Altered autonomic response in patients with persistent postural-perceptual dizziness during simulated vertical self-motion

Persistent postural-perceptual dizziness (PPPD) is a chronic psychosomatic condition characterized by dizziness, unsteadiness, and swaying or rocking vertigo. Despite the well-known relationship between the autonomic nervous system (ANS) and the vestibular system ANS, involvement in PPPD has not yet been investigated. We studied HRV in fifteen patients with PPPD and fifteen healthy controls (HCs), during a virtual reality task that simulated self-motion in horizontal and vertical directions with different kinematic conditions (accelerated, decelerated, constant), to elicit vestibular stimulation via kinematic visual inputs. Subject, condition-, direction, kinematic- and trial- specific HRV indices values were compared through mixed models. In PPPD patients (as compared to HC), we observed a) lower parasympathetic tone (p<0.001), lower variability of parasympathetic tone (p<0.02) higher sympathovagal balance (p<0.001). We also observed lower variability of parasympathetic tone in vertical motion as opposed to horizontal motion (p=0.03). Our findings are consistent with the hypothesis that PPPD, like many other psychosomatic conditions, alters the physiological regulation of the ANS. This, in turn, might impact on the processing of gravity and balance-related signal and lead to the characteristic symptoms of PPPD. The reverse scenario (i.e., that pre-existing ANS dysfunctions drive abnormalities in the visuo-vestibular system and leads to PPPD) is equally likely.