Impaired Sleep Reduces Quality of Life in Chronic Obstructive Pulmonary Disease
Disturbed sleep is reportedly common in chronic obstructive pulmonary disease (COPD), but the impact of quality of sleep on health-related quality of life (HRQL) has not been previously investigated in these individuals. The purpose of this study was to assess the impact of quality of sleep on HRQL in patients with COPD. In 30 clinically stable patients with moderate to very severe COPD, we evaluated subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and HRQL using the Saint George’s Respiratory Questionnaire. Additionally, lung function was assessed by spirometry, severity of dyspnea by the Modified Medical Research Council scale, and functional exercise capacity by the Six-Minute Walk Test. Twenty-one (70%) patients showed poor quality of sleep (PSQI > 5). HRQL was significantly correlated with quality of sleep (P = 0.02), post-bronchodilator FEV1 (P = 0.04), and severity of dyspnea (P < 0.01). Multiple regression analysis showed that quality of sleep was the best predictor of quality of life in our subjects. Our data suggest that quality of sleep is major determinant of HRQL in COPD. Increased efforts to diagnose and treat sleep problems, including measures to improve factors that adversely affect sleep should receive great attention in the daily management of these patients.
KeywordsChronic obstructive pulmonary disease Quality of life Quality of sleep
Chronic obstructive pulmonary disease (COPD) is a major public health problem. It is a leading cause of morbidity and mortality worldwide, affecting 6% of the general population . In adults aged 40 years and older, the prevalence of COPD may reach 9–10% . Deaths attributed or associated with COPD have been increasing steadily during the past 20 years .
Chronic obstructive pulmonary disease imposes a significant burden in terms of disability and impaired quality of life . It has been demonstrated that patients with stable disabling COPD have lower health-related quality of life (HRQL) than healthy individuals and patients with other disabilities . Health-related quality of life is considered a major outcome for studies on COPD . Poor HRQL is an important predictor for subsequent hospitalization and mortality in these patients . Several factors have been recognized as predictors of impaired HRQL in COPD, including body mass index, frequency of exacerbation, chronic dyspnea, and exercise performance [6, 7].
Poor sleep is a common feature of COPD [8, 9]. Sleep-related complaints are ranked third, after dyspnea and fatigue, in frequency of complaints of these patients . Delayed sleep onset, reduced rapid eye movement (REM) sleep, decreased sleep time, and frequent changes in sleep stages have been described in patients with COPD [11, 12]. Sleep problems have been associated with daytime symptoms and chronic fatigue commonly found in COPD . Although sleep disturbances have been shown to reduce HRQL in several chronic illness and have been related to decreased survival, the effect of poor sleep on HRQL in COPD has not been previously evaluated [14, 15, 16]. The objective of this study was to assess the impact of quality of sleep on HRQL in patients with COPD.
Patients and Methods
The study population consisted of 30 ambulatory-based patients attending the COPD Clinic at the University Hospital of the Federal University of Ceará, Brazil.
Ninety consecutive patients regularly attending the Outpatient Clinic for a routine appointment were initially referred for the study. Subjects were individually recruited if they were aged 40 years or older, had a medical diagnosis of COPD stage II to IV according to GOLD criteria , and were considered to be in a clinically stable condition. Exclusion criteria were disease exacerbation 4 weeks before the study, current use of oral steroids, methylxantines, or hypnotic-sedative medication, nocturnal oxygen therapy, shiftwork, suspected obstructive sleep apnea, congestive heart failure, and severe psychiatric disorders.
The study protocol was approved by the local research ethics committee and written informed consent was obtained in all cases.
Study Design and Measurements
This was a cross-sectional study on the quality of sleep and HRQL in clinically stable patients with moderate to very severe COPD. Quality of sleep was assessed by the Pittsburgh Sleep Quality Index (PSQI) and HRQL by the Saint George’s Respiratory Questionnaire (SGRQ). Additionally, lung function was evaluated by spirometry, severity of dyspnea by the Modified Medical Research Council scale, and exercise capacity by the Six-Minute Walk Test.
The PSQI is a seven component scale, each one dealing with a major aspect of sleep: (1) subjective sleep quality; (2) sleep latency; (3) sleep duration; (4) sleep efficiency; (5) sleep disturbances; (6) use of sleep medication; and (7) daytime dysfunction. These components are weighted equally on a 0–3 scale, with a global score ranging from 0 to 21. A global PSQI score >5 has been found to have a sensitivity of 89.6% and specificity of 86.5% in differentiating good from poor sleepers . Component #6 always scored zero because individuals taking sleep medications were not included in this study.
The SGRQ is a widely used standardized HRQL questionnaire. It consists of 50 items, divided into 3 domains: symptoms, activity, and impact. A score is calculated for each domain and a total score also is calculated. Scores range from 0 to 100, with lower scores indicating better quality of life [19, 20].
Spirometry was performed according to standard technique . Measurements included FEV1, FVC, and FEV1/FVC ratio, and the results were compared with previously published normal values . The body mass index was calculated as weight in kilograms divided by height in meters.
The degree of dyspnea was assessed by the Modified Medical Research Council (MMRC) dyspnea scale . Scores range from 0 (only gets breathless with strenuous exercise) to 4 (too breathless to leave the house or becomes breathless when dressing or undressing).
Functional exercise capacity was evaluated by the Six-Minute Walk Test. This is a standardized and practical simple test that measures the distance a patient can quickly walk on a flat, hard surface in a period of 6 min . The test was completed in an enclosed corridor on a flat course 20 m in length. Patients were asked to walk at their highest rate from one end of the corridor to the other end as many times as possible within the established time. The test was performed under the control of one of the investigators who encouraged the patients. The distance walked by the patient at the end of the 6-min period was measured.
Statistical analyses were conducted with Statistical Package for Social Sciences version 15.0 . Pearson correlation coefficients were calculated to study the relationship between the HRQL measures and other variables. Stepwise multiple regression was used to identify the factors that were most strongly related to HRQL scores. The following measures of HRQL were used as dependents: SGRQ total, symptoms, activity, and impact. The independent variable was PSQI total corrected for the covariates FEV1, MMRC, and body mass index. Data are quoted as mean (±SD) and the level of significance was set at P < 0.05.
Demographic and clinical characteristics, quality of sleep, and health-related quality of life of 30 patients with stable COPD
65.6 ± 8.9
24.09 ± 4.1
Smoking history (pack-years)
47.83 ± 32.04
52.11 ± 9.85
PSQI (global score)
7.37 ± 3.6
SGRQ total score
46.28 ± 20.35
49.28 ± 21.77
54.8 ± 27.88
40.47 ± 20.87
Correlation between health-related quality of life, as measured by the SGRQ, and quality of sleep, degree of airflow obstruction, severity of dyspnea, smoking history, functional exercise capacity, and body mass index
Quality of life
Smoking history (pack-years)
SGRQ symptoms domain
Smoking history (pack-years)
SGRQ activity domain
Smoking history (pack-years)
SGRQ impact domain
Smoking history (pack-years)
Results of the stepwise multiple regression analyses of 30 patients with the SGRQ total score and impact as the dependent variable
SGRQ total score
SGRQ impact score
Our results show that quality of sleep has a major impact on HRQL in COPD. The “impact” domain of the SGRQ is the most affected by impaired sleep in these patients. This domain measures the overall impact of the disease in social and professional life and in the psychological condition of the patient .
Almost two-thirds of our patients with moderate-to-very severe COPD had poor quality sleep. Recently, Lewis and coworkers (2008) in a study of 59 patients with moderate-to-severe COPD found that 61% had poor quality sleep (PSQI > 5) . Although it is generally accepted that sleep disruption is a common feature of COPD [8, 12], the actual impact of poor sleep on quality of life has, to our knowledge, not been systematically investigated in this disease. Van Manen and coworkers (2001) evaluated the added value of 23 common diseases in predicting HRQL on a group of patients with mild-to-severe COPD from general practice. They used the Short-Form 36 (SF-36) to assess HRQL and a questionnaire was used to look for the presence of comorbidity. Those investigators found that all domains of the SF-36 were best predicted by the presence of three or more comorbid diseases. When individual diseases were investigated, only insomnia seemed to be related to HRQL .
A limitation of the present study is that sleep quality was assessed by the PSQI, and no objective measures of sleep were obtained. Although the PSQI has not been specifically validated for patients with COPD, it has been largely used to assess subjective quality of sleep in various clinical conditions [29, 30, 31, 32]. Sleep quality is a complex phenomenon, despite being an easily accepted clinical construct. Due to its largely subjective nature, sleep quality correlates with, but is not accurately defined by, sleep laboratory measures. It has been reported that subjective criteria are superior to polysomnography in differentiating insomniacs from control subjects .
Impaired sleep in COPD has been attributed to multiple factors, including nocturnal hypoxemia, cough and dyspnea, use of medication, and the effects of ageing and comorbidities. Sleep-related hypoxemia is usually more prominent during rapid eye movement (REM) sleep, and increased hypoventilation is considered the major mechanism for this abnormality . McKeon and coworkers (1989) studied 23 consecutive patients with COPD (aged 42–74 years; FEV1 = 0.81 ± 0.32 l) and concluded that supplemental oxygen, despite improving nocturnal oxygenation, does not immediately improve the quality of sleep in the laboratory in these patients .
Confirming previous reports, we found that HRQL is associated with the degree of dyspnea [26, 28, 36], severity of airflow limitation, as assessed by FEV1 percent predicted [26, 28, 37, 38], and functional exercise capacity, as assessed by the Six-Minute Walk Test [7, 26, 36]. Previously, the degree of dyspnea has been found to correlate with HRQL more strongly than the FEV1, as observed in our subjects [36, 39]. Smoking history was not significantly associated with SGRQ total score, although there was a correlation with its “symptom” domain score. Recently, it was reported that the smoking status does not significantly affect the SGRQ . We were unable to demonstrate a significant correlation between body mass index and HRQL, contrary to previous reports .
Our study shows that poor quality of sleep is a major determinant of HRQL in COPD. Adequate diagnosis and management of sleep abnormalities could lead to a great improvement in the overall sense of well being in the lives of patients with COPD.
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