Impact of nasal continuous positive airway pressure therapy on markers of platelet activation in patients with obstructive sleep apnea

Background: Considerable evidence implicates CD40 signaling in the pathogenesis of atheromas. Exposure to CD40 ligand induces platelet-leukocyte conjugation, a heightened expression of inflammatory cytokines, matrix-degrading enzymes, and procoagulant factors. Objectives: To investigate the association between plasma soluble CD40 ligand (sCD40L) and platelet-monocyte aggregates in patients with obstructive sleep apnea (OSA) and to determine whether treatment of OSA with nasal continuous positive airway pressure (nCPAP) alters this relationship. Methods: Twelve patients with OSA who were free of other diseases and 12 healthy controls matched for age, gender, and body mass index had blood drawn for sCD40L and platelet-monocyte aggregate measurements. A repeat assessment was obtained following 8 weeks of nCPAP therapy. Results: Subjects with OSA had significantly higher plasma sCD40L levels and exhibited elevated platelet-monocyte aggregates compared to nonapneic subjects (7.6 ± 4.3 versus 1.7 ± 1.1, p = 0.004; and 41.3 ± 23.7 versus 6.7 ± 4.9, p = 0.001, respectively). Both parameters correlated positively with the percentage of time spent with SpO₂ <90% (r = 0.69, p = 0.01 and r = 0.6, p = 0.03, respectively). After 8 weeks of nCPAP treatment, sCD40 levels declined by 47% (p = 0.003) and platelet-monocyte aggregates by 42% (p = 0.002). None of the controls showed any changes in either sCD40L or platelet- monocyte aggregates after nCPAP therapy. Conclusions: OSA is associated with upregulation of circulating sCD40L levels and platelet-monocyte aggregation that may account for the increased incidence of cardiovascular events in this population. Treatment with nCPAP may alleviate this risk.