Original ArticlesFree Access

Effects of a Single Session of Acupuncture Treatment on Blood Pressure and Heart Rate Variability in Patients with Mild Hypertension

    Published Online:15 Apr 2021https://doi.org/10.1089/acm.2020.0324

    Abstract

    Objective: The aim of the present study was to compare the effects of acupuncture treatment on arterial blood pressure (BP) and heart rate (HR) in patients with mild hypertension with high sympathetic tone with those of normotensive patients and to examine the effects on cardiac sympathetic nerve activity (CSNA) and vagal activity using heart rate variability (HRV) analysis.

    Design: Eight male patients with prehypertension or stage I hypertension and eight normotensive age-matched patients were included in this study. All patients had their systolic BP (SBP), diastolic BP (DBP), HR, and HRV measured. In addition, the ratio of low-frequency (LF) to high-frequency (HF) HRV and the power of the HF of the HRV were recorded. The study was conducted at Kansai University of Health Sciences in Japan.

    Interventions: Each patient underwent a single, 15-min-long acupuncture session. Acupuncture was applied to PC6, LI4, ST36, LR3 on both sides, and GV20.

    Results: SBP and HR decreased significantly in the hypertensive group during and after acupuncture compared with the baseline SBP and HR (p < 0.05). LF/HF was significantly reduced during acupuncture (p < 0.05), and HF was significantly increased after acupuncture in the hypertensive group (p < 0.05). However, there were no significant changes in LF/HF or HF in the control group.

    Conclusions: Acupuncture may reduce the BP and HR in patients with mild hypertension. An HRV analysis suggests that acupuncture may suppress the enhanced basal CSNA activity and increase the vagal nerve activity in patients with mild hypertension.

    Clinical Trial Registration number: UMIN000041249.

    Introduction

    Hypertension is the most common cardiovascular disease, and it affects more than one quarter of the adult population worldwide.1 It is a significant independent risk factor for heart attacks, heart failure, strokes, and kidney disease.2 The prevalence of hypertension increases with age. Blood pressure (BP) can be lowered by several classes of antihypertensive medications and lifestyle changes, such as weight loss, exercise, and restriction of salt intake. However, hypertension in most individuals remains untreated or uncontrolled.3 Lifestyle changes can be difficult to achieve and maintain. Pharmacotherapy is limited by its cost, availability, and adverse effects.2,4 Therefore, developing a new effective method of lowering BP is important for the treatment of hypertension.

    Acupuncture has long been used for cardiovascular diseases including hypertension. Recently, it has attracted interest as an adjunctive therapy to conventional antihypertensive therapies or lifestyle changes as it has fewer side effects and is cost-effective.5 In recent years, large-scale, high-quality, randomized controlled trials on the hypotensive effect of acupuncture on essential hypertension have been conducted in Europe and Korea.6–8 These high-quality clinical studies reported that acupuncture is a promising adjunctive therapy for lowering BP in patients with mild essential hypertension compared with placebo. It has been shown that acupuncture in the lower limbs of anesthetized rats lowered the BP and heart rate (HR), thereby reducing the renal sympathetic nerve activity and cardiac sympathetic nerve activity (CSNA).9,10

    In general, the effects of acupuncture treatment seem to be more pronounced when the patient's sympathetic tone is higher than normal at baseline. It is reported that the magnitude of the depressor response to acupuncture is greater in spontaneous hypertensive rats (SHRs) than in normal rats.11,12 It is also known that sympathetic tone is higher in SHRs than in normotensive rats.13,14 These previous studies suggest that the magnitude of the sympathetic inhibitory response to acupuncture may depend on the basal activity of the sympathetic nervous system.

    Power spectral analysis of heart rate variability (HRV) has been used as a sensitive indicator of autonomic nervous system activity in humans.15–17 CSNA has been reported to be enhanced in patients with mild hypertension compared with that in normotensive subjects.18,19 It is also known that acupuncture not only suppresses the sympathetic nervous system but also activates the vagal nerve activity in humans.20–22 In this study, the authors compared the effects of acupuncture on BP and HR in patients with mild essential hypertension with those of normotensive patients and analyzed the effects of acupuncture on CSNA and vagal nerve activity using HRV analysis. The authors hypothesized that acupuncture treatment may cause sympathetic inhibition, which may cause a decrease in BP and HR in mildly hypertensive patients.

    Materials and Methods

    Subjects

    From December 2017 to December 2019, 10 patients with mild hypertension were screened for inclusion in this study. Inclusion criteria were based on the Japanese Society of Hypertension 2019 criteria and included prehypertension (systolic BP [SBP] 130–139 mmHg or diastolic BP [DBP] 80–89 mmHg) or stage I hypertension (SBP 140–159 mmHg or DBP 90–99 mmHg). The exclusion criteria were secondary hypertension; diabetes; a history of cerebrovascular or cardiovascular disease; kidney, liver, thyroid gland, or hemorrhagic disease; and infectious disease. Two patients were excluded from this study: one did not meet the exclusion criteria while one declined to participate. The control group included eight age-matched male subjects with normal BPs (SBP <120 mmHg and DBP <80 mmHg). All control subjects were not taking any medications and were free of cardiovascular or neuromuscular diseases, based on their medical history and physical examination. The final analysis included eight patients with prehypertension or stage I hypertension and eight normotensive age-matched controls. The study was conducted at Kansai University of Health Sciences, and all subjects completed the study. This study was approved by the Human Investigation Committee of Kansai University of Health Sciences. Each subject was informed of the purposes and risks of the study before providing their written consent. The study was carried out in accordance with the approved guidelines and was registered at ClinicalTrials.gov.

    Measurements

    Three disposable electrodes were attached to the chest for electrocardiogram (ECG) monitoring. ECG was performed using a bio-amplifier (Model ML132; AD Instruments, Bella Vista, Australia). Signals were sampled at 1,000 Hz via an A/D converter (Power Lab8S; AD Instruments), and digitalized ECG signals were stored on a personal computer. The R waves on the ECG were detected, and the HR was measured from the R-R interval. The R-R interval data were transferred to a computer loaded with HRV analysis software (Tonam2C Version 1.0 for Windows; Suwa Trust Ltd., Tokyo, Japan). A frequency domain analysis of HRV was performed for 60 sec using the maximum entropy method, which can estimate the spectrum from short data and obtain a very stable spectrum with high resolution. This method was used for frequency analysis from HRV. The power of the R-R interval (ms2) with low-frequency (LF; 0.04–0.15 Hz) and high-frequency (HF; 0.15–0.4 Hz) bands was estimated. The power of the HF and the LF/HF ratio were used as indices of vagal activity and CSNA, respectively.15–17 BP was measured manually by auscultation. SBP and DBP were measured in 2-min intervals at baseline, during acupuncture, and during the recovery period.

    Acupuncture

    The patient and control groups were treated with a standardized acupuncture. After the skin was cleaned with alcohol, acupuncture needles (0.20 × 40 mm; Seirin Kasei Co., Shizuoka, Japan) were inserted into the acupoints based on the theory of Traditional Chinese Medicine: PC6 on the anterior aspect of the forearms, LI4 on the backs of the hands, ST36 on the anterior aspect of the lower legs, LR3 on the dorsal aspect of the feet, and GV20 on the top of the head. These acupoints have been frequently used in previous studies on acupuncture for hypertension.23,24 After obtaining data regarding the de qi sensation (a distinct sensation of heaviness or numbness) induced by needle manipulation, the inserted needles remained in place at a depth of 5 mm for 15 min. Acupuncture was performed by a certified acupuncturist with more than 10 years of experience.

    Experimental protocols

    Patients reported to the laboratory between 3 PM and 4 PM wearing shorts and t-shirts and rested in the supine position in a quiet room for 10 min (ambient temperature, 26.5°C ± 0.5°C) (control period). After obtaining the baseline data during 10 min of rest (control period), acupuncture was applied for 15 min (acupuncture period), followed by the removal of the needles and continuation of data recording for 20 min (recovery period). SBP, DBP, and HR were measured continuously during the control, acupuncture, and recovery periods.

    Data analysis

    The changes in SBP, DBP, and HR (ΔSBP, ΔDBP, and ΔHR) were calculated. Measurements obtained after 2 min of rest during the control period were considered baseline values. In the HRV analysis, the 10 min resting LF/HF ratio and the HF power were averaged to obtain the baseline values that were compared with the average of the measurements obtained during the final 10 min of the acupuncture period and recovery period. Serial changes in each parameter relative to the baseline values and differences between groups were examined for statistical significance using two-way analysis of variance including Tukey's post hoc analysis. The data are presented as mean ± standard error of the mean (SEM). Statistical significance was set at p < 0.05.

    Results

    The mean age ± SEM was 34.8 ± 3.7 years (range, 25–50 years) in patients with mild hypertension and 34.6 ± 4.0 years (range, 26–50 years) in control patients.

    Baseline data of the SBP, DBP, HR, body mass index (BMI, in kg/m2), LF/HF ratio, and HF are shown in Table 1. There was no difference between the two groups in terms of age or BMI. Baseline SBP, DBP, and HR were significantly higher in the hypertensive group than in the control group (p < 0.05). Baseline values of HF were significantly lower in the patient group (p < 0.05). LF/HF was higher in the patient group than in the control group (p = 0.052).

    Table 1. Baseline Characteristics of Patients and Controls

    CharacteristicPatients (n = 8)Controls (n = 8)p-Value
    Age (years)34.8 ± 3.733.5 ± 2.7NS
    SBP (mmHg)140.2 ± 0.2111.9 ± 0.4<0.05
    DBP (mmHg)89.8 ± 0.870.2 ± 0.6<0.05
    HR (bpm)73.5 ± 0.465.6 ± 0.4<0.05
    BMI (kg/m2)27.6 ± 1.723.7 ± 0.8NS
    HF (ms2)161.1 ± 6.9347.7 ± 23.9<0.05
    LF/HF of HRV5.0 ± 1.22.9 ± 0.3NS

    Data are presented as mean ± standard error of the mean. p < 0.05: controls versus patients with mild hypertension.

    BMI, body mass index; bpm, beats per minute; DBP, diastolic blood pressure; HF, high frequency; HR, heart rate; HRV, heart rate variability; LF, low frequency; NS, not significant; SBP, systolic blood pressure.

    The mean SBP in the hypertensive group was 133.9 ± 0.3 mmHg during the acupuncture period and 133.5 ± 0.3 mmHg during the recovery period. The mean SBP in the control group was 111.4 ± 0.4 mmHg during the acupuncture period and 111.9 ± 0.4 mmHg during the recovery period. There was a significant difference in the ΔSBP during the acupuncture period between the hypertensive group (−5.0 ± 1.5 mmHg) and the control group (−0.2 ± 2.1 mmHg, p < 0.05, Fig. 1A). The ΔSBP in the hypertensive group was significantly decreased during the acupuncture period compared with the baseline values (p < 0.05). The ΔSBP in the hypertensive group remained significantly lowered until the end of the recovery period.

    FIG. 1.

    FIG. 1. (A) Δ Systolic blood pressure, (B) Δ diastolic blood pressure, and (C) Δ heart rate recorded during the study. Data are presented as mean ± standard error of the mean. *p < 0.05, compared with the baseline values; #p < 0.05, control versus patients.

    The mean DBP in the hypertensive group was 85.8 ± 0.3 mmHg during the acupuncture period and 86.8 ± 0.2 mmHg during the recovery period. The mean DBP in the control group was 70.8 ± 0.3 mmHg during the acupuncture period and 71.3 ± 0.3 mmHg during the recovery period. There was a significant difference in the ΔDBP between the hypertensive group (−3.0 ± 1.8 mmHg) and the control group (−0.1 ± 1.7 mmHg, p < 0.05, Fig. 1B) at 2 min from start of the acupuncture treatment. No significant differences were observed over time for the ΔSBP and ΔDBP in the control group (Fig. 1A, B). The ΔHR was significantly decreased in the hypertensive group during acupuncture compared with the baseline values (patient group, −5.8 ± 1.6 beats per minute [bpm], control group, −2.5 ± 1.6 bpm, p < 0.05, Fig. 1C).

    The mean HR in the hypertensive group was 68.9 ± 0.2 mmHg during the acupuncture period and 68.4 ± 0.3 mmHg during the recovery period. The mean HR in the control group was 63.3 ± 0.2 mmHg during the acupuncture period and 62.9 ± 0.3 mmHg during the recovery period. The ΔHR in the hypertensive group remained significantly lowered until the end of the recovery period (p < 0.05). There was no significant difference in ΔHR between the two groups throughout the experimental period (Fig. 1C).

    Figure 2 shows the typical patterns of the trend graphs of the R-R intervals and power spectrum of the HRV analysis in a representative patient from the hypertensive group. The R-R interval and its variation increased during and after the acupuncture. The power spectrum showed an increase in the HF power during acupuncture. The increase in the HF power continued even after acupuncture.

    FIG. 2.

    FIG. 2. Trend graph of the R-R intervals (A) and power spectrum of the heart rate variability analysis (B) during the study in a representative subject of the patient group. HF, high frequency; LF, low frequency.

    The mean LF/HF ratio in the hypertensive group was 4.4 ± 0.5 mmHg during the acupuncture period and 4.2 ± 0.4 mmHg during the recovery period. The mean LF/HF ratio in the control group was 3.5 ± 0.3 mmHg during the acupuncture period and 4.2 ± 0.2 mmHg during the recovery period. As shown in Figure 3A, the changes in the LF/HF ratio relative to the baseline ratio decreased significantly in the hypertensive group (60.3% ± 6.1%) during acupuncture (p < 0.05). The LF/HF ratio was also lower in the hypertensive group than in the control group during the acupuncture period (60.3% ± 6.1% and 103.7% ± 22.4%, respectively) and the recovery period (72.2% ± 15.5% and 129.8% ± 36.3%, respectively). The LF/HF ratio in the control group did not show any significant changes during the acupuncture period or the recovery period.

    FIG. 3.

    FIG. 3. (A) Percentage changes in the LF/HF ratio and (B) the HF power during the rest, acupuncture, and recovery periods. Data are presented as mean ± standard error of the mean. *p < 0.05, compared with the baseline values; #p < 0.05, control versus patients. HF, high frequency; LF, low frequency.

    The mean HF power in the hypertensive group was 228.6 ± 11.1 ms2 during the acupuncture period and 270.7 ± 14.1 ms2 during the recovery period. The mean HF power in the control group was 409.8 ± 9.1 ms2 during the acupuncture period and 428.4 ± 10.1 ms2 during the recovery period. As illustrated in Figure 3B, the changes in the HF power in the hypertensive group increased significantly during the recovery period (221.4% ± 38.9%) compared with the baseline values (p < 0.05). The HF power was also significantly higher in the hypertensive group (181.0% ± 23.2%) than in the control group (119.2% ± 8.2%) during acupuncture (p < 0.05). The HF power in the control group did not show any significant changes during the acupuncture period or the recovery period.

    Discussion

    This study examined the effects of acupuncture on BP, HR, and HRV in patients with mild hypertension and found that acupuncture reduced SBP and HR in patients with mild hypertension, whereas SBP and HR did not change significantly in the control subjects. The results of the HRV analysis suggest that acupuncture may decrease CSNA and increase vagal activity in patients with mild hypertension, resulting in a decrease in BP and HR.

    In general, the effect of acupuncture is more significant when the sympathetic tonus is increased. Acupuncture has been shown to inhibit sympathetic nerve activity and lower HR and BP in anesthetized animals.9,10,25 Yao et al.11,12 found that the magnitude of the depressor response produced by the inhibition of sympathetic nerve activity by acupuncture is greater in SHRs than in normotensive controls. In addition, sympathetic tone in SHRs is known to be higher than that in normotensive controls.13,14 The authors recently reported that acupuncture at ST36 induced a depressor response; however, no significant changes in the muscle sympathetic nerve activity (MSNA) in normotensive healthy subjects were identified.26 Although acupuncture did not suppress resting MSNA in healthy subjects, it may inhibit MSNA in patients with enhanced MSNA, such as those with essential hypertension.27 In this study, patients with mild hypertension had greater reductions in BP and HR than normotensive controls. The LF/HF ratio and the HF power are indicators of CSNA and vagal nerve activity, respectively. The HRV analysis showed that the basal LF/HF values were higher in the hypertensive group than in the control group and decreased during and after acupuncture. Watanabe and Hotta28 reported that the direction of the HR response to mechanical pressure stimulation of the muscles is dependent on the tonic levels of CSNA and resting HR. When the tonic activity of CSNA is high, bradycardia occurs, and when the tonic activity of CSNA is low, tachycardia occurs. Imai and Kitakoji29 also showed that the degree of bradycardia induced by acupuncture in humans was greater in the sitting position (when the tonic activity of CSNA is high) than in the supine position (when the tonic activity of CSNA is low), and the sitting position is associated with a higher resting HR. The patients with mild hypertension had higher basal CSNA than the normotensive controls in this study, which is consistent with previous reports. Thus, acupuncture may have reduced CSNA and elicited depressor and bradycardia responses in patients with mild hypertension.

    In contrast, Uchida et al.30 revealed that the inhibitory effect of the acupuncture on HR was attenuated by hypercapnia, which increased the tonic level of CSNA. The authors of that study suggested that the effect of acupuncture might be different between the state in which the sympathetic tonus is chronically increased and the state in which the sympathetic tonus is acutely increased, such as in hypercapnia. Given that CSNA is chronically elevated in patients with mild hypertension, it is possible that acupuncture reduced CSNA.

    In this study, acupuncture increased the HF component of HRV, indicating increased vagal activity. Acupuncture at ST36 has also been shown to enhance the vagal activity.31 Other researchers showed that acupuncture at PC6 and LI4 affected the vagal activity in humans.32,33 Ouyang et al.34 examined the effects of electroacupuncture (EA) at PC6 and ST36 on gastric myoelectrical and vagal activities by performing an HRV analysis in dogs. EA promoted emptying of the stomach, and the promotion of gastric motility was associated with an increase in the vagal activity. Imai et al.35 showed that EA at ST36 significantly increased the gastric motility and decreased the LF/HF ratio in conscious rats. In contrast, EA at abdominal ST25 significantly inhibited the gastric motility and increased the LF/HF ratio. Studies have indicated that EA at ST36 induces a gastric contraction, which is accompanied by the increase in vagal activity, and EA at ST25 induces gastric inhibition, which is accompanied by the increase in sympathetic nerve activity. Recently, Nakahara et al.36 reported that acupuncture induces autonomic-mediated cardiovascular responses and that these responses differ depending on the site of acupuncture. Acupuncture stimulation at ST36 elicited depressor and bradycardic responses and is considered to be effective for the treatment of hypertension. The decrease in HR and BP in patients with mild essential hypertension suggests that CSNA suppression and vagal activity enhancement are involved. The results of the present study suggest that acupuncture treatment suppresses CSNA and increases vagal nerve activity, resulting in a decrease in HR and cardiac output, which in turn decreases BP. The decreased sympathetic nerve activity caused by acupuncture treatment may lead to decreased peripheral vascular resistance and decreased BP.

    The present study examined the effect of a single acupuncture treatment on BP and HR in patients with mild hypertension. There have been few studies comparing short-term acupuncture treatment with multiple long-term acupuncture treatments. A previous study has reported that long-term acupuncture treatment over a period of weeks to months reduced BP in some patients, and HRV analysis has shown a reduction in LF/HF.37 However, BP levels in hypertensive patients were not reported in this previous study, and the acupoints and methods used (manual and EA) were not uniform among the patients. The results of the present study cannot be generalized to the effects of chronic acupuncture and do not suggest a sustained depressor effect. However, the authors found that a single acupuncture session reduced BP and HR in patients with mild hypertension. Mild hypertensive patients also had lower CSNA and increased vagal activity, which differed from normotensive controls. These findings suggest that acupuncture treatment at PC6, LI4, ST36, LR3, and GV20 may be useful for the treatment of mild hypertension as it may increase vagal activity and suppress CSNA.

    Limitations

    This study is not without limitations. First, the authors only measured the effects up to 20 min after the acupuncture procedure. Further studies are needed to determine how long the depressor effect of acupuncture lasts.

    Conclusions

    In this study, the patients with mild hypertension had a lower BP and HR after acupuncture than the normotensive controls. HRV analysis showed that acupuncture reduced the LF/HF ratio and increased the HF power during and after the acupuncture. These results suggest that both CSNA suppression and enhanced vagal activity may be involved in the reduction of BP and HR observed in patients with mild hypertension.

    Authors' Contributions

    K.K. and Y.K. designed and conducted the trial. K.K. performed acupuncture and analyzed the HRV data. K.K. and Y.K. performed the statistical analysis. K.K. and F.T. wrote the article. All the authors reviewed and approved the article.

    Author Disclosure Statement

    No competing financial interests exist.

    Funding Information

    This work was supported in part by a Grant-in-Aid for Scientific Research (C) from the Ministry of Education, Culture, Sports, Science, and Technology (17K09338).

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