Sympathetic nervous system alterations in sleep apnea. The relative importance of respiratory disturbance, hypoxia, and sleep quality.

Numerous alterations in the sympathetic nervous system have been reported in patients with obstructive sleep apnea. It is unclear whether such alterations can be attributed to the respiratory disturbance itself, the resulting hypoxia, or disruption of sleep. We examined urinary norepinephrine levels in 45 individuals with varying amounts of respiratory disturbance and sleep disruption. All were of similar age (40 to 60 years) and body weight (100 to 160% ideal body weight), and all were free from antihypertensive medications that could influence norepinephrine levels. Twenty-four-hour urinary norepinephrine levels were correlated with respiratory disturbance index (r = 0.39, p < 0.01) and mean oxygen saturation (r = -0.36, p < 0.05). These variables, together with the time in slow-wave sleep, accounted for a statistically significant but modest percentage of the variance in urinary norepinephrine (R2 = 0.19, p < 0.05). However, the variables were so tightly intercorrelated that no single variable independently predicted norepinephrine levels in multiple regression analysis.