State of the somatic segmental reflex mechanisms in humans subjected to irradiation because of the Chernobyl' nuclear catastrophe

Abstract

State of the afferent, central, and efferent links of the somatic segmental reflex mechanisms was studied in the persons, involved in the cleanup and repair after the catastrophe at the Chernobyl' nuclear power station in 1986; clinical and electroneuromyographic tests were performed. Among 233 investigated individuals, 100 persons received rather high absorbed doses and suffered from acute radiation syndrome (group I). Among the rest of the investigated individuals subjected to lower doses, 49 persons worked at the nuclear plants before and after their participation in the cleanup of the catastrophe (group II), while 84 persons were involved only in the works carried out in 1986 (group III). Comparison with a control group (20 persons) showed that the amplitude of evoked potentials (EP), recorded from the projections ofn. medianus after supramaximum transcutaneous stimulations of the branches of this nerve, innervating II and III fingers, considerably decreased in cleanup workers (on average, by 9.3, 50.8, and 10.0% in groups I–III, respectively). The conduction velocity for EP also dropped (at the finger-wrist region to a greater extent than at the wrist-elbow region, by 12.3–15.0% and 1.1–5.4%, respectively). The maximum amplitude of M responses, recorded from them. abductor pollicis after stimulation of then. medianus, decreased in the groups of cleanup workers by 14.8–17.4%, while the conduction velocity via efferent fibers of then. medianus demonstrated only a slight trend toward a drop in group II. In the groups of cleanup workers the thresholds of H reflex and M response in them. soleus, evoked by stimulation of then. tibialis post., increased, while the amplitudes of these responses decreased. At the same time, the latencies of H and M responses showed no considerable changes. In nearly all cases, the shifts of the above parameters were the greatest in group II. Thus, radiation factors, related to the Chernobyl' catastrophe, induce significant functional distortions in the somatic segmental reflex mechanisms, especially in the distal parts of their afferent and, to a somewhat lesser extent, efferent links. The crucial significance of the duration of radiation influence in the development of the above changes is emphasized. A concept for radiation-induced genesis of the above phenomena is justified. Microcirculatory and metabolic impairments, largely related to the dysfunction of the sympathetic section of the autonomic nervous system, together with direct influences of radiation on the components of the peripheral and central nervous system, are regarded as probable mechanisms of the above modifications; these changes are induced upon long-lasting irradiation even in the case of its low intensity.