Usefulness of blood parameters, especially viscosity, for the diagnosis and elucidation of pathogenic mechanisms of the hand-arm vibration syndrome.

M. Usefulness of blood parameters, especially viscosity, for the diagnosis and elucidation of pathogenic mechanisms of the hand-arm vibration syndrome. Scand J Work Environ Health 13 (1987) 358-362. In the present study it was found that, in vibrating-tool operators with Raynaud's phenomenon, whole blood viscosity was significantly higher than in operators without Raynaud's phenomenon at shear rates from 230 to 11.5 S-I. In addition rats were experimentally exposed to local vibration (60 Hz, 5 g) on their hind limbs for 4 hid for 30 or 90 d. In the case of 30-d exposure, the smallarteries in the exposed site did not change. However, after exposure for 90 d, disruption of the internal elastic lamina was observed in the small arteries. The disrupti on was followed by focal cell proliferation with regenerative formation of collagen and elastic fibers. The fibro cellular thickening of the intima was further augmented, and, in addition, a complete stenosis of the small lumen of the small artery was observed. Medial thickness did not show significant differences between the control and exposed groups for either exposure duration. The whole blood viscosity was significantly increased by the 90-d but not by the 30-d exposure. These results suggest that there are some relationships between the increase in whole blood viscosity and the intimal thickening of some small arteries in the exposed site. chronic on

To clarify the mechanism of the occurrence of Raynaud's phenomenon, which is a c ha racteristic sym ptom of the h and-arm vib ra tio n syndrome, our department has studied the occurrence o f intimal th ickening in the peripheral artery of the rat at the site of lo cal chronic exposure to vibra tio n in the rat. The present st u d y aimed at evaluating the possible relationship between histological ch anges in the peripheral arter ies and blood viscosity on the b asis of data from a field survey and an an imal experiment.

Measurement of blood viscosity in the f ield survey
The study group consisted of II wor kers with and 18 without Raynaud ' s phenom enon. All the subjects regularly worked with chain saws. The two groups were similar with respect to age and the length of use of vibrating tool s. Whole blood and plasma viscosity, plasma cyclic AMP (adenosin-rnonophosphate), and GMP (guano sin-monophosphate) were determin ed. The whole blood and plasma viscosity were measured at 37°C with a Wells-Brook field cone-plate microviscometer (model LVT) at the following five shear rates: 230, 115,46,23, and 11.5 S -I . The plasma cyclic AMP and cyclic GMP levels were determined with the radioimmunologic meth od developed by Honm a et al (3).

Experim ental study
Twenty male Wistar rat s, initially weighing 230 -250 g, were used. Each group consisted of five rats. The rat s were exposed to local vibration on their hind legs for 4 hid for either 30 or 90 d . Th e appa ratus used for the vibration exposure consisted of an electromagn etic shaker with a shaking power of 7.5 kg (vibration frequency range 5 -5 000 Hz) cou pled to an amp lifier, a function oscillato r, and a vibratio n meter. The animals were placed in individual mesh cages, in the prone position. The hind legs were out side the cage, their plant ar surfaces horizont ally fixed to the vibratin g plate with doublesided adhesive tape, so that the vibration would be transmitted only to the hind legs. Th e part of the cage containing the rest of the rat bod y was fixed on a non vibrati ng plate separated from the shaker. Th e hind legs were exposed to vertical sinusoidal vibrati on with a freq uency of 60 Hz under a consta nt accelerat ion of 5 g (50 rn-s -! ). Before the experiments, the rats were trained for one week to accept this exposure . The contro l group, in each experiment, was kept in wire mesh cages like the ones used for the exposed group. Th e contro l animal cages were placed near the operat ing electromagnetic shaker during the exposure experiment so that the exposure to noise would be equal in both grou ps. The temperat ure of the animal room was kept at 20 ± 2°C , and a l2-h "li ght-d ark cycle" was maintained. Food and water were pro vided ad libitu m before the start of the exposu re experiment . Eighteen ho urs afte r the last exposure , samples for electro n microscopic examination were obtaine d fro m the dor sal side of the foo t, and blood was then collected after decapitati on.
Whole blood viscosity was measured in this study with a Wells-Brookfield cone-plate microviscometer at the shear rates of 230 and 11 5 S-I . A microscopic examination was mad e Table 1. Whole blood viscosity, plasma viscosity, and hematocrit measured at37" C in the vibration-exposed workers with and without Raynaud's phenomenon.  , Shearrate (s ').
of cross-sections of formalin-fixed specimens obtained from the foot, 1.5 cm distal of the ankle, and stained with hematoxylin eosin and Elastica-Van Gieson. According to Suwa's histometrical method (2), cross-sections of arteries were reduced to the state in which the internal elastic lamina was perfectly stretched, and the thickness of the media (D) and the radius (R) could be measured. Samples for the electron microscopic examination were fixed with 2.5 070 glutaraldehyde for I h and postfixed in 2 070 Osmium tetroxide for I h, both of which were buffered with 0.1M sodium cacodylate at pH 7.4. After dehydration, the samples were embedded in Epon 812-filled gelatin capsules. Thin sections were obtained with an LKB Ultrotome, stained with uranyl acetate and lead citrate, and observed in a Hitachi H-500 electron microscope operating at 75 kV. Table I sho ws the whole blood and plasma viscosity of the vibrating tool opera tors with and without Raynaud 's phenom enon. In the group with Raynaud's phenomenon , the whole blood viscosity was statistically significa ntly higher at each shear rat e in comparison with that of the group without Raynaud's phenomenon . No significan t difference s in plasma viscosity were observed between the two groups. The se result s indi cate th at whole blood viscosity ma y play an importan t role in the a ppearance of the vascu lar symptom or signs of the hand-arm vibration syndrome. In addition , the data impl y that it is possible to discri minate between a group with Raynaud 's phenomenon and a group without it by mea suring whole blood viscosity . The plasma cyclic AMP and GMP levels showed no gro up differences wit h statistica l significan ce. Several investigators ha ve studied the effects of hand-arm vibra tio n on blo od components (7) (ta ble 2), and there are indi cati on s that many blood component s may be af fected by hand-arm vibra tion. However, some of the reports lack pertinent stati stical tests.

Results and discussion
In the pr esent work 30-d exposure did not cause any histologic al changes in the small arteries at the exposed site. Ho wever, a fter 90 d , there were cha nges in the small art eries of the hind leg of the rat s with the following findin gs: disruption of the interna l elastic lam ina , focal cell proliferation, and regenerative for- Blood bet a-th rornboqtobuttn Increase Kanamori et al (198 2) Coagulation system activity Increase Kondo et al (5)  According to the hypothesis recently pr esented by Ross et al (8), atheroscleroti c lesion s ma y ar ise as a result of injury to the endothelium and result in desqu amation follow ed by the adherence, aggregation, and release of platelets at the site of the injury" During th e process of platelet release, a mito genic factor, secreted from th e platelets, gains entry into the ar tery wall and cau ses focal proliferation of int imal smooth mu scle cells. If the injury is a single event , the lesions may heal and regress, a slightly th ickened intima being the result. How ever, if the injury to the endothelium is repeated or chro nic, th e initial thickening ma y be pronounced. Figur e 6 describ es a hypothesis for the mechani sm of vibration-induced intimal thickening of

Endoth elial Injury
Caused by Local V ibra tio n.

Les ions. Leaving a Slightly
Thickened Int imal Layer.  small art eries; the hypothesis is supported by the finding of a fresh fibrin thrombus after 9O-d exposure in the present exper iment.
Azuma et al (1) reported that, after vibratory stimulation, the responsiveness of arterial smooth muscle to noradrenaline markedly increa sed, and the vasoconstrictive activity of noradrenaline was also markedly elevated . Kobori (4) obser ved that an injection of methoxamine hydrochl oride (a vasocon strictive agent) cau sed endothelial injury in the mesenteric artery. It is proposed by us that the sensitivity of the arterial vessels to noradrenaline increases after vibration exposure, and the artery constricts or goes into spasm , resulting in endothelial injury. The hypothetical mechanism o f repeated or chronic endothelial injury by vibration, as causing an intima l thickening, receives support from the present result s.
Vibration-indu ced medial thickening of the art ery has been paid greater attention than intimal thickening (9). In the present study there was no statistically significant difference in medial thickness between the control and exposed gro ups with either exposure duration ( figure 7). Furthermore, Furu yama (2) reported on a stat istically significant correlation bet ween the thickne ss of the media in the mesente ric and femor al arteries and blood pressure, a finding which calls for caution when biop sy data from vibration-exposed workers are being interpreted .
Whole blood viscosity at shear ra tes o f 11 5 and 230 s I did not differ statistically significantly between the control and exposed group s after 30 d of exposure (figure 8). After 90 d, ho wever, the exposed group showed a significantly higher blood viscosity at each shear rate as compared with the control group . The se results indicate some relationship between the increase in whole blood viscosity and the intimal th ickening of some small arteries in the exposed site. In addition , 362 whole blood viscosity is implied as a useful parameter in the diagnosis of the hand-arm vibration syndrome.
A hypothesis for the pathogenic mechani sm o f Raynaud' s phenomenon is described in figure 9. On the basis of the findings in the present study, it is suggested that some relation ship exists between intimal thickening of small arteries and the occurrence and severity of Raynaud 's phenomenon.