AUGMENTED RESTING SYMPATHETIC ACTIVITY IN AWAKE PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

Muscle nerve sympathetic activity (MSA) was recorded during wakefulnes s in 11 patients with obstructive sleep apnea (OSA) and in 9 sex- and age-matched healthy control subjects. Plasma levels of norepinephrine (NE) and neuropeptide Y were analyzed. Five patients had established h ypertension (resting supine systolic BP/diastolic BP greater-than-or-e qual-to 160/95 mm Hg). The investigation was performed after a minimum of 3 weeks' washout period of antihypertensive medication. Muscle sym pathetic activity during supine rest was higher in patients compared w ith controls (p<0.01) with no difference between normotensive and hype rtensive patients. However, systolic, but not diastolic, BP was positi vely related to resting MSA (n=20, p<0.01). There was no significant c orrelation between body mass index and MSA. Resting MSA was unrelated to disease severity expressed as apnea frequency or minimum SaO2 durin g the overnight recording. Both the arterial and venous plasma norepin ephrine was higher in patients compared with controls (p<0.05). Plasma levels of NE correlated to resting MSA (p<0.01) in the whole study gr oup (patients and controls) but not within the respective subgroups. N o significant correlation, however, was found between plasma NE (arter ial and venous) and BP. Plasma neuropeptide Y-like immunoreactivity wa s similar in patients and controls. However, one patient with hyperten sion had approximately twice this level in repeated samples. It is con cluded that neurogenic sympathetic activity as well as circulating pla sma NE is increased in patients with OSA. This increased sympathetic a ctivity during awake supine rest may reflect a pathophysiologic adapta tion to hypoxia and hemodynamic changes occurring at repetitive apneas during sleep. The correlation between MSA and systolic BP implies tha t this mechanism may be directly or indirectly involved in the develop ment of cardiovascular complications in OSA.