Health-related quality of life and functional status in end-stage COPD: a longitudinal study.

Since there is still a dearth of information about the end stage of chronic obstructive pulmonary disease (COPD), the main aim of this study was to examine the development of health-related quality of life (HRQoL) and functional status over time in COPD patients in Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage IV. 82 Dutch COPD patients completed the St George's Respiratory Questionnaire (SGRQ) for HRQoL and the Groningen Activities for Daily Living Restriction Scale (GARS) for functional status every 3 months during the year following enrolment. Survival was followed up to 5 yrs after enrolment. Data were analysed by stratifying the study population into severity subgroups according to the lowest, intermediate and highest tertile of SGRQ and GARS at baseline. Outcome measures were change in SGRQ and GARS scores over time and survival time. In the majority of patients, scores on the SGRQ and GARS declined gradually over time. In the subgroup of 32 patients that died within 2 yrs of enrolment, these scores also declined gradually, without steep deteriorations. In patients with end-stage COPD, HRQoL and functional status deteriorated gradually over time, indicating that clinicians did not gain much additional support for differentiating the end stage of COPD by considering HRQoL and functional status using the SGRQ and GARS.

A simple G-computation algorithm to quantify the causal effect of a secondary illness on the progression of a chronic disease.

Progression of a chronic disease can lead to the development of secondary illnesses. An example is the development of active tuberculosis (TB) in HIV-infected individuals. HIV disease progression, as indicated by declining CD4 + T-cell count (CD4), increases both the risk of TB and the risk of AIDS-related mortality. This means that CD4 is a time-dependent confounder for the effect of TB on AIDS-related mortality. Part of the effect of TB on AIDS-related mortality may be indirect by causing a drop in CD4. Estimating the total causal effect of TB on AIDS-related mortality using standard statistical techniques, conditioning on CD4 to adjust for confounding, then gives an underestimate of the true effect. Marginal structural models (MSMs) can be used to obtain an unbiased estimate. We describe an easily implemented algorithm that uses G-computation to fit an MSM, as an alternative to inverse probability weighting (IPW). Our algorithm is simplified by utilizing individual baseline parameters that describe CD4 development. Simulation confirms that the algorithm can produce an unbiased estimate of the effect of a secondary illness, when a marker for primary disease progression is both a confounder and intermediary for the effect of the secondary illness. We used the algorithm to estimate the total causal effect of TB on AIDS-related mortality in HIV-infected individuals, and found a hazard ratio of 3.5 (95 per cent confidence interval 1.2-9.1).