Effect of sensory stimulation (acupuncture) on sympathetic and parasympathetic activities in healthy subjects

It has been postulated that sensory stimulation (acupuncture) affects the cardiovascular system via the autonomic nervous system. Previously, skin temperature, thermography, plethysmography and blood pressure changes have been used in evaluation of sympathetic nerve activity following acupuncture. By using power spectral analysis, the low frequency and high frequency components of heart rate variability can be calculated reflecting the sympathetic and parasympathetic activity. The purpose of this study was to investigate to what extent acupuncture applied into the thenar muscle and into the cavum concha of the ear induced changes in the sympathetic and/or parasympathetic nervous system in healthy subjects. Materials and Methods. Twelve healthy volunteers, six men and six women, mean age 34.4 (range 23–48) participated in three balanced, randomly distributed sessions. At an individual initial visit the 12 volunteers were introduced to the needle sensation by having a needle inserted into the point LI 11. The needle sensation was evoked and the subject was trained to identify the characteristic needle sensation. The introduction was followed by three test sessions. Session A. A short acupuncture needle, (Seirin no 3, ∅0.20×15 mm) was inserted perpendicular into the earpoint, Lu 1, in the left inferior hemi-conchae. Session B. An acupuncture needle (Hwato, ∅0.30×30 mm) was inserted perpendicular into the Hegu point (LI 4) in the middle of the right dorsal thenar muscle. Session C. An acupuncture needle (Hwato, ∅0.30×30 mm) was inserted perpendicular superficially into the skin overlying the Hegu point on the left hand. Results. Stimulation of the ear induced a significant increase in the parasympathetic activity during the stimulation period of 25 min (P<0.05) and during the post-stimulation period of 60 min (P<0.05). No significant changes were observed in either the sympathetic activity, blood pressure or heart rate. Stimulation of the thenar muscle resulted in a significant increase in the sympathetic and the parasympathetic activity during the stimulation period (P<0.01) and during the post-stimulation period (P<0.01 and P<0.001, respectively). A significant decrease in the heart rate frequency (P<0.05) at the end of the post-stimulation period was also demonstrated. The superficial needle insertion into the skin overlaying the right thenar muscle caused a pronounced balanced increase in both the sympathetic and parasympathetic activity during the post stimulation period of 60 min (P<0.01) while no changes were observed during the stimulation period. Conclusion. It is indicated that sensory stimulation (acupunctura) in healthy persons is associated with changed activity in the sympathetic and parasympathetic nervous system depending on site of stimulation and period of observation.