The mechanism of a human reaction to vibration stress by palmar sweating in relation to autonomic nerve tone

Objectives: To clarify the mechanism of a human reaction to vibration stres s by palmar sweating in relation to the autonomic nerve tone. Methods: The autonomic nerve tone was divided into four types by using digital photoelec troplethysmography (PTG) with auditory stimuli: normal (N), hyperreactive ( I and D), and hyporeactive (P) types. Palmar sweating and digital PTG were simultaneously measured on the right palm and middle finger, respectively, in 20 healthy men. The left hand gripping the handle with a grasp strength of 49 N was exposed to vibration at a frequency of 125 Hz and acceleration magnitudes of 0 m/s(2) (as a control), 30 m/s2, or 50 m/s(2) for 3 min. The volume of palmar sweating was recorded before, during, and 30 min after vi bration load. Three kinds of drugs related to the autonomic nervous system were orally administered to the subjects. Then 80 min after administration, the experiments were repeated. Results: Of 20 subjects, 17 showed normal a utonomic nerve tone (N type), and 3 hyperreactive (I type). The palmar swea ting reaction to vibration in I-type subjects was greater and lasted longer than that in N-type subjects. Vibration with an acceleration of 50 m/s(2) produced the greatest reaction which was about 7 times larger than that at 0 m/s(2) and 2.5 times that at 30 m/s(2) (P < 0.01). Sulpiride decreased pa lmar sweating during vibration, while prazosin and scopolamine inhibited it . Conclusions: The palmar sweating reaction to vibration stress was related to the background level of the autonomic nerve tone. The sweating volume w as in direct proportion to the acceleration magnitude of vibration. The rea ction of palmar sweating to vibration stress may be mediated through both t he adrenergic and cholinergic fibers of the autonomic nervous system.