Comparison of Effects of Transcutaneous Electrical Nerve Stimulation of Auricular, Somatic, and the Combination of Auricular and Somatic Acupuncture Points on Experimental Pain Threshold

This study compared the effects of high intensity, low frequency transcutaneous electrical nerve stimulation of auricular, somatic, and combined auricular and somatic acupuncture points on experimental pain threshold measured at the wrist. Sixty-seven healthy adults, aged 18 to 39 years, were assigned randomly to one of four groups: 1) the Auricular Group (n = 17) received TENS to auricular acupuncture points, 2) the Somatic Group (n = 17) received TENS to somatic acupuncture points, 3) the Combined Group (n = 17) received TENS to both auricular and somatic acupuncture points, and 4) the Control Group (n = 16) received no TENS and served as controls. Pain threshold was measured immedi­ately before and after treatment or rest. Pain threshold significantly increased (p < .05) in the Auricular, Somatic, and Combined Groups following treatment, with no statistically significant differences in mean pain threshold change scores among treatment groups. The Control Group demonstrated no statistically signifi­cant change in pain threshold. The results indicate that TENS applied to any of the three sets of acupuncture points equally increases pain threshold, thus possibly increasing options in choosing stimulation sites for treating patients with pain. [Lein DH Jr, Clelland JA, Knowles CJ, et al: Comparison of effects of transcutane­ous electrical nerve stimulation of auricular, somatic, and the combination of auricular and somatic acupuncture points on experimental pain threshold. Phys Ther 69:671-678, 1989]

Key Words: Acupressure/acupuncture, Electric stimulation, Pain, Transcutaneous electrical nerve stimulation.

Donald H Lein, Jr Jo Ann Clelland Cheryl J Knowles James R Jackson

Pain is a problem confronted by phys­ical therapists daily, often preventing

treatment of accompanying or under­lying disorders until analgesia is

D Lein, MS, PT, is Physical Therapist, University of Alabama Hospitals, 619 19th St, Birmingham, AL 35294 (USA). He was a graduate student, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham, Birmingham, AL 35294, when this study was completed in partial fulfillment of the requirements of his Master of Science degree.

J Clelland, MS, PT, is Associate Professor and Associate Director, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham.

C Knowles, MS, PT, is Assistant Professor, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham.

J Jackson, PhD, is Assistant Professor, Office of Educational Development, School of Medicine, The University of Alabama at Birmingham.

This article was submitted August 1, 1988; was with the authors for revision for 17 weeks; and was accepted February 27, 1989.

achieved. Physical therapists use various methods to relieve pain, including transcutaneous electrical nerve stimulation. Low frequency, high intensity TENS applied to somatic acupuncture points is called "acupuncture-like" TENS. Like acu­puncture, high intensity TENS delivers intense peripheral stimulation. The practice of acupuncture in various forms has been used to relieve pain for thousands of years.1

Studies have shown that somatic acu­puncture point stimulation decreases both experimental2-3 and clinical

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pain.4-7 Berlin et al found that healthy subjects' pain tolerances, as measured by a pain-terminating response, signif­icantly increased after electrical stimu­lation of appropriate somatic acupuncture points, whereas electrical stimulation of inappropriate points did not increase pain tolerance.2

These results suggested that pain relief from acupuncture point stimula­tion was a physiological effect and not a placebo effect.2 Ashton et al showed that acupuncture to somatic points significantly elevated cold-induced experimental pain threshold in 46 healthy, young volunteers.3 Somatic acupuncture point stimulation also has been reported to produce analge­sia in patients with various pain com­plaints, including pain secondary to tennis elbow,4 menstrual pain,5 and chronic pain.67

Stimulation of acupuncture points on the auricle, or auriculotherapy, also is used for pain relief. Studies performed by Oliveri et al,8 Krause et al,9 and Noling et al10 showed that low frequency, high intensity TENS applied to appropriate auricular points increased experimental pain threshold in healthy subjects. These studies indicated that auriculotherapy possibly could decrease pain in patients. Auricular TENS significantly decreased pain in 15 patients suffering with various distal extremity disorders.11 Abbate et al found that after auricular electroacupuncture, 12 patients tolerated decreased dosages of anesthetics during thoracic surgery and decreased analgesic use during recovery.12 Chun and Heather observed that in 46 patients with chronic pain, 84% of the patients' 57 chronic pain syndromes improved at least 25% after auricular electroacupuncture.13 Melzack and Katz, however, conducted a controlled crossover study of 31 patients with chronic pain and found that electrical stimulation of appropriate auricular points did not give any greater pain relief than electrical stimulation to either inappropriate or placebo auric­ular points.14

Stimulating a combination of auricular and somatic acupuncture points is a

third method reported to decrease pain.15-17 After several electrical stimu­lation treatments to both somatic and auricular acupuncture points, a child with reflex sympathetic dystrophy was able to perform all activities of daily living without pain.15 Three months later the child was still asymp­tomatic.15 Paris et al stimulated both auricular and somatic points, in addi­tion to providing conventional physi­cal therapy, to treat second-degree ankle inversion sprains.16 When com­pared with conventional physical ther­apy alone, the addition of acupunc­ture decreased both pain and rehabilitation time.16 The reduction of rehabilitation time, however, was the only statistically significant finding between these two variables.16 Follow­ing electroacupuncture stimulation to both auricular and somatic acupunc­ture points, 20 patients with chronic pain reported significant improve­ment of both pain and psychiatric symptoms.17

Researchers have proposed similar mechanisms for analgesia after either somatic acupuncture point stimulation or auriculotherapy. In addition to the Chinese meridian theory,1 researchers have linked both somatic acupuncture and auriculotherapy to the release of morphine-like substances known as endogenous opiates. Sjolund et al observed that after acupuncture-like TENS, patients with chronic pain experienced analgesia with a con­current segmental increase in cere­brospinal fluid β-endorphins.7 Malizia et al found increased amounts of 0-endorphins secreted in the blood fol­lowing electroacupuncture.18 Abbate and co-workers observed a significant increase of (3-endorphin immunore-activity following auriculotherapy to patients undergoing thoracic surgery.12

Other studies have suggested that serotonin6 and met-enkephalin17 also might be involved in relief of pain following acupuncture. Chapman et al found that the opiate antagonist nalox­one failed to reverse dental acupunc­ture analgesia, indicating a mecha­nism other than release of endogenous opiates.19 Terman et al

found that both opioid and nonopioid analgesic systems exist in the midbrain.20 The mescencephalon, through descending pathways, is believed to modulate the transfer of nociceptive information from periph­eral nerve fibers to ascending paths.20

Terman et al showed that stimulation of both the periaqueductal gray and the dorsal raphe area of the midbrain produced analgesia, but only stimula­tion of the dorsal raphe was blocked by naloxone.20 Perhaps acupuncture can cause analgesia through stimula­tion of several different peptide trans­mitters as well as opioid and nonopi­oid areas.3

Only one study indicated differences between the effects of auricular acu­puncture point stimulation and somatic acupuncture point stimula­tion. Kitade and Hyodo observed that LI 4 stimulation in five healthy men increased pain threshold more rapidly than stimulation of auricular points.21

The internal validity of this study, however, could be questioned because the authors failed to mention whether they controlled for the effects of time or for carry-over effects from previous stimulation. No studies have compared the effects of the combina­tion of auricular and somatic acupuncture point stimulation with the effects of auricular or somatic acu­puncture point stimulation alone. If one of these treatments could be determined to be more effective than the other, physical therapists might attain better clinical results when treating patients with pain. The pur­pose of our study was to compare the effects of unilateral high intensity TENS on experimental pain threshold when applied to auricular acupunc­ture points, somatic acupuncture points, and a combination of auricular and somatic acupuncture points. We expected statistically significant changes would occur in experimental pain thresholds, measured at the wrist, after stimulation of either auric­ular, somatic, or the combination of auricular and somatic acupuncture points. We hypothesized that these changes would be significantly greater than changes in experimental pain

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thresholds measured after a rest period in a control group.

Method

Subjects

Sixty-seven healthy female and male subjects, aged 18 to 39 years, partici­pated in this study. Most of these sub­jects were students, staff, or faculty from The University of Alabama at Birmingham (Birmingham, Ala). Any subjects who were pregnant, used cardiac pacemakers, had neurological disorders, or took opiate pain medica­tions or central nervous system depressants or stimulants were excluded from this study. All subjects were naive to the study's procedure and the anticipated effects. We received informed consent from each subject. The Institutional Review Board for Human Use at The Univer­sity of Alabama at Birmingham aooroved this studv.

Instrumentation

We determined experimental pain threshold with a TECA CH3 chronaxie meter,* which produces a measurable low voltage direct current. The stimu­lating electrode was a 2-mm diameter pencil electrode; the dispersive elec­trode was a 10- x 8-cm electrode pad moistened with water. We used a Staodyn Insight TENS unit,† equipped with a 1-mm diameter spring-loaded pencil probe for stimulation and a 4-x 5-cm dispersive electrode to stimu­late both auricular and somatic acu­puncture points. A Staodyn point loca­tor stimulator† was used to help locate somatic acupuncture points. The reference electrode was 4 × 5 cm, and the tip of the probe was 3 mm in diameter.

Procedure

Subjects were assigned randomly to one of four groups. The Auricular Group subjects (n = 17) received

unilateral TENS for four auricular points: wrist, shenmen, lung, and der­mis (Fig. 1). These auricular points were the same as those used in stud­ies by Oliveri et al,8 Krause et al,9 and Noling et al,10 which resulted in ele­vated experimental pain threshold at the wrist. In the Somatic Group (n = 17), unilateral TENS was applied to four somatic points: 1) Waiguan (SJ 5), 2) Yangchi (SJ 4), 3) Yangxi (LI 5), and 4) Hegu (LI 4) (Fig. 2). All of the somatic acupuncture points are indi­cated for wrist pain.1 All eight auricu­lar and somatic acupuncture points were stimulated unilaterally on sub­jects in the Combined Group (n = 17). The Control Group (n = 16) served as controls. The subjects in this group received no TENS but instead rested for 15 minutes, the maximum amount of time needed to complete the treatment for subjects in the three stimulation groups.

All subjects lay supine on a treatment table, and experimental pain thresh­old was measured immediately before and after treatment or rest. To reduce skin resistance, electrode sites were cleaned with cotton gauze and isopro-pyl alcohol before electrode place­ment.

Pain threshold measurement Before the experiment began, the subjects were allowed to feel the elec­trical current at their right wrists to familiarize themselves with the sensa­tion. We instructed the subjects to recognize and verbally report the instant they perceived any electrical sensation at the right wrist and then again when they experienced a mildly painful pinprick sensation. To deter­mine each subject's experimental pain threshold, electrical stimulation was applied to the skin over the distal end of the left radius (Fig. 3); the disper­sive electrode was applied behind the subject's neck, between the levels of the seventh cervical vertebra and the upper thoracic vertebrae. The point over the distal radius was marked

Fig. 1. Selected auricular points for Auricular and Combined Groups.

with ink to ensure that all measure­ments were taken at the same point. Acupuncture point LI 5, located near the distal end of the radius, was avoided.

The current consisted of 100-Hz rectan gular waves of 5-msec duration. The intensity was increased systematically by 0.25-mA increments at one-second intervals until the subject verbally reported a distinct painful pinprick sensation. This sensation was recorded as the subject's experimen­tal pain threshold. We obtained and averaged three pain threshold mea­surements in each session to deter­mine each subject's mean experimen­tal pain threshold. The reliability of this mean was found to be .98 for pretreatment measurements using an intraclass correlation coefficient (ICC[3,k])22 as the index of reliability.

Treatment The subjects removed all jewelry before treatment. Each subject held the dispersive electrode in the left hand. With the assistance of somatic and auricular acupuncture point charts and an audio or visual signal from the stimulating unit to detect decreased skin resistance, we located appropriate auricular and somatic acupuncture points for each subject according to group assign­ment. If the stimulating unit was not sensitive enough to locate the somatic acupuncture points, we used the Stay-odyn point locator stimulator to locate them. The TENS current used to stim­ulate the acupuncture points was a positive-polarity direct current with a maximum output of 1,000 µA, deliv-*TECA Instruments Corp, 3 Campus Dr, Pleasantville, NY 10570.

† Staodynamics, Inc, PO Box 1379, Longmont, CO 80502.

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ered at a frequency of 1 Hz. The cur­rent duration was constant, as preset in the TENS unit. Subjects responded verbally when they first began to feel the stimulus and then again when the intensity reached each subject's toler­ance. Each point was stimulated for 60 seconds at this intensity. Stimulus intensity was lowered slightly during treatment if requested by the subject. Experimental pain thresholds were measured again immediately after treatment or rest. This treatment tech­nique and the experimental pain threshold determination technique were similar to those used previously by Oliveri et al,8 Krause et al,9 and Noling et al.10

Data Analysis

Descriptive statistics for pain thresh­old were calculated by group for the pretreatment and posttreatment mea­surements and for the change between measurements. A two-factor analysis of variance (ANOVA) was used to test the data for statistical sig­nificance. The two factors were group (Auricular, Somatic, Combined, and Control Groups) and time of mea­surement (pretreatment, posttreat­ment); the time of measurement was a repeated-measures factor. For this design, the interaction effect in the ANOVA is a test of the difference among the mean pretreatment-posttreatment changes for the four groups. The ANOVA also provides tests of simple main effects, which can be used to determine the difference among pretreatment-posttreatment group means as well as the differ­ences between the pretreatment and posttreatment means within each group. Pair-wise comparisons between groups were made with Tukey's Honestly Significant Differ­ence (HSD) test. An alpha level of .05 was selected for all tests.

Results

Each group's demographic informa­tion is depicted in Table 1. Mean pain threshold values are shown in Table 2. The ANOVA showed a statistically significant interaction effect; therefore, there was a statistically significant dif-

Fig. 2 . Selected somatic acupuncture points for Somatic and Combined Groups.

Fig. 3 . Location of stimulating electrode for experimental pain threshold determination.

ference among the groups in terms of pretreatment-posttreatment change (Tab. 3). Pair-wise comparisons using Tukey's HSD test showed that the

mean change for each of the stimula­tion groups was significantly different (p < .05) from the Control Group; however, the stimulation groups did

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not differ significantly from each other. Tests of simple main effects revealed that the group means were not different at the pretreatment measurement session and that each of the stimulation groups showed a statistically significant increase (p < .05) from pretreatment to posttreatment measurement. The mean pretreatment and posttreat­ment pain thresholds are shown in Figure 4 for all four groups.

This study supported our expectation that significant changes would occur in experimental pain threshold, mea­sured at the wrist, after stimulation of auricular, somatic, and the combina­tion of both types of acupuncture points. The hypothesis that these changes in experimental pain thresh­old would be significantly greater than the changes in experimental pain threshold in the control group also was supported. No significant differ­ences were found among the three stimulation groups' mean change val­ues from pretreatment to posttreat­ment measurement.

Discussion

Other studies have shown that stimula­tion of auricular8-10,21 or somatic2'319-21

acupuncture points resulted in statis­tically significant increases in experi­mental pain threshold. We also found statistically significant pain threshold elevation following either auricular or somatic acupuncture point stimu­lation. In addition, stimulation of the combination of auricular and somatic acupuncture points significantly increased experimental pain thresh­old. No other studies have evaluated the effect of the combination of auricular and somatic acupuncture point stimulation on experimental pain threshold. Stimulation of the combined acupuncture sites, how­ever, resulted in decreased clinical pain in disorders such as reflex sym­pathetic dystrophy,15 ankle sprains,16

and chronic pain.17 Individual stimu­lation of either auricular11-13 or somatic4-7 acupuncture points has also lowered pain in various clinical syndromes.

Table 1 - Characteristics of Total Sample (N = 67)

Characteristic

Female subjects Male subjects Age (yr)

s

Group Auricular (n = 17)

10 7

25.1 5.21

Somatic (n = 17)

9 8

23.1 3.03

Combined (n = 17)

12 5

22.4 3.14

Control (n = 16)

10 6

24.9 4.08

The results of our study suggest that stimulation of auricular, somatic, or the combination of both types of these acupuncture points is equally effective in increasing experimental pain threshold. In our study, somatic acupuncture point stimulation resulted in the greatest pain threshold change (Tab. 2). This change, how­ever, was not significantly different from the pain threshold changes in the other two groups that received TENS. Clinically, this finding implies that a physical therapist may legiti­

mately stimulate the set of acupunc­ture points (ie, auricular, somatic, combination of both) that is most convenient, tolerable, and accessible on each individual patient. The anal­gesic effects may be the same after stimulation of any one of these three sets of acupuncture points.

The increases in mean pain threshold observed in the three stimulation groups were all less than 1 mA (Tab. 2). This increase, however, rep­resented mean pain threshold

Table 2 . Mean Pain Threshold Measurements (in Microamperes)

Group

Auricular (n = 17) Pretreatment Posttreatment Change

Somatic (n = 17) Pretreatment Posttreatment Change

Combined (n = 17) Pretreatment Posttreatment Change

Control (n = 16) Pretreatment Posttreatment Change

Pain Threshold

1.23 1.61 0.39

1.56 2.28 0.72

1.42 2.01 0.58

1.28 1.23

-0.05

s

0.53 0.73 0.40

0.73 1.04 0.48

0.45 0.76 0.59

0.38 0.39 0.16

Median

1.33 1.58 0.25

1.50 2.17 0.75

1.42 1.92 0.42

1.46 1.42

-0.08

Range

(0.42-2.25) (0.42-3.00)

(-0.42-1.17)

(0.58-3.42) (1.00-4.67) (0.00-1.58)

(0.58-2.08) (0.83-3.50)

(-0.17-1.92)

(0.50-1.67) (0.50-1.75)

(-0.33-0.33)

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Table 3. Analysis-of-Variance Summary for Pain Threshold

ss

8.82 49.21

1.15 10.42 55.31 5.66 1.28 4.41 2.89 0.02 2.75 6.10

MS

2.94 0.78 0.38 3.47 0.44 5.66 1.28 4.41 2.89 0.02 0.92 0.10

F

3.76a

0.88 7.91a

58.40a

13.21a

45.49a

29.83a

0.18 9.45a

changes of 30.9%, 46.2%, and 41.5% in the Auricular, Somatic, and Com­bined Groups, respectively. Significant increases in mean pain threshold of 16.3% and 11.7% were reported by Oliveri et al8 and Noling et al,10

respectively, immediately following auricular TENS. Similar to our study, Berlin and colleagues found that pain tolerance significantly increased immediately after 20 minutes of somatic electroacupuncture.2 No other study has measured experimental pain threshold immediately following combined stimulation of auricular and somatic acupuncture points. Our study, however, suggested that imme­diate increases in experimental pain threshold should be anticipated.

Other studies have shown that a delay exists before maximum analgesia occurs in experimental pain threshold following either auricular or somatic acupuncture point stimulation.3,10,21

Noling et al reported that the change in mean pain threshold increased from 11.7% immediately following auricular acupuncture point stimula­tion to 25.6% 10 minutes after treatment.10 Ashton et al found that cold-induced pain threshold increased with time, reaching a maximum 35 minutes following somatic acupunc­

ture point acupuncture.3 Kitade and Hyodo measured experimental pain threshold both during and after either auricular or somatic acupuncture point stimulation.21 They also reported that maximum analgesia was not achieved immediately posttreatment.21 Kitade and Hyodo observed that experimental pain threshold reached its maximum at 30 or 50 minutes into somatic acupunc­ture point stimulation.21 In all of these studies, maximum pain threshold lev­els were not achieved immediately, regardless of whether pain threshold was measured following or during either auricular or somatic acupunc­ture point stimulation.310-21 This delay before maximum analgesia could be the time required for the maximal release and function of endorphins. All of these studies also showed that pain threshold remained elevated after cessation of either auricular or somatic acupuncture point stimulation.31021 Our study showed that auricular, somatic, or the combi­nation of auricular and somatic acu­puncture point stimulation resulted in immediate increases in experimental pain threshold; further posttreatment measurements were not taken. Future studies should determine whether experimental pain threshold will con­

tinue to increase or remain signifi­cantly elevated over time following either individual or combined stimu­lation of auricular and somatic acu­puncture points.

Further research should also examine whether auricular, somatic, or the combination of auricular and somatic acupuncture point stimulation increases pain threshold to its maxi­mum level more rapidly over time. Kitade and Hyodo observed that auricular acupuncture point stimula­tion did not increase pain threshold as quickly as somatic acupuncture point stimulation.21 Our study showed that mean pain threshold changes from pretreatment to posttreatment measurement were not significantly different among the stimulation groups. Rather than insertion of nee­dles to apply 50 minutes of electro-acupuncture, we used surface elec­trodes and stimulated the acupuncture points for only 60 seconds.21 Comparisons between our study and that of Kitade and Hyodo21

are difficult to make because different methods of acupuncture point stimu­lation were used. Different methods of acupuncture point stimulation have yielded various degrees of analgesia.2-19,21

Duration of treatment also has been shown to be a factor in effective auric­ular acupuncture point stimulation. Oliveri et al8 and Noling et al10 stimu­lated the same four auricular points used in our study for 90 seconds and observed 16.3% and 11.7% increases, respectively, in mean pain threshold. Krause et al also stimulated the same four auricular points for 45 seconds and found mean pain threshold increased by 12.2%.9 In our study, the application of auricular TENS for 60 seconds resulted in a 30.9% increase in experimental pain threshold. Other studies should be conducted to deter­mine whether 60 seconds of auricular TENS achieves the greatest increases in pain threshold. Studies should also be performed to determine the dura­tion of treatment required to achieve optimal increases in pain threshold with TENS to somatic and the combi-

aStatistically significant (p < .05). bTest of simple main effects.

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Source df

Group Error

Group at pretreatmentb

Group at posttreatmenta

Error Time of measurement

Auricular Groupa

Somatic Groupa

Combined Groupa

Control Group*3

Interaction Error

3 63 3 3

126 1 1 1 1 1 3

63

nation of somatic and auricular acu­puncture points.

Studies should be performed to com­pare the effects of individual and combined stimulation of auricular and somatic acupuncture points in specific patient populations. Comparisons between experimental pain and clini­cal pain were not made in this study because they may differ in their response to acupuncture point stimu­lation. Clinical studies may show that, of the sets of acupuncture points investigated in this study, one set may be more effective in alleviating clinical pain. Nonetheless, experimental pain suppression studies, such as this study, may be an important first step in evaluating and understanding potentially effective means of pain alleviation in the clinic.9

Conclusion

In a group of 67 healthy subjects, low frequency, high intensity TENS admin­istered to auricular, somatic, or the combination of auricular and somatic acupuncture points resulted in statisti­cally significant increases in experi­mental pain threshold. The Control Group demonstrated no significant increase in experimental pain thresh­old following 15 minutes of rest. No statistically significant differences existed in the elevated pain threshold change values among the three stimu­lation groups following TENS treat­ment, but changes in all stimulation groups were significantly greater than the Control Group changes. These results suggest that auricular, somatic, and the combination of auricular and somatic acupuncture point stimulation are equally effective for increasing experimental pain threshold. Because

Auricular Somatic Combined Control

F i g . 4. Experimental pain threshold (pretreatment and posttreatment) for the four groups.

these results imply that stimulation of any of the cited sets of acupuncture points might be equally effective, the clinician could select appropriate acu­puncture points in terms of acupunc­ture point accessibility, patient toler­ance, and clinician convenience. Further research to compare the efficacy of auricular, somatic, and the combination of auricular and somatic acupuncture points with patients with specific pain conditions is needed.

References

1 Essentials of Chinese Acupuncture. Beijing, China, Foreign Languages Press, 1980, pp 1—37 48-59, 111-117, 217-222, 399-414 2 Berlin FS, Bartlett RL, Black JD: Acupuncture and placebo: Effects on delaying the terminat­ing response to a painful stimulus. Anesthesi­ology 42:527-531, 1975 3 Ashton H, Ebenezer I, Golding JF, et al: Effects of acupuncture and transcutaneous electrical nerve stimulation on cold-induced pain in normal subjects. J Psychosom Res 28:301-308, 1984 4 Brattburg G: Acupuncture therapy for tennis elbow. Pain 16:285-288, 1983 5 Neighbors LE, Clelland JA, Jackson JR, et al: Transcutaneous electrical nerve stimulation for pain relief in primary dysmenorrhea. Clinical Journal of Pain 3:17-22, 1987 6 Mao W, Ghia JN, Scott DS, et al: High versus low intensity acupuncture analgesia for treat­ment of chronic pain: Effects on platelet sero­tonin. Pain 8:331-342, 1980 7 Sjolund BH, Terenius L, Eriksson MBE: Increased cerebrospinal fluid levels of endor­phins after electro-acupuncture. Acta Physiol Scand 100:382-384, 1977 8 Oliveri AC, Clelland JA, Jackson JR, et al: Effects of auricular transcutaneous electrical nerve stimulation on experimental pain threshold. Phys Ther 66:12-16, 1986 9 Krause AW, Clelland JA, Knowles CJ, et al: Effects of unilateral and bilateral auricular tran; cutaneous electrical nerve stimulation on cuta­neous pain threshold. Phys Ther 67:507-511, 1987 10 Noling LB, Clelland JA, Jackson JR, et al: Effect of transcutaneous electrical nerve stimu­lation at auricular points on experimental cuta neous pain threshold. Phys Ther 68:328-332, 1988 11 Longobardi AG, Clelland JA, Knowles CJ, et al: Effects of auricular transcutaneous electrical nerve stimulation on distal extremity pain: A pilot study. Phys Ther 69:10-17, 1989 12 Abbate D, Santamaria A, Brambilla A, et al: β-Endorphin and electroacupuncture. Lancet 2:1309, 1980 13 Chun S, Heather AJ: Auriculotherapy: Micro-current application on the external ear—Clinical analysis of a pilot study on 57 chronic pain syndromes. Am J Chin Med 2:399-405, 1974 14 Melzack R, Katz J: Auriculotherapy fails to relieve chronic pain: A controlled crossover study. JAMA 251:1041-1043, 1984

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15 Leo KC: Use of electrical stimulation at acupuncture points for the treatment of reflex sympathetic dystrophy in a child: A case report. Phys Ther 63:957-959, 1983 16 Paris DL, Baynes F, Gucker B: Effects of the Neuroprobe in the treatment of second-degree ankle inversion sprains. Phys Ther 63:35-40, 1983 17 Kiser RS, Gatchel RJ, Bhatia K, et al: Acu­puncture relief of chronic pain syndrome cor­

relates with increased plasma met-enkephalin concentrations. Lancet 2:1394-1396, 1983 18 Malizia E, Andreucci G, Paolucci D, et al: Electroacupuncture and peripheral β-endor-phin and ACTH levels. Lancet 2:535-536, 1979 19 Chapman CR, Benedetti C, Colpitts YH, et al: Naloxone fails to reverse pain thresholds elevated by acupuncture: Acupuncture analge­sia reconsidered. Pain 16:13-31, 1983

20 Terman GW, Shavit Y, Lewis JW, et al: Intrinsic mechanisms of pain inhibition: Activa­tion by stress. Science 226:1270-1276, 1984 21 Kitade T, Hyodo M: The effects of stimula­tion of ear acupuncture points on the body's pain threshold. Am J Chin Med 7:241-252, 1979 22 Shrout PE, Fleiss J: Intraclass correlations: Uses in assessing rater reliability. Psychol Bull 86:420-428, 1979

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