PubMed Health⌕ Search

Biomedical subjects

A R Rubinfeld

Publications and source records attributed to A R Rubinfeld.

10 recordsLinked to original sources
PubMed1992

Accuracy of asthma death statistics in Australia.

Asthma mortality statistics issued by the Australian Bureau of Statistics (ABS) were compared with clinical data from a survey of asthma mortality. Deaths in Victoria from May 1986 to April 1987 containing 'asthma' in Parts 1 or 2 of the death certificate (N = 405) were reviewed. For each subject, the cause of death attributed by the Victorian Asthma Mortality Survey was compared with the ABS cause of death, by age and sex of the subject. Information on 393 of the 405 deaths investigated by the Victorian Asthma Mortality Survey was analysed. The ABS estimate of the total number of asthma deaths in Victoria was 47 per cent higher than the estimate of the Victorian Asthma Mortality Survey. In subjects under 50 years of age the two estimates were within 10 per cent. The difference between the estimates increased with age at death for persons over 50 years old and was equivalent for males and females. If the assessment by the Victorian Asthma Mortality Survey of the number of deaths due to asthma is accepted as accurate, then the ABS estimate of asthma deaths was reliable for those under 50 years of age. In those who died at an older age, the ABS significantly overestimated the number of deaths due to asthma in Victoria.

Asthma↗
PubMed1979

Depressed cyclic AMP levels in airways smooth muscle from asthmatic dogs.

We tested mongrel dogs by intradermal injection and tracheobronchial aerosol challenge with Ascaris suum antigen extract. All dogs were skin-test positive but could be segregated, on the basis of airways resistance measurements, into "asthmatic" (bronchoreactive) and "nonasthmatic" (nonbronchoreactive) groups. By using tracheal rings from these dogs, we measured the abilities of the beta-adrenergic agonist, isoproterenol, to relax tracheal smooth muscle contracted by methacholine and to cause cyclic AMP (cAMP) accumulation in the presence and absence of methacholine. The magnitude of relaxation induced by any concentration of isoproterenol was always less in the smooth muscle from "asthmatic" dogs. In the same tissues the concentrations of cAMP after in vitro equilibration, but prior to isoproterenol addition, were significantly less in the "asthmatic" than "nonasthmatic" samples. The accumulation of cAMP due to isoproterenol was similar in both groups for every dose of isoproterenol so that the initial difference between groups in cAMP concentration was maintained in an additive fashion over the entire dose-response curve. Total protein content of trachealis muscles from both groups of dogs was the same. We conclude that beta-adrenergically sensitive adenylate cyclase is not impaired in tracheal smooth muscle from "asthmatic" dogs; rather, the basal concentration of cAMP is depressed in "asthmatic" airway smooth muscle, and this difference is maintained throughout the isoproterenol dose-response curve. The depressed intracellular cAMP concentrations may be related to the decreased relaxation induced by isoproterenol in the "asthmatic" tracheal smooth muscle.

Animals↗
PubMed1978

Gas exchange during acute experimental canine asthma.

The inert gas infusion technique was used to recover distributions of ventilation-perfusion ratios in anesthetized dogs during 17 episodes of acute asthma produced experimentally by broncho-provocation with aerosolized Ascaris suum extract, methacholine, or histamine. Regardless of the agent used, 2 general patterns of ventilation/perfusion maldistribution were observed. During mild attacks of bronchospasm, a broadening of the normal unimodal distribution of ventilation-perfusion ratios occurred. During more severe attacks, the ventilation/perfusion distributions were clearly bimodal (with true right-to-left shunt of more than 4 per cent present on only one occasion), suggesting that there are, in general, 2 populations of gas-exchanging units in the lung under these conditions. One population has approximately normal ratios of ventilation to blood flow. The second is a population centered on a low ventilation-perfusion ratio (average, 0.14) that can be explained by ventilation of lung units with completely obstructed bronchi via collateral pathways. The postmortem appearances of the lungs and the time course of the gas-exchange abnormalities suggest that the chief cause of the bronchial occlusion responsible for the low ventilation-perfusion units was excessive mucus in the lumen. The presence of collateral pathways of ventilation in the canine lung appeared to protect the animals from developing areas of true shunt under these conditions. The ventilation/perfusion distributions were similar to those seen in human patients with bronchial asthma.

Acute Disease↗
PubMed1977

Bronchial provocation in the study of sensations associated with disordered breathing.

1. Lung volumes, airway resistance and flow/volume curves were measured in ten asthmatic subjects at times when tightness in the chest was just sensed (threshold symptom). 2. These measurements when the threshold symptom was induced by methacholine inhalation were compared with those when a similar symptom occurred spontaneously, in the same subjects. 3. Values during the methacholine-induced thresholds were very similar to those observed when threshold symptoms developed spontaneously. 4. Controlled bronchial provocation mimics spontaneous asthma sufficiently well to allow this technique to be used in the study of sensations associated with breathing. This has some advantages over the already established models utilizing external hindrances to breathing.

Adult↗
PubMed1977

How mild is mild asthma?

Nineteen asthmatic volunteers underwent methacholine-induced asthma to the point when tightness in the chest was just sensed (threshold symptom). Changes in the following indices of lung function were measured--static lung volumes, forced expiratory volume in one second, and airways conductance. The increase in airways resistance necessary for threshold detection was at least double that previously reported in experiments using external resistive loads. Despite the mildness of the symptom, increases in lung volumes to the levels previously described during acute and severe asthma were occasionally found. It is emphasised that there may be little leeway in respiratory reserve between the development of minor and severe symptoms in some asthmatic patients.

Airway Resistance↗
PubMed1977

Relationship between bronchial reactivity, airway caliber, and severity of asthma.

Indices of bronchial reactivity were obtained in 11 asthmatic subjects. These were based on the responses of specific airway conductance to timed cumulative doses of methacholine aerosol. The relationship of bronchial reactivity both to initial airway caliber and to current severity of asthma was then assessed. There was no correlation between initial airway caliber and the degree of bronchial reactivity for the group. Furthermore, a subject's bronchial response to methacholine, when expressed as a percentage of initial specific airway conductance, remained stable, even in the presence of moderate fluctuations in initial specific airway conductance. There was also no correlation between bronchial reactivity and severity of asthma for the group. Each subject's bronchial responses remained stable, even in the presence of moderate fluctuations in severity of asthma. These data confirm that a simple relationship between intrinsic bronchial reactivity and the severity of clinical asthma is not apparent.

Adult↗
PubMed1977

Conscious perception of bronchospasm as a protective phenomenon in asthma.

Ten initially asymptomatic asthmatic subjects underwent methacholine-induced attacks of asthma on a number of occasions, to the point when tightness in the chest was just sensed (threshold point). As baseline lung volumes increased and the caliber of the airways decreased, the relative changes needed to attain a threshold point generally became smaller. Although pulmonary function can deteriorate chronically without increasing dyspnea, it is possible that a mechanism exists at the level of consciousness to protect a subject's breathing at times when pulmonary function is acutely impaired.

Adaptation, Physiological↗
PubMed1976

Perception of asthma.

Subjective assessment and objective measurements of airways obstruction were compared in 82 patients during methacholine-induced asthma. 15% of the patients were unable to sense the presence of marked airways obstruction (forced expired volume in 1 s less than 50% of the predicted normal value). These subjects could not be characterised as a distinct group on the basis of their sex, age, or duration of their asthma. This reinforces the need for objective measurement of lung function in the management of asthma.

Adult↗