The purpose of this study was to investigate the changes of peripheral circulation through silver spike point (SSP) therapy in 22 male forestry workers exposed to hand-arm vibration by analyzing fingertip photoplethysmogram. The association between the changes of peripheral circulation and the response of autonomic nervous function was also evaluated using the coefficient of variation of R-R interval (CVR-R), total number of white blood cells (WBC), and the ratio of granulocyte (GC) and lymphocyte (LC) as indices.

The SDPTG-index and –b/a, indices of plethysmogram wave pattern, increased significantly due to the therapy, suggesting the improvement of peripheral circulation. The average heart rate (HR) tended to decrease and the CVR-R did not change significantly. The total number of WBC and the ratio of LC decreased significantly as the result of the therapy.

The subjects were divided into two subgroups according to the CVR-R values;​ low-value group (n=8), high-value group (n=14). In the low-value group, the HR decreased while the SDPTG-index and c/a increased. In the high-value group, the CVR-R and the LC decreased while the WBC increased significantly.

These results suggest that the SSP therapy may improve the peripheral circulatory function through the enhancement of parasympathetic nerve activity of the subjects with impaired parasympathetic nervous function. Furthermore, the therapy suppresses the parasympathetic nervous function of the subjects with enhanced parasympathetic nervous function.