Reduction in sympathetic activity after long-term CPAP treatment in sleep apnoea: cardiovascular implications

Twelve patients with severe obstructive sleep apnoea were included in an open, long-term, prospective, follow-up study addressing the effects of nasal continuous positive airway pressure (CPAP) on sympathetic activity, cardiac structure and blood pressure. Plasma norepinephrine (P-NE) (daytime at rest), daytime and night-time urinary excretion of NE (U-NE), vanylmandelic acid and metanephrines, together with 24 h noninvasive blood pressure (BP) recording and Doppler-echocardiography, were assessed before and after a mean of 20.5 (range 14-26) months of CPAP. 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, which 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) at baseline was correlated to daytime systolic BP and P-NE. Long-term CPAP treatment reduced biochemical markers of sympathetic activity. P-NE decreased by approximately 50%, and daytime and night-time vanylmandelic acid and metanephrine by 32-54%. In contrast, there were no overall reductions in BP or LVMI. It is concluded that obstructive sleep apnoea is associated with high sympathetic activity both during sleep and waking periods. Urinary metanephrine excretion seemed to reflect blood pressure, but neither daytime nor night-time catecholamine excretion was directly related to disease severity in patients with severe obstructive sleep apnoea.(ABSTRACT TRUNCATED AT 250 WORDS)