ALTERED CARDIOVASCULAR VARIABILITY IN OBSTRUCTIVE SLEEP-APNEA

Background-Altered cardiovascular variability is a prognostic indicato r for cardiovascular events. Patients with obstructive sleep apnea (OS A) are at an increased risk for cardiovascular disease. We tested the hypothesis that OSA is accompanied by alterations in cardiovascular va riability, even in the absence of overt cardiovascular disease. Method s and Results-Spectral analysis of variability of muscle sympathetic n erve activity, RR interval, and blood pressure were obtained during un disturbed supine rest in 15 patients with moderate-to-severe OSA, 18 p atients with mild OSA, and 16 healthy control subjects in whom sleep d isordered breathing was excluded by complete overnight polysomnography . Patients with OSA were newly diagnosed, never treated for OSA, and f ree of any other known diseases. Patients with moderate-to-severe OSA had shorter RR intervals (793+/-27 ms) and increased sympathetic burst frequency (49+/-4 bursts/min) compared with control subjects (947+/-4 2 ms; 24+/-3 bursts/min; P=0.008 and P<0.001, respectively). In these patients, total variance of RR was reduced (P=0.01) and spectral analy sis of RR variability showed an increase in low frequency normalized u nits, a decrease in high frequency normalized units, and an increase i n the ratio of low to high frequency tall P<0.05). Even though blood p ressure was similar to that of the control subjects, blood pressure va riance in patients with moderate-to-severe OSA was more than double th e variance in control subjects (P=0.01). Patients with mild OSA also h ad a reduction in RR variance (P=0.02) in the absence of any significa nt difference in absolute RR interval. For all patients with OSA, line ar regression showed a positive correlation (r=0.40; P=0.02) between s leep apnea severity and blood pressure variance. Conclusion-Cardiovasc ular variability is altered in patients with OSA. This alteration is e vident even in the absence of hypertension, heart failure, or other di sease states and may be linked to the severity of OSA. Abnormalities i n cardiovascular variability may be implicated in the subsequent devel opment of overt cardiovascular disease in patients with OSA.