Pulmonary rehabilitation for chronic obstructive pulmonary disease: a pilot study evaluating a once-weekly versus twice-weekly supervised programme.

Objectives: To compare the effectiveness of a once-weekly supervised pulmonary rehabilitation programme with a standard twice-weekly format.

Design: Randomised trial of equivalency.

Setting: Pulmonary rehabilitation service of a primary care trust delivered at two physiotherapy outpatient departments.

The interaction of asbestos and smoking in lung cancer: a modified measure of effect.

Objectives: The ratio of the relative risk of lung cancer due to asbestos exposure in non-smokers to that in smokers has been termed the relative asbestos effect (RAE). In a review, Liddell [Liddell FDK (2001) Ann Occup Hyg; 45: 341-56] estimated that the RAE was approximately 2. This measure is satisfactory when there is an appreciable relative risk due to asbestos but does not generalize to lower levels of exposure.

The combination of effects on lung cancer of cigarette smoking and exposure in quebec chrysotile miners and millers.

Although it is well known that both cigarette smoke and microscopic airborne asbestos fibres can cause lung cancer, evidence as to how these two agents combine is nebulous. Many workers have believed in the multiplicative theory, whereby asbestos increases the risk in proportion to the risk from other causes. However, evidence against this theory is mounting: a recent review concluded that the multiplicative hypothesis was untenable, and that the relative risk of lung cancer from asbestos exposure was about twice as high in non-smokers as in smokers, a finding largely independent of type of asbestos fibre.

The interaction of asbestos and smoking in lung cancer.

Both cigarette smoke and inhaled asbestos fibres can cause lung cancer, but the assessment of how these agents act in combination is a matter of great difficulty. In non-smokers, the condition is so rare that, in any cohort of asbestos workers, the standardised mortality ratio (SMR, that is the ratio of the numbers of deaths observed and expected) is quite imprecise. The SMR for smokers, with which it has to be compared, is also subject to sampling error, making the interaction even more unstable.

Dust exposure and lung cancer in Quebec chrysotile miners and millers.

A large cohort of men born between 1891 and 1920 and employed for at least a month in the chrysotile producing industry of Quebec has been under study since 1966. These men were followed from first employment (the earliest in 1904) to 1992, by which time over 8000 had died, 657 from lung cancer. The current study is of 488 cases of lung cancer formerly employed at three places, viz.

The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992.

This paper draws together the mortality experience for a cohort of some 11000 male Quebec Chrysotile miners and millers, reported at intervals since 1971 and now again updated. Of the 10918 men in the complete cohort, 1138 were lost to view, almost all never traced after employment of only a month or two before 1935; the other 9780 men were traced into 1992. Of these, 8009 (82%) are known to have died: 657 from lung cancer, 38 from mesotheliona, 1205 from other malignant disease, 108 from pneumoconiosis and 561 from other non-malignant respiratory diseases (excluding tuberculosis).

The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88.

A cohort of some 11,000 men born 1891-1920 and employed for at least one month in the chrysotile mines and mills of Quebec, was established in 1966 and has been followed ever since. Of the 5351 men surviving into 1976, only 16 could not be traced; 2508 were still alive in 1989, and 2827 had died; by the end of 1992 a further 698 were known to have died, giving an overall mortality of almost 80%. This paper presents the results of analysis of mortality for the period 1976 to 1988 inclusive, obtained by the subject-years method, with Quebec mortality for reference.

The mortality of amphibole miners in South Africa, 1946-80.

A cohort was established in 1981 of all 7317 white male employees in the amosite and crocidolite mines in South Africa whose names had appeared in the personnel records (initiated between 1945 and 1955) of the major companies. Some of the men had been employed as early as 1925, but only 8% had had more than 10 years of service. Three subcohorts were defined: 3212 men whose only exposure to asbestos was to amosite; 3430 exposed to crocidolite; and 675 to both amphiboles.

The development of cohort studies in epidemiology: a review.

An historical outline of the evolution of cohort (or incidence) studies spans well over 100 years, from the work of Farr and Snow in the 1850s, through an appraisal of analytical methods in 1977, after which the literature mushroomed. Since the early 1950s, analysis has conventionally taken the form of comparing subcohorts that had suffered varying degrees of exposure to factor(s) under investigation. For this purpose, the "subject-years" approach to data reduction has now become virtually universal.

Relations between asbestos exposure and lung cancer SMRs in occupational cohort studies.

It has long been accepted that excessive exposure to asbestos may produce lung cancer but not that there is a consistent "biological gradient." This can only be evaluated reliably in studies where, for every individual, exposure has been measured in terms of both duration and intensity. Even now, there are only at most eight such cohort studies of asbestos workers, while femoral methods of analysis have been available only recently.

Fibre exposure and mortality from pneumoconiosis, respiratory and abdominal malignancies in chrysotile production in Quebec, 1926-75.

To define the relationships between chrysotile exposure in fibre terms and death from specific cancers, and pneumoconiosis, all 11,379 persons born 1891-1920 who had worked in the asbestos mines and mills of Quebec for a month or more before 1967 were followed to the end of 1975. Among the 10,939 men, there had been 4,463 deaths, 634 from these causes. For each death, referents were randomly selected from among men in the cohort born in the same year as the case and known to have survived to a greater age.

Simple exact analysis of the standardised mortality ratio.

The standardised mortality ratio is the ratio of deaths observed, D, to those expected, E, on the basis of the mortality rates of some reference population. On the usual assumptions--that D was generated by a Poisson process and that E is based on such large numbers that it can be taken as without error--the long established, but apparently little known, link between the Poisson and chi 2 distributions provides both an exact test of significance and expressions for obtaining exact (1-alpha) confidence limits on the SMR. When a table of the chi 2 distribution gives values for 1-1/2 alpha and 1/2 alpha with the required degrees of freedom, the procedures are not only precise but very simple.

Simplified exact analysis of case-referent studies: matched pairs; dichotomous exposure.

In a case-referent study of matched pairs with a single dichotomous exposure variable, the relative risk R is estimated from the "discordant pairs," r and s, by R = r/s. In this paper the exact (1 - alpha) confidence limits, RL and RU, have been simplified, and a new exact test of the null hypothesis that R = 1 has been derived. The exact methods depend on the F distribution; they are simple to calculate and all have been fully validated.

Motor vehicle accidents (1973-6) in a cohort of Montreal drivers.

In 1973-4 nearly 10 000 Montreal drivers, interviewed by telephone, provided information about medical and associated factors and about driving habits, in particular annual mileage. Records of accidents suffered by these drivers in the Province of Quebec over 39 months (1973-6) were also collected. The 7634 current drivers, with appropriate permits, and all of whose data passed reliability edits, were placed into nine sets-that is, three classes: women; men with the usual permit; and men with a chauffeur's permit to drive taxis, heavy vehicles, etc; further subdivided into three age groups.

Follow-up respiratory measurements in Quebec chrysotile asbestos miners and millers.

In 1974 changes in dyspnea, lung function, and pneumoconiotic radiographic abnormalities were recorded among the 1,015 Quebec chrysotile miners and millers surveyed in 1967-1968. The aim was to relate these changes to dust exposure--age, smoking, and earlier health status being taken into account. Dyspnea and lung function were assessed in 722 men, and for 277 recent radiographs were read separately by three experts for changes in the parenchyma and pleura.

Autonomic responsiveness in obesity with and without hypertension.

Evidence from animals models of obesity, eg the ob/ob mouse, and from studies in man are consistent with the autonomic regulation of brown tissue being one of the principal pathways involved in the normal thermogenic regulation of energy balance. Studies in man on other components of the sympathetic nervous system do not suggest generalized autonomic abnormalities in obese patients. Patients placed on a reduced carbohydrate intake show a fall in metabolic rate, a reduction in cardiovascular indices of sympathetic activity and a fall in venous noradrenaline concentrations.

Radiological findings as predictors of mortality in Quebec asbestos workers.

Two cohorts of chrysotile miners and millers in Quebec were selected to study the extent to which chest radiographs taken while still employed predict mortality. The paper presents mainly findings in much the larger cohort, which consisted of 4559 men (two-thirds past workers) whose latest radiograph had been assessed by one of six experienced readers into what became the UICC/Cincinnati (U/C) classification; by the end of 1975 there had been 1543 deaths in this cohort. The findings were generally confirmed in the other cohort, comprising 988 current male workers, who had been examined in 1967-8 by questionnaires on respiratory symptoms and smoking and by lung function tests, and for whom all six readers had assessed their 1966 radiographs into the U/C classification; 130 men had died by the end of 1975.

Dust exposure and mortality in chrysotile mining, 1910-75.

We report a further follow-up of a birth cohort of 11 379 workers exposed to chrysotile. The cohort consisted of 10 939 men and 440 women, born 1891-1920, who had worked for at least a month in the mines and mills of Asbestos and Thetford Mines in Quebec. For all subjects, length of service and estimates of accumulated dust exposure were obtained, with a smoking history for the vast majority.

The effect of levodopa with carbidopa (Sinemet R) on the metabolic response to semistarvation.

It has been reported that levodopa will prevent the adaptive fall in the resting metabolic rate (RMR) on a weight-reducing diet. Whether levodopa has a central or peripheral effect on the RMR has been investigated by giving carbidopa, a peripheral dopa decorboxylase inhibitor with levodopa (as SinemetR) to four obese subjects on a low-energy diet. SinemetR failed to prevent the adaptive reduction in the RMR to energy restriction suggesting that levodopa maintains the RMR by a peripheral effect or effects.