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Biomedical subjects

A D Mackay

Publications and source records attributed to A D Mackay.

At least 19 recordsLinked to original sources
PubMed2006

Gastrointestinal nematode parasites of sheep: a dynamic model for their effect on liveweight gain.

This paper presents an individual-based model for gastrointestinal nematode parasites of sheep and includes the effect of these parasites on the liveweight performance of young sheep. Parasitism is known to affect the host animal in at least two ways. The first induces a loss of appetite in the host, which reduces pasture consumption compared with the parasite-free animal. This effect is examined in the first part of the study. The second major effect of parasitism is a reduction in the metabolic efficiency of the host which decreases nutrients available for maintenance and growth. The latter part of the paper examines the consequences of incorporating this effect on the liveweight changes in individuals in a group of sheep. Previous models addressing this issue have only given mean liveweight and worm burden changes.

Animal Husbandry↗
PubMed1998

Effect of topographical aspect and farm system on the population dynamics of Trichostrongylus larvae on a hill pasture.

The population dynamics of Trichostrongylus colubriformis larvae were compared over two years on contrasting topographical aspects north (warm and dry) and south-facing (cool and moist) hill slopes) on paddocks which form part of the 'non-chemical' and conventional' farm systems at the AgResearch Ballantrae Hill Country Station located in a summer-moist region of New Zealand. Sheep faeces containing 50,000 Trichostrongylus eggs were incubated for 4 days at 25 degrees C and then deposited on each of 36 sub-plots in each of 8 plots in a 2 x 2 factorial design in the summer (summer trial) and again in autumn (autumn trial). Pasture was removed to ground level and larvae extracted from six sub-plots from each plot 2, 4, 6, 8, 11 and 14 weeks after contamination in all trials. Larvae were recovered from two strata, 0-5 cm above the soil surface and > 5 cm above the soil surface. Fewer (p < 0.001) larvae were recovered from herbage (47 vs. 118) and residual faeces (28 vs. 246) from the autumn than from the summer trials. This coincided with more rapid (p < 0.001) faecal disappearance in the autumn trials. In the summer trials, fewer (p < 0.003) larvae were recovered from the herbage (101 vs. 182) and residual faeces (140 vs. 352) from plots on the south than the north facing aspect. In the autumn trials there was a rapid (p < 0.0001) faecal disappearance from the south-facing aspect. In the autumn trials there was a non-significant (p < 0.10) trend for fewer larvae to be recovered from the south-facing aspect (2 vs. 54). This also coincided with more rapid faecal disappearance from the south-facing aspect. There was no effect of farm system on the number of larvae recovered. Despite greater (p < 0.0001) numbers of larvae recovered from the bottom stratum of herbage, the density of larvae (L3/kg DM) tended (p < 0.12) to be higher in the top stratum of herbage. It was concluded that season and aspect have a marked effect on the number of larvae recovered from herbage and that this was inversely related to the rate of faecal disappearance.

Agrochemicals↗
PubMed1991

Theophylline analysis at the chest clinic--comparison of a portable versus conventional system.

The running cost and clinical application of a new, portable, direct-injection, high-performance, liquid chromatograph for the measurement of theophylline was compared with conventional laboratory-based analysis by studying the two methods in two parallel chest clinics. Thirty-six patients were managed with the portable method and 33 by the conventional system. They were already receiving theophylline preparations for treatment of their asthma or chronic airflow limitation. Over the 12-week period of study, the percentage of patients with levels in the therapeutic range rose from 33% to approximately 87% in both clinics, but this change was achieved in only 6 weeks using the portable system. Patients whose theophylline levels were increased into the therapeutic range had improved symptom scores as measured by visual analogue scales but we were unable to demonstrate any significant change in spirometry. The cost of the portable system compared favourably with laboratory analysis, and had the additional benefit of quicker detection of non-compliance and facility for discussion with the patients at the time of consultation.

Adult↗
PubMed1990

Changes in hospital management of acute severe asthma by thoracic and general physicians in Birmingham and Manchester during 1978 and 1985.

Hospital management of acute severe asthma in 14 large hospitals in Birmingham and Manchester was audited in a random 20% of 1196 patients aged 15-45 years admitted in 1985. Of the 239 admissions randomised, 192 were suitable for study. Results were compared with those from a study in the same hospitals using the same methods in 1978. The age and sex of the patients and their smoking history, duration of asthma, and hospital attendance were similar in 1978 and 1985. A much smaller proportion of patients presented with symptoms of over seven days' duration in 1985 (8.5%) than in 1978 (26%). The inpatient management of asthma appears to have improved in both thoracic and general units, with more thorough functional assessments, more frequent performance of relevant investigations (arterial blood gases and peak expiratory flow rates) and more frequent use of recommended treatment (nebulised bronchodilators, oral and intravenous corticosteroids). Less difference was found in 1985 between units with a specialist thoracic interest and those without, though some differences remained in 1985 in monitoring of peak expiratory flow rate and arterial blood gases, outpatient prescribing, and follow up arrangements. Inhaled preventive medication was prescribed more frequently than in 1978. In 1985 there was a 56% increase in admissions for asthma. The proportion of severely ill patients was similar to that in 1978, but in the most severe functional grade mean arterial carbon dioxide tension was higher in 1985 and more patients were ventilated. Our results suggest that hospital management by thoracic and general physicians has improved over the period 1978-85. Patients presented earlier in 1985, though there seems to have been an increase in asthma of all grades of severity.

Adolescent↗
PubMed1984

The problems of tuberculosis in the elderly.

A prospective study of tuberculosis notifications from 1976 to 1980 in the North Staffordshire Health District (NSHD), an area with only a small immigrant population, has been carried out. The notification rate for all new cases of tuberculosis in white patients over 55 years of age in the NSHD was twice that reported for England and Wales by the Medical Research Council (1980). Of 433 cases in all ethnic groups 52 (12 per cent) were diagnosed only at necropsy. In addition 48 (11 per cent) died before treatment was completed. Tuberculosis was the only cause of death in 39 of these 100 cases and contributed to death in a further 19 cases, the site of disease being thoracic in 86. Of those who died before completion of treatment, tuberculosis was the cause of death or contributory in 23 and 16 of the 23 (70 per cent) had been on treatment for less than 13 weeks. Death occurred more commonly before or during treatment with increasing age. In a retrospective study of treatment during 1979 and 1980, major unwanted drug-induced effects occurred in 40 per cent of all treated cases in the over-65 age group, mostly related to rifampicin. The survey highlighted the problems of tuberculosis in the elderly white population. They present with advanced disease, are diagnosed late and their course is complicated by other disease and a poor tolerance of therapy.

Adolescent↗
PubMed1983

Action of intravenously administered aminophylline on normal airways.

The changes in airway caliber and plasma cyclic-AMP levels after intravenously administered aminophylline, and the effect of DL- and D-propranolol on these responses have been investigated in a double-blind manner in normal subjects. Aminophylline 5.6 mg/kg was given intravenously over a 10-min period and the airway response was measured as change in specific airway conductance (delta SGaw) in the body plethysmograph. In the initial study in 6 subjects, orally administered placebo or propranolol was followed 2 h later by intravenously administered aminophylline. Neither placebo nor propranolol alone caused any change in SGaw at 2 h. After placebo, intravenously injected aminophylline produced a 30% increase in SGaw, reaching a peak 5 min after injection. This response was equivalent to 77% of the maximal response to 400 micrograms inhaled albuterol in the same subjects. After propranolol, the airway response to aminophylline was attenuated, with a 53% reduction in delta SGaw at the time of peak response. In a further study on 6 subjects, intravenously given aminophylline produced a 25% increase in SGaw and a 51% increase in plasma cyclic-AMP levels after placebo tablets. Pretreatment with 40 and 80 mg DL-propranolol caused a dose-dependent reduction of both the airway and plasma cyclic-AMP response to aminophylline. The airway response to aminophylline was not attenuated by D-propranolol so the effect of DL-propranolol is thought to be due to beta-adrenoceptor blockade. The absence of any detectable change in SGaw after DL-propranolol suggests there is little resting sympathetic tone to the airways in normal subjects. In the absence of sympathetic stimulation, the rapid response to aminophylline is unlikely to be due to phosphodiesterase inhibition. The attenuation of the airway and cyclic-AMP response by propranolol suggests that part of the action of aminophylline may be due to beta-agonist activity.

Adult↗
PubMed1981

How important is the sequence of administration of inhaled beclomethasone dipropionate and salbutamol in asthma.

Sixty patients with fairly stable asthma of mild or moderate severity entered a multicentre, double-blind cross-over trial, comparing the efficacy of inhaled beclomethasone dipropionate preceded 10 minutes earlier by inhalation of salbutamol with that of beclomethasone followed 10 minutes later by salbutamol during two consecutive three-month periods. Patients received beclomethasone 100 microgram and salbutamol 200 microgram four times daily. Analysis of occurrence of exacerbations, usage of additional inhaled salbutamol, peak expiratory flow rate and symptom scores showed no evidence that regular beclomethasone was more effective when preceded by salbutamol rather than when followed by it.

Adult↗
PubMed1981

Assessment of bronchial beta blockade after oral bevantolol.

We have applied a new method for quantitative measurement of bronchial beta adrenoceptor blockade to a new beta adrenoceptor antagonist, bevantolol. Dose-response curves to a beta agonist, albuterol, were obtained in six normal subjects by measuring specific airway conductance (sGaw) after increasing doses of inhaled albuterol. These were repeated on three separate occasions 2 hr after subjects had taken oral placebo or bevantolol (75 or 150 mg), double-blind in random order. The dose-response curves after bevantolol 75 mg were displaced in the right of placebo in four subjects and after 150 mg were displaced to the right of placebo in all subjects. The mean dose ratios for bevantolol 75 or 150 mg were 1.02 and 2.77, much the same as those obtained in the same subjects after practolol 100 and 200 mg and considerably less than that after propranolol 40 mg. The mean reductions in exercise heart rate were 25% and 29% after bevantolol 75 and 150 mg. Our data show that bronchial beta blockade after a beta blocking drug can be assessed quantitatively in many by a double-blind technique.

Adrenergic beta-Antagonists↗
PubMed1981

Bronchial and cardiac beta-adrenoceptor blockade--a comparison of atenolol, acebutolol and labetalol.

Bronchial and cardiac beta-adrenoceptor blockade have been compared in six normal subjects after three beta-adrenoceptor antagonists. Single and double doses of atenolol (50 and 100 mg), acebutolol (100 and 200 mg) and labetalolol (150 and 300 mg) were studied on separate occasions. 2 Salbutamol airway dose-response curves were obtained by measuring the airway response as the change in specific airway conductance (sGaw) after increasing doses of inhaled salbutamol. Bronchial beta-adrenoceptor blockade was assessed after each drug as the dose of salbutamol needed to cause a 50% increase in sGaw (sGaw D50). 3 Cardiac beta-adrenoceptor blockade was assessed after the same doses of each beta-adrenoceptor antagonist, by measuring the percentage reduction in exercise heart rate from control, after exercise for 5 min at 70% of the subject's maximum work rate. 4 Atenolol 50 and 100 mg caused least bronchial beta-adrenoceptor blockade and the greatest reduction in exercise heart rate. 5 Acebutolol 100 and 200 mg and labetalol 150 and 300 mg produced more bronchial beta-adrenoceptor blockade than atenolol. 6 With this approach new beta-adrenoceptor antagonists can be assessed without putting asthmatic patients at risk.

Acebutolol↗
PubMed1980

Ketotifen in adult asthma.

The efficacy and adverse effects of ketotifen 1 mg twice daily and 2 mg twice daily were compared with placebo in 50 patients with atopic asthma in a multicentre, double-blind study. Ketotifen in the higher dosage caused a slight reduction in salbutamol usage and a modest improvement in breathing in patients not already receiving inhaled corticosteroids. The drug was ineffective in patients receiving inhaled corticosteroids. Drowsiness was a troublesome effect causing withdrawal from treatment or reduction of dosage in seven patients while receiving ketotifen compared with only three while receiving placebo.

Adolescent↗