Diurnal variation of circulating microvesicles is associated with the severity of obstructive sleep apnoea.

Purpose: Microvesicles (MVs) have been implicated in the pathomechanism of obstructive sleep apnoea (OSA); however, the results are inconsistent, possibly due to an unrevealed temporal variation in circulating MV levels. We aimed to investigate the diurnal changes of MV fractions in OSA.

Methods: Peripheral blood was taken from 18 patients with OSA and 9 healthy subjects at different time points (11:00, 17:00, 21:00, 01:30 and 06:00). Samplings were repeated in nine OSA patients after 2 months of continuous positive airway pressure (CPAP) therapy. CD41+, CD62P+, glycophorin A+ and Annexin V+ MVs were determined with flow cytometry. Areas under the MV concentrations-time curves (AUC) were calculated and correlated with the severity of OSA.

Results: A significant diurnal variability of plasma CD41+ and Annexin V+ MVs was observed only in OSA with a marked peak at 17:00. There was a direct correlation between CD41+ MV AUCs and the severity of OSA. CPAP treatment reduced diurnal variability in both CD41+ and Annexin V+ MV levels.

Conclusions: The relationship between the diurnal variability of CD41+ MVs and disease severity as well as the effect of CPAP treatment on MV levels support the role of MVs in the pathophysiology of OSA. More importantly, considering the significant diurnal variation in circulating MV levels, introduction of strict protocols for blood sampling is required for MV measurements.