Abstract
STUDY OBJECTIVES: Obstructive sleep apnea (OSA) is associated with chronic inflammation likely triggered by nocturnal, intermittent hypoxemia and increased adrenergic tone. The neutrophil-to-lymphocyte ratio (NLR) was recently described as a measure of subclinical systemic inflammation. Studies on the effect of continuous positive airway pressure (CPAP) therapy in OSA on subclinical inflammation measured by NLR are lacking. We hypothesize that NLR levels would improve as chronic inflammation diminishes in patients with OSA treated with CPAP. METHODS: We retrospectively reviewed patients in whom OSA was diagnosed and who were treated with CPAP therapy. Complete blood count (CBC) were obtained pretreatment and posttreatment for calculation of NLR, which was calculated by dividing the number of neutrophils by the number of lymphocytes. Patients with conditions known to affect NLR such as chronic infections, inflammatory diseases, active cardiovascular disease, and malignancies were excluded from the study. CPAP adherence downloads were obtained for all patients. RESULTS: Out of 184 patients in whom OSA was diagnosed and who were treated with CPAP, 109 met our study criteria, including baseline polysomnogram, baseline and posttreatment CBC, and available adherence download. We compared the NLR before and after treatment with CPAP. There was a significant difference in NLR before and after treatment with CPAP (P < .0001). There was also a significant difference in apnea-hypopnea index before and after treatment (P < .0001). We also assessed the relationship between CPAP adherence (percentage of days used for > 4 hours) and the change in NLR. NLR decreased significantly in both the adherent (CPAP use ≥ 70% of days; P = .014) and nonadherent groups (CPAP use < 70% of days; P = .0003). Finally, we noticed a significant direct correlation between CPAP adherence beyond 70% and the change in NLR (ΔNLR) (P = .046) in patients who had ≥ 70% adherence with CPAP, which was not observed in patients with < 70% adherence. CONCLUSIONS: The NLR may be a useful marker for monitoring improvement, as CPAP had a desirable effect on the chronic inflammation induced by OSA when measured by NLR in this study. Our results specifically suggest that the NLR values decrease significantly in patients using CPAP regardless of adherence, but with a more direct relationship in those who use it beyond 70% of days, at least 4 hours a day.