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Effects of High Voltage Electro-auriculotherapy on Experimental Pain Threshold
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Effects of High Voltage Electro-auriculotherapy on Experimental Pain Threshold
Key Words Auriculotherapy, experimental pain threshold, electro-acupuncture, high voltage electrical stimulation. by Maryam Zoghi Shapour Jaberzadeh
Summary Background and Purpose Approaches to pain management have improved over the years, but many of them are still invasive or have serious side-effects. Electro-acupuncture is accepted as a non-invasive and non-addictive method of pain management. Although much work in this area has been done to date, more studies need to be conducted to ascertain: ■ The effect of high voltage electrical stimulation at auricular acupuncture points on experimental pain threshold measured at the wrist. ■ The target specificity of auricular acupuncture points for its effects on experimental pain threshold. ■ The changes in effect over time. Subjects Ninety healthy subjects participated in this study. The subjects were assigned randomly to one of three treatment groups. Group 1 (n = 30) received high voltage electrical stimulation to four real auricular points for wrist pain, group 2 (n = 30) received high voltage electrical stimulation to four sham auricular points, and group 3 (n = 30) received no high voltage electrical stimulation. Method A double-blind within-subject design was used in this study. A baseline cutaneous experimental pain threshold to rectangular electrical pulses was determined at the volar aspect of the left wrist. After localisation of auricular points using an electronic point finder, subjects in groups 1 and 2 received 10 minutes high voltage electrical stimulation on real and sham auricular points respectively, while group 3 received no stimulation. The experimental pain thresholds were again measured immediately after treatment, and at 5 and 10 minutes after treatment. Results Groups 1 and 2 had a statistically significant increase in experimental pain threshold at the third post-treatment measurement (10 minutes). There was no significant difference between groups 1 and 2 in pre- and post- treatment measurements. The changes in pain threshold were not significant in group 3. Conclusion These results suggest that the increase in experimental pain threshold following high voltage electrical stimulation of auricular points increases up to 10 minutes but may continue to increase beyond this time. The results also suggest that treatment of sham points was as effective as treatment of specific auricular points.
Zoghi, M and Jaberzadeh, S (2002). ‘Effects of high voltage electroauriculotherapy on experimental pain threshold’, Physiotherapy, 88, 11, 658-666.
Introduction Traditional acupuncture therapy has been used in China for more than 3000 years (Wie, 1979). Acupuncture has gained great popularity in Western countries and is increasingly being introduced into a wide range of healthcare approaches. In the United Kingdom and some other countries many physiotherapists are using acupuncture and its related techniques
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alongside other modalities. These techniques are applied to a variety of conditions, particularly acute or chronic pain syndromes (Rapson et al, 1997). Auriculotherapy is a method of stimulating the acupuncture points on the external ear for therapeutic purposes. Auricular acupuncture points were first recognised as a reflex system by the French physician Nogier in the 1950s. He
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discovered that some of his patients had been treated successfully for sciatica with cauterisation of a certain point on the external ear (Nogier, 1950). Over a period of twenty years he mapped out various areas on the ear which seemed to relate to different parts of the body. This led to widespread use of auriculotherapy as a therapeutic modality. In 1989, auriculotherapy was officially recognised by the World Health Organisation as a viable medical modality (Kuhn, 1999). In auriculotherapy, ear points can be stimulated by different methods such as inserting acupuncture needles (Kitade and Hyodo, 1979), ear stapling and acupressure (Chan, 1981) using laser rays (King et al, 1990), electrical pulses (Oliveri et al, 1986; Noling et al, 1988) and moxibustion, ultrasound, and injection of various substances (Chan, 1981; Lee, 1977). Auricular electro-acupuncture applies transcutaneous electrical nerve stimulation (TENS) along auricular points on the external ear (Paris et al, 1983, Oliveri et al, 1986; Krause et al, 1987; Noling et al, 1988). This method is a non-invasive and non-addictive approach to pain management (Longobardi et al, 1989) that has been used by physiotherapists for more than two decades. Auriculotherapy is an alternative method of pain management in cases such as patients with burns (Lewis et al, 1990), open wounds or limbs in casts over which pain management techniques cannot be applied in the affected area. The effects of auricular electroacupuncture on experimental pain threshold have been studied by several authors. Oliveri et al (1986) compared the effects of electrical stimulation of real and sham auricular points on experimental pain threshold in the wrist area. They concluded that stimulation of auricular points with high intensity TENS could increase the pain threshold in that area. The same conclusion was drawn from similar study by Noling et al (1988), who also suggested that experimental pain threshold might increase with the passage of time. In a study of auricular electroacupuncture on distal extremity pain, Longobardi et al (1989) reported that application of auricular acupuncture-like TENS could be an alternative method to relieve pain. Katz and Melzack (1991) studied the effects of auricular electroacupuncture on phantom pain relief
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and found that auricular stimulation produced significant relief of pain compared to a no-stimulation control group. Most electrical stimulators used in these studies were low-voltage units, although high voltage electrical stimulation units are also used for pain management. It was proposed that high voltage electrical stimulation provides some physiological and technical advantages compared to low voltage electrical units: ■ High voltage electrical stimulation units are designed as constant-voltage rather than constant-current units. The clinical advantage of a constant voltage stimulator is the automatic diminution of current when electrode size is reduced or if electrode contact with the skin becomes loose (Gerleman and Barr, 1999). ■ Negligible, if any, voltage drop when current is passed through skin. In a circuit composed of resistors and capacitors, the high voltage stimulus avoids areas of high resistance, flowing towards capacitors with little energy waste (Procacci et al, 1974). ■ These units deliver much less charge per phase (up to 12.5 µC) compared with other units (20-40 µC). Therefore there is negligible, if any, acid or base build-up under the electrodes (Newton and Karselis, 1983). Consequently this may produce less heat and vasodilation under the electrodes and also greater current density in deeper target tissues for effective stimulation of sensory, motor and pain-conducting fibres. The reason for this effectiveness is explained by the law of excitation, which states that at shorter phase durations, less charge is needed to cause threshold excitation. ■ A problem with using very small electrodes is the proportional relationship between skin resistance and electrode size (Alon, 1985; Alon et al, 1994). Using high voltage electrical stimulation allows clinicians to apply electrical stimulus even through small electrodes with a 1 mm2 tip or through needle electrodes. This capability is related to short pulse duration with a high peak intensity but low average current of high voltage currents.
Authors Mrs Maryam Zoghi MSc BASppSc (Physiotherapy) is a PhD student in the department of physiology, Adelaide University. At the time of this study she was a master’s degree candidate in the School of Physiotherapy, Iran Medical Science University. This manuscript is adapted from her MSc thesis. Shapour Jaberzadeh PhD MSc MAppSc (Manipulative Physiotherapy) BAppSc (Physiotherapy) is a NH&MRC post-doctoral research Fellow in the Department of Physiology, Adelaide University. The authors certify that they have made a substantial contribution to the conception, design, analysis, interpretation of data, drafting and revising the manuscript. This article was received on July 4, 2000, and accepted on February 26, 2002. Address for Correspondence Shapour Jaberzadeh, Medical School South, Level 4, Frome Road, Department of Physiology, Adelaide University, Adelaide SA 5005, Australia. Email: shapour.jaberzadeh@ adelaide.edu.au
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Alon (1987) also suggested that high voltage stimulation might be effective in reducing pain. No published reports, however, appear to exist on the effectiveness of high voltage electrical stimulation on auricular points to reduce pain. The aims of the current study were to determine: ■ The effects of high voltage electrical stimulation at auricular acupuncture points on experimental pain threshold. ■ The target specificity of auricular acupuncture points for its effects on experimental pain threshold at the wrist. ■ The changes in the effect over time. Method Subjects A total of 90 naive asymptomatic subjects (54 men and 36 women aged 18 to 31 years) volunteered for this study. All were full-time physiotherapy students in the first year of their course. The mean (SD) age of subjects was 22.3 (0.96) years, height 169.8 (4.5) cm and weight 61.7 (6.4) kg. Subjects were excluded if they had suffered previous injury including burns or fractures, or had undergone surgery to the wrist area, or had a history of known neurological disorders and systemic disease such as diabetes, or current use of analgesic or anti inflammatory medicine. All participants signed an informed consent form. Ethical approval was received from Ahwaz Medical Science University Ethics Committee (Ahwaz, Iran). Instrumentation The experimental pain threshold at the volar surface of the distal end of the right radius was measured by an electrical stimulation unit (Dynatron 438, Enraf Nonius, Holland). A pencil electrode with a diameter of 2 mm2 was the stimulating electrode, and a conductive rubber electrode (8 cm × 6 cm) was the dispersive electrode. To determine the location of the acupuncture points, an electrical pointfinder unit (ITO-Japan model IC-4107) was used to detect areas of reduced electrical resistance on the surface of the right ear. Since slight variations in applied pressure can alter the measured level of electrical current, a metal tip probe was specially constructed with a spring-loaded Physiotherapy November 2002/vol 88/no 11
stylus with 1 mm diameter. This probe provided constant pressure during location of auricular acupuncture points. A dispersive hand-held electrode was used to complete the electrical circuit. A high voltage unit (Intelect model 500-S, Chattanooga) was used to deliver high voltage currents to auricular points on the right ear. To stimulate the auricular acupuncture points, the springloaded probe (1 mm2) and a moist pad electrode (8 × 10 cm) were used to complete the electrical circuit. Although most clinical acupuncture involves manual manipulation of needles, the application of electrical current through sur face electrodes produces more clinically efficacious analgesia, and is also a more repeatable stimulus for scientific studies. Procedure In this double-blind study, the subjects were assigned randomly to one of three treatment groups, each comprising 30 young subjects. The average age and proportion of men and women in each group was similar. The three groups were compared in a pre-test/post-test control group design. The subjects in group 1 (experimental group) received high voltage electrical stimulation on four auricular points (lung, dermis, wrist and shen-men) which have been reported repeatedly in the literature as analgesic points (Huang, 1975; Oleson et al, 1980; Oliveri et al, 1986; Noling et al, 1988). These points were termed related or real auricular points (fig 1). The subjects in
Shen-men
Wrist
Lung Dermis Mandible Real treatment points
Tongue Eye
Face
Sham treatment points
Fig1: Selected auriculotherapy points for experimental and treated control groups
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group 2 (treated control group) received high voltage electrical stimulation to auricular points (eye, face, tongue and mandible) which theoretically are not related to analgesia at the wrist area (Huang, 1975). These points were termed ‘unrelated’ or ‘sham’ treatment points (fig 1). The subjects in group 3 (nontreated control group) did not receive electrical stimulation. In this study the assessment of experimental pain threshold and application of high voltage electrical stimulation were performed by two senior physiotherapists with at least five years experience in application of electro-therapeutic modalities. Baseline Experimental Pain Threshold Determination The protocol employed in this study for determination of pain threshold was a revised version of the protocol in previous studies (Notermans, 1975; Jette, 1986; Krause et al, 1987; Noling, 1988). The most prominent point at the distal end of the radius on the right side was marked by one researcher ‘pain threshold assessor’. To reduce skin impedance, a standard skin preparation procedure of disinfecting, shaving and abrading (Glimore and Meyers, 1983) was performed for the skin at the electrode sites. The dispersive electrode of the electrical stimulation unit was placed behind the subject’s upper thoracic area. After explanation of the procedure, all subjects were familiarised with the feeling of the stimulating current on the opposite wrist.
Location of stimulating electrode
Fig 2: Location of stimulating electrode for determination of experimental pain threshold
The active pencil electrode was then held on the skin overlying the volar surface of the distal end of the radius (fig 2). The stimulus consisted of 100 Hz rectangular waves with 5 msec duration, delivered every half second. The electrical characteristics fall within the range for frequency and duration recommended by Notermans (1975) for producing a safe and reliable ‘pin-prick’ sensation for the determination of experimental pain threshold. In each step the intensity was systemically increased by 0.3 mA and stopped for about 3 seconds. During gradual increases in stimulus intensity, the subjects were instructed to report the moment at which the feeling of the applied stimulus changed to a painful pin-prick sensation. To increase the reliability of experimental pain threshold the intensity of the stimulus at this threshold value was recorded three times with 30-second intervals between tests and then the averaged values were determined as the baseline pain threshold value for each subject. At this time the ‘pain threshold assessor’ left the room and the second researcher ‘treating clinician’ came in to determine the location of the auricular points and apply the high voltage electrical stimulation.
Acknowledgements The authors wish to thank Dr Hassan Ashayeri, neuropsychologist and Dr Firooz Azordegan, statistician, at the Iran Medical Science University for their valuable input to the study, and Dr Sheila Scutter, neurophysiologist, at the University of South Australia, for her review and critique of this manuscript.
Auricular Points Locations Auricular points were located using acupuncture charts and the point finder unit. This device produces extremely low voltage current, which is enough to flow only through auricular points of low impedance. When this current flows, it activates auditory signals indicating the sites of the points. These points were then marked for later use. High Voltage Electrical Stimulation of Auricular Points The skin on the surface of the ear was cleaned by alcohol. The dispersive handheld electrode was placed in the left hand of the subject to complete the electrical circuit. The spring-loaded tip of the active probe was moved over the marked auricular points and was applied with enough pressure to ensure good contact. This spring-loaded tip allowed application of a standard pressure during stimulation of different points in one subject or between different subjects, which may increase repeatability of active probe application. Then the high voltage Physiotherapy November 2002/vol 88/no 11
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currents were increased gradually to the highest level the patient could tolerate for 2 minutes (Huang, 1975). This procedure was repeated for all four points in each group. The ‘treating therapist’ then covered the ear and left the room. The ‘pain threshold assessor’ came in again and the pain threshold was re-measured at the wrist, immediately and 5 and 10 minutes after intervention. In the untreated control group, after location of the related auricular points, the probe was applied by the treating therapist on the auricular points without application of high voltage electrical stimulation. Since neither the experimental pain threshold assessor nor the subjects were aware of which treatment each subject received, the experimental design was in effect double-blind. Data Analysis A mixed-design (3 × 3) repeated-measures analysis of variance (MANOVA) with one between-subjects factor (group) and one within-subject factor (time) was used to determine whether there were significant differences between experimental pain threshold in three groups of subjects and before and after electrical stimulation of auricular points and whether there was a significant interaction between group of subjects and time at an alpha level of 0.05. Post hoc comparisons were calculated by Tukey’s honestly significant difference (Tukey’s HSD) method. This uses the Studentised range statistic, given the symbol q. To apply Tukey’s HSD to these data, the minimum significant difference (MSD) was calculated: MSD = q √ MSe n
Experimental pain threshold (mA)
8 Experimental group Treated control group 7
Untreated control group
6
5
4 Pre-treatment
0 min post treatment
5 min post treatment
10 min post treatment
Fig 3: M changes at three specific time periods after treatment
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Where MSe is the mean square error, n is the number of subjects in each group, and the critical value of q is taken from a statistical table (critical values of the studentised range statistics, q (Tukey’s HSD and Newman-Keuls comparisons), for the desired level of a degree of freedom associated with the error term (dfe) in the analysis of variance. The q statistic is influenced by the overall number of means that are being compared. In this table the number of means being compared is given the symbol r (Scheffe, 1959). If the absolute difference between a pair of means is equal to or greater than the minimum significant difference, then the difference is considered significant. Results The mean of post-treatment experimental pain threshold changes for each group at each point in time is illustrated in figure 3. The changes in pain threshold showed a tendency to increase over the three post-treatment time periods in both experimental and treated control groups. These changes were more prominent in the experimental group. The pain threshold remained unchanged in the control group. The analysis of variance results show significant main effects for groups, time and interaction between group and time (table 1). Post hoc analysis for group factor revealed that the mean changes of pain threshold for both experimental and treated control groups were statistically different (P < 0.05) from the untreated control group (table 2). This test for time factor showed that there was a significant difference between mean changes of experimental pain threshold between first and third post-treatment time in experimental and treated control groups (table 3). The results of post hoc analysis for interaction of group and time were summarised in table 4. Discussion In the present study, high voltage electrical stimulation on both real and sham auricular points had a significant effect on increasing pain threshold in experimentally induced pain. This effect varied with post-treatment time. These findings suggest that high voltage electrical stimulation of auricular points increases experimental pain threshold. The results of this study are partially in agreement
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with results of previous studies on experimentally induced pain in healthy subjects (Oliveri et al, 1986; Krause et al, 1987; Noling et al, 1988). The results also indicate that the changes in experimental pain threshold in both real and sham auricular points is time-dependent and that five minutes is not long enough to produce significant changes. It was also shown that the increase in experimental pain threshold following high voltage electrical stimulation of auricular points increases up to 10 minutes but this may continue to increase beyond this time. These results are consistent with previous researches suggesting that the effects of low frequency acupuncture are time-dependent (Ebenzor, 1984; Whitlock, 1984; Watkins, 1984). The effectiveness of high voltage electrical stimulation and other electrical modalities compared to other intense forms of stimulation, such as manual handling of needles and heat, indicate that acupuncture is just one of many ways to produce analgesia by an intense sensory input (Le Bars et al, 1983). Traditional Chinese acupuncture is based on metaphysical concept of body energy that runs through hypothesised channels called meridians. Increasingly, research publications gave strong evidence that acupuncture could be explained on a physiological rather than a metaphysical basis. Ullet et al (1998) summarised some of the previous works on the physiological mechanisms of electroacupunctureinduced analgesia in the past 25 years. Based on induction and recovering profiles of acupuncture analgesia they concluded that humeral factors are involved. This belief was supported by cross-perfusion experiments in which acupuncture-induced analgesic effect was transferred from a donor rabbit to a recipient rabbit when cerebrospinal fluid was transferred. Electro-acupunctureinduced analgesia can be prevented by naloxone and by antiserum against endorphins. This finding may suggest release of endorphins into cerebrospinal fluids following electro-acupuncture. The results in the current study may also suggest involvement of hormonal factors for decreasing pain perception. The high voltage electrical stimulation in the current study may activate the brainstem mechanisms, which could exert an inhibitory effect on transmission
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Table 1: Summary of analysis of variance Source of variance
df
SS
MS
F
Sig
Group
2
31.75
15.88
3.21
0.045
Time
2
23.63
11.81
23.83
0.000
Group by time
4
7.66
1.92
3.86
0.005
Table 2: Minimal significance difference: 0.26 Groups
Experimental (1.2)
Experimental
(1.2 )
Treated control
(0.88)
Untreated control
(0.68)
Treated control (0.88)
–
–0.32*
Untreated control (0.68) –0.52*
–
–0.2 –
Table 3: Minimal significance difference: 0.65 Time
T1 (0.3)
T1
(0.3)
T2
(1.02)
–
T3
(1.43)
T2 (1.02)
T3 (1.43)
0.72*
1.13*
–
0.41 –
Table 4: Minimal significance difference: 1.01 Groups
Experimental T1 T2 T3 0.511.20 1.88
Treated control Untreated control T1 T2 T3 T1 T2 T3 0.12 1.08 1.43 0.28 0.79 0.98
Experimental T1 0.51 – 0.69 1.37* –0.39 0.57 0.92 –0.23 0.28 0.47 T2 1.20 – 0.68 –1.08* –0.12 0.23 –0.92 –0.41 –0.22 T3 1.88 – –1.76* –0.8 –0.45 –1.6* –1.09* –0.9 Treated control
T1 0.12 T2 1.08 T3 1.43
Untreated control
T1 0.28 T2 0.79 T3 0.98
–
0.96 1.31* 0.16 0.67 0.86 – 0.35 –0.8 –0.29 –0.1 – –1.15*–0.64 –0.45 –
0.51 –
0.7 0.19 –
T1 = Immediately after treatment T2 = 5 minutes after treatment T3 = 10 minutes after treatment * significant differences using Tukey’s HSD test (a = 0.05)
through the dorsal horns (Melzack, 1971; Watkins and Mayer, 1982; Le Bars et al, 1983). Basically these inputs activate small-diameter fibres which project to cells in the pre-aqueductal grey matter. Since this area contains endorphin and endorphin receptors (Snyder, 1980), the obser vation that naloxone reverses electro-acupuncture analgesia (Sjolund and Erikson, 1979) provided strong evidence that acupuncture and related Physiotherapy November 2002/vol 88/no 11
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forms of treatment are mediated by brainstem neural loops. The results also suggest that the effect of high voltage electrical stimulation is not point specific. This finding suggests that high voltage electrical stimulation of sham auricular points is as effective as high voltage electrical stimulation of real points in increasing experimental pain thresholds in healthy human subjects. This finding seems consistent with the results of previous acupuncture studies in different parts of the body (Gaw et al, 1975; Taub et al, 1977; Co et al, 1979). It is more likely, however, that it is stimulation within a large area of the ear and not merely at particular points that has an effect. Therefore it seems that the painful stimulation, rather than the precise site, appears to be the crucial factor (Ghia et al, 1976; Lewit, 1979). Owing to the differences between experimental pain and clinical pain syndromes, it is not possible to extrapolate the results of this study to clinical pain. Additional clinical studies are necessary to establish the value of high voltage electrical stimulation of auricular points on various types of acute and chronic pain syndromes. Further research with longer post-treatment measurements of experimental pain threshold is needed to investigate long-term after-effects of high voltage electrical stimulation of auricular points. This technique can also be used for double-blind studies on treatment of depression, addiction, anxiety and other relevant disorders. Clinical Implications Traditional acupuncture relies on the use of fine needles being inserted into specific points and then varying amounts of manual stimulation being exerted to give a desired effect, ie rotating a needle
slowly or more quickly, applying heat to the needle or applying leverage to the needle. Other methods of stimulation may include pressure or applying cold which are much less precise. The success and the repeatability of these methods therefore depend on the skill of practitioners in locating the points accurately and then being able to stimulate them effectively. On the other hand, in electro-acupuncture a precise amount of energy can be applied. Adjustment of the frequency, amplitude and other parameters on an electrical stimulator unit may eliminate inconsistency of results and practitioners’ skillrelated errors. Another major benefit of electro-acupuncture is that blood-borne disease risks such as HIV/AIDS and hepatitis B are eliminated, as is the risk of potentially serious unintentional injury such as puncturing. Furthermore, electroacupuncture of auricular points is a non-invasive and non-addictive approach that can be used by physiotherapists as an alternative method of pain management. In cases such as patients with burns (Lewis et al, 1990), open wounds or limbs in casts where pain management techniques cannot be applied over the affected area, auricular electro-acupuncture can be used as the method of choice. Conclusion The results of this study suggest that high voltage electrical stimulation of auricular points can cause significant increases in experimental pain threshold in normal young adults. This increase is timedependent. The lack of target specificity of the auricular points in this study indicated that stimulation is the necessary factor, and the specific designation of a stimulation site is less important.
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Key Messages ■ High voltage electrical stimulation of sham auricular points is as effective as stimulation of real points in increasing experimental pain threshold, indicating that the effect of electro-acupuncture is not point specific. ■ The effect of auricular electroacupuncture on experimental pain threshold is mediated by brainstem neural loops and is time-dependent.
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■ Auricular electro-acupuncture is a non-invasive and non-addictive method of pain management in cases such as patients with burns, open wounds, or limbs in casts, where pain management techniques cannot be applied directly over the affected area.
Effects of High Voltage Electro-auriculotherapy on Experimental Pain Threshold
Key Words Auriculotherapy, experimental pain threshold, electro-acupuncture, high voltage electrical stimulation. by Maryam Zoghi Shapour Jaberzadeh
Summary Background and Purpose Approaches to pain management have improved over the years, but many of them are still invasive or have serious side-effects. Electro-acupuncture is accepted as a non-invasive and non-addictive method of pain management. Although much work in this area has been done to date, more studies need to be conducted to ascertain: ■ The effect of high voltage electrical stimulation at auricular acupuncture points on experimental pain threshold measured at the wrist. ■ The target specificity of auricular acupuncture points for its effects on experimental pain threshold. ■ The changes in effect over time. Subjects Ninety healthy subjects participated in this study. The subjects were assigned randomly to one of three treatment groups. Group 1 (n = 30) received high voltage electrical stimulation to four real auricular points for wrist pain, group 2 (n = 30) received high voltage electrical stimulation to four sham auricular points, and group 3 (n = 30) received no high voltage electrical stimulation. Method A double-blind within-subject design was used in this study. A baseline cutaneous experimental pain threshold to rectangular electrical pulses was determined at the volar aspect of the left wrist. After localisation of auricular points using an electronic point finder, subjects in groups 1 and 2 received 10 minutes high voltage electrical stimulation on real and sham auricular points respectively, while group 3 received no stimulation. The experimental pain thresholds were again measured immediately after treatment, and at 5 and 10 minutes after treatment. Results Groups 1 and 2 had a statistically significant increase in experimental pain threshold at the third post-treatment measurement (10 minutes). There was no significant difference between groups 1 and 2 in pre- and post- treatment measurements. The changes in pain threshold were not significant in group 3. Conclusion These results suggest that the increase in experimental pain threshold following high voltage electrical stimulation of auricular points increases up to 10 minutes but may continue to increase beyond this time. The results also suggest that treatment of sham points was as effective as treatment of specific auricular points.
Zoghi, M and Jaberzadeh, S (2002). ‘Effects of high voltage electroauriculotherapy on experimental pain threshold’, Physiotherapy, 88, 11, 658-666.
Introduction Traditional acupuncture therapy has been used in China for more than 3000 years (Wie, 1979). Acupuncture has gained great popularity in Western countries and is increasingly being introduced into a wide range of healthcare approaches. In the United Kingdom and some other countries many physiotherapists are using acupuncture and its related techniques
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alongside other modalities. These techniques are applied to a variety of conditions, particularly acute or chronic pain syndromes (Rapson et al, 1997). Auriculotherapy is a method of stimulating the acupuncture points on the external ear for therapeutic purposes. Auricular acupuncture points were first recognised as a reflex system by the French physician Nogier in the 1950s. He
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discovered that some of his patients had been treated successfully for sciatica with cauterisation of a certain point on the external ear (Nogier, 1950). Over a period of twenty years he mapped out various areas on the ear which seemed to relate to different parts of the body. This led to widespread use of auriculotherapy as a therapeutic modality. In 1989, auriculotherapy was officially recognised by the World Health Organisation as a viable medical modality (Kuhn, 1999). In auriculotherapy, ear points can be stimulated by different methods such as inserting acupuncture needles (Kitade and Hyodo, 1979), ear stapling and acupressure (Chan, 1981) using laser rays (King et al, 1990), electrical pulses (Oliveri et al, 1986; Noling et al, 1988) and moxibustion, ultrasound, and injection of various substances (Chan, 1981; Lee, 1977). Auricular electro-acupuncture applies transcutaneous electrical nerve stimulation (TENS) along auricular points on the external ear (Paris et al, 1983, Oliveri et al, 1986; Krause et al, 1987; Noling et al, 1988). This method is a non-invasive and non-addictive approach to pain management (Longobardi et al, 1989) that has been used by physiotherapists for more than two decades. Auriculotherapy is an alternative method of pain management in cases such as patients with burns (Lewis et al, 1990), open wounds or limbs in casts over which pain management techniques cannot be applied in the affected area. The effects of auricular electroacupuncture on experimental pain threshold have been studied by several authors. Oliveri et al (1986) compared the effects of electrical stimulation of real and sham auricular points on experimental pain threshold in the wrist area. They concluded that stimulation of auricular points with high intensity TENS could increase the pain threshold in that area. The same conclusion was drawn from similar study by Noling et al (1988), who also suggested that experimental pain threshold might increase with the passage of time. In a study of auricular electroacupuncture on distal extremity pain, Longobardi et al (1989) reported that application of auricular acupuncture-like TENS could be an alternative method to relieve pain. Katz and Melzack (1991) studied the effects of auricular electroacupuncture on phantom pain relief
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and found that auricular stimulation produced significant relief of pain compared to a no-stimulation control group. Most electrical stimulators used in these studies were low-voltage units, although high voltage electrical stimulation units are also used for pain management. It was proposed that high voltage electrical stimulation provides some physiological and technical advantages compared to low voltage electrical units: ■ High voltage electrical stimulation units are designed as constant-voltage rather than constant-current units. The clinical advantage of a constant voltage stimulator is the automatic diminution of current when electrode size is reduced or if electrode contact with the skin becomes loose (Gerleman and Barr, 1999). ■ Negligible, if any, voltage drop when current is passed through skin. In a circuit composed of resistors and capacitors, the high voltage stimulus avoids areas of high resistance, flowing towards capacitors with little energy waste (Procacci et al, 1974). ■ These units deliver much less charge per phase (up to 12.5 µC) compared with other units (20-40 µC). Therefore there is negligible, if any, acid or base build-up under the electrodes (Newton and Karselis, 1983). Consequently this may produce less heat and vasodilation under the electrodes and also greater current density in deeper target tissues for effective stimulation of sensory, motor and pain-conducting fibres. The reason for this effectiveness is explained by the law of excitation, which states that at shorter phase durations, less charge is needed to cause threshold excitation. ■ A problem with using very small electrodes is the proportional relationship between skin resistance and electrode size (Alon, 1985; Alon et al, 1994). Using high voltage electrical stimulation allows clinicians to apply electrical stimulus even through small electrodes with a 1 mm2 tip or through needle electrodes. This capability is related to short pulse duration with a high peak intensity but low average current of high voltage currents.
Authors Mrs Maryam Zoghi MSc BASppSc (Physiotherapy) is a PhD student in the department of physiology, Adelaide University. At the time of this study she was a master’s degree candidate in the School of Physiotherapy, Iran Medical Science University. This manuscript is adapted from her MSc thesis. Shapour Jaberzadeh PhD MSc MAppSc (Manipulative Physiotherapy) BAppSc (Physiotherapy) is a NH&MRC post-doctoral research Fellow in the Department of Physiology, Adelaide University. The authors certify that they have made a substantial contribution to the conception, design, analysis, interpretation of data, drafting and revising the manuscript. This article was received on July 4, 2000, and accepted on February 26, 2002. Address for Correspondence Shapour Jaberzadeh, Medical School South, Level 4, Frome Road, Department of Physiology, Adelaide University, Adelaide SA 5005, Australia. Email: shapour.jaberzadeh@ adelaide.edu.au
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Alon (1987) also suggested that high voltage stimulation might be effective in reducing pain. No published reports, however, appear to exist on the effectiveness of high voltage electrical stimulation on auricular points to reduce pain. The aims of the current study were to determine: ■ The effects of high voltage electrical stimulation at auricular acupuncture points on experimental pain threshold. ■ The target specificity of auricular acupuncture points for its effects on experimental pain threshold at the wrist. ■ The changes in the effect over time. Method Subjects A total of 90 naive asymptomatic subjects (54 men and 36 women aged 18 to 31 years) volunteered for this study. All were full-time physiotherapy students in the first year of their course. The mean (SD) age of subjects was 22.3 (0.96) years, height 169.8 (4.5) cm and weight 61.7 (6.4) kg. Subjects were excluded if they had suffered previous injury including burns or fractures, or had undergone surgery to the wrist area, or had a history of known neurological disorders and systemic disease such as diabetes, or current use of analgesic or anti inflammatory medicine. All participants signed an informed consent form. Ethical approval was received from Ahwaz Medical Science University Ethics Committee (Ahwaz, Iran). Instrumentation The experimental pain threshold at the volar surface of the distal end of the right radius was measured by an electrical stimulation unit (Dynatron 438, Enraf Nonius, Holland). A pencil electrode with a diameter of 2 mm2 was the stimulating electrode, and a conductive rubber electrode (8 cm × 6 cm) was the dispersive electrode. To determine the location of the acupuncture points, an electrical pointfinder unit (ITO-Japan model IC-4107) was used to detect areas of reduced electrical resistance on the surface of the right ear. Since slight variations in applied pressure can alter the measured level of electrical current, a metal tip probe was specially constructed with a spring-loaded Physiotherapy November 2002/vol 88/no 11
stylus with 1 mm diameter. This probe provided constant pressure during location of auricular acupuncture points. A dispersive hand-held electrode was used to complete the electrical circuit. A high voltage unit (Intelect model 500-S, Chattanooga) was used to deliver high voltage currents to auricular points on the right ear. To stimulate the auricular acupuncture points, the springloaded probe (1 mm2) and a moist pad electrode (8 × 10 cm) were used to complete the electrical circuit. Although most clinical acupuncture involves manual manipulation of needles, the application of electrical current through sur face electrodes produces more clinically efficacious analgesia, and is also a more repeatable stimulus for scientific studies. Procedure In this double-blind study, the subjects were assigned randomly to one of three treatment groups, each comprising 30 young subjects. The average age and proportion of men and women in each group was similar. The three groups were compared in a pre-test/post-test control group design. The subjects in group 1 (experimental group) received high voltage electrical stimulation on four auricular points (lung, dermis, wrist and shen-men) which have been reported repeatedly in the literature as analgesic points (Huang, 1975; Oleson et al, 1980; Oliveri et al, 1986; Noling et al, 1988). These points were termed related or real auricular points (fig 1). The subjects in
Shen-men
Wrist
Lung Dermis Mandible Real treatment points
Tongue Eye
Face
Sham treatment points
Fig1: Selected auriculotherapy points for experimental and treated control groups
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group 2 (treated control group) received high voltage electrical stimulation to auricular points (eye, face, tongue and mandible) which theoretically are not related to analgesia at the wrist area (Huang, 1975). These points were termed ‘unrelated’ or ‘sham’ treatment points (fig 1). The subjects in group 3 (nontreated control group) did not receive electrical stimulation. In this study the assessment of experimental pain threshold and application of high voltage electrical stimulation were performed by two senior physiotherapists with at least five years experience in application of electro-therapeutic modalities. Baseline Experimental Pain Threshold Determination The protocol employed in this study for determination of pain threshold was a revised version of the protocol in previous studies (Notermans, 1975; Jette, 1986; Krause et al, 1987; Noling, 1988). The most prominent point at the distal end of the radius on the right side was marked by one researcher ‘pain threshold assessor’. To reduce skin impedance, a standard skin preparation procedure of disinfecting, shaving and abrading (Glimore and Meyers, 1983) was performed for the skin at the electrode sites. The dispersive electrode of the electrical stimulation unit was placed behind the subject’s upper thoracic area. After explanation of the procedure, all subjects were familiarised with the feeling of the stimulating current on the opposite wrist.
Location of stimulating electrode
Fig 2: Location of stimulating electrode for determination of experimental pain threshold
The active pencil electrode was then held on the skin overlying the volar surface of the distal end of the radius (fig 2). The stimulus consisted of 100 Hz rectangular waves with 5 msec duration, delivered every half second. The electrical characteristics fall within the range for frequency and duration recommended by Notermans (1975) for producing a safe and reliable ‘pin-prick’ sensation for the determination of experimental pain threshold. In each step the intensity was systemically increased by 0.3 mA and stopped for about 3 seconds. During gradual increases in stimulus intensity, the subjects were instructed to report the moment at which the feeling of the applied stimulus changed to a painful pin-prick sensation. To increase the reliability of experimental pain threshold the intensity of the stimulus at this threshold value was recorded three times with 30-second intervals between tests and then the averaged values were determined as the baseline pain threshold value for each subject. At this time the ‘pain threshold assessor’ left the room and the second researcher ‘treating clinician’ came in to determine the location of the auricular points and apply the high voltage electrical stimulation.
Acknowledgements The authors wish to thank Dr Hassan Ashayeri, neuropsychologist and Dr Firooz Azordegan, statistician, at the Iran Medical Science University for their valuable input to the study, and Dr Sheila Scutter, neurophysiologist, at the University of South Australia, for her review and critique of this manuscript.
Auricular Points Locations Auricular points were located using acupuncture charts and the point finder unit. This device produces extremely low voltage current, which is enough to flow only through auricular points of low impedance. When this current flows, it activates auditory signals indicating the sites of the points. These points were then marked for later use. High Voltage Electrical Stimulation of Auricular Points The skin on the surface of the ear was cleaned by alcohol. The dispersive handheld electrode was placed in the left hand of the subject to complete the electrical circuit. The spring-loaded tip of the active probe was moved over the marked auricular points and was applied with enough pressure to ensure good contact. This spring-loaded tip allowed application of a standard pressure during stimulation of different points in one subject or between different subjects, which may increase repeatability of active probe application. Then the high voltage Physiotherapy November 2002/vol 88/no 11
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currents were increased gradually to the highest level the patient could tolerate for 2 minutes (Huang, 1975). This procedure was repeated for all four points in each group. The ‘treating therapist’ then covered the ear and left the room. The ‘pain threshold assessor’ came in again and the pain threshold was re-measured at the wrist, immediately and 5 and 10 minutes after intervention. In the untreated control group, after location of the related auricular points, the probe was applied by the treating therapist on the auricular points without application of high voltage electrical stimulation. Since neither the experimental pain threshold assessor nor the subjects were aware of which treatment each subject received, the experimental design was in effect double-blind. Data Analysis A mixed-design (3 × 3) repeated-measures analysis of variance (MANOVA) with one between-subjects factor (group) and one within-subject factor (time) was used to determine whether there were significant differences between experimental pain threshold in three groups of subjects and before and after electrical stimulation of auricular points and whether there was a significant interaction between group of subjects and time at an alpha level of 0.05. Post hoc comparisons were calculated by Tukey’s honestly significant difference (Tukey’s HSD) method. This uses the Studentised range statistic, given the symbol q. To apply Tukey’s HSD to these data, the minimum significant difference (MSD) was calculated: MSD = q √ MSe n
Experimental pain threshold (mA)
8 Experimental group Treated control group 7
Untreated control group
6
5
4 Pre-treatment
0 min post treatment
5 min post treatment
10 min post treatment
Fig 3: M changes at three specific time periods after treatment
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Where MSe is the mean square error, n is the number of subjects in each group, and the critical value of q is taken from a statistical table (critical values of the studentised range statistics, q (Tukey’s HSD and Newman-Keuls comparisons), for the desired level of a degree of freedom associated with the error term (dfe) in the analysis of variance. The q statistic is influenced by the overall number of means that are being compared. In this table the number of means being compared is given the symbol r (Scheffe, 1959). If the absolute difference between a pair of means is equal to or greater than the minimum significant difference, then the difference is considered significant. Results The mean of post-treatment experimental pain threshold changes for each group at each point in time is illustrated in figure 3. The changes in pain threshold showed a tendency to increase over the three post-treatment time periods in both experimental and treated control groups. These changes were more prominent in the experimental group. The pain threshold remained unchanged in the control group. The analysis of variance results show significant main effects for groups, time and interaction between group and time (table 1). Post hoc analysis for group factor revealed that the mean changes of pain threshold for both experimental and treated control groups were statistically different (P < 0.05) from the untreated control group (table 2). This test for time factor showed that there was a significant difference between mean changes of experimental pain threshold between first and third post-treatment time in experimental and treated control groups (table 3). The results of post hoc analysis for interaction of group and time were summarised in table 4. Discussion In the present study, high voltage electrical stimulation on both real and sham auricular points had a significant effect on increasing pain threshold in experimentally induced pain. This effect varied with post-treatment time. These findings suggest that high voltage electrical stimulation of auricular points increases experimental pain threshold. The results of this study are partially in agreement
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with results of previous studies on experimentally induced pain in healthy subjects (Oliveri et al, 1986; Krause et al, 1987; Noling et al, 1988). The results also indicate that the changes in experimental pain threshold in both real and sham auricular points is time-dependent and that five minutes is not long enough to produce significant changes. It was also shown that the increase in experimental pain threshold following high voltage electrical stimulation of auricular points increases up to 10 minutes but this may continue to increase beyond this time. These results are consistent with previous researches suggesting that the effects of low frequency acupuncture are time-dependent (Ebenzor, 1984; Whitlock, 1984; Watkins, 1984). The effectiveness of high voltage electrical stimulation and other electrical modalities compared to other intense forms of stimulation, such as manual handling of needles and heat, indicate that acupuncture is just one of many ways to produce analgesia by an intense sensory input (Le Bars et al, 1983). Traditional Chinese acupuncture is based on metaphysical concept of body energy that runs through hypothesised channels called meridians. Increasingly, research publications gave strong evidence that acupuncture could be explained on a physiological rather than a metaphysical basis. Ullet et al (1998) summarised some of the previous works on the physiological mechanisms of electroacupunctureinduced analgesia in the past 25 years. Based on induction and recovering profiles of acupuncture analgesia they concluded that humeral factors are involved. This belief was supported by cross-perfusion experiments in which acupuncture-induced analgesic effect was transferred from a donor rabbit to a recipient rabbit when cerebrospinal fluid was transferred. Electro-acupunctureinduced analgesia can be prevented by naloxone and by antiserum against endorphins. This finding may suggest release of endorphins into cerebrospinal fluids following electro-acupuncture. The results in the current study may also suggest involvement of hormonal factors for decreasing pain perception. The high voltage electrical stimulation in the current study may activate the brainstem mechanisms, which could exert an inhibitory effect on transmission
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Table 1: Summary of analysis of variance Source of variance
df
SS
MS
F
Sig
Group
2
31.75
15.88
3.21
0.045
Time
2
23.63
11.81
23.83
0.000
Group by time
4
7.66
1.92
3.86
0.005
Table 2: Minimal significance difference: 0.26 Groups
Experimental (1.2)
Experimental
(1.2 )
Treated control
(0.88)
Untreated control
(0.68)
Treated control (0.88)
–
–0.32*
Untreated control (0.68) –0.52*
–
–0.2 –
Table 3: Minimal significance difference: 0.65 Time
T1 (0.3)
T1
(0.3)
T2
(1.02)
–
T3
(1.43)
T2 (1.02)
T3 (1.43)
0.72*
1.13*
–
0.41 –
Table 4: Minimal significance difference: 1.01 Groups
Experimental T1 T2 T3 0.511.20 1.88
Treated control Untreated control T1 T2 T3 T1 T2 T3 0.12 1.08 1.43 0.28 0.79 0.98
Experimental T1 0.51 – 0.69 1.37* –0.39 0.57 0.92 –0.23 0.28 0.47 T2 1.20 – 0.68 –1.08* –0.12 0.23 –0.92 –0.41 –0.22 T3 1.88 – –1.76* –0.8 –0.45 –1.6* –1.09* –0.9 Treated control
T1 0.12 T2 1.08 T3 1.43
Untreated control
T1 0.28 T2 0.79 T3 0.98
–
0.96 1.31* 0.16 0.67 0.86 – 0.35 –0.8 –0.29 –0.1 – –1.15*–0.64 –0.45 –
0.51 –
0.7 0.19 –
T1 = Immediately after treatment T2 = 5 minutes after treatment T3 = 10 minutes after treatment * significant differences using Tukey’s HSD test (a = 0.05)
through the dorsal horns (Melzack, 1971; Watkins and Mayer, 1982; Le Bars et al, 1983). Basically these inputs activate small-diameter fibres which project to cells in the pre-aqueductal grey matter. Since this area contains endorphin and endorphin receptors (Snyder, 1980), the obser vation that naloxone reverses electro-acupuncture analgesia (Sjolund and Erikson, 1979) provided strong evidence that acupuncture and related Physiotherapy November 2002/vol 88/no 11
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forms of treatment are mediated by brainstem neural loops. The results also suggest that the effect of high voltage electrical stimulation is not point specific. This finding suggests that high voltage electrical stimulation of sham auricular points is as effective as high voltage electrical stimulation of real points in increasing experimental pain thresholds in healthy human subjects. This finding seems consistent with the results of previous acupuncture studies in different parts of the body (Gaw et al, 1975; Taub et al, 1977; Co et al, 1979). It is more likely, however, that it is stimulation within a large area of the ear and not merely at particular points that has an effect. Therefore it seems that the painful stimulation, rather than the precise site, appears to be the crucial factor (Ghia et al, 1976; Lewit, 1979). Owing to the differences between experimental pain and clinical pain syndromes, it is not possible to extrapolate the results of this study to clinical pain. Additional clinical studies are necessary to establish the value of high voltage electrical stimulation of auricular points on various types of acute and chronic pain syndromes. Further research with longer post-treatment measurements of experimental pain threshold is needed to investigate long-term after-effects of high voltage electrical stimulation of auricular points. This technique can also be used for double-blind studies on treatment of depression, addiction, anxiety and other relevant disorders. Clinical Implications Traditional acupuncture relies on the use of fine needles being inserted into specific points and then varying amounts of manual stimulation being exerted to give a desired effect, ie rotating a needle
slowly or more quickly, applying heat to the needle or applying leverage to the needle. Other methods of stimulation may include pressure or applying cold which are much less precise. The success and the repeatability of these methods therefore depend on the skill of practitioners in locating the points accurately and then being able to stimulate them effectively. On the other hand, in electro-acupuncture a precise amount of energy can be applied. Adjustment of the frequency, amplitude and other parameters on an electrical stimulator unit may eliminate inconsistency of results and practitioners’ skillrelated errors. Another major benefit of electro-acupuncture is that blood-borne disease risks such as HIV/AIDS and hepatitis B are eliminated, as is the risk of potentially serious unintentional injury such as puncturing. Furthermore, electroacupuncture of auricular points is a non-invasive and non-addictive approach that can be used by physiotherapists as an alternative method of pain management. In cases such as patients with burns (Lewis et al, 1990), open wounds or limbs in casts where pain management techniques cannot be applied over the affected area, auricular electro-acupuncture can be used as the method of choice. Conclusion The results of this study suggest that high voltage electrical stimulation of auricular points can cause significant increases in experimental pain threshold in normal young adults. This increase is timedependent. The lack of target specificity of the auricular points in this study indicated that stimulation is the necessary factor, and the specific designation of a stimulation site is less important.
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Key Messages ■ High voltage electrical stimulation of sham auricular points is as effective as stimulation of real points in increasing experimental pain threshold, indicating that the effect of electro-acupuncture is not point specific. ■ The effect of auricular electroacupuncture on experimental pain threshold is mediated by brainstem neural loops and is time-dependent.
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■ Auricular electro-acupuncture is a non-invasive and non-addictive method of pain management in cases such as patients with burns, open wounds, or limbs in casts, where pain management techniques cannot be applied directly over the affected area.