Effect of acupuncture-point stimulation on diastolic blood pressure in hypertensive subjects: a preliminary study

By: Williams, Tim,Mueller, Karen,Cornwall, Mark W.

T Williams, BS, PT, is Staff Physical Therapist, Havasu Samaritan Regional Hospital, Lake Havasu City, AZ 86403. He was a senior physical therapy student at Northern Arizona University, Flagstaff, AZ. when this article was written.

K Mueller, MS, PT, is Assistant Professor, Department of Physical Therapy, Northern Arizona University, PO Box 15105, Flagstaff, AZ. 86011-5105 (USA). Address all correspondence to Ms Mueller.

MW Cornwall, PhD, PT, is Assistant Professor, Department of Physical Therapy, Northern Arizona University.

The results of this study were presented in poster format at the Annual Conference of the American Physical Therapy Association, june 11 15, 1989, Nashville, TN.

This study was approved by the Northern Arizona University Human Subjects Institutional Review Board.

This article was submitted July 31, 1989, and was accepted March 6, 1991.

Electrical stimulation of four specific acupuncture points Liver 3, Stomach 36, Large Intestine 11, and the Groove for Lowering Blood Pressure) was examined in order to determine the effect of this stimulation on diastolic blood pressure in 10 subjects with diastolic hypertension. Subjects were randomly divided into two groups. (1) an Acu-ES group, which received electrical stimulation applied to the four antibypertensive acupuncture points, and (2) a Sham-ES group, which received electrical stimulation applied to non-acupuncture-point areas A repeated-measures analysis of variance revealed a significant, immediate poststimulation reduction of diastolic blood pressure for the Acu-Es group versus the Sham-ES group. Further studies are needed to determine whether there are other acupuncture points, stimulation characteristics, or modalities that can enhance this treatment effect and whether the treatment effect can last for a clinically significant period of time. [Williams T, Mueller K, Cornwall MW. Effect of acupuncture-point stimulation on diastolic blood pressure in hypertensive subjects.- a preliminary study. Phys Ther. 1991;71:523-529.]

Key Words: Acupuncture/acupressure,. Blood pressure; Electrotherapy, electrical stimulation; Hypertension.

Research exploring the physiologic mechanisms underlying acupuncture suggests that somatic processes may be altered through the production of systemic vasodilation, increased endorphin release, and alterations in hormonal secretion.(1) Such research has facilitated an increasing acceptance of acupuncture in western medicine, in which it has been used successfully for the production of analgesia during surgery, pain control in conditions such as migraine headache, and treatment of cardiovascular disorders such as angina pectoris and hypertension.(1-5)

Traditional acupuncture involves the use of small-diameter needles, which are inserted into the skin. The literature suggests that effective stimulation of acupuncture points may also he produced through direct pressure,(6) the use of ultrasound(7,8) and heliumneon lasers,(9-11) and the application of electric currents via the use of surface or implanted electrodes.(12-16) The effective use of acupuncture, regardless of the method used, involves the accurate detection of acupuncture points on the body surface.

Previous studies(17,19) have shown acupuncture points to have a markedly lower electrical resistance than the skin around them. This finding has allowed clinicians to use devices such as an ohmmeter to accurately locate acupuncture points.

Hypertension is a major risk factor for coronary artery disease and stroke, which are, respectively, the first and third highest causes of mortality in the United States.20 Current treatment for hypertension includes sodium restriction, pharmacologic management, and lifestyle modifications such as stress management and exercise.(21) Although these methods of treatment are generally considered to be effective, they frequently require permanent lifestyle changes. Thus, poor patient compliance is common. The drawbacks of antihypertensive medication include side effects, such as fatigue, electrolyte imbalance, and impotence, which often result in patient intolerance.(21) The substantial cost of long-term medication can also be problematic.

These disadvantages suggest a need for alternative strategies in the management of hypertension. The use of needle acupuncture as a method of treatment for hypertension has been explored in both western and Chinese literature. Tam and found that acupuncture produced a significant reduction in systolic and diastolic blood pressure (BP) immediately upon stimulation. In a study exploring the physiologic mechanisms of this effect, Omura(1) measured circulatory changes during acupuncture in 400 patients and reported a generalized vasodilation response, which coincided with a decrease in systolic and diastolic BP. He also found that slight decreases in BP often occurred in patients receiving acupuncture, regardless of the condition treated. Furthermore, the most dramatic decreases were found in patients with essential hypertension.(1) Peng(23) suggested that acupuncture stimulation may cause vasodilation. There is little research on the effect of electrical stimulation of acupuncture points on systolic and diastolic BP. Studies by Yao et al(24) and Hoffman and Thoren(25) have demonstrated a significant reduction of systolic and diastolic BP in hypertensive rats following the application of low-frequency electrical stimulation to the sciatic nerve.

The purpose of this study was to determine the effect of electrical stimulation of selected acupuncture points on diastolic BP in hypertensive subjects immediately following and 5 minutes after stimulation. We hypothesized that hypertensive subjects who received electrical stimulation of four selected acupuncture points would show a significant decrease in diastolic BP immediately following treatment, whereas there would be no immediate posttreatment change in a group of hypertensive subjects who received electrical stimulation applied to non-acupuncture-point areas.

Method

Subjects

Subjects were selected on the basis of two inclusion criteria: (1) a resting diastolic BP between 90 and 120 mm Hg and (2) no past or present use of antihypertensive medication.

All subjects were patients under the care of two physicians with a specialty in family practice. in addition, all subjects had been diagnosed with borderline hypertension within the previous 6 months. The diagnosis of borderline hypertension was assigned by these physicians to any patient with a diastolic BP greater than 90 mm Hg during two consecutive office visits. Patients diagnosed with borderline hypertension were counseled by the physicians about dietary modifications and exercise and were instructed to monitor their BP at home. Subsequently, if these patients reported three consecutive at-home diastolic BP readings above 90 mm Hg, their diagnosis was changed from borderline to essential hypertension. All subjects who participated in this study were still considered by these physicians to be borderline hypertensive.

The two physicians contacted 22 subjects who met the study's inclusion criteria, 12 of whom agreed to participate (2 subjects showed normotensive diastolic BPs when they arrived for the first data-collection session and were excluded from the study). Of the 10 subjects who completed the study, 2 were female and 8 were male. Their mean age was 46 years (range=27-72 years). All subjects gave written informed consent.

Test Environment

The testing environment was carefully controlled in order to minimize factors that could influence diastolic testing was performed in an acoustically insulated audiology booth in which the temperature was maintained between 23[deg] and 25[deg]C. In order to minimize psychological factors affecting diastolic BP, the following steps were taken to ensure a relaxed atmosphere during testing. Subjects were instructed to wear loose and comfortable clothing. The investigators refrained from wearing laboratory coats during all sessions, because the use of such apparel has been associated with increased BP ("white-coat hypertension") in some patients.28 Except for a standing mercury column sphygmomanometer and a stethoscope, the testing equipment was placed away from the subject's view. Finally, a large poster of a pleasant outdoor scene was placed on the wall facing the subject.

Procedure

T Williams, BS, PT, is Staff Physical Therapist, Havasu Samaritan Regional Hospital, Lake Havasu City, AZ 86403. He was a senior physical therapy student at Northern Arizona University, Flagstaff, AZ. when this article was written.

K Mueller, MS, PT, is Assistant Professor, Department
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of Physical Therapy, Northern Arizona University, PO Box 15105, Flagstaff, AZ. 86011-5105 (USA). Address all correspondence to Ms Mueller.

MW Cornwall, PhD, PT, is Assistant Professor, Department of Physical Therapy, Northern Arizona University.

The results of this study were presented in poster format at the Annual Conference of the American Physical Therapy Association, june 11 15, 1989, Nashville, TN.

This study was approved by the Northern Arizona University Human Subjects Institutional Review Board.

This article was submitted July 31, 1989, and was accepted March 6, 1991.

Electrical stimulation of four specific acupuncture points Liver 3, Stomach 36, Large Intestine 11, and the Groove for Lowering Blood Pressure) was examined in order to determine the effect of this stimulation on diastolic blood pressure in 10 subjects with diastolic hypertension. Subjects were randomly divided into two groups. (1) an Acu-ES group, which received electrical stimulation applied to the four antibypertensive acupuncture points, and (2) a Sham-ES group, which received electrical stimulation applied to non-acupuncture-point areas A repeated-measures analysis of variance revealed a significant, immediate poststimulation reduction of diastolic blood pressure for the Acu-Es group versus the Sham-ES group. Further studies are needed to determine whether there are other acupuncture points, stimulation characteristics, or modalities that can enhance this treatment effect and whether the treatment effect can last for a clinically significant period of time. [Williams T, Mueller K, Cornwall MW. Effect of acupuncture-point stimulation on diastolic blood pressure in hypertensive subjects.- a preliminary study. Phys Ther. 1991;71:523-529.]

Key Words: Acupuncture/acupressure,. Blood pressure; Electrotherapy, electrical stimulation; Hypertension.

Research exploring the physiologic mechanisms underlying acupuncture suggests that somatic processes may be altered through the production of systemic vasodilation, increased endorphin release, and alterations in hormonal secretion.(1) Such research has facilitated an increasing acceptance of acupuncture in western medicine, in which it has been used successfully for the production of analgesia during surgery, pain control in conditions such as migraine headache, and treatment of cardiovascular disorders such as angina pectoris and hypertension.(1-5)

Traditional acupuncture involves the use of small-diameter needles, which are inserted into the skin. The literature suggests that effective stimulation of acupuncture points may also he produced through direct pressure,(6) the use of ultrasound(7,8) and heliumneon lasers,(9-11) and the application of electric currents via the use of surface or implanted electrodes.(12-16) The effective use of acupuncture, regardless of the method used, involves the accurate detection of acupuncture points on the body surface.

Previous studies(17,19) have shown acupuncture points to have a markedly lower electrical resistance than the skin around them. This finding has allowed clinicians to use devices such as an ohmmeter to accurately locate acupuncture points.

Hypertension is a major risk factor for coronary artery disease and stroke, which are, respectively, the first and third highest causes of mortality in the United States.20 Current treatment for hypertension includes sodium restriction, pharmacologic management, and lifestyle modifications such as stress management and exercise.(21) Although these methods of treatment are generally considered to be effective, they frequently require permanent lifestyle changes. Thus, poor patient compliance is common. The drawbacks of antihypertensive medication include side effects, such as fatigue, electrolyte imbalance, and impotence, which often result in patient intolerance.(21) The substantial cost of long-term medication can also be problematic.

These disadvantages suggest a need for alternative strategies in the management of hypertension. The use of needle acupuncture as a method of treatment for hypertension has been explored in both western and Chinese literature. Tam and found that acupuncture produced a significant reduction in systolic and diastolic blood pressure (BP) immediately upon stimulation. In a study exploring the physiologic mechanisms of this effect, Omura(1) measured circulatory changes during acupuncture in 400 patients and reported a generalized vasodilation response, which coincided with a decrease in systolic and diastolic BP. He also found that slight decreases in BP often occurred in patients receiving acupuncture, regardless of the condition treated. Furthermore, the most dramatic decreases were found in patients with essential hypertension.(1) Peng(23) suggested that acupuncture stimulation may cause vasodilation. There is little research on the effect of electrical stimulation of acupuncture points on systolic and diastolic BP. Studies by Yao et al(24) and Hoffman and Thoren(25) have demonstrated a significant reduction of systolic and diastolic BP in hypertensive rats following the application of low-frequency electrical stimulation to the sciatic nerve.

The purpose of this study was to determine the effect of electrical stimulation of selected acupuncture points on diastolic BP in hypertensive subjects immediately following and 5 minutes after stimulation. We hypothesized that hypertensive subjects who received electrical stimulation of four selected acupuncture points would show a significant decrease in diastolic BP immediately following treatment, whereas there would be no immediate posttreatment change in a group of hypertensive subjects who received electrical stimulation applied to non-acupuncture-point areas.

Method

Subjects

Subjects were selected on the basis of two inclusion criteria: (1) a resting diastolic BP between 90 and 120 mm Hg and (2) no past or present use of antihypertensive medication.

All subjects were patients under the care of two physicians with a specialty in family practice. in addition, all subjects had been diagnosed with borderline hypertension within the previous 6 months. The diagnosis of borderline hypertension was assigned by these physicians to any patient with a diastolic BP greater than 90 mm Hg during two consecutive office visits. Patients diagnosed with borderline hypertension were counseled by the physicians about dietary modifications and exercise and were instructed to monitor their BP at home. Subsequently, if these patients reported three consecutive at-home diastolic BP readings above 90 mm Hg, their diagnosis was changed from borderline to essential hypertension. All subjects who participated in this study were still considered by these physicians to be borderline hypertensive.

The two physicians contacted 22 subjects who met the study's inclusion criteria, 12 of whom agreed to participate (2 subjects showed normotensive diastolic BPs when they arrived for the first data-collection session and were excluded from the study). Of the 10 subjects who completed the study, 2 were female and 8 were male. Their mean age was 46 years (range=27-72 years). All subjects gave written informed consent.

Test Environment

The testing environment was carefully controlled in order to minimize factors that could influence diastolic testing was performed in an acoustically insulated audiology booth in which the temperature was maintained between 23[deg] and 25[deg]C. In order to minimize psychological factors affecting diastolic BP, the following steps were taken to ensure a relaxed atmosphere during testing. Subjects were instructed to wear loose and comfortable clothing. The investigators refrained from wearing laboratory coats during all sessions, because the use of such apparel has been associated with increased BP ("white-coat hypertension") in some patients.28 Except for a standing mercury column sphygmomanometer and a stethoscope, the testing equipment was placed away from the subject's view. Finally, a large poster of a pleasant outdoor scene was placed on the wall facing the subject.

Procedure

Subjects were randomly divided into two groups by the use of a coin toss. Four subjects comprised the Acu-Es group (test group), which received electrical stimulation applied to the four acupuncture points, and six subjects formed the Sham-ES group (control group), which received electrical stimulation applied to non-acupuncture-point areas. The two subjects who were excluded from the study had previously been assigned to the Acu-ES group. Because they were the last two subjects scheduled for data collection, an uneven distribution of subjects resulted.

All diastolic BP measurements were performed by one investigator (KM), who was blinded as to the subject's group assignment. Prior to the study, this investigator established a test-retest reliability of .99 for diastolic BP using an intraclass correlation coefficient ICC[1,k])(29) as the index of reliability.

The diastolic BP of 10 subjects was measured twice, with a 1-minute interval between the first and second measurements, and the measurements were compared for consistency. Diastolic BP was measured according to American Heart Association guidelines.30 All electrical stimulation was performed by one investigator (TW) as well.

A Neuroprobe(R) System IV stimulator* was used to detect acupuncture points and to provide electrical stimulation. We used a remote hand-held treatment probe with a metal tip measuring 22 mm long and 3 mm wide. No conductive medium was used.

The Neuroprobe(R) System IV provides both auditory and visual signals when the active hand-held treatment probe is in contact with skin areas of low resistance. As previously mentioned, these areas correspond to acupuncture points.

The Neuroprobe(R) System IV provides a medium-frequency sinusoidal signal of 10,000 Hz. All subjects in the study received continuous electrical stimulation at 10,000 Hz (the "MF continuous" pulse-rate setting on the Neuroprobe(R) System IV). This stimulation was divided into two 30-second doses applied to each selected acupuncture point, with a 5- to 7-second interval between each dose. The output intensity of each dose was set at the lowest point at which the subject could detect the stimulation.

The test procedure for each subject was as follows. The subject was seated in a comfortable chair inside the treatment booth. The Neuroprobe(R) System IV setup began with the application of a NeuroAid 3.5 model 7790(TM) disposable gel electrode' on the volar surface of the subject's rightforearm. The subject was fitted with a BP cuff on the right arm and allowed to sit quietly for 5 minutes. Following this 5-minute period, a pretreatment diastolic BP measurement was taken.

Immediately after the pretreatment diastolic BP measurement, the groups received their respective treatments. A second diastolic BP measurement was taken immediately after treatment. The subjects remained seated for an additional 5 minutes, whereupon the final diastolic BP measurement was taken.

Treatment for subjects in the Acu-ES group consisted of electrical stimulation of four selected acupuncture points. Selection of these points was based on acupuncture texts(1-5) and discussions with three certified acupuncture practitioners. The four acupuncture points selected received the highest number of recommendations from these sources.

Electrical stimulation was applied to acupuncture points on the left side of all subjects in the Acu-ES group.

Figure 1 illustrates the anatomical locations of the four acupuncture points. These anatomical locations were used to detect the general area of the acupuncture points, and the hand-held treatment probe was used to determine the exact area for electrical stimulation. The first point stimulated was Liver 3, located on the dorsal surface of the foot, between the first and second metatarsals, at the metatarsophalangeal joints. The second point stimulated was Stomach 36.

This point is located 3.8 cm (1.5 in) distal to the lower border of the patella and 1.3 cm (0.5 in) lateral to the anterior tibial ridge. The third point stimulated was Large Intestine 11. This point is located at the lateral end of the elbow flexion fold. The fourth point is known as the Groove for Lowering Blood Pressure. This is the groove that is found behind the ear when the auricle is folded down. This order was followed for all subjects.

The exact location of the acupuncture points in Acu-ES group subjects was determined by using the hand-held treatment probe to find the area in the region of the acupuncture point with the lowest electrical resistance. Subjects in the Sham-ES group received a control treatment using electrical stimulation characteristics identical to those used for the Acu-ES group; however, this stimulation was applied to non-acupuncture-point areas. These non-acupuncture-point areas were located by placing the probe over the general anatomical area of the acupuncture point as described previously, then moving the probe approximately 15 cm (6 in) away to an area at which a high electrical resistance was encountered. These areas were also stimulated on the subjects' left side in the same order as for the Acu-ES group.

Data Analysis

The test for differences in diastolic BP between immediate posttreatment and 5-minute posttreatment measurements as well as for differences in diastolic BP between the two experimental groups was performed using a mixed two-way analysis of variance (ANOVA). The factor of time (pretreatment- immediately after treatment versus pretreatment-5 minutes after treatment) was designated as the repeated-measures variable. An alpha level of .05 was used for the determination of significant differences.

Results

Table 1 shows the diastolic BP readings of each subject before, immediately after, and 5 minutes following electrical stimulation. The results of an independent Student's t test revealed no statistically significant difference (t = -.93, df= 8, P >.05) for the pretreatment measurements of the Acu-ES and Sham-ES groups. Table 2 shows the between-group means and standard deviations of the diastolic changes between immediate posttreatment and pretreatment measurements and between 5-minute posttreatment and pretreatment measurements.

Table 3 shows the ANOVA results, which demonstrate a significant difference df=1, P<.05) between treatment groups and between the two posttreatment measurement sessions. No significant interaction (P>.05) was found between the treatment groups and the two posttreatment measurement sessions. Figure 2 graphically illustrates the mean changes in diastolic BP over time for the two groups.

Discussion

The results of this preliminary study support the hypothesis that medium-frequency electrical stimulation of selected acupuncture points results in a significant reduction in diastolic BP.

The magnitude and duration of this reduction, however, are insufficient for such stimulation to be of current clinical value as a means of treatment for hypertension. Nonetheless, the results of this study suggest the possibility that furiher research may lead to the discovery of stimulation characteristics, modalities, and acupuncture points that will promote a sustained reduction of diastolic BP into the therapeutic range. The discovery of such factors could, in turn, result in the use of electrical stimulation of acupuncture points as a viable method of treatment for hypertension.

A major limitation of this study was the small number of subjects. Because of the risk for stroke and heart disease associated with untreated hypertension, however, many physicians choose not to delay the prescription of antihypertensive medication. For this reason, we were only able to recruit a small group of subjects who met the inclusion criteria for our study. In spite of the difficulty of recruiting appropriate subjects, we based our selection criteria on the work of Tam and Yiu,(22) who suggested that acupuncture is more effective in lowering BP in subjects who have no history of antihypertensive medication use than in subjects with a history of antihypertensive medication use. These investigators also found that results are even greater when the diagnosis of hypertension has been recent.(22)

Results of studies investigating the use of acupuncture on pharmacologically managed hypertensive subjects suggest that antihypertensive medication may interfere with the effects of acupuncture treatment. Sugioka et al(31) found that the use of acupuncture had no effect on patients who had just completed a course of antihypenensive medication. Clearly, there is a need for further studies to explore how antihypertensive medications and length of time since the diagnosis of hypertension interact with the electrical stimulation of acupuncture points.

Another limitation of this study was the transient duration of the reduction in diastolic BP. In designing a preliminary study, our objective was to determine the efficacy of electrical stimulation as a means of lowering diastolic BP. Because environmental factors can have a profound effect on BP, major emphasis was given to the reduction of patient anxiety. Accordingly, we selected electrical stimulation characteristics that would produce the most immediate treatment effect. These stimulation characteristics resulted in an average treatment time of about 5 minutes. As previously mentioned, the literature suggests that a frequency of 10,000 Hz produces an immediate, but short-lasting, treatment effect.(32,33) The results of our study support this literature, because the differences in diastolic BP between the Acu-ES and Sham-ES groups were no longer significant 5 minutes posttreatment. Further studies are needed to determine whether longer treatment durations at a frequency of 10,000 Hz will result in longer periods of treatment effectiveness.

Although our study involved the use of 10,000-Hz electrical current, further research involving lower frequencies may prove beneficial. Research by Fox and Melzack(13) suggests that a lowerfrequency, long-duration current (such as that used in transcutaneous electrical nerve stimulation) may produce longer-lasting treatment effects.

Electrotherapeutic modalities are widely used by physical therapists for the treatment of musculoskeletal problems. The acupuncture points used to treat musculoskeletal problems are different from those used to reduce BP. Whether an indirect antihypericnsive effect results from such treatment, however, remains to be determined.

Further research on the indirect effects of electrical stimulation of acupuncture points for the treatment of musculoskeletal problems in normotensive and hypertensive subjects may prove to be enlightening. Perhaps it is possible that desirable reductions in BP occur in hypertensive patients receiving electrotherapy for musculoskeletal problems.

The four acupuncture points used in this study are among several that are stated in the acupuncture literature to have an antihypertensive effect. Pericardium 6; Gall Bladder 20, 21, and 41; Stomach 9 and 37; Kidney 1; Spleen 1 and 2; and Heart 7 are other acupuncture points that can be used to lower BP.(1-5) We suggest that future studies be conducted using one or more of these alternative acupuncture points. Bilateral stimulation to selected acupuncture points may also prove to be effective.

In summary, the results of this study suggest numerous possibilities for future research. We suggest several replications of this study, manipulating the variables of treatment duration, electrical modality used, stimulation characteristics, and acupuncture points selected.

Conclusion

This study was designed to validate the current literature concerning the electrical stimulation of acupuncture points affecting diastolic BP and to provide a basis for future research.

Thus, we designed a preliminary study, with an emphasis on accuracy of acupuncture-point detection, using a clinically available modality that produces a quick, but short-lasting, therapeutic effect. The results of our study indicate that stimulation of four selected acupuncture points with a current of 10,000 Hz produces a significant reduction in diastolic BP in hypertensive subjects. Although the duration and magnitude of this effect were insufficient to be of clinical value, the results of this study support the efficacy of electrical stimulation as a means of lowering diastolic BP.

Acknowledgments

We would like to express our thanks to the following individuals: Michael Ryan, MD, and Corwin Demarse, MD, for their assistance in locating subjects; Kay Evje and Susan Nassan, licensed acupuncturists, for their advice; Graydon Bell, PhD, for his contribution to our statistical analysis; and Paul Hansen, PhD, PT, for his editorial comments. Finally, we extend special thanks to all of our subjects.

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