Spectral analysis of heart rate variability reveals an enhanced sympathetic activity in narcolepsy with cataplexy

To test the autonomic control of cardiovascular reflexes and heart rate variability (HRV) at rest and during orthostatic stress in narcolepsy with cataplexy (NC).

Ten NC patients with a hypocretin deficit and 18 control subjects underwent head-up tilt test (HUTT), Valsalva manoeuvre, deep breathing and cold face under controlled laboratory conditions. Heart rate variability (HRV) was analysed during supine rest and HUTT considering the normalized unit of LF and HF power (LFnu; HFnu), using autoregressive (AR) and fast Fourier transform (FFT) algorithms.

Cardiovascular changes during HUTT, Valsalva manoeuvre, deep breathing, isometric handgrip and cold face were normal and comparable in the two groups. AR and FFT analysis showed an increased LF/HF ratio in NC patients during supine rest. As expected, LFnu increased and HFnu decreased in the control group during HUTT, but did not change in narcoleptics being comparable to values in the supine condition.

NC patients showed an increased sympathetic drive on heart rate (HR) in the supine condition that did not further increase during HUTT.

These results suggest the proper functioning of cardiovascular reflexes in NC but support an impairment of HR modulation at rest in favour of an enhanced sympathetic activity.