Cardiovascular fitness in narcolepsy is inversely related to sleepiness and the number of cataplexy episodes
Abstract
Objective: Cardiopulmonary fitness depends on daily energy expenditure or the amount of daily exercise. Patients with narcolepsy spent more time being sleepy or asleep than controls; thus we may speculate that they have a lower quantity and quality of physical activity.
The aim of the present study was thus to test the hypothesis that exercise tolerance in narcolepsy negatively depends on sleepiness. Patients and methods: The cross-sectional study included 32 patients with narcolepsy with cataplexy, 10 patients with narcolepsy without cataplexy, and 36 age-and gender-matched control subjects, in whom a symptom-limited exercise stress test with expired gas analysis was performed.
A linear regression analysis with multivariate models was used with stepwise variable selection. Results: In narcolepsy patients, maximal oxygen uptake (VO2peak) was 30.1 +/- 7.5 mL/kg/min, which was lower than 36.0 +/- 7.8 mL/kg/min, p = 0.001, in controls and corresponded to 86.4% +/- 20.0% of the population norm (VO2peak%) and to a standard deviation (VO2peakSD) of -1.08 +/- 1.63 mL/kg/min of the population norm.
VO2peak depended primarily on gender (p = 0.007) and on sleepiness (p = 0.046). VO2peak% depended on sleepiness (p = 0.028) and on age (p = 0.039).
VO2peakSD depended on the number of cataplexy episodes per month (p = 0.015) and on age (p = 0.030). Conclusions: Cardiopulmonary fitness in narcolepsy and in narcolepsy without cataplexy is inversely related to the degree of sleepiness and cataplexy episode frequency.