[Long term effect of autoadjusting positive airway pressure on C-reactive protein and interleukin-6 in men with obstructive sleep apnoea syndrome].

BACKGROUND AND OBJECTIVES: Obstructive sleep apnoea (OSA) has been increasingly linked to cardiovascular disease. Inflammatory processes associated with OSA may contribute to this morbidity. Some studies have reported serum levels of high sensitivity C-reactive protein (hs-CRP) and interleukin-6 (IL-6) to be increased in these patients.

PRIMARY OBJECTIVE: investigate the impact of short and long-term autoadjusting positive airway pressure (APAP) therapy on IL-6 and hs-CRP serum levels in patients with moderate to severe obstructive sleep apnoea. Secundary Objective: evaluate the basal hs-CRP and IL-6 levels in OSA patients and its possible relation to OSA severity, independently of confounders and compare the hs-CRP levels in OSA patients with those in community controls.

PATIENTS AND METHODS: This is a prospective study including 98 male patients with moderate to severe OSA confirmed by domiciliary sleep study. Malignancy and chronic inflammatory diseases were exclusion criteria. hs-CRP and IL-6 serum levels were evaluated before APAP, 9 days and 6 months after therapy. Community controls (n=103) were selected using random digit dialing, and matched by age and body mass index (BMI) for comparison of hs-CRP levels at baseline.

RESULTS: The studied population had a mean age of 55.3+/-10.7 years, mean BMI 33.2+/-5.0kg/m(2), mean apnoea-hypopnoea index 51.7+/-21.3/h and mean desaturation index 86.3+/-5.3/h. The APAP compliance was good: 91.27%+/-20.45 days usage and 5.76+/-1.59h/night of usage. Mean basal hs-CRP and IL-6 serum values were 0.52+/-0.53microg/l and 17.7+/-22.5microg/l, respectively. CRP levels at baseline correlated significantly with apnoea-hypopnoea index, desaturation index and minimum nocturnal oxygen saturation. IL-6 levels at baseline correlated significantly and negatively with minimum nocturnal oxygen saturation. When adjusting for confounding factors found in this study, all these relations lost significance. CRP is significantly increased in patients when compared to controls (p=0.002) and when considering hs-CRP cardiovascular risk stratified categories, cases had significantly more patients at high risk of cardiovascular events than controls (p=0.002). After adjustment for BMI and arterial hypertension, cases had an almost twofold moderate risk of cardiovascular events and more than a twofold severe risk of cardiovascular events when compared to controls. We found no significant difference between hs-CRP and IL-6 concentrations pre-treatment and in two moments post-treatment (9 days and 6 months) (CRP: p=0.720 and p=0.387, respectively; IL-6: p=0.266 and p=0.238, respectively).

CONCLUSIONS: OSA is associated with a low-grade inflammatory process; hs-CRP serum levels are elevated in OSA patients when comparing to community controls, independently of age and BMI and the former have a significantly higher risk of cardiovascular events when compared to the latter. There was no significant decrease of both inflammatory mediators (hs-CRP, IL-6) after short and long-term APAP therapy.