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Biomedical subjects

M Morgan

Publications and source records attributed to M Morgan.

At least 325 records · Page 18Linked to original sources
PubMed1984

Role of heart rate in pathophysiology of chronic stable angina.

11 patients with chronic, stable, effort angina, off medication apart from glyceryl trinitrate, were monitored continuously by electrocardiogram (ECG) during normal, unrestricted daily activity. Computerised ECG analysis demonstrated during 33 twenty-four hour periods of monitoring, 278 episodes of transient ischaemic ST segment depression of which 52 were associated with angina. In the 15 minutes preceding the onset of ischaemia, heart rate did not increase in 164 episodes, increased slightly (greater than or equal to 5 beats/min) in 61, and increased moderately or markedly (greater than or equal to 10 beats/min) in 53. Findings were similar when episodes with or without angina or episodes of different severity were analysed separately. In all patients, periods of sinus tachycardia exceeding the control rate by more than 30 beats/min and lasting more than 10 minutes, often occurred in the absence of angina and/or ST segment depression. Also, in 65% of the ischaemic episodes, heart rate at the beginning of the ST change was either below or less than 10 beats/min above the modal value of the twenty-four hour heart rate. This suggests that increased myocardial demand is not necessarily the only or the most common cause of acute ischaemia in patients with chronic effort angina during unrestricted daily activity. Factors which only transiently interfere with myocardial oxygen supply are probably important in this syndrome.

Aged↗
PubMed1984

Failure to demonstrate a chromosome 2 deletion in adenomatous colorectal polyposis patients.

A group of researchers recently reported a specific chromosome abnormality consisting of a deletion in the long arm (q) of chromosome 2 in patients with adenomatous colorectal polyposis. Using a high resolution chromosome banding technique and a blind study design, the authors karyotyped two patients with Gardner syndrome, two patients with familial polyposis, and four normal controls. No deletion was found in chromosome 2.

Adult↗
PubMed1984

Social networks and psychosocial support among disabled people.

Analysis of the network characteristics and nature of social ties among physically disabled people living in an inner London borough showed network size rather than network type was related to the availability of psychosocial support, reflecting the important role of both related and non-related people in the provision of this form of support. The study also questioned three commonly held assumptions. Firstly, in contrast to the image of physically disabled people as lacking social ties, those with a high level of disability, although having a lower level of social contact outside the household than other groups, did not differ significantly in other aspects of their network structures and support. Secondly, in contrast to the characterisation of inner city areas as relatively homogeneous and as lacking locally based ties, the inner London area studied comprised a variety of network types with a large proportion of respondents deriving support from people living in close proximity. Thirdly, whereas the presence of household members, and especially a spouse, tend to be equated with the availability of strong emotional support, considerable numbers of married people lacked such support. This suggests measures to promote psychosocial support need to be fairly broadly based and cautions against using marital status as a proxy measure of support.

Adolescent↗
PubMed1984

Biological availability of lead in a paint aerosol. 2. Absorption, distribution and excretion of intratracheally instilled lead paint particles in the rat.

Four groups of rats received by intratracheal instillation (1) a lead chromate paint particulate suspension, (2) lead tetraoxide suspension, (3) lead acetate solution, or (4) saline. Lead-dosed animals received an equivalent dose of 1 mg lead/kg body weight. Distribution of lead was monitored through assays of urine, feces, and tissues (lung, bone, muscle kidney, liver) obtained at post-mortem 5 weeks after exposure. Delta-aminolevulinic acid dehydratase (ALA-D) activity was measured to determine the effect of lead on heme biosynthesis. The vast majority of the dosed lead in the paint matrix remained in the lung. In contrast, in the lead acetate-dosed animals, little remained in the lung, but significant elevations were found in bone and kidney. Blood ADA-D was significantly depressed in the lead acetate-treated animals, but was not significantly different from control animals in the animals dosed with lead paint or lead tetraoxide. These findings suggest that lead chromate in an alkyd resin paint matrix is poorly absorbed from the lung compared with lead acetate and lead tetraoxide.

Absorption↗
PubMed1984

Computer system for analysis of ST segment changes on 24 hour Holter monitor tapes: comparison with other available systems.

The accuracy of a computer system that was developed for the analysis of ST segment changes recorded on Holter ambulatory electrocardiographic monitoring tapes was compared with conventional visual scrutiny, beat by beat analog printouts and a commercial J point trend system. The program calculates and plots multiple electrocardiographically derived variables in a high temporal resolution trend format. Fifty tapes of good recording quality obtained from 19 patients (13 with chronic stable angina and 6 with variant angina) were assessed visually and with the computer system; of these, 20 were analyzed by all four techniques. In the 50 tapes, 629 episodes of diagnostic ST segment changes (all true positive results) were identified by using the computer system. In contrast, only 507 were identified by visual scrutiny; none of these 507 episodes was missed by computer analysis. On the 20 tapes assessed using computer, visual, beat by beat analog and J point trend system analysis, 268, 221, 230 and 178 episodes, respectively, were documented. For the four techniques, false negative and positive results were 0, 47, 38 and 90 and 0, 10, 6 and 24, respectively. The results indicate that, of the systems assessed in this study, the computer program provides the highest accuracy for detection of transient ST segment changes. This is probably accreditable to the compact presentation of multiple electrocardiographically derived variables, allowing a detailed quantitative assessment of 24 hour tapes. It is of particular value for pathophysiologic and pharmacologic studies.

Angina Pectoris↗
PubMed1984

Effects of medroxalol on renal function and the renin-angiotensin-aldosterone axis.

Ten subjects with hypertension received medroxalol, which blocks both alpha- and beta-adrenergic receptors, has intrinsic sympathomimetic beta 2-agonist properties and is a direct vasodilator. Renal function tests consisting of inulin clearance and p-amino hippuric acid (PAH) clearance, plasma renin activity (PRA) in recumbent and upright postures, and aldosterone excretion rate were performed. After intravenous medroxalol, inulin clearance and PAH clearance rose, renal vascular resistance fell, recumbent PRA was unchanged, and the rise in PRA with upright posture was blunted. After 1 mo on oral medroxalol, blood pressure was controlled while inulin clearance, PAH clearance, and renal vascular resistance were unchanged. The rise in PRA with upright posture remained blunted. Urinary aldosterone excretion was unchanged after 1 mo on medroxalol.

Adrenergic alpha-Antagonists↗
PubMed1984

The relationship between space and time in the perception of stimuli moving behind a slit.

When a shape defined by a set of dots plotted along its contour is presented in a sequence of frames within the boundaries of a slit, and in each frame only one dot (featureless frame) or two dots (feature frame) are displayed, a whole moving dotted shape is perceived. Masking techniques and psychophysical measures have been used to show that a dynamic random-dot mask interferes with shape identification, provided the interframe interval is greater than about 15 ms, and there are no stimulus features for recognition in individual frames. A similar pattern of results was obtained when the observer had only to detect the movement of a single dot or a pair of dots against a dynamic-noise background. It is concluded that the visual system can resolve the correspondence problem in both apparent movement (one moving dot) and aperture viewing (featureless-frame condition) by extracting motion before the extraction of features in each frame. However, the results also show that where feature identification in each frame is possible, it can also be used to identify the moving targets.

Female↗
PubMed1984

Amplification of sodium- and potassium-activated adenosinetriphosphatase in HeLa cells by ouabain step selection.

A multistep selection for ouabain resistance was used to isolate a clone of HeLa S3 cells that overproduces the plasma membrane sodium, potassium activated adenosinetriphosphatase (Na+,K+-ATPase). Measurements of specific [3H]ouabain-binding to the resistant clone, C+, and parental HeLa cells indicated that C+ cells contain 8-10 X 10(6) ouabain binding sites per cell compared with 8 X 10(5) per HeLa cell. Plasma membranes isolated from C+ cells by a vesiculation procedure and analyzed for ouabain-dependent incorporation of [32P]phosphate into a 100,000-mol-wt peptide demonstrated a ten- to twelvefold increase in Na+,K+-ATPase catalytic subunit. The affinity of the enzyme for ouabain on the C+ cells was reduced and the time for half maximal ouabain binding was increased compared with the values for the parental cells. The population doubling time for cultures of C+ cells grown in dishes was increased and C+ cells were unable to grow in suspension. Growth of C+ cells in ouabain-free medium resulted in revertant cells, C-, with biochemical and growth properties identical with HeLa. Karyotype analysis revealed that the ouabain-resistant phenotype of the C+ cells was associated with the presence of minute chromosomes which are absent in HeLa and C- cells. This suggests that a gene amplification event is responsible for the Na+,K+-ATPase increase in C+ cells.

Cell Membrane↗
PubMed1984

Dose requirements of ICI 35,868 (propofol, 'Diprivan') in a new formulation for induction of anaesthesia.

In order to avoid Cremophor-related reactions and reduce the incidence of pain on injection, diisopropylphenol (ICI 35,868; propofol) has been reformulated as an emulsion. One hundred and fifteen patients received an induction dose of propofol in the new formulation. The dose required to induce anaesthesia in 95% of healthy, unpremedicated patients was 2.5 mg/kg. Induction was associated with a degree of cardiovascular and respiratory depression. There were no adverse reactions although there were a number of minor side-effects. The incidence of pain on injection was low (3%) and the overall quality of induction was assessed as good or adequate in 92% of patients.

Adolescent↗
PubMed1984

An assessment of the Humphrey ADE anaesthetic system in the Mapleson A mode during spontaneous ventilation.

The Humphrey ADE anaesthetic breathing system in the Mapleson A mode has been compared with the Magill system in spontaneously breathing conscious volunteers and anaesthetised patients. In the latter, rebreathing occurred at a significantly lower fresh gas flow with the ADE system than when the Magill system was used (mean 45.6 ml/kg/minute and 56.5 ml/kg/minute respectively). There was no significant difference between the fresh gas flow at which rebreathing occurred in conscious volunteers.

Adult↗
PubMed1984

Failure of large tidal volumes to improve oxygen availability during anaesthesia.

Eight patients undergoing peripheral vascular surgery were ventilated with small (5.3 ml/kg) and large (16.3 ml/kg) tidal volumes at a constant respiratory rate. Carbon dioxide was added to the inspired gases to maintain normal end-tidal levels. The use of large tidal volumes resulted in a significant increase in arterial oxygen tension and content, but, due to a reduction in cardiac output, failed to improve oxygen availability.

Aged↗
PubMed1984

Macular electroretinograms: their accuracy, specificity and implementation for clinical use.

The pattern and the focal electroretinogram (ERG) are both non-invasive, electrophysiological responses recorded from circumscribed retinal areas and are most easily recorded from the macula. This paper describes how our department has incorporated these tests into our clinical protocol, shows how the recording technique and the method of electrode construction may be improved, and describes the normal limits of the macular responses we obtain. The ERG signal-noise ratio we obtained was better than that of the binocular visual evoked potentials (VEPs) recorded simultaneously. Pattern and focal ERGs, using improved methods of recording, show promise of being a valuable addition to the clinical investigation of subtle maculopathies and some forms of optic nerve dysfunction. Three illustrative cases are described. The first demonstrates normal macular ERG responses with abnormal Ganzfeld ERGs due to peripheral retinal damage. The second reveals differential pattern ERG reduction with normal focal ERG in recent optic neuritis. The third case demonstrates reversible simultaneous loss of Ganzfeld ERGs and macular ERGs in vitamin A deficiency.

Adult↗
PubMed1983

Myocardial ischaemia during daily life in patients with stable angina: its relation to symptoms and heart rate changes.

In thirty patients with stable angina and positive exercise tests, ambulatory ST segment monitoring was used to record episodes of transient myocardial ischaemia during daily life. All patients had four consecutive days of monitoring and in 20 patients long-term variability was assessed by repeated 48 hour monitoring and exercise testing over 18 months. There were 1934 episodes of rectilinear or downsloping ST-depression (911, 1 mm; 638, 2 mm; 385, greater than 3 mm) in 446 days of recording, of which only 470 (24%) were accompanied by angina. Positron tomography showed evidence of regional myocardial ischaemia during both symptomatic and asymptomatic ST depression. On average, heart rate at the onset of both symptomatic and asymptomatic ST episodes was significantly lower than the rate at the onset of ST depression during exercise testing (98 +/- 20.5 vs 124 +/- 17 beats/minute). Heart rate rose by more than 10 beats in the minute preceding ST depression in only 23% of episodes. Over 18 months, 8 (40%) patients exhibited marked variability in the number of daily ST episodes. Variability of ST depression was consistently underestimated by symptoms and not reflected by exercise testing. Thus, patients with stable angina showed frequent, variable, and often asymptomatic electrocardiographic evidence of ischaemia. Heart rate increase was not common before myocardial ischaemia, suggesting that, in such patients, transient impairment in coronary supply may be at least as important as excessive increase in demand in the genesis of ischaemia during daily life.

Activities of Daily Living↗