MMP9 and obstructive sleep apnea syndrome: The most striking finding of our study was that the beneficial effect of CPAP on key MMPs implicated in the progression of atherosclerosis was not sustained over the long-term as by the end of the 5 year follow-up period, the levels of MMP-8, MMP-9 and TIMP-4 increased beyond even those detected at the time of OSA diagnosis.