Overvibration Induced Microvascular Injury And Hypoxia In The Formation Of Vocal Fold Benign Lesions

Vocal fold benign lesions hold an high morbidity, especially in the professional voice users. Vocal fold benign lesions included vocal nodules, polyps and Reinke’s edema, there are significant overlapping on histologic features among them, edema and capillary proliferation are typical findings. We still know little about its pathogenesis, normally, voice overuse and misuse were thought to be the major reason. Recently, VEGF, MMP and COX-2were reported to play a role in the formation of vocal fold benign lesions, and a more recent study concluded that vocal nodules and edema may be due to vibration-induced rises in capillary pressure. Nevertheless, we take the hypothesis that overvibration induced hemodynamic and shear stress changes can also leads to the formation of a hypoxic zone of injury and the release of a cascade of cytokines. To test our hypothesis, we investigated three part as below.Part one:Expression of HIF-1α and VEGF in vocal polypsExpression patterns of HIF-1α and VEGF in surgical specimens of vocal polyps from36patients were analyzed using the immunohistochemistry and western blot method. Normal vocal fold mucosa from26patients who underwent total laryngectomy were collected and used as the control group. The expression of HIF-1α and VEGF were detected both in the vocal polyps group and the control group, while the expression of HIF-la and VEGF levels were significantly higher when compared to normal vocal fold mucosa (p<.05). The increased expression of HIF-la in vocal polyps indicates that there is hypoxia stress reaction in vocal polyps and it may play an important role in the pathogenetic mechanism of vocal polyps.Part two:Vibration induced blood perfusion and vascular permeability changesWe established a vascular vibration platform to observe8rabbit auricle microvascular perfusion under non-vibration,62.5Hz/lmm,125Hz/lmm and250Hz/0.5mm vibration. After4hours125Hz/lmm vibration,12rabbit auricle microvascular permeability were compared between the vibration group and histamine+vibration group. Results showed a significant blood perfusion decline as the vibration frequency increases (p<.05); there was a significant changes in microvascular permeability in the histamine+vibration group (p<.05), but not in the vibration group. All the above indicated that overvibration could significantly influence blood perfusion, and worsen edema during inflammation situations.Part three:Observation of vibration induced vascular injuryWe established the rat tail central artery vibration platform, and30rats were randomly divided into five groups:control group, restraint group,62.5Hz/1mm gruop、125Hz/1mm group and250Hz/0.5mm group. After4hours/1day vibration, the artery endothelia cells were observed under transmission electron microscope and the expression of NFATc3in endothelia cells were investigated with immunofluorescence. Another30rats were also divided into the above five groups. After4hours/9day vibration, the vascular diameter changes and expression of HIF-2a were compared among them. The results showed that,4hours/1day vibration induced significant endothelia cells damage; and after4hours/9day vibration, there were significant vasoconstriction between vibration and non-vibration group (p<.05), and there were HIF-2a expression in the125Hz/1mm group. These indicated that vibration induced vascular endothelia cell injury, vasoconstriction and the hypoxia stress reaction.Based on the above three part experiment, we draw the following conclusion:Overvibration could induce microvascular injury and vasoconstriction and then lead to microcirculation disorder and hypoxia stress reaction, which activate the expression of HIF, cause the release of a series of cytokines, form the circulation of intermittent hypoxia and inflammation, and overvibration accelerate this process. That may be the inflammation basis of the formation of vocal fold benign lesions induced by voice overuse.