MMP9 and obstructive sleep apnea syndrome: When the patients with OSA were grouped into the T90 quartiles (< 1%, 1–4.0%, 4.1–11.4%, ≥ 11.5%), the serum MMP-9 levels of the patients with OSA in the highest T90 quartile were higher than those in the lowest T90 quartile and the controls (90.6 ± 56.3 ng/mL vs. 56.9 ± 31.9 ng/mL, p = 0.022; 90.6 ± 56.3 ng/mL vs. 49.0 ± 18.6 ng/mL, p = 0.002, respectively; Fig. 1B).