Factors associated with dynamic balance in people with Persistent Postural Perceptual Dizziness (PPPD): a cross-sectional study using a virtual-reality Four Square Step Test

Abstract

Background: Persistent postural-perceptual dizziness (PPPD) is a condition characterized by chronic subjective dizziness and exacerbated by visual stimuli or upright movement. Typical balance tests do not replicate the environments known to increase symptoms in people with PPPD-crowded places with moving objects. Using a virtual reality system, we quantified dynamic balance in people with PPPD and healthy controls in diverse visual conditions.

Methods: Twenty-two individuals with PPPD and 29 controls performed a square-shaped fast walking task (Four-Square Step Test Virtual Reality-FSST-VR) using a head-mounted-display (HTC Vive) under 3 visual conditions (empty train platform; people moving; people and trains moving). Head kinematics was used to measure task duration, movement smoothness and anterior-posterior (AP) and medio-lateral (ML) ranges of movement (ROM). Heart rate (HR) was monitored using a chest-band. Participants also completed a functional mobility test (Timed-Up-and-Go; TUG) and questionnaires measuring anxiety (State-Trait Anxiety Inventory; STAI), balance confidence (Activities-Specific Balance Confidence; ABC), perceived disability (Dizziness Handicap Inventory) and simulator sickness (Simulator Sickness Questionnaire). Main effects of visual load and group and associations between performance, functional and self-reported outcomes were examined.

Results: State anxiety and simulator sickness did not increase following testing. AP-ROM and HR increased with high visual load in both groups (p < 0.05). There were no significant between-group differences in head kinematics. In the high visual load conditions, high trait anxiety and longer TUG duration were moderately associated with reduced AP and ML-ROM in the PPPD group and low ABC and high perceived disability were associated with reduced AP-ROM (|r| = 0.47 to 0.53; p < 0.05). In contrast, in controls high STAI-trait, low ABC and longer TUG duration were associated with increased AP-ROM (|r| = 0.38 to 0.46; p < 0.05) and longer TUG duration was associated with increased ML-ROM (r = 0.53, p < 0.01).

Conclusions: FSST-VR may shed light on movement strategies in PPPD beyond task duration. While no main effect of group was observed, the distinct associations with self-reported and functional outcomes, identified using spatial head kinematics, suggest that some people with PPPD reduce head degrees of freedom when performing a dynamic balance task. This supports a potential link between spatial perception and PPPD symptomatology.

Keywords: Anxiety; Chronic dizziness; FSST; HTC Vive; Kinematics; Visual stimuli.

Fig. 1

The traditional four-square step test sequence: a participant is asked to walk as fast as possible clockwise (broken arrows) and counterclockwise (dotted arrows) over four walking canes arranged in a cross-shaped form, while looking forward. The participant should step through using both feet, as the starting and ending point are similar (square 1)

Fig. 2

FSST-VR visual conditions: a Left: An individual wearing the head mounted display while performing the FSST-VR. Right: the respective virtual environment viewed via the HMD. b Varying visual loads, from simple (left): empty subway platform, to complex (center): people moving in the AP direction; to Complex + (right): additional trains moving around the platform

Fig. 3

Results of Analysis of Variance (ANOVA) for kinematic variables and heart-rate across groups (red = PPPD, blue = Control) and conditions (Simple = empty platform, Complex = busy platform, and Complex +  = busy platform with trains). Error bars denote 95% confidence intervals

Fig. 4

Three representative traces of head movement for two people with PPPD during performance of FSST-VR. Traces are aligned to a common starting point, marked by a black dot. a P02: STAI trait = 50, DHI = 84, ABC = 62.5. b P07: STAI trait = 25, DHI = 18, ABC = 88.8

Fig. 5

Correlations between self-reported and functional outcomes and mediolateral range of motion (m) in people with PPPD during performance of the FSST-VR under high visual load