification of the "gated" method, which presents the changes in ventricular volume throughout the cardiac cycle, without needing computer facilities, is a useful non-invasive means for assessment of left ventricular function.

Angiography↗
PubMed1975

Weight carrying after myocardial infarction.

The blood-pressure responses to carrying a 15 kg. weight in a shoppong basket, and in a rucksack on the back, were compared in 13 ambulant male patients who were convalescing from an uncomplicated myocardial infarction. In 8 of the patients a sustained-handgrip test was also performed. Carrying the weight in the hand produced a distinct increase in blood-pressure, which did not occur when the weight was carried on the back. There was also a significant increase in blood-pressure during sustained handgrip. In view of the lack of symptoms with these circulatory changes, it is concluded that more specific advice about the possible dangers of sustained static exercise should be given to patients recovering from myocardial infarction.

Activities of Daily Living↗
PubMed1975

Cardiorespiratory effects of rapid saline infusion in normal man.

We have studied the cardiorespiratory effects of the rapid infusion (100 ml/min) of 2 liters of saline in four normal seated subjects. Cardiac output and pulmonary arterial pressure increased, while vital capacity (VC) and total lung capacity (TLC) decreased. There was an increase in closing volume (CV) without any detectable change in lung compliance or flow-volume characteristics. There was an increase in Pao2 during infusion period which can be related to better matching of ventilation to perfusion and to improved hemoglobin transport. In the recovery stage as cardiac output, pulmonary arterial pressure, TLC, and VC all returned toward control values CV remained high. In two subjects CV occurred within the normal tidal range of ventilation and in these two subjects Pao2 fell significantly below values obtained in the control period. The results suggest that rapid saline infusion in man can cause interstitial edema and lead to premature airway closure and hypoxemia.

Airway Resistance↗
PubMed1975

Effect of alveolar liquid on distribution of blood flow in dog lungs.

Previous studies have shown that a shift in blood flow away from edematous regions does not occur until the alveoli contain liquid. The present experiments were designed to examine the separate effect of air space liquid, air space plus interstitial liquid, and reduced lung volume on blood flow. We found that reduced lung volume was not associated with significant changes in blood flow and that no systematic change in blood flow occurred when alveoli were filled with isosmotic liquid (autologous plasma). However, when hyposmotic liquid (dilute plasma) was instilled so that both the air space and the alveolar wall interstitial space were filled, blood flow was systematically reduced. This suggested that interstitial liquid was responsible raising vascular resistance in these experiments and that it might also be important in raising local vascular resistance in pulmonary edema. This latter hypothesis was tested in isolated perfused lobes where rapid freezing and quantitative histology showed that the number of open capillaries was significantly reduced in the liquid-filled alveoli (P less than 0.001). These observations suggest that interstitial pressure rises in pulmonary edema with the result that the transmural pressure of the alveolar vessels falls and vascular resistance is increased.

Animals↗