Vibration stress and the autonomic nervous system.

Raynaud's phenomenon has been considered to be due to activation of the central sympathetic vasoconstrictor reflex, and may represent part of a larger dysfunction of higher autonomic centers. Symptoms, such as sweating disturbances, orthostatic hypotension, insomnia and impotence have been reported to be more common among vibration exposed workers. We studied 217 male forest workers and selected samples of this population for electromyographic (N = 80), autonomic nervous system function, controlled breathing, tilting bed and valsalva manoeuvre (N = 88) tests, and a full clinical neurological examination. Mean alcohol consumption was estimated to be 3.0 kg absolute alcohol/year. The total mean vibration exposure time was 14,100 hours. The prevalence of Raynaud's phenomenon was 5%. The variations in heart rate (HRV) at rest and during deep breathing were observed. The traditional indexes of HRV (CV, CVS, MEAN) were computerized and calculated. There was a significant difference (p less than 0.001) between the HRV indexes during the deep breathing test in those with the shortest and the longest exposure to vibration. The values of HRV indexes were age dependent; and in multiple regression analysis, the total exposure time to vibration had an independent negative association to HRV. Also association of sensory neural hearing loss to Raynaud's phenomenon among vibration exposed workers indicates that there is an involvement of the central nervous system in the pathogenesis of vibration syndrome. The question, does vibration cause permanent changes in autonomic centers of the brain or do these centers only mediate vibration stress to end organs, remains unsettled.