title: Sleep-disordered Breathing in Cardiac Rehabilitation: Prevalence, Predictors, and Influence on the Six-Minute Walk Test.
abstract: BACKGROUND
  Identification of non-traditional risk factors is an important component of cardiac rehabilitation (CR). However, the prevalence and predictors of sleep-disordered breathing (SDB) and its influence on exercise performance in patients attending CR remain poorly described.
  
  
  METHODS
  Patients enrolled in a national CR centre were eligible for a comprehensive SDB screening program. Screening questionnaires for SDB, overnight sleep study, and the 6-minute walk test (6MWT) were conducted.
  
  
  RESULTS
  We recruited 332 patients (mean age 62±10 years, 62.4% male) attending CR for primary (29.2%) or secondary (70.8%) prevention, of which 209 successfully completed the overnight sleep study. Sleep-disordered breathing group patients (n=68, 32.5%) were older and had a higher body mass index (BMI) and neck and waist circumferences than the non-SDB group patients. After adjusting for neck and waist circumference, age (OR=1.06; 95% CI 1.02-1.10; p=0.001) and BMI (OR=1.19; 95% CI 1.10-1.30; p<0.001) remained independent predictors of SDB. A high risk of SDB based on the Berlin Questionnaire (43.4% versus 35.5%, p=0.277) or STOP-BANG questionnaire (63.2% versus 53.2%, p=0.170) and excessive daytime sleepiness (Epworth Sleepiness Scale >10, 23.9% versus 17.7%, p=0.297) were similar between the groups. The 6MWT scores were significantly lower in the SDB than non-SDB group (mean difference -32 m; 95% CI -57-7; p=0.013). The relationship was no longer significant after adjusting for age, sex, and waist circumference.
  
  
  CONCLUSIONS
  Sleep-disordered breathing is prevalent in CR patients and is independently predicted by ageing and obesity. The association between SDB and poorer exercise performance may be explained by age, sex, and waist circumference.
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Germaine
authors.initials: G
authors.lastname: Loo
authors.affiliation: Department of Medicine, Jurong General Hospital, Jurong Health, Singapore.
authors.forename: Ai-Ping
authors.initials: AP
authors.lastname: Chua
authors.affiliation: Singapore Heart Foundation, Singapore.
authors.forename: Hung-Yong
authors.initials: HY
authors.lastname: Tay
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore.
authors.forename: Ruth
authors.initials: R
authors.lastname: Poh
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
authors.forename: Bee-Choo
authors.initials: BC
authors.lastname: Tai
authors.affiliation: Department of Cardiology, National University Heart Centre Singapore, Singapore; Yong Loo Lin School of Medicine, National University of Singapore, Singapore. Electronic address: mdclchr@nus.edu.sg.
authors.forename: Chi-Hang
authors.initials: CH
authors.lastname: Lee
mesh_terms: D000368:Aged; D000072038:Cardiac Rehabilitation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012119:Respiration; D012307:Risk Factors; D012893:Sleep Wake Disorders / Q000453:epidemiology / Q000503:physiopathology / Q000534:rehabilitation; D000070857:Walk Test
keywords: Cardiology; Exercise performance; Predictors; Rehabilitation; Screening; Sleep