Effects of whole body vibration on human contrast sensitivity function

Introduction: Vibration is a known aeromedical stressor in rotary-winged aircraft and is known to affect visual acuity (VA). In aerospace operational conditions, contrast sensitivity (CS) takes the upper hand over VA for optimal visual performance. Examination of the effects of low frequencies whole body vibration of short duration on CS was the desired objective of the study. Material and Methods: Thirty healthy volunteers were exposed to low frequency whole body vibration using Multi-axial Vibration Simulator. Vibration frequency along the Z-axis varied from 4 to 20 Hz over a period of 30 min. CS was recorded in no vibration, under vibration and 30 min following exposure to vibration using CSV-1000 equipment at spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd). Results: CS, after an initial degradation, gradually improved with the increase in frequencies of vibration for the lower spatial frequencies (3, 6 cpd). The increasing trend was also noticed for higher spatial frequencies (12, 18 cpd) till 16 Hz; thereafter, a significant dip (P = 0.048) was observed at 20 Hz of vibration. No significant difference was observed following 30 min of post exposure. Conclusion: In contrast to the popular belief, an improvement in CS with increasing frequencies of vibration could be concluded from the results of the study. However, the sudden decrement in CS at higher CPD at higher frequencies of vibration could adversely affect visual performance of an aircrew.