Autonomic nervous system function in narcolepsy

A disturbance of the autonomic nervous system (ANS) in narcolepsy has been suggested, based on abnormalities on pupillometry, ejaculatory and cardiovascular function. The ANS function was studied by measuring the variation in the heart rate and blood pressure during provocations, using the following tests: deep breathing test, Valsalva test and Orthostatic test for heart rate reactivity measurements, and Orthostatic test for blood pressure control. Each test session gave seven variables, and these were compared to age-adjusted reference values in healthy normals. In 22 unmedicated narcoleptics (median age 50.5 y, range 18-70 y) the results did not differ from these. Seventeen of the patients were included in a controlled stimulant medication trial (selegiline 10-40 mg daily), and they showed no significant changes in the ANS variables except for a dose-dependent rise in heart ratio (placebo 1.32+/-1-0.13 and 40 mg 1.14+/-0.05; mean+/-SD) and a decrease in systolic blood pressure (placebo 5.8+/-9.7 and 40 mg 30.1+/-21.5 mmHg) on Orthostatic test. Although blood pressure decreases >/=30 mmHg (maximally 72 mmHg) occurred in 9 patients, they were asymptomatic. These changes are considered primarily to reflect the known characteristic of monoamine oxidase inhibitors to cause postural hypotonia. Abnormalities using these methods were not found, thus supporting the view that cardiovascular reflex abnormalities would be characteristic of narcolepsy.