REDUCTION IN SYMPATHETIC ACTIVITY AFTER LONG-TERM CPAP TREATMENT IN SLEEP-APNEA - CARDIOVASCULAR IMPLICATIONS

Twelve patients with severe obstructive sleep apnoea were included in an open, long-term, prospective, follow-up study addressing the effect s of nasal continuous positive airway pressure (CPAP) on sympathetic a ctivity, cardiac structure and blood pressure. Plasma norepinephrine ( P-NE) (daytime at rest), daytime and night-time urinary excretion of N E (U-NE), vanylmandelic acid and metanephrines, together with 24 h non invasive blood pressure (BP) recording and Doppler-echocardiography, w ere assessed before and after a mean of 20.5 (range 14-26) months of C PAP. Average self-reported use of CPAP was 89% (range 65-100%) of time spent in bed. Resting daytime P-NE ranged 0.35-0.83 ng . ml(-1), whic h is elevated compared to healthy controls. Only night-time U-NE, mean daytime BP and average 24 h BP were related to severity of OSA. Night -time metanephrine was related to daytime and night-time diastolic, as well as night-time systolic, BP. Left ventricular mass index (LVMI) a t baseline was correlated to daytime systolic BP and P-NE. Longterm CP AP treatment reduced biochemical markers of sympathetic activity. P-NE decreased by approximately 50%, and daytime and night-time vanylmande lic acid and metanephrine by 32-54%. In contrast, there were no overal l reductions in BP or LVMI. It is concluded that obstructive sleep apn oea is associated with high sympathetic activity both during sleep and waking periods. Urinary metanephrine excretion seemed to reflect bloo d pressure, but neither daytime nor night-time catecholamine excretion was directly related to disease severity in patients with severe obst ructive sleep apnoea. In spite of a marked reduction of catecholamine excretion at followup, BP and cardiac structure remained unchanged. Al though increased sympathetic activity may act as a contributory trigge r for cardiovascular disease in sleep apnoea, a reduction of activity after nasal CPAP is not associated with changes in blood pressure or c ardiac structure.