Makoto Ariizumi

Effect of whole body vibration on the rat brain content of serotonin and plasma corticosterone

SummaryTo investigate the effects of whole body vibration on the central nervous system, rats were exposed to various whole body vibrations and changes in whole brain levels of Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were then determined. Changes in plasma corticosterone levels were also determined and related to the changes in the whole brain levels of 5-HT and 5-HIAA. The dose-related changes in the 5-HT and 5-HIAA levels were observed as acceleration increased from 0.4G to 5.0G. Changes in vibration frequency also affected the 5-HT and 5-HIAA levels of brain: they were significantly elevated at a frequency of 20 Hz (P<0.05). Plasma corticosterone levels increased as acceleration increased from 0.4G to 5.0G. As the vibration frequency was changed from 5 Hz to 30 Hz, plasma corticosterone levels also rose significantly (P<0.05) but the extent of elevation was approximately the same at each frequency. The correlation between brain 5-HT and plasma corticosterone levels with increasing acceleration (r=0.93, P<0.01) was significant.

Preliminary evaluation of dose-effect relationships for vibration induced white finger in Japan

SummaryHabitual use of many vibrating tools has been found to be connected with the appearance of various disorders affecting the blood vessels, nerves, bones, joints, muscles or connective tissues of the hand and forearm. The vibration exposures required to cause these diseases are not known exactly, either with respect to vibration intensity and the vibration frequency spectrum, or with respect to daily exposure time and total exposure period. The purpose of this study is to investigate available data on the physical conditions in Japan that have caused vibration induced white finger (VWF) and attempt to establish approximate relationships between vibration conditions and prevalence of VWF. The vibration conditions were evaluated using the method of vibration assessment recommended by the International Standardized Organization, which uses the weighted vibration level of the frequency weighted, dominant, single axis component of vibration directed into the hand. A clear correlation between level, prevalence of VWF and exposure period can be found. The results also suggest the relationship between the weighted levels and latent intervals. These dose-effect relationships enable the prediction of the average latent interval for a population group and the range of progression of the disorders—all from a measurement of the vibration entering the hands. In Japanese cases, 4, 8, and 15% of VWF prevalence correspond with 10, 20, and 40% of VWF prevalence in the Draft International Standard ISO/DIS 5349 (1982) within the weighted vibration level range of 2 to 50m · s¨.

Changes in cerebral norepinephrine induced by vibration or noise stress

SummaryTo investigate the effects of whole body vibration on the central nervous system, rats were exposed to various whole body vibrations and examined for changes in the levels of norepinephrine (NE) in whole brain or regions of the brain. Whole brain NE had decreased significantly (p<0.05) after an acceleration of 5.0G with a frequency of 20 Hz; and the decrease was also observed in the hypothalamus (p<0.01) and the hippocampus (p<0.10). Exposure to noise [100 dB (A)] caused a significant decrease in NE. This decrease related particularly to a significant decrease in midbrain NE (p<0.05) and a non-significant decrease of NE in the hypothalamus.

Experimental studies on the effects of vibration and noise on sympathetic nerve activity in skin

SummaryMulti-unit sympathetic activity was recorded at elbow level from median nerve fascicles supplying glabrous skin of the left hand in five healthy subjects. The resultant vasomotor responses accompanying the neural activity were monitored by simultaneous recordings of skin blood flow using the laser doppler method and skin temperature in the innervation zones. No significant change in sympathetic activity was observed during handgrip exercise of the right hand under a constant gripping force of 2 kg. Subjects maintained the same gripping force of the right hand during exposure in random order to local vibration and/or noise, each type of exposure lasting 5 min with intervals of 20 min. A two-peaked significant increase in outflow from sympathetic nerves was observed during local exposure of the right hand to vibration with a frequency of 60 Hz and an acceleration of 50 m·s−2, followed by a postexposure period which revealed a relative suppression of sympathetic nerve activity and a significant increase in blood flow. Noise at 100 dB(A) showed only an initial effect on skin sympathetic nerve activity (SSA), whereas when combined with local vibration at 60 Hz, a pronounced increase in neural activity was noticed, indicating a combined effect of vibration and noise. These results from direct recordings of SSA suggest a sympathetic vasomotor reflex mechanism triggered by local vibration stimuli to the hand.

Study on the perceptible level for infrasound

The human perception of infrasound was investigated by a field survey. Experiments on the perceptible level of infrasound were performed at various places, such as under a bridge, inside an automobile and around a cooling tower, where infrasounds were predominantly observed. The dose-response relationship was also evaluated under various levels of infrasound with a single predominant frequency. Examinees were asked whether they could feel infrasound as pressure on the ears and head, and/or as reverberation in the chest and abdomen. In the frequency range between 6 and 23 Hz, the 50% response level (threshold value) had a slope of −10 dB/octave, and at 10 Hz was about 93–94 dB. The 20% response level was nearly 6 dB lower than the 50% response level, and the 80% response level was nearly 6 dB higher than the 50% response level. The response level for the chest and abdomen was 6–9 dB higher than that of the total response for the ear, head, chest and abdomen.

Study on the mechanism of the appearance of noise effects

SummaryThis study was undertaken to investigate the dose-response relationship between the biological effect and noise exposure, and to consider the mechanism of the appearance of noise effects. Rats were exposed to noise at intensities of 60 dB (A), 80 dB (A) and 100 dB (A) for 240 min and examined for the change of activities of dopamine-Β-hydroxylase (DBH) in serum and adrenal glands. Plasma cyclic adenosine 3′,5′-monophosphate (c-AMP) levels were also measured. Some rats were given 6-hydroxydopamine (6-OHDA) as a chemical sympathectomyzing agent 20 h before noise exposure in order to consider the mechanism of the appearance of noise effects. By noise exposure, serum DBH activity was significantly (P<0.01) increased at each intensity compared with the control group, but there were no remarkable changes in adrenal DBH activity. Plasma c-AMP level was also significantly elevated in response to the noise stress. When the rats, which had been pretreated with 6-OHDA, were exposed to noise with an intensity of 100 dB (A), the response of serum DBH activity was no longer observed. Therefore it is suggested that the effect due to noise exposure appears through the post-ganglionic sympathetic nerve fiber.