Abstract
Purpose :
The vestibulo-sympathetic reflex (VSR) is a reflex arc that helps maintain blood pressure and cerebral perfusion during changes in posture and head orientation. Originating in the vestibular organs and other body graviceptors, this reflex modulates sympathetic outflow. Through selective stimulation of the vestibular organs via off-vertical, head eccentric delivery of whole-body oscillations in the horizontal plane, we aim to characterize sympathetic responses (i.e., changes in blood pressure and pupil dilation) during testing to understand the relationship between balance control and physical homeostasis.
Methods :
Vertical sinusoidal harmonic acceleration (vSHA) testing was performed in healthy controls (n=18) at 0.08, 0.16, and 0.64 Hz in a manually reclined (60°) rotary chair (Neurolign USA, LLC, Pittsburgh, PA) with the head turned either 45° to the left (LARP) or right (RALP). Eye position and pupil size were measured using a binocular infrared video-oculography system at 250 fps. Vertical semicircular canal gain was calculated as the ratio between the peak slow phase component of vertical eye velocity to peak pitch gyro velocity. Participants wore a wireless, noninvasive cardiovascular output monitor (Caretaker Medical LLC, Charlottesville, VA) for continuous measurements.
Results :
Gain values for LARP and RALP increased in a frequency-dependent manner. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and pupil area (PA [mm2]) increased significantly from baseline during SHA testing. At 0.08 Hz, the mean change in SBP, DBP, MAP, and PA was 5.65 (±13.31), 2.68 (±6.41), 3.13 (±8.64), and 17.63 (±10.97) & 14.92 (±11.58) for the left & right eyes, respectively. Similarly, at 0.16 Hz, the mean change in SBP, DBP, MAP, and PA from baseline was 7.56 (±14.68), 3.65 (±7.04), 4.36 (±9.52), and 14.52 (±12.03) for the left eye and 12.73 (±11.31) for the right eye. Lastly, at 0.64 Hz, only PA changed significantly from baseline, with a mean change of 15.30 (±11.25) and 13.35 (±10.75) for the left & right eyes, respectively.
Conclusions :
vSHA testing reliably evokes VSRs. PA may be especially useful in dynamically evaluating these responses during vestibular stimulation. Incorporating higher frequencies is essential for practical development of targeted interventions for conditions like orthostatic hypotension or motion sickness.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.