Systematic literature review of patient-reported outcome measures used in assessment and measurement of sleep disorders in chronic obstructive pulmonary disease

Figures & data

Table 1 Summary of the occurrence of common sleep disorders in COPD populations

Sleep disorder	Author	Occurrence in COPD
Insomnia (chronic sleep disturbance with impaired daytime functioning)	Budhiraja et al^Citation11	27%
Excessive sleepiness	Ali Zohal et al^Citation12	35%
Restless legs syndrome	Kaplan et al^Citation8	29%
Obstructive sleep apnea	McNicholas^Citation13	1%

Abbreviation: COPD, chronic obstructive pulmonary disease.

Table 2 Number of papers found and excluded or included in the review

Outcome measures	SCOPUS references (n)	References to COPD (n)	Excluded	Reviewed
COPD and Asthma Sleep Impact Scale^Citation25	8	6	5	1
Basic Nordic Sleep Questionnaire^Citation26	200	6	5	1
Berlin Questionnaire^Citation27	720	22	21	1
Epworth Sleepiness Scale^Citation28	4,720	153	133	20
International Restless Legs Syndrome^Citation29	548	4	3	1
Pittsburgh Sleep Quality Index^Citation30	4,144	71	52	19
Sleep Disorders Questionnaire^Citation31	262	8	7	1
Total	10,602	270	226	44

Abbreviation: COPD, chronic obstructive pulmonary disease.

Figure 1 Flow diagram showing the total number of studies screened, assessed for eligibility and included in the review.

Abbreviation: COPD, chronic obstructive pulmonary disease.

Table 3 Psychometric properties of COPD and Asthma Sleep Impact Scale

Conceptual and measurement model
Rationale for deriving scale scores	Items generated from focus group discussions in UK and US samples
Scale structure	15 item scale scored 1= never to 5= very often – transferred onto a 0–100 scale
Variability	Mean score COPD patients (n=112) 47.1±24.0
Reliability
Inter-intra observer repeatability	Not tested
Item correlations	9 items highly correlated r>0.75; 6 items indicating item redundancy
Internal consistency	Cronbach’s alpha 0.91
Stability over time	2-week test-retest repeatability ICC 0.84
Validity
Convergent validity	Correlated with SGRQ r=0.68 P=0.0001 Correlations between CASIS scores and number of bad days r=0.61, overall health status (0.5), and higher mean CASIS scores in COPD patients receiving oxygen treatment (51.4 vs 43.3) Correlates with living with COPD questionnaire 0.58
Responsiveness to change	Not tested

Abbreviations: COPD, chronic obstructive pulmonary disease; CASIS, COPD and Asthma Sleep Impact Scale; ICC, intra-class correlation coefficient; SGRQ, St George’s Respiratory Questionnaire.

Table 4 Summary of studies that used the Epworth Sleepiness Scale

Reference	Study focus	COPD study sample	Measures of COPD severity	ESS (mean ± SD/median and range)	ESS >10 (%)	Associations with ESS score
Aras et al^Citation36	RLS symptoms in COPD patients during an exacerbation period	22 male inpatients	GOLD stage IV: FEV1 30% or 50% plus chronic respiratory failure; mean FEV1 39.4%±9.97%	Not reported	Not reported	Free thyroxine values negatively correlated with ESS (rs =−0.481 P=0.043)
Bednarek et al^Citation46	Prevalence of SDB and COPD in a representative urban sample aged 41–72 years	676 participants from the electoral register	FEV1/FEV <0.7, 10.6%	6.4±3.9	Not reported	Mean ESS in people with excessive sleep disorder: men 12.6±2.0 versus women 12.9±2.4 (P>0.05)
Budhiraja et al^Citation11	Prevalence of insomnia in patients with COPD, and characteristics associated with insomnia in COPD patients	183 hospital patients	GOLD stage I, 3%; stage II, 39%; stage III, 29%; stage IV, 28%; % predicted post-bronchodilator FEV 45.9±18.6. FEV1/FVC ratio 49.6±12.5	Not reported	Not reported	Daytime sleepiness (ESS >10) greater in patients with insomnia (36.5% versus 14.6%, P=0.004)
Cavalcante et al^Citation35	Occurrence and associations with RLS in a COPD population	104 hospital outpatient attenders	mMRC 0 (4.8%); 1 and 2 (48.1%); 3 (34.6%); 4 (12.5%)	6.9±5.1	20.2	No difference in mean values between patients without RLS (6.6±4) versus with RLS (7.7±6.0). ESS positively correlated with BMI (P<0.003)
De Lima et al^Citation47	Whether clinically stable COPD patients without cognitive symptoms may present with subtle cognitive impairments	30 hospital outpatients	Mean FEV1 42.1±15.9	6.7±3.7	Not reported	Not reported
Kapella et al^Citation39	Feasibility and assessment of the impact of a CBT intervention for people with COPD and insomnia	23 patients recruited from advertisements and word of mouth	FEV1/FVC ratio <70% ^Citation1	9.2±5.0	Not reported	Not reported
Karachaliou et al^Citation32	Association between OSAHS-related symptoms and physician-diagnosed asthma and COPD	1,501 primary care patients (323 with COPD)	GOLD stage I, 28.8%; stage II, 53.3%; stage III, 15.2%; stage IV, 2.8%	Not reported	Not reported	Increased odds of people with COPD having an ESS score ≥10; OR 2.04, 95% CI (1.33–3.14)
Lewis et al^Citation48	Variability of nocturnal desaturation in COPD over a 3-week period and impact the variability may have on clinical decision-making	26 stable COPD hospital outpatients	Mean post-bronchodilator FEV1 28.6%	4.1±6.2; range 0–11	Not reported	Not reported
Lewis et al^Citation49	Prevalence and clinical impact of nocturnal desaturation in a typical outpatient population with COPD	59 COPD outpatients	Mean predicted FEV1 37.2±14.9; FVC 1.9 ±0.9; FVC predicted 62.1±17.6; TB90% 38.4±34.9	5.0; range 2.0–8.0	Not reported	No significant difference between desaturators and nondesaturators (P=0.88)
Lo Coco et al^Citation33	Prevalence, severity, and associations with RLS in COPD patients	87 COPD outpatients	GOLD stage II, 42.5%; stage III, 40.2%; stage IV, 17.3%	8.98±3.89	Not reported	Significant difference in mean ESS score between COPD with RLS and controls with RLS 11.81±1.09 versus 8.62±3.66 (P=0.009)
McNicholas et al^Citation50	Placebo-controlled, double-blind trial of severe, stable COPD patients comparing the effect of tiotropium on sleeping oxygen saturation	56 hospital outpatients	FEV1 <65% predicted; FEV1/FVC <70%; Awake paO2 <9.98 kPa (75 mmHg) prior to entry	5.7 in intervention group versus 6.4 in control group	Not reported	None reported
Nunes et al^Citation51	Sleep quality in COPD patients at home using actigraphy and association between sleep quality and daytime somnolence	26 hospital patients	GOLD stage II, 50%; stage III, 3 8.5%; stage IV, 11.5%; FEV1% predicted 47.62±16.04	8.27±4.4	61.5	No difference between COPD and controls (8.27±4.4 versus 6.07±3.9, P=0.12). No difference in proportion with ESS ≥10 COPD (61% versus controls 86%; P=0.09)
Oliveira et al^Citation52	Evaluate accuracy of a portable monitoring device in detection of OSA in patients with COPD	26 hospital outpatients	FEV1/FVC 0.6±0.10; FEV1 (%) post-BD 55±0.08; FVC (%) post-BD 77±8.9	10.5±4.1	Not reported	None reported
Scharf et al^Citation53	Correlation between disturbed sleep and COPD	180 pulmonary clinic patients	GOLD stage I, 10.6%; stage II, 3 0.6%; stage III, 46.1%; stage IV, 12.8%. FEV1 % predicted 47.6±15.2	7.0±4.8	24.7	No associations with ESS and other symptoms
Soriano et al^Citation54	Natural history of the most common respiratory chronic conditions, including COPD and OSA	500 primary care patients	GOLD stage I (27%); stage II (58%); stage III (15%)	Not reported	29.2	None reported
Stege et al^Citation34	Effects of long-term use of a benzodiazepine (temazepam) on breathing, dyspnea, and gas exchange during sleep, sleep quality, and sleepiness	14 respiratory clinic patients	FEV1 % predicted 33.5±9.2; FEV1/FVC% 32.7±13.0; FEV1 (L) 0.99 ±0.30	6.0±4.0	50.0	No difference between temazepam (5.0±4.0) and controls (6.0±4.0; P=0.13)
Toraldo et al^Citation55	Pattern of daytime clinical variables that distinguish desaturator patients from nondesaturator COPD patients using cluster analysis	51 consecutive hospital patients	FEV1 % predicted 53 (SE 1.5); FEV1/FVC ratio 37.6 (SE 0.5); FVC % predicted 81.5 (SE 1.2); AHI 2.8 (SE 0.1). Daytime paO2 values 60–70 mmHg	3.9 (SE ±0.1)	None	No difference between desaturators and nondesaturators, both 3.8 (± SE 0.4)
Toraldo et al^Citation56	Effect of regular use of nCPAP in patients with overlap syndrome	12 hospital outpatients	FEV1 (%) 60.3±1.3; FEV1/FVC (%) 69.5±0.7	16.58±0.86	Not reported	Reductions in ESS score between baseline and 3 months (16.6±0.86 versus 11.7±0.46; P=0.0001); 3 months and 12 months (11.7±0.46 versus 5.7±0.4; P=0.0001), and 12 and 24 months (5.67±0.4 versus 4.75±0.49; P=0.033)
Trauer et al^Citation57	Relationship between 24-hour oximetry and resting partial pressure of oxygen	35 community-living patients	GOLD stage II, 20%; stage III, 4 9%; and stage IV, 31%; FEV1 % predicted 37.5±13.2	Median 4 (IQR 2, 8)	Not reported	Negative correlation between ESS and time below 90% SpO2 −24 hours −0.18 (0.29); waking hours −0.13 (0.46); sleeping hours −0.17 (0.24)
Tsolaki et al^Citation58	Effect of non-invasive ventilation as an additional treatment for severe COPD patients	24 hospital outpatients	FEV1 (%) 34.7±11.3; FVC (%) 50.8±15.7	9.2±3.7	Not reported	Significant reductions in ESS score between baseline and 1 month in patients who received noninvasive ventilation (10.3 versus 4.9; P=0.0001). ESS was an independent predictor of the Mental Component Score of the SF-36 (P<0.001)

Abbreviations: AHI, apnea-hypopnea index; BD, bronchodilator; BMI, body mass index; CI, confidence interval; OR, odds ratio; COPD, chronic obstructive pulmonary disease; RLS, restless legs syndrome; SDB, sleep-disordered breathing; CBT, cognitive behavioral therapy; OSAHS, obstructive sleep apnea/hypopnea syndrome; mMRC, modified Medical Research Council Dyspnoea scale; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; GOLD, Global initiative for chronic Obstructive Lung Disease; SpO₂, oxygen saturation; ESS, Epworth Sleepiness Scale; SE, standard error; pO₂, oxygen partial pressure; paO₂, arterial oxygen tension; IQR, interquartile range; TB90%, time spent with saturation below 90%; SF-36, Short-Form 36 Health Survey; nCPAP, nasal continuous positive airway pressure; SD, standard deviation; OSA, obstructive sleep apnea.

Table 5 Summary of papers that used the Pittsburgh Sleep Quality Index

Reference	Study focus	COPD study sample	Measures of COPD severity	PSQI (mean ± SD)	PSQI >5 (%)	Associations with PSQI score
Akinci and Yildirim^Citation37	Associations between quality of life and breathlessness, fatigue, sleep quality, and FEV1 % predicted in patients with COPD	79 stable hospital outpatients	FEV1 (%) 51.5±16.1 (range 18–80); FEV1/FVC (%) 63.4±9.3 (range 34.6–70.2)	7.1±3.9	Not reported	Correlations between SGRQ and PSQI total scores (0.428, P<0.001); daytime dysfunction (0.400, P<0.001); sleep disturbance (0.481, P<0.001), habitual sleep efficiency (0.271, P<0.05); sleep latency (0.309, P<0.01); subjective sleep quality (0.421, P<0.001) but not sleep duration or use of sleep medication
Aras et al^Citation36	RLS symptoms in COPD patients during an exacerbation	22 male inpatients	GOLD stage IV: FEV1 30% or 50%, plus chronic respiratory failure; mean FEV1 39.4%±9.97%	6.0±3.81	Not reported	PSQI score was higher in patients with RLS symptoms (7.76±3.74) compared with patients without RLS symptoms (3.44±2.18; P<0.05)
Cavalcante et al^Citation35	Occurrence and associations with RLS in a COPD population	104 hospital outpatients	mMRC 0 (4.8%); 1 and 2 (48.1%); 3 (34.6%); 4 (12.5%)	7.6 ±4.3	59.6%	PSQI correlated with Fatigue Severity Scale (P<0.005). Patients with RLS had poor quality sleep (P<0.002). PSQI score correlated with mMRC (P<0.005); higher BMI (P=0.01); serum ferritin (P=0.005). mMRC and creatinine influenced PSQI sleep quality
Hynninen et al^Citation38	Factors affecting health status in COPD patients with comorbid anxiety or depression	58 hospital outpatients/responders to newspaper advertisements	29 (50%) had mild-moderate COPD and 29 (50%) had severe/very severe COPD. Mean FEV1 53.79±23.96; 50% had FEV1 ≥50%	Men 8.1±3.6; women 9.2±3.8	Not reported	PSQI total scores not correlated with SGRQ. PSQI daytime functioning correlated with SGRQ total (0.57, P≤0.001); symptoms (0.374, P≤0.01); activity (0.364, P<0.01); impact (0.56, P≤0.001). PSQI sleep disturbance correlated with SGRQ total (0.404 P≤0.01); symptoms (0.378, P<0.01), and impact (0.409, P≤0.01)
Hynninen et al^Citation40	Effect of CBT on anxiety and depression compared with usual care and associations with age and sex	25 hospital patients/respondents to newspaper advertisements	FEV1 (%) 59.8±21.1	9.8±4.4	Not reported	No significant difference between pre- and post-treatment sleep quality or at 6 months follow-up as a result of the CBT intervention
Ito et al^Citation59	Prevalence and associations between depression and sleep disorders in COPD patients and whether depression and sleep disorders are risk factors for exacerbations, hospitalization, and mortality due to COPD	85 hospital patients	GOLD stage I, 21.2%; stage II, 38.8%; stage III, 28.2%; stage IV, 11.8%. Mean post-BD FEV1 1.6±0.7 L; FVC 3.3±0.9 L; FEV1/FVC % 47.1±13.9	5.5±3.3	43.5%	PSQI scores higher in COPD versus non-COPD patients (5.5±3.3 versus 4.1±2.6; P=0.0076). An increase in RR in patients with COPD versus non-COPD controls (RR 1.82, 95% CI 1.03–3.22; P=0.042). A weak correlation between PSQI scores and CESD scores (r=0.22; P=0.044). Annual number of exacerbations was higher in COPD patients with depression (3.3±3.5) compared with patients having sleep problems alone
Kapella et al^Citation39	Feasibility and impact of a CBT intervention for people with COPD and insomnia	23 patients recruited from advertisements and word of mouth	FEV1/FVC ratio <70% predicted. Mean FEV1 % predicted 62±18; mean FEV1/FVC 50±10	11.0±3.6	Not reported	PSQI scores reduced following COPD treatment (11.0±3.6 versus 6.5±3.4; P=0.0002). Within group effect size 1.02
Lewis et al^Citation48	Variability of nocturnal desaturation in COPD as measured by OPO and the impact the variability may have on clinical decision-making	26 stable hospital outpatients	Mean FEV1 % 28.6±10.6	Not reported	Not reported	No significant association between PSQI and resting pO2 (P=0.89)
Lewis et al^Citation49	Prevalence and clinical impact of nocturnal desaturation in COPD outpatients	59 consecutive outpatient and pulmonary rehabilitation patients	FEV1 <60% predicted and FEV1/FVC <70% predicted; mean FEV1 % predicted 37.2±14.9; mean FVC % predicted 37.2±14.9; mean FEV1 0.9±0.4 L	Median 7 (IQR 4, 11)	61%	No significant difference in PSQI total score between desaturators and nondesaturators (8 [IQR 4, 11] versus 7 [IQR 4, 11]; P=0.63)
Nisbet et al^Citation60	Occurrence of overnight desaturation; if resting oxygen saturation predicts overnight desaturation and whether desaturation correlates with HRQoL and sleep quality	38 consecutive outpatient and pulmonary rehabilitation patients	FEV1 <60% predicted and FEV1/FVC ratio <70% predicted. Mean FEV1 (L) 0.8±0.37; mean FVC (L) 2.1±0.65	7.1±3.99	Not reported	No significant difference in PSQI total score between desaturators and nondesaturators (6.7±3.78 versus 7.1±3.99; P=0.82)
Nunes et al^Citation14	Impact of sleep quality on HRQoL in COPD	30 hospital COPD patients	GOLD stage II, 50.0%; stage III, 33.3%; stage IV, 16.7%; mean FEV1% predicted 48.55±17.27 FEV1/FVC % 52.11±9.85	7.37±3.6	70.0%	Significant positive correlation between PSQI total score and SGRQ total score (r=0.42; P=0.02) and impact domain score (r=0.47; P=0.01); global PSQI score was a predictor of SGRQ total score (adjusted r^2 0.373, P=0.001) and SGRQ impact score (adjusted r^2 0.329, P=0.001)
Nunes et al^Citation51	Sleep quality in COPD patients at home using actigraphy and association between sleep quality and daytime somnolence	26 stable respiratory outpatients	GOLD stage II, 50%; stage III, 38.5%; stage IV, 11.5%; mean FEV1 % predicted 47.62±16.04	6.96±3.5	57.7%	Mean PSQI total score significantly worse in COPD than in controls (6.96±3.5 versus 4.8±2.4; P=0.043); no significant correlation between PSQI and actigraphy variables
Oh et al^Citation61	Characteristics of fatigue in patients with chronic lung disease	128 hospital patients, 80% of whom had COPD, 13% had bronchiectasis, and 4% had interstitial lung disease	Mean FEV1 64.5±28.8	Mean score 1.9±0.7 (range 0–3)	Not reported	In the regression analysis, sleep quality was not independently associated with fatigue; standardized β coefficient 0.02: t=0.25 P=0.8
Reishtein^Citation62	Impact of dyspnea, fatigue, and sleep difficulty on functional performance	30 home and 47 clinic patients	FEV1 <60% predicted; mean FEV1 41.2±11.79	8.69±4.33	Not reported	Weak non-significant correlation between sleep difficulty and functional performance (−0.17, P>0.05)
Scharf et al^Citation53	Extent of sleep problems in COPD; predictors of HRQoL and the contribution of sleep disturbance to HRQoL	180 pulmonary clinic patients	GOLD stage I, 10.6%; stage II, 30.6%; stage III, 46.1%; stage IV, 12.8%; mean FVC% predicted 64.7±16.3; FEV1/FVC % 57.5 ±12.3; FEV1 (L) 1.24±0.50 FVC (L) 2.17±0.70	11.0±5.4	77.7	HRQoL and SGRQ scores significantly associated with PSQI (adjusted r^2 HRQoL 0.24 and SGRQ 0.23 both P<0.0001). HRQoL and SGRQ were independently associated with PSQI score (r^2 0.06, P=0.0002 and r^2 0.05, P=0.0005, respectively)
Suh et al^Citation63	Effect of anxiety on heart rate variability, depression, and sleep in COPD	30 COPD pulmonary rehabilitation patients and 30 non-COPD controls	COPD patients with anxiety PSQI 12.0 (4.06) versus healthy patients with anxiety 7.8 (4.02) GOLD criteria: stage I, 13.3%; stage 2, 43.3%; stage 3, 30%; stage 4, 13.3%	12.0±4.02	Not reported	COPD patients with anxiety had poorer sleep quality than non-COPD controls with anxiety (12.0 versus 7.8; t=2.74, P=0.01). The COPD only group had significantly lower PSQI scores than COPD anxiety group (6.9 versus 12.0; t=−3.49, P=0.002)
Soler et al^Citation64	PR improves sleep quality in chronic lung disease	46 obstructive 13 restrictive 5 mixed	FEV1 % predictive Obstructive 44.2 (12.3) Restrictive 82.2 (6.8) Mixed 62.7 (11.5)	6.6 (3.9) obstructive 8.2 (3.7) restrictive 6.6 (4.7) mixed	58	Poor sleep quality was reported by 58% of patients before PR and 47% after PR (P<0.001)
Halvani et al^Citation65	Evaluation of exogenous melatonin administration in improvement of sleep quality in patients with COPD	48 stable hospital patients	Confirmed diagnosis of GOLD stage II, GOLD stage IV	Intervention 11.63±3.96 Controls 10.66±2.48	Not reported	Melatonin group Baseline 11.63±3.96; follow-up 8.7±4.15 (P=0.002). Placebo group Baseline 10.66±2.48; follow-up 10.11±2.66 (P=0.065)
Bhatt et al^Citation66	NPPV in subjects with stable COPD	15 stable hospital patients who received NPPV versus 12 controls	FEV1/FVC ratio <0.70 PaCO2 <52 mmHg	3.7 (3.0) NPPV 6.1 (3.2) Controls	Not reported	Results after 6 months NPPV 3.7 (3.0) versus 3.4 (2.0; P=0.2) Controls 6.1 (3.3) vs 5.7 (3.2) P=0.77

Abbreviations: BMI, body mass index; CI, confidence interval; COPD, chronic obstructive pulmonary disease; RLS, restless legs syndrome; mMRC, modified Medical Research Council Dyspnea scale; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; GOLD, Global initiative for chronic Obstructive Lung Disease; IQR, interquartile range; nCPAP, nasal continuous positive airway pressure; PR, pulmonary rehabilitation; RR, relative risk; BD, bronchodilator; CBT, cognitive behavioral therapy; SD, standard deviation; NPPV, noninvasive positive pressure ventilation; PaCO₂, partial pressure of carbon dioxide; HRQoL, health-related quality of life; PSQI, Pittsburgh Sleep Quality Index; OPO, overnight pulse oximetry; SGRQ, St George’s Respiratory Questionnaire; CESD, Center for Epidemiologic Studies-Depression.

Table 6 Summary of articles using generic sleep measures

Outcome measure and authors	Study focus	COPD study sample	Measures of COPD severity	Outcome reported (mean ± SD)	Associations
Berlin Questionnaire Cavalcante et al^Citation35	Occurrence and associations with RLS in a COPD population	104 hospital outpatient attenders	mMRC 0 (4.8%); 1 and 2 (48.1%); 3 (34.6%); 4 (12.5%)	30 (29%) of patients had a high probability of OSA	Risk of OSA not associated with RLS (P=0.25)
BNSQ Saaresranta et al^Citation41	Sleep quality and excessive daytime sleepiness in ambulatory patients with moderate to severe COPD	15 consecutive female clinic outpatients	FEV1 predicted <65% of daytime hypoxemia (PaO2 <10.0 kPa) and/or hypercapnia (PaCO2 >6.0 kPa); FEV1 % 36±12; FVC % 63±14; FEV1 (L) 0.73±0.45 (range 0.25–1.8); FVC (L) 1.3±0.45	BNSQ 9.9±3.0	BNSQ score higher than controls (9.9±3.0 versus 7.6±3.2; P=0.025) and correlated with insulin levels (r=0.59, P=0.027) and body movements (r=0.52, P=0.047)
IRLSG Lo Coco et al^Citation33	Prevalence, severity, and associations with RLS in COPD patients	87 COPD outpatients	GOLD stage II, 42.5%; stage III, 40.2%; stage IV, 17.3%	IRLSG score 32 (36.8%)	IRLSG score in COPD patients 20.5±2.8 versus 18.0±3.5 in controls (P=0.016); moderate correlation between ESS and IRLSG score (Spearman correlation 0.489, P=0.01)
SDQ Valipour et al^Citation42	Differences in symptoms and polysomnographic parameters in COPD patients	52 consecutive hospital outpatients	FEV1% predicted 60±10; FVC % predicted 93±12; FEV1/FVC 60±8	SA 36.0±6.9 PLM 25.2±7.1 PSY 18.0±6.0 Narcolepsy 22.1±5.5	COPD patients had higher scores in PLM (25.2±7.1 versus 21.1±6.2, P=0.0003) and PSY (18.0±6.0 versus 15.3±5.0, P=0.035) Minimum SaO2 had an independent effect on SDQ subscale scores: SA (P=0.045), PLM (P=0.051), PSY (P=0.037), and narcolepsy (P=0.053) Mean overnight SaO2 was a significant predictor of PSY score (P=0.015)

Abbreviations: BNSQ, Basic Nordic Sleep Questionnaire; COPD, chronic obstructive pulmonary disease; PLM, periodic limb movement; SDQ, Sleep Disorders Questionnaire; PSY, psychiatric sleep disorder; RLS, restless leg syndrome; IRLSG, International Restless Leg Study Group; SA, sleep apnea; FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; OSA, obstructive sleep apnea; mMRC, modified Medical Research Council Dyspnea scale; GOLD, Global initiative for chronic Obstructive Lung Disease; SaO₂, arterial oxygen saturation; ESS, Epworth Sleepiness Scale; PaCO₂, partial pressure of carbon dioxide; PaO₂; hypercapnia PaCO.

Figure 2 Point estimates and variability in studies that used the ESS.

Abbreviation: ESS, Epworth Sleepiness Scale.

Figure 3 Point estimates and variability in studies that used the PSQI.

Abbreviation: PSQI, Pittsburgh Sleep Quality Index.

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