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Biomedical subjects

A M Macdonald

Publications and source records attributed to A M Macdonald.

At least 19 recordsLinked to original sources
PubMed2002

The effect of posture on Quantec measurements.

The effect of moving the patient's centre of gravity from one extreme to the other, where the weight is entirely supported on the left or right foot at either extreme, was investigated in 33 patients attending for surface topography measurements with the Quantec Spinal Measurement System. Average changes of about 20 were seen in the measured curvature of the lower spine line and pelvic tilt, but there was considerable variation between individual patients. When such extremes of stance were included, the reproducibility of measurements of the curvature of the lower spine, pelvic tilt and vertical alignment was poorer, but not to the extent that a significant improvement in reproducibility would be expected if the patient's centre of gravity was closely controlled with, for example, a force platform.

Analysis of Variance↗
PubMed2002

Monitoring the thoracic sagittal curvature in kyphoscoliosis with surface topography: a trend analysis of 57 patients.

Records of Quantec measurements of tlie kypliotic curvature of the back were reviewed for all patients attending the children's orthopaedic clinic who were referred for back shape measurements. Of these, 57 children had five or more preoperative visits allowing trends to be calculated. Linear trends were found in 30 of the patients, with gradients ranging from 1.1 degree/yr to 7.2(0)1/yr. On average, the scatter of measurements about the trend line, or about the mean value in the other 27 cases, compared well with that expected from repeatability studies but the amount of scatter varied from one patient to another. This may well be due to sampling. Where such measurements are monitored for evidence of change in an individual patient, the possibility of larger than average scatter about any emerging trend should be considered.

Analysis of Variance↗
PubMed2000

Parsing executive processes: strategic vs. evaluative functions of the anterior cingulate cortex.

Event-related functional MRI and a version of the Stroop color naming task were used to test two conflicting theories of anterior cingulate cortex (ACC) function during executive processes of cognition. A response-related increase in ACC activity was present when strategic processes were less engaged, and conflict high, but not when strategic processes were engaged and conflict reduced. This is inconsistent with the widely held view that the ACC implements strategic processes to reduce cognitive conflicts, such as response competition. Instead, it suggests that the ACC serves an evaluative function, detecting cognitive states such as response competition, which may lead to poor performance, and representing the knowledge that strategic processes need to be engaged.

Analysis of Variance↗
PubMed1999

Heritability estimates for psychotic disorders: the Maudsley twin psychosis series.

BACKGROUND: Previous twin studies have supported a genetic contribution to the major categories of psychotic disorders, but few of these have employed operational diagnostic criteria, and no such study has been based on a sample that included the full range of functional psychotic disorders. METHODS: A total of 224 twin probands (106 monozygotic, 118 dizygotic) with a same-sex co-twin and a lifetime history of psychosis was ascertained from the service-based Maudsley Twin Register in London, England. Research Diagnostic Criteria psychotic diagnoses were made on a lifetime-ever basis. Main-lifetime diagnoses of DSM-III-R and International Statistical Classification of Diseases, 10th Revision schizophrenia were also made. Probandwise concordance rates and correlations in liability were calculated, and biometrical model fitting applied. RESULTS: A substantial genetic contribution to variance in liability was confirmed for the major diagnostic categories except Research Diagnostic Criteria depressive psychosis and unspecified functional psychosis, where familial transmission was confirmed, but the relative contribution of genetic and common environmental factors was unclear. Heritability estimates for Research Diagnostic Criteria schizophrenia, schizoaffective disorder, mania, DSM-III-R schizophrenia, and International Statistical Classification of Diseases, 10th Revision schizophrenia were all between 82% and 85%. None of the estimates differed significantly from any other. CONCLUSIONS: Heritability estimates for schizophrenia, schizoaffective disorder, and mania were substantial and similar. Population morbid risk estimates were inferred rather than directly measured, but the results were very similar to those from studies where morbid risks were directly estimated.

Adult↗
PubMed1999

Twin mothers, pregnancy hypertension and pre-eclampsia.

OBJECTIVE: To estimate the maternal genetic contribution to the hypertensive diseases of pregnancy. DESIGN: A cohort study of female twins with information on hypertensive diseases of pregnancy obtained by questionnaire screening, and verification of diagnosis from hospital or general practitioner records. SETTING: A volunteer twin registry in the UK with recruitment through the media without reference to pregnancies or disease status. POPULATION: Adult female, same-sex twin pairs who completed a pregnancy history questionnaire and consented to record inspection. MAIN OUTCOME MEASURE: Self-reported and hospital-validated diagnosis of non-proteinuric pregnancy hypertension and of pregnancy hypertension with proteinuria (pre-eclampsia). RESULTS: Self-reported pre-eclampsia had a heritability of 0.221 and non-proteinuric hypertension of 0. 198. However, none of the pairs who were self-reported as concordant for pre-eclampsia were confirmed from hospital records. Using hospital records, the heritability of pre-eclampsia was 0 and 0.375 for non-proteinuric hypertension. Using a model treating pre-eclampsia as a separate disease from non-proteinuric hypertension, and assuming that the next pair identified was both monozygotic and concordant for pre-eclampsia, the estimated heritability of pre-eclampsia remained 0 (95% CI 0-0.49). Using a threshold model in which non-proteinuric hypertension is treated as a mild form of pre-eclampsia, heritability is estimated at 0.247 (95% CI 0.23-0.454). CONCLUSION: Neither non-proteinuric hypertension nor pre-eclampsia are inherited in simple Mendelian fashion. The genetic contribution to multi-factorial inheritance is smaller than hitherto believed.

Adolescent↗
PubMed1997

Development of computerized storage facilities for twin data: a relational database system for a twin register.

Many twin registers hold information on flat file systems such as those provided by statistical packages or spreadsheets. Demographic details may be maintained separately from data collected in multiple different studies, leading to considerable problems with data consistency, redundancy, and integration. Ad hoc requests may be difficult. Implementation of a relational database system permits storage and maintenance of all records, simple data entry and validation procedures, linking of information from different projects with security of access, and the flexibility to provide rapid answers to ad hoc enquiries using standard Structured Query Language (SQL). Twin data provide a challenge for relational database design which rests on the technique of normalization and the use of unique identifiers to access associated groups of variables; for twins, "uniqueness" must preserve identification of both the pair and the individual twin subjects in the data structure to enable flexible access to and analysis of the data. An application on the Institute of Psychiatry Volunteer Twin Register (IOPVTR) database is described, through reference to one study of a sample of the twins, with simulated data. We show how a balance of adherence to database design principles and attention to ongoing clerical and research procedures has been used to produce an integrated, flexible, and open-ended system.

Data Collection↗
PubMed1997

British motor neuron disease twin study.

OBJECTIVES: To investigate the cause of sporadic motor neuron disease (MND) by twin study, so allowing (1) estimation of the genetic contribution, and (2) collection of matched pairs for a case-control study of possible environmental factors. METHODS: 10872 death certificates bearing the diagnosis MND were collected from 1979 to 1989 inclusive. Inspection of individual birth entries allowed identification of potential twins. The status of each co-twin was determined and contact made through the National Health Service Central Register (NHS-CR) and their general practitioner (GP). The diagnosis of MND was verified via the co-twin and relatives, and medical records where available. Zygosity was assessed using a recognised questionnaire. Details concerning environmental exposures and health were gathered by interview of cotwin and relatives using a semistructured questionnaire. Heritability (h2) of MND was estimated, and the environmental information was analysed by conditional logistic regression modelling. RESULTS: Seventy seven probands were identified, of whom 26 were monozygotic and 51 dizygotic. Four monozygotic probands were concordant, but two probands came from a family known to have familial MND. The estimated heritability was between 0.38 and 0.85. Most environmental risk factors were not significant. Regular vehicle maintenance (odds ratio (OR) = 7.0; 95% confidence interval (95% CI) 1.3-89.9) and occupational paint usage (OR = 3.75; 95% CI 1.0-17.1), however, occurred significantly more often in the affected cases. CONCLUSIONS: This "death discordant" method for twin collection has proved to be viable, and has allowed the ascertainment of a large population sample in a rare disease. The genetic role in sporadic MND is substantial, and higher than expected. Exposure to industrial chemicals, particularly constituents of petrochemicals and paints, may contribute to the aetiology of MND.

Adult↗
PubMed1992

Helicobacter pylori and hypergastrinaemia during proton pump inhibitor therapy.

The rise in serum gastrin and pepsinogen I after 5 days' treatment with the proton pump inhibitor pantoprazole (40 mg/day) was examined in eight duodenal ulcer patients with Helicobacter pylori infection and compared with eight in whom it had been eradicated. Before treatment, the post-prandial serum gastrin concentrations were higher in the H. pylori-positive than -eradicated patients (p less than 0.05). The median rise in pre-prandial serum gastrin concentrations on treatment was similar in the H. pylori-positive (41%) and -eradicated patients (45%). The rise in post-prandial serum gastrin was also similar in the H. pylori-positive (81%) and -eradicated patients (69%), resulting in significantly higher gastrin concentrations during treatment in the former. The median rise in serum pepsinogen I on treatment was greater in the H. pylori-positive (114%) than in the -eradicated patients (8%), resulting in significantly higher concentrations during treatment in the former. These observations indicate that eradication of H. pylori may be a means of moderating the hypergastrinaemia caused by acid-inhibitory therapy. They also indicate that H. pylori-related hypergastrinaemia is not due to an increase of the antral surface pH by the bacterium's urease activity.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1991

Genetic susceptibility to naevi--a twin study.

The risk of malignant melanoma to an individual is strongly related to their total number of benign melanocytic naevi. To investigate the possibility that numbers of naevi may have an inherited basis, naevi were examined in 23 monozygotic and 22 dizygotic twin pairs. A strong correlation in total numbers of naevi 3 mm or more in diameter was observed between MZ twins (intraclass correlation 0.83), but there was no significant correlation between DZ twins (correlation -0.24). There was no increased concordance in presence of naevi 5 mm or more over that expected by chance, for MZ or DZ twins. The results suggest a strong inherited basis for total naevus count and hence melanoma risk, perhaps involving a number of interacting genes.

Adult↗
PubMed1991

Controlled study of the effects of intravenous famotidine on intragastric pH in bleeding peptic ulcers.

As blood coagulation and platelet aggregation are abolished at pH less than 5.4 the failure of antisecretory drugs to promote haemostasis in bleeding peptic ulcers may reflect inadequate pH control. This study examined the ability of famotidine, a potent, long-acting H2 blocker to maintain intragastric pH above 5.4 in patients presenting with bleeding peptic ulcers. Twenty patients with acute upper gastrointestinal haemorrhage confirmed endoscopically to be related to peptic ulceration (17 duodenal, 3 gastric ulcers), were entered into the study within 24 h of presentation. Each patient was randomly allocated to receive either intravenous famotidine (n = 10) administered as a 10 mg bolus followed by a constant infusion of 3.2 mg/h or similarly administered placebo (n = 10). All patients remained fasted over the 22-h study period. Their median intragastric pH values ranged from 6.8 to 7.9 (median 7.1) in the famotidine group and from 1.1 to 6.9 (median 1.6) in the placebo group (P less than 0.001). Over this same period intragastric pH was greater than 6 for 64%-100% (median 98%) of the recording time in the famotidine group compared with 0%-93% (median 13%) in the placebo group (P less than 0.001). We conclude that intravenous famotidine can maintain intragastric pH greater than 6 in fasting patients with acute upper gastro-intestinal bleeding from peptic ulceration. This provides a rational basis for further studies assessing its clinical efficacy in such patients.

Adult↗
PubMed1991

Rebound hypersecretion after H2-antagonist withdrawal--a comparative study with nizatidine, ranitidine and famotidine.

Our previous study demonstrated rebound nocturnal acid hypersecretion after a 4-week course of nizatidine. Nocturnal acid output was increased by 77% two days after discontinuing treatment compared with pretreatment values. To confirm this effect with other H2-blockers we assessed daytime intragastric pH, fasting and meal-stimulated plasma gastrin and nocturnal acid output in 9 duodenal ulcer patients in remission before, during and two days after treatment with three different drugs. Each patient received 4-week courses of 300 mg ranitidine, 40 mg famotidine or 300 mg nizatidine, taken at 20.00 hours in randomized order with a 'washout' period of 4 weeks between each course of drug. Median nocturnal acid output (mmol/10 h) decreased during treatment with ranitidine to 3 (range 0-17), famotidine to 4 (1-12) and nizatidine 6 (0-40) compared with the respective pre-treatment values, 49 (20-126; P less than 0.01), 52 (22-105; P less than 0.01) and 32 (23-114; P less than 0.01). Two days after discontinuing treatment nocturnal acid output was increased after ranitidine at 77 (28-237; P less than 0.04) and after nizatidine at 64 (17-130; P less than 0.05) compared with pre-treatment values. There was no significant change in nocturnal acid output after famotidine at 57 (27-107) compared with the pre-treatment value. There was no change in daytime intragastric pH with any drug during or after treatment compared with the pre-treatment values. Fasting and meal-stimulated plasma gastrin concentrations were increased on the final treatment day with ranitidine and famotidine but had returned to pretreatment levels two days after treatment. The rebound acid hypersecretion may contribute to the high ulcer relapse rate after discontinuation of H2-receptor antagonists.

Adult↗
PubMed1991

Effect of increasing Helicobacter pylori ammonia production by urea infusion on plasma gastrin concentrations.

It has been proposed that the hypergastrinaemia in subjects with Helicobacter pylori infection is caused by the action of the ammonia produced by the organism's urease activity on the antral G cells. To investigate this hypothesis we examined the effect on plasma gastrin of increasing the bacterium's ammonia production by infusing urea intragastrically to eight H pylori positive duodenal ulcer patients. After a 60 minute control intragastric infusion of dextrose solution at 2 ml/minute, a similar infusion containing urea (50 mmol/l) was continued for four hours. During the urea infusion, the median gastric juice urea concentration rose from 1.1 mmol/l (range 0.3-1.6) to 15.5 mmol/l (range 7.9-21.3) and this resulted in an increase in the ammonium concentration from 2.3 mmol/l (range 1.3-5.9) to 6.1 mmol/l (range 4.2-11.9) (p less than 0.01). This appreciable rise in ammonia production did not result in any change in the plasma gastrin concentration. The experiment was repeated one month after eradication of H pylori, at which time the median basal gastrin was 20 ng/l (range 15-25), significantly less than the value before eradication (30 ng/l range 15-60) (p less than 0.05). On this occasion, the gastric juice ammonium concentration was considerably reduced at 0.4 mmol/l (range 0.1-0.9) and the urea infusion did not raise the ammonium concentration or change the plasma gastrin concentration. In conclusion, augmenting H pylori ammonia production does not cause any early change in plasma gastrin.

Adult↗
PubMed1984

Myasthenia gravis and atracurium. A case report.

The degree, duration of and recovery from neuromuscular blockade induced by atracurium in a patient with myasthenia gravis were monitored and recorded using the evoked compound muscle action potentials (EMG). The anaesthetic and perioperative management were simplified by the use of this technique. The significance of the behaviour of atracurium is discussed.

Action Potentials↗