Hemodynamic changes in skin microcirculation induced by vibration stress in the conscious rabbit

Cutaneous microcirculatory responses to vibration stress were observed by microphotoelectric plethysmography in a transparent round window installed in the ears of conscious rabbits. Vertical vibrations at frequencies ranging from 8 to 250 Hz were applied to the abdomen of the rabbits for 5 min. The vibrations produced an increase in heart rate and the index of discomfort, and a decrease in blood flow in the skin microcirculation. The maximum response was observed at 63 Hz. Rhythmic fluctuations in microcirculation were associated with two components: component A had a small amplitude and high frequency, and component B had a large amplitude and low frequency. Vibration exposure led to a large increase in component B and a smaller increase in component A. During vibration exposure, component A was suppressed by treatment with diltiazem, a calcium channel blocker, and was not affected by bunazosin, an alpha-1 adrenoceptor antagonist. The opposite changes were observed for component B. This indicates that components A and B of the rhythmic fluctuations are regulated by myogenic and neurogenic activities, respectively. Thus, the hemodynamic changes of skin microcirculation induced by vibration may actually be due to a neurogenic factor, especially sympathetic nerve activity. The responses appear to depend on the frequency of the vibrations.