Lung

, Volume 187, Issue 3, pp 159–163 | Cite as

Impaired Sleep Reduces Quality of Life in Chronic Obstructive Pulmonary Disease

  • Deuzilane Muniz Nunes
  • Rosa Maria Salani Mota
  • Osvaldo Leite de Pontes Neto
  • Eanes Delgado Barros Pereira
  • Veralice Meireles Sales de Bruin
  • Pedro Felipe Carvalhedo de Bruin
Article

Abstract

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.

Keywords

Chronic obstructive pulmonary disease Quality of life Quality of sleep 

Introduction

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 [1]. In adults aged 40 years and older, the prevalence of COPD may reach 9–10% [2]. Deaths attributed or associated with COPD have been increasing steadily during the past 20 years [3].

Chronic obstructive pulmonary disease imposes a significant burden in terms of disability and impaired quality of life [2]. 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 [4]. Health-related quality of life is considered a major outcome for studies on COPD [5]. Poor HRQL is an important predictor for subsequent hospitalization and mortality in these patients [6]. 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 [10]. 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 [13]. 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 [17], 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 [18]. 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 [21]. Measurements included FEV1, FVC, and FEV1/FVC ratio, and the results were compared with previously published normal values [22]. 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 [23]. 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 [24]. 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 Analysis

Statistical analyses were conducted with Statistical Package for Social Sciences version 15.0 [25]. 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.

Results

Thirty patients (18 males) aged 46 to 79 years (mean ± SD = 65.6 ± 8.9 years) were included in the study. Severity of disease was classified as moderate in 15 subjects (50%), severe in 10 (33.3%), and very severe in 5 (16.7%). Clinical and anthropometric characteristics are summarized in Table 1.
Table 1

Demographic and clinical characteristics, quality of sleep, and health-related quality of life of 30 patients with stable COPD

 

Patients

Age (yr)

65.6 ± 8.9

Men/women

18/12

BMI (kg/m2)

24.09 ± 4.1

Smoking history (pack-years)

47.83 ± 32.04

MMRC (points)

 

    0–1

19

    2–3

11

6MWD (m)

344.14 (±69.35)

COPD (GOLD)

 

    Moderate

15

    Severe

10

    Very severe

5

FEV1% predicted

48.55% (±17.27)

FEV1% FVC

52.11 ± 9.85

PSQI (global score)

7.37 ± 3.6

SGRQ total score

46.28 ± 20.35

    Symptoms domain

49.28 ± 21.77

    Activity domain

54.8 ± 27.88

    Impact domain

40.47 ± 20.87

BMI  body mass index, MMRC Modified Medical Research Council, 6MWD Six-Minute Walk Distance, FEV1 Forced Expiratory volume in 1 second, FVC Forced Vital Capacity, PSQI Pittsburgh Sleep Quality Index, SGRQ Saint George’s Respiratory Questionnaire

Health-related quality of life, as measured by SGRQ, ranged from 1.46 to 83.22. Poor quality of sleep (PSQI > 5) was present in 21 patients (70%). A positive correlation between the PSQI global score and the SGRQ total score (r = 0.42; P = 0.02) and impact domain score (r = 0.47; P < 0.01) was found. The SGRQ total score also was correlated with post-bronchodilator FEV1% predicted (r = −0.37; P = 0.04) and severity of dyspnea, as assessed by Modified Medical Research Council scale (r = 0.56; P < 0.01). The FEV1% predicted was correlated with SGRQ symptom domain score (r = −0.39; P = 0.03) and activity domain score (r = −0.39; P = 0.03). As for severity of dyspnea, there also was a correlation with SGRQ activity domain score (r = 0.65; P < 0.001) and impact domain score (r = 0.43; P = 0.02). There was a positive correlation between number of pack-years and SGRQ symptom domain score (r = 0.39; P = 0.04). Functional exercise capacity, as evaluated by the Six-Minute Walk Distance, showed a negative correlation with SGRQ activity domain score (r = −0.38; P = 0.04; Table 2).
Table 2

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

Parameter

R

P value

SGRQ total

PSQI global

0.42

0.02

FEV1% predicted

−0.37

0.04

MMRC

0.56

<0.01

Smoking history (pack-years)

0.16

0.39

6MWD

−0.29

0.12

BMI

0.06

0.76

SGRQ symptoms domain

PSQI global

0.08

0.69

FEV1% predicted

−0.39

0.03

MMRC

0.31

0.1

Smoking history (pack-years)

0.39

0.04

6MWD

−0.05

0.79

BMI

−0.13

0.5

SGRQ activity domain

PSQI global

0.35

0.06

FEV1% predicted

−0.39

0.03

MMRC

0.65

<0.001

Smoking history (pack-years)

0.13

0.5

6MWD

−0.38

0.04

BMI

−0.02

0.93

SGRQ impact domain

PSQI global

0.47

<0.01

FEV1% predicted

−0.26

0.17

MMRC

0.43

0.02

Smoking history (pack-years)

0.07

0.7

6MWD

−0.22

0.25

BMI

0.16

0.4

SGRQ Saint George’s Respiratory Questionnaire, PSQI Pittsburgh Sleep Quality Index, FEV1 Forced Expiratory Volume in 1 second, MMRC Modified Medical Research Counci, 6MWD Six-Minute Walk Distance, BMI body mass index

Multiple regression analysis was used to identify the independent variables considered as indicators of the effect measured by the SGRQ (dependent variable). A model was built taking into account the problems of confounding factors and colinearity. The best predictors with standardized coefficients and corresponding significance are shown in Table 3. Overall, with the PSQI included in the model, 37% (adjusted R2) of the overall SGRQ variance was explained. Global PSQI score was the best predictor (partial R = 0.56) followed by FEV1% (partial R = −0.54). SGRQ impact score showed that PSQI again explained most of the variance (partial R = 0.57) followed by FEV1% (partial R = −0.44).
Table 3

Results of the stepwise multiple regression analyses of 30 patients with the SGRQ total score and impact as the dependent variable

Outcome/predictors

Coefficient

SE

P value

Partial R

Adjusted R2

SGRQ total score

(Constant)

52.582

9.833

0

  

FEV1% predicted

−0.599

0.179

0.002

−0.541

 

PSQI global

3.09

0.86

0.001

0.569

0.373

SGRQ impact score

(Constant)

39.397

10.426

0.001

  

FEV1% predicted

−0.485

0.19

0.017

−0.441

 

PSQI global

3.341

0.912

0.001

0.576

0.329

SGRQ Saint George’s Respiratory Questionnaire, FEV1 Forced Expiratory Volume in 1 s, PSQI Pittsburgh Sleep Quality Index

Discussion

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 [26].

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) [27]. 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 [28].

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 [33].

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 [34]. 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 [35].

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 [37]. We were unable to demonstrate a significant correlation between body mass index and HRQL, contrary to previous reports [7].

Conclusions

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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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Deuzilane Muniz Nunes
    • 1
  • Rosa Maria Salani Mota
    • 2
  • Osvaldo Leite de Pontes Neto
    • 1
  • Eanes Delgado Barros Pereira
    • 1
  • Veralice Meireles Sales de Bruin
    • 1
  • Pedro Felipe Carvalhedo de Bruin
    • 1
  1. 1.Department of Clinical MedicineFederal University of CearaFortalezaBrazil
  2. 2.Department of Statistics and Applied MathematicsFederal University of CearaFortalezaBrazil

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