The effects of physical vibration on heart rate variability as a measure of drowsiness

N. Zhang, M. Fard, M. H. U. Bhuiyan, D. Verhagen, M. F. Azari, S. R. Robinson

We investigated the effects of low frequency whole body vibration on heart rate variability (HRV), a measure of autonomic nervous system activation that differentiates between stress and drowsiness. Fifteen participants underwent two simulated driving tasks for 60 minutes each: one involved whole-body 4-7 Hz vibration delivered through the car seat, and one involved no vibration. The Karolinska Sleepiness Scale, a subjective measure of drowsiness, demonstrated a significant increase in drowsiness during the task. Within 15-30 minutes of exposure to vibration, autonomic (sympathetic) activity increased (p < 0.01) in response to the stress of maintaining alertness and performance when drowsy, and peaked at 60 minutes (p < 0.001). Changes in three other HRV domains (higher LF/HF ratios, lower RMSSD (ms), and pNN50 (%) values) were consistent with increased sympathetic activation. These findings have implications for the future development of equivalent drowsiness contours leading to improvements in road safety. Practitioner Summary: The effects of physical vibration on driver drowsiness have not been well investigated. This laboratory-controlled study found characteristic changes in heart rate variability (HRV) domains that indicated progressively increasing neurological effort in maintaining alertness in response to low frequency vibration, which became significant within 30 minutes.