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Biomedical subjects

A C Tweddel

Publications and source records attributed to A C Tweddel.

At least 19 recordsLinked to original sources
PubMed1996

Quantification of extracorporeal white cell and platelet deposition in cardiopulmonary bypass: comparison of membrane and bubble oxygenators.

Cardiopulmonary bypass is known to activate both white cells and platelets. The aim of this study was to investigate whether the use of bubble and membrane oxygenators results in different degrees of deposition in the filter and oxygenator of the bypass circuit. Dual-isotope imaging techniques were employed, with white cells labelled with 99Tcm and platelets with 111In, and with subsequent imaging of the filters and oxygenators on a gamma camera fitted with a medium-energy, parallel-hole collimator, relative to a known standard. The percentage white cell oxygenator deposition ranged from 0.011 to 4.91% in the bubble group (n = 20) and was not different from the membrane group (0.001 to 4.22%). Similarly, no difference in platelet deposition was found, with 0.605-45.17% deposited in the bubble oxygenators and 0.001-15.26% deposited in the membrane oxygenators. Filter deposition of both types of cell was substantially lower in both membrane and bubble groups with no difference between groups. The striking feature of the data is the non-normal distribution of the deposition in both types of oxygenator. This study demonstrated that both white cell and platelet deposition in the cardiopulmonary bypass circuit can be quantified using radiolabelled cells. No differences in oxygenator or filter deposition were found in patients randomly allocated to membrane or bubble oxygenation.

Blood Platelets↗
PubMed1994

A comparison of adenosine and exercise stress 201T1 scintigraphy.

A detailed comparison of stress thallium images utilizing exercise (symptom-limited bicycle ergonometer) and adenosine (infused at 50 micrograms kg-1 min-1 increasing by 25 micrograms kg-1 min-1 every 2 min to a maximum tolerated dose) was performed in 20 patients with angiographically documented coronary disease. Ten patients were receiving beta-blockade at the time of both tests. Triple-, double- and single-vessel disease was present in eight, seven and five patients, respectively. Exercise produced a large increase in double product (8970 +/- 288 to 20,-984 +/- 690 mm Hg min-1) while adenosine produced no significant change (8440 +/- 280 to 9086 +/- 600 mm Hg min-1). Each of the three gated planar images (anterior 40 degrees and 70 degrees left anterior oblique) was divided into five equal segments. Exercise produced 44/90, 44/95 and 45/95 abnormal segments in the anterior, 40 degrees and 70 degrees views while adenosine produced 53/100, 44/100 and 52/100 abnormal segments for the same views. The total number of abnormal segments was similar in both groups (133/280 exercise and 149/300 adenosine). Each abnormal segment was analysed for degree of change between stresses using a five-point scoring system. Exercise produced eight segments which were larger by one point and 44 segments larger by two points while adenosine produced 17 and 44 segments larger by one and two points respectively. Left ventricular uptake (as % injected dose) was significantly greater in the adenosine group (1.12 +/- 0.06% versus 0.64 +/- 0.05%, P < 0.01) but right ventricular uptake was similar (0.15 +/- 0.1% versus 0.14 +/- 0.09%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1994

Biocompatibility of cardiopulmonary bypass: influence on blood compatibility of device type, mode of blood flow and duration of application.

The biocompatibility of artificial organs is recognised as an area presenting difficulties in terms of the complexity of the situation. The nature of the blood response involving interactions of systems, pattern and extent of change, patient status and the influence of the whole device contribute to the complexity. Recognising these, the profile of the blood response to cardiopulmonary bypass (CPB), with respect to type of device, mode of blood flow, duration of the procedure and patient status, has been evaluated by monitoring contact phase activation [Factor XII-like activity (FXIIA)], fibrinolytic activity [Fibrin degradation products (X-FDP's)], complement activation (C3a, C5a), leucocyte activation [Granulocyte elastase (GE)] and platelet and white cell imaging. FXIIA, X-FDP's, and GE rose gradually during CPB, with levels remaining elevated post-operatively for up to 48 h. In contrast, C3a levels rose sharply with no significant elevation in the post-operative period, while C5a did not show significant changes during bypass. The use of pulsatile perfusion resulted in lesser activation of the parameters, although these were significantly less only for GE. The alterations in FXIIA, X-FDP's, C3a and GE correlated positively with the duration of CPB, with this effect pronounced in the post-operative period for FXIIA, X-FDP's and GE. However, these changes had no apparent influence on clinical outcome and the majority of patients had uncomplicated post-operative recoveries. With respect to the use of bubble/membrane oxygenators, platelet and white cell deposition and the patterns of change for FXIIA and C3a were similar in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible Materials↗
PubMed1993

A comparison of dobutamine and maximal exercise as stress for thallium scintigraphy.

In the assessment and evaluation of patients with suspected coronary artery disease there is a need for pharmacological stress combined with thallium scintigraphy. Thallium images were obtained following stress both with dobutamine infusion (5-20 micrograms kg-1 min-1) and with symptom-limited bicycle ergometry in 20 patients (age 39-70 years) with chest pain who had been admitted for coronary angiography. Percentage thallium uptake was calculated using a region of interest technique. Detailed comparison was performed of the presence, size and distribution of left ventricular thallium perfusion defects; the percentage thallium uptake in ventricles, lung and liver; and the haemodynamic response to stress. Each stress produced a similar number of abnormal segments in each of three views (total EX 166/300; DOB 167/295), but exercise produced larger defects in the anterior view (P < 0.025). Thallium uptake in left and right ventricles and relative uptake to lungs were similar, but dobutamine produced higher relative liver uptake [EX 1.55 (0.67); DOB 2.97 (1.23) P < 0.0001]. Fourteen patients were able to tolerate dobutamine 20 micrograms kg-1 min-1. The ratio of peak stress to rest double product was smaller with dobutamine in both patients with (DOB 1.3; EX 2.0; P < 0.0047) and patients without beta-blockade (DOB 1.5; EX 2.4; P < 0.008). Dobutamine produced fewer conventional stress endpoints of chest pain and ST depression. In conclusion, dobutamine produces a well-tolerated incremental pharmacological stress with thallium images similar to maximal exercise, and provides a useful alternative stress in patients unable to perform adequate dynamic exercise.

Coronary Angiography↗
PubMed1992

A comparison of maximal exercise and dipyridamole thallium-201 planar gated scintigraphy.

Both symptom-limited maximal exercise and intravenously given dipyridamole stress (0.56 mg/kg over 4 min with a 2 min walk) gated thallium scans were performed in 22 patients undergoing coronary arteriography for the assessment of chest pain. All scans were acquired gated to the electrocardiogram in 3 projections and were reported for the presence and extent of defects in 5 myocardial segments in each view. In addition, left and right ventricular myocardial uptake and estimates of right and left lung and liver to left ventricular uptake were assessed relative to the injected dose of thallium-201. Overall, 190/310 segments were abnormal with exercise compared with 169/310 with dipyridamole. Segments were scored greater in extent in 90/310 cases with exercise, compared with 46/310 in which the defect was more extensive with dipyridamole (P less than 0.0005). Non-attenuation corrected percentage myocardial thallium uptakes were similar for both stresses: anterior percentage uptakes, 0.785% +/- 0.230% with exercise versus 0.870% +/- 0.217% with dipyridamole (NSD). Left and right lung and liver to left ventricle ratios were all significantly higher with dipyridamole than with exercise (1.587 +/- 0.408 versus 1.446 +/- 0.518, P less than 0.02; 1.78 +/- 0.479 versus 1.46 +/- 0.502, P less than 0.002; 2.598 +/- 0.788 versus 1.265 +/- 0.386, P less than 0.001, respectively). High right and left lung uptakes with dipyridamole were strongly correlated with high exercise values (r = 0.756, P less than 0.001; r = 0.809, P less than 0.001). The liver uptake was weakly correlated between the 2 different stress tests (r = 0.483, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The influence of arm position and cardiac output on bolus clearance from the arm.

The importance of arm position and cardiac output on the clearance of a bolus injection from the arm was assessed in 63 patients using technetium-99m. Injections were made in the left arm which was either adducted, abducted or adducted with the forearm flexed over the lower chest. The clearance of isotope was assessed by measuring the amount of radioactivity remaining in the arm at 10 s intervals and calculating it as a fraction of the injected dose. The clearance of Tc-99m was significantly faster and more complete from the abducted arm than from the adducted arm. There was no correlation between clearance and cardiac output.

Arm↗
PubMed1992

Symptomatic and silent myocardial ischaemia in hypertensive patients with left ventricular hypertrophy.

OBJECTIVE: To assess the prevalence of symptomatic and silent myocardial ischaemia in patients with hypertensive left ventricular hypertrophy. DESIGN: Cross sectional study. SETTING: University department of medical cardiology. PATIENTS: 90 patients (68 men and 22 women; mean age 57 (range 25 to 79)) with left ventricular hypertrophy due to essential hypertension. INTERVENTIONS: 48 hour ambulatory ST segment monitoring (all patients), exercise electrocardiography (n = 79), stress thallium scintigraphy (n = 80), coronary arteriography (n = 35). RESULTS: 43 patients had at least one episode of ST segment depression on ambulatory electrocardiographic monitoring. The median number of episodes was 16 (range 1 to 84) with a median duration of 8.6 (range 2 to 17) min. Over 90% of these episodes were clinically silent. 26 patients had positive exercise electrocardiography and 48 patients had reversible thallium perfusion defects despite chest pain during exercise in only five patients. 18 of the 35 patients who had coronary arteriography had important coronary artery disease. Seven of these patients gave no history of chest pain. CONCLUSIONS: Symptomatic and silent myocardial ischaemia are common in hypertensive patients with left ventricular hypertrophy, even in the absence of epicardial coronary artery disease.

Adult↗
PubMed1992

Thallium scans in syndrome X.

OBJECTIVE: To review thallium scans in patients with angina and normal coronary arteriograms. DESIGN: Retrospective review of data. SETTING: Regional cardiac centre in Glasgow. PATIENTS: 100 patients selected from those undergoing diagnostic angiography for typical angina who had normal arteriograms (around 10%), no other cardiovascular abnormality, and available thallium scans (performed routinely before angiography). MAIN OUTCOME MEASURES: Coronary arteriography, exercise tests, and gated thallium scans at peak exercise. RESULTS: The exercise test was positive in 30 and negative in 70 patients. Thallium defects were found in 98 patients, but no consistent pattern and no significant correlation existed between the extent of thallium defect and positive exercise test or exercise tolerance. CONCLUSIONS: Thallium defects described in 98 of 100 patients with angina and normal coronary arteriograms suggest that microvascular angina may be commoner than is generally appreciated.

Adult↗
PubMed1992

Balanced triple-vessel disease: enhanced detection by estimated myocardial thallium uptake.

Maximal stress thallium scans may prove to be 'normal' in some patients with triple-vessel disease due to global reduction in flow resulting in no focal perfusion defect. The aim of this study was to attempt to identify patients with global reduction in flow by estimating total thallium delivery to the left ventricle. Myocardial thallium uptake was calculated as a percentage of injected dose as a mean of three projections in 90 patients undergoing diagnostic arteriography and in 10 normal volunteers. These volunteers and nine patients who proved to have normal coronary arteries established a normal range. Values for myocardial thallium uptake were: 1.166 +/- 0.352% in normals (n = 19); 0.671 +/- 0.184% in patients with single- or double-vessel disease (n = 26); 0.708 +/- 0.245% in patients with triple-vessel disease (n = 55). Thallium scans were normal in 11 of 55 patients with triple-vessel disease and eight of 26 with single- or double-vessel disease. However, eight of these 11 and 5 of the eight proved to have abnormal myocardial thallium uptake. Thus combining the tests improved sensitivity from 76.5% for the scan alone to 94.5% for the scan and myocardial thallium uptake, with no reduction in specificity. Measurement of myocardial thallium uptake is a readily and reliably quantified parameter from a thallium scan which leads to enhanced detection of coronary artery disease.

Adult↗
PubMed1989

Improved detection of coronary artery disease by estimated myocardial thallium uptake.

Myocardial thallium uptake has been assessed at the time of thallium scanning in a group of 50 male patients undergoing coronary arteriography and 10 young healthy volunteers. The net thallium dose injected was obtained by counting the dose prior to injection using the gamma camera and counting the syringe and IV cannula after injection. Significantly higher levels of myocardial thallium uptake were obtained in both the volunteers and patients with normal coronary anatomy (1.36% +/- 0.32%, n = 10 and 0.93% +/- 0.26%, n = 9, respectively) compared to patients with single, double or triple vessel coronary artery disease (0.63% +/- 0.19%, n = 11; 0.70% +/- 0.20%, n = 15; 0.67 +/- 0.18, n = 15, respectively). Exercise tests were positive in 46% of patients with coronary artery disease with an overall predictive accuracy of 56%. Thallium scans were positive in 68% of patients at a specificity of 89%. If the range of myocardial thallium uptake from the patients with normal coronary arteries is used to define a lower limit of normal, then the sensitivity of the thallium scan with thallium uptake is 90% with a predictive accuracy of 90% in the detection of significant coronary artery disease in this group of patients. Thus, estimation of total % thallium uptake is a simple index which yields useful diagnostic clinical information.

Adult↗
PubMed1989

An automated analysis technique for thallium images.

The use of stress thallium-201 scans in the non-invasive assessment of myocardial perfusion is well established, despite several reports of considerable inter-observer variability in the assessment of perfusion defects. By applying a simple statistical algorithm to a set of normal thallium images and using a well defined criterion of abnormality, the threshold of normality in these 'statistical images' was obtained for each of four projections. Subsequently a test set of images from both normal volunteers and patients with arteriographically documented coronary artery disease were reported using statistical images at four levels (70, 75, 80 and 85% of the mean of the hottest pixels) and standard thallium images viewed on the computer monitor in both colour and black and white. Significant reductions in the inter-observer disagreement and enhanced predictive accuracy in the detection of significant coronary artery disease were obtained using the statistical images. The technique described and assessed would permit the reporting of thallium scans at a preselected value of sensitivity and specificity depending on the requirements of the particular study. It could be readily implemented, after local validation, in any department performing thallium scans where the gamma camera is interfaced to a computer.

Adult↗
PubMed1989

Perfusion imaging.

The term perfusion has varied connotations in different situations. The word perfusion comes from the Latin to pour or diffuse through or over. Myocardial perfusion depends on (a) coronary artery or vessel flow, and (b) myocardial or muscle flow. The factors which determine perfusion at rest and during stress in coronary vessels and within the myocardium are clearly related but not with a predictable linear relationship. In animals there is extensive literature concerning the regulation of coronary flow and perfusion obtained by many sophisticated methods. In contrast, the techniques that are applicable to humans are relatively crude. To date, the clinical data available suggests that the normal control of coronary flow in man and in dogs is fairly similar but that models of pathology in animals bear little relation to the compensatory changes found in the coronary circulation in man. Although the data available is limited and subject to many technical inaccuracies, this article is confined to the assessment of myocardial perfusion in clinical practice.

Coronary Circulation↗
PubMed1988

Sustained haemodynamic effects of felodipine in patients with chronic cardiac failure.

1. The efficacy of felodipine a new calcium channel blocker with selective vasodilator activity in the management of severe low output cardiac failure, secondary to coronary heart disease, was determined in 10 patients. 2. Haemodynamic measurements were made at rest and during dynamic exercise and left ventricular function was assessed by radionuclide ventriculography. 3. Significant increases in cardiac index, stroke volume index and ejection fraction were found particularly during exercise, both acutely and following 4 weeks administration of felodipine therapy. 4. Felodipine could well have a significant role in the long term management of the patient with chronic cardiac failure.

Adult↗