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.