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.