Nicolae-Marius Barlea(1), Horatiu Sibianu(2), Radu V. Ciupa (3)
(1)Technical University of Cluj-Napoca,
Physics Department, Romania, E-mail: firstname.lastname@example.org
(2)Technical University of Cluj-Napoca, Physics Engineering student, Romania
(3)Technical University of Cluj-Napoca, Electrotechnics Department, Romania
ABSTRACT: Comparative total impedance measurements for normal skin and acupuncture points are presented. The behavior of the impedance and admittance with the frequency for active points and indifferent skin is analyzed. It is indicated the optimum frequency domain for the detection of the acupuncture points.
Acupuncture points (AP) are very important for medical diagnosis and therapy. The malfunction of the internal organ correlated with the AP lowers the electrical resistance of the AP.
The AP has a lower electrical resistance and a greater electrical capacitance than normal skin. In literature  is stipulated an AP resistance of tens kiloohms, with 20-50% lower than the normal skin and an AP capacitance few hundred times greater than that of the normal skin.
The human body is a large electrolytic system with complex electrochemical reactions. There are only few direct electrical methods for the human body investigation and for this reason we consider important understanding the skin impedance behavior.
2. EXPERIMENTAL METHOD
We measured the impedance of the skin for various frequencies and different effective applied electrical tensions. The electrical set-up consists of a Hewlett Packard Function Generator (HP3310A), a Hung Chang digital multimeter HC4520A with 4 1/2 digits. The test electrode is made from graphite (inert material electrode) with 2mm diameter (3,14 mm2 section area) and the reference electrode is made from silicone rubber with graphite (4 cm2 area and 120W electrical resistance), or alternative lead foil.
Fig. 1. The experimental arrangement for the skin impedance measurement
The measurements were done especially for the point P1 on the lung meridian placed near the corner of the thumbnail and comparatively for the IG1 and IG4 points. We made measurements using signals both square wave and sine wave. The sensitivity was greater for square wave signal than sine wave.
We put the reference electrode either on the indifferent skin or in mouth on the tongue. The best results (stability of the digital microampermeter indications) were obtained with the reference electrode on the tongue. The test electrode was applied with a light pressure on the skin. Because we pressed the electrode with the free hand, the applied pressure was variable modifying the measured skin impedance. The measured values scattering was tolerable, between 10% and 20% of medium value. Much more difficult to handle was the position effect at low frequency (under 100 Hz). Here the smallest deviation from the AP position greatly changes the measured value of the impedance.
3. EXPERIMENTAL RESULTS
The effective tension applied was of 2,05V and the signal shape was square wave. Experimental results are displayed in table 1, where Zindif is the skin impedance, Zactiv is acupuncture point impedance and S is the sensitivity of the method, the ratio between Zindif and Zactiv .
|f (Hz)||Zindif (kW )||Zactiv (kW )||S=ZI /Za|
The impedance diagram of normal skin versus frequency Zindif = F(f) and especially the admittance (1/Zindif) diagram versus frequency, fig.2, reveals the characteristic behavior for an electrical capacitance:
1/Zindif = 2×p× C× f
i.e. 1/Z is a linear function of frequency. In reference  the skin impedance is about 1kW for a 10 ms pulse but only 50W for a 0.1 ms pulse.
Fig. 2. The impedance Z and the admittance 1/Z of the skin versus frequency
There is a slight non-linearity in the range of low frequencies (between 50 and 200 Hz) which could have an experimental origin, but this phenomenon need further investigations because in the same frequency domain there are a clear anomalous behavior of the AP impedance, i. e. there it is a low impedance region of the AP centered on 100 Hz.
The acupuncture points have clearly lower impedance than normal skin. The graph of the frequency dependence of the AP impedance is more complex as we see in fig.3. The capacitive behavior of the AP impedance is less pronounced comparatively to that of the normal skin.
Fig. 3. The impedance and the admittance of the acupuncture point P11 versus frequency
For reliable detection of the acupuncture points it is necessary to exist a clear difference between normal skin and active points. At low frequencies (under 20Hz) the AP impedance is few times lower than the normal skin impedance, but it is very difficult to localize the point because for a displacement under 1mm the impedance measured value became that for the normal skin. At high frequencies (over 500Hz) the normal skin impedance is very close to the AP impedance, as seen in fig.4, but the transition from the normal skin impedance to the AP impedance is smoother.
Fig. 4. Method sensitivity S=Zindif / Zactiv versus frequency
A good choice for the measuring frequency could be somewhere between 20 and 200 Hz, probably 100 Hz for a good noise rejection.
 Dumitrescu I. Fl., Constantin D., Modern scientific acupuncture (in Romanian), Junimea Publishing House, Iaºi 1977
 Low J., Reed A., Dyson M., Electrotherapy explained, Butterworth-Heinemann, 1990