Original ArticleDisturbed sleep among COPD patients is longitudinally associated with mortality and adverse COPD outcomes
Introduction
Sleep quality is likely to be particularly important in the setting of a chronic, symptomatic, and progressive disease such as chronic obstructive pulmonary disease (COPD). COPD may lead to worse sleep quality and insomnia by virtue of respiratory symptoms, such as nocturnal cough and dyspnea. Moreover, poor sleep quality could contribute to poor COPD-related outcomes such as exacerbations or even mortality risk. Such adverse effects could operate through various pathways. Poor sleep quality could lead to impaired cognition, thus impairing COPD self-management behaviors [1], [2]. Alternatively, poor sleep quality may impair immune function, contributing to the likelihood or severity of COPD exacerbations [3], [4]. Poor sleep quality may act in ways that depend on the presence of underlying COPD, which underscores the need to study sleep disturbance specifically in COPD populations.
In a recent review of sleep abnormalities in COPD, Krachman and colleagues conclude that it is unknown whether there is a relationship between sleep quality and disease severity in COPD [5]. They furthermore note that it has yet to be determined whether poor sleep quality in patients with COPD has an effect on neurocognition [5]. This knowledge gap may reflect the cross-sectional nature of the limited studies that have demonstrated a link between respiratory symptoms and sleep complaints in COPD patients [6], [7]. Indeed, there has been a dearth of longitudinal studies examining the consequences of disturbed sleep in COPD, especially with respect to the outcome of mortality.
In this analysis we sought to address these gaps in the published literature. First, we wished to confirm the anticipated association between insomnia symptoms and COPD symptoms and severity, since such a cross-sectional relationship provides biological coherence to any sleep-related adverse effects we might observe longer-term. Next, we examined whether sleep disturbance predicted adverse outcomes, including: COPD exacerbations, emergency health services utilization, and overall survival. We also wished to investigate whether such an association with sleep disturbance, if present, might be explained solely by COPD severity and whether cognitive dysfunction, depression, or anxiety might mediate part of the relationship between disturbed sleep and poor outcomes. We conducted our study on an on-going population-based longitudinal COPD cohort, utilizing such data as COPD severity and lung function assessments, structured cognitive function evaluations, and longitudinal health care utilization information, with linkage to mortality data.
Section snippets
Overview
In 98 subjects from a population-based study with spirometrically-confirmed COPD we administered structured telephone interviews and, to obtain measurements of cognitive and lung function, we conducted subject home visits. Sleep disturbance was evaluated using four survey items which assessed insomnia symptoms. Disease severity was quantified with the COPD Severity Score based on interview responses. Lung function was measured spirometrically. Cognitive function was assessed using directly
Subject characteristics
Baseline subject characteristics are presented in Table 1. Among 98 study participants, the mean age was 67.6 years (SD = 5.4), 56% of patients were women, and 85% where white, non-Latino. There was a broad range of BMI categorizations: 6% underweight, 32% normal weight, 34% overweight, and 29% obese or morbidly obese. The degree of COPD was moderately advanced, with a mean FEV1% predicted of 54% (SD = 22%). Staged by GOLD criteria, where higher stage represents more advanced COPD, 15% of subjects
Discussion
In this population-based, longitudinal study of persons with COPD, we found that disturbed sleep is predictive of exacerbations, respiratory-related emergency utilization, and all-cause mortality. This longitudinal relationship persisted even after controlling for both FEV1 and COPD Severity Score, suggesting that disturbed sleep is playing an independent role as a risk factor for poor outcomes in COPD, rather than simply being a marker of worse disease.
Although sleep disturbance was not
Funding
Dr. Omachi was supported by K23 HL102159-01 from the National Heart, Lung, and Blood Institute, National Institutes of Health. Dr. Katz, Dr. Blanc and recruitment of the UCSF COPD cohort were supported by R01 HL067438 from the National Heart, Lung, and Blood Institute, National Institutes of Health.
Conflict of Interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: doi:10.1016/j.sleep.2011.12.007.
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