SLEEP DISORDERED BREATHING

Cardiovascular risk markers in obstructive sleep apnoea syndrome and correlation with obesity

Silke Ryan^1,2, Geraldine M Nolan¹, Evelyn Hannigan³, Sean Cunningham⁴, Cormac Taylor², Walter T McNicholas^1,2

¹ Sleep Research Laboratory, St Vincent’s University Hospital, Dublin, Ireland
² School of Medicine and Medical Science, The Conway Institute, University College Dublin, Ireland
³ Department of Immunology, St Vincent’s University Hospital, Dublin, Ireland
⁴ Department of Biochemistry, St Vincent’s University Hospital, Dublin, Ireland

Correspondence to:
Professor W T McNicholas
Deprtment of Respiratory Medicine, St Vincent’s University Hospital, Elm Park, Dublin 4, Ireland; walter.mcnicholas{at}ucd.ie

Background: High C-reactive protein (CRP) and homocysteine levels are risk factors for cardiovascular disease. Some, but not all, previous studies have reported increased levels of CRP and homocysteine in patients with obstructive sleep apnoea syndrome (OSAS). A study was undertaken to investigate the levels of these factors in carefully selected patients with OSAS and matched normal controls.

Methods: CRP and homocysteine levels were measured in 110 subjects following polysomnography (PSG). Non-OSAS patients (group 1) were compared with two patient groups (mild/moderate OSAS (group 2) and severe OSAS (group 3)) group-matched for body mass index (BMI), and a fourth group of patients with severe OSAS who were more obese (group 4). All were free of other disease and similar in age, smoking habits and cholesterol levels. 50 suitable patients were commenced on continuous positive airway pressure (CPAP) treatment after PSG and 49 were reassessed 6 weeks later.

Results: CRP levels were similar in groups 1, 2 and 3 (median (interquartile range (IQR)) 1.11 (0.76–2.11) mg/l vs 1.82 (1.20–3.71) mg/l vs 2.20 (1.16–3.59) mg/l; p = 0.727, Kruskal-Wallis test), but were significantly higher in group 4 than in the other groups (5.36 (2.42–9.17) mg/l, p<0.05 by individual group comparisons). In multivariate analysis of all subjects, BMI was an independent predictor for CRP levels (ß = 0.221; p = 0.006) but apnoea-hypopnoea index and other measures of OSAS were not. There was no difference in homocysteine levels between all four groups (p = 0.1). CPAP did not alter CRP (2.29 (1.32–4.10) vs 2.84 (1.13–5.40) mg/l; p = 0.145) or homocysteine levels (8.49 (3.66) vs 9.90 (4.72) µmol/l; p = 0.381).

Conclusion: CRP and homocysteine levels are not associated with OSAS severity in men but CRP is independently associated with obesity.

Abbreviations: AHI, apnoea-hypopnoea index; BMI, body mass index; CPAP, continuous positive airway pressure; CRP, C-reactive protein; DI, desaturation index; ESS, Epworth Sleepiness Scale; OSAS, obstructive sleep apnoea syndrome; PSG, polysomnography; TNF, tumour necrosis factor ; TST, total sleep time

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