Pathophysiological Effects of Vibration with Inner Ear as a Model Organ

Hand-arm vibration syndrome (HAVS) is a symptom entity that consists of disturbances in the circulation of the fingers (Vibration White Finger or VWF), peripheral nerves of the hands and arms, and possibly muscle, joint and autonomic nervous system disorders. Changes in HAVS were assessed in a cross-sectional and in a longitudinal study of forestry workers. Sensorineural and musculoskeletal symptoms were studied. Changes in vibrotactile perception threshold were evaluated and the tonic vibration reflex was measured in posturography. An animal model was created to assess inner ear damage after vibration exposure. The prevalence of vibration-induced white finger (VWF) decreased from 17 to 8 percent in the cohort of 52 forestry workers. Numbness increased. Rotator cuff syndrome was diagnosed in 19% of men on the right side. Hand-arm vibration associated with the right rotator cuff syndrome. Numbness was associated with pain in upper extremities. Subjects with tension neck had excessive deviation of position in the lateral and anteroposterior direction in posturography during and after vibration-induced stimulation of neck and lumbar area. In vibrotactile perception threshold measurement, tactile acuity worsened in the cohort study. The threshold metric was the summed normalized threshold shift constructed for each subject. The positive predictive value of the metric was 71%. In an animal model, temporal bone vibration was used to assess the hearing loss caused by vibration. After bone vibration 60 % of the guinea pigs developed a threshold shift exceeding 10 decibel (dB) at least at two frequencies. Exposure to vibration at higher frequencies (500-1000 Hertz, Hz) produced stronger TS than exposure to frequencies 32-250 Hz. Temporal bone vibration caused expression of tumor necrosis factor alpha (TNF-α) and its‟ receptors (TNF R1, TNF R2) in the cochlea. The expression of TNF R2 was stronger than that of TNF R1. Vibration also induced vascular endothelial growth factor VEGF and its‟ receptor (VEGF R2) expression in the cochlea. The results indicate that VWF and numbness have possibly different pathophysiological mechanism. In the forestry workers, the strenuous work was associated with musculoskeletal disorders and partly explains the numbness. The animal model provides a new understanding of mechanisms leading to vibration-induced cochlear changes and cellular damage. The frequency of vibration influences the threshold shift of hearing in the vibrated cochlea. In the animal model, the expression of TNF-α and VEGF in the vibrated cochlea seems to cause tissue remodeling. The inner ear changes may also model vibration-induced damages in the hand-arm vibration syndrome. Shift to lower frequencies of vibration is advisable. National Library of Medicine Classification: WA 400, WE 805, WV 270 Medical Subjects Headings: Biomechanics; Cochlea; Cohort Studies; Cross-Sectional Studies; Forestry; Guinea Pigs; Hand-Arm Vibration Syndrome/etiology; Hand-Arm Vibration Syndrome/physiopathology; Hearing Loss, Sensorineural; Mechanoreceptors/physiology; Musculoskeletal Diseases; Neck Muscles: Innervation, Neck Pain/physiopathology; Occupational diseases; Occupational Exposure; Posture/physiology; Receptors, Tumor Necrosis Factor type I, Receptors, Tumor Necrosis Factor type II, Stress; Mechanical; Tumor Necrosis Factoralpha; Vascular Endothelial Factoralpha; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-1, Vascular Endothelial Growth factor Receptor-2; Vibration/adverse effects To Erkki, Laura, Tuuli, Martti and Anton