The 2 Hz and 15 Hz electroacupuncture induced reverse effect on autonomic function in healthy adult using a heart rate variability analysis.

The purpose of the present study was to investigate effect of electro-acupuncture (EA) at different frequencies on autonomic function. Twenty healthy adult volunteers were studied, and underwent 4 sessions of EA (sham, 2 Hz, 15 Hz, and 50 Hz). Sham, 2 Hz, 15 Hz, and 50 Hz EA was applied to the bilateral Leg Three Li ( zú sān lǐ, ST-36) and Upper Great Hollow ( shàng jù xū, ST-37) acupoints. The intensity of electrical stimulation was adjusted to obtain visible twitching of the anterior tibial muscle about 2.0-2.5 mA except sham without electrical stimulation. The components of heart rate variability (HRV) and blood pressure were measured before EA (BLP), EA (EAP), and post-EA periods (PEP). The results indicated that the natural logarithmic high frequency power (lnHF) of HRV was greater during PEP than during the BLP in the 2 Hz EA sessions. The natural logarithmic low frequency power (lnLF) of HRV was greater during the PEP than during the BLP in 15 Hz EA sessions, suggesting that 2 Hz EA apply to Leg Three Li ( zú sān lǐ, ST-36) and Upper Great Hollow ( shàng jù xū, ST-37) acupoints increased vagal activity, whereas 15 Hz EA increased sympathetic activity.

Introduction

Electro-acupuncture (EA) is now widely used for the treatment of disease worldwide. The needle stimulation at the ear point (耳穴 ěr xué, Lu-1; located at the left inferior hemi-conchae) can induce an increase in parasympathetic activity, while acupuncture at Union Valley (合谷 hé gǔ, LI-4; located at the middle of the right dorsal thenar muscle) can increase the activities of the sympathetic and parasympathetic nervous systems (Haker et al., 2000). Therefore, acupuncture applied to different specific sites can produce different activities of sympathetic or parasympathetic nerves. Our previous studies showed that 2 Hz EA at both Leg Three Li (足三里 zú sān lǐ, ST-36) acupoints may maintain a prolonged effect in reduction of the pulse rate than a 100 Hz EA (Hsieh et al., 1999). Several studies have reported that 2 and 15 Hz EA induce the release of endomorphin, encephalin, and β-endomorphin in the central nervous system, and is mediated via μ and/or δ opoid receptor, whereas 15 and 100 Hz induce the release of dynorphin, and is mediated via κ opoid receptor to produce an analgesic effect (Han, 2003; Ulett et al., 1998). Therefore, EA at a specific frequency delivered to the body site may cause specific neuropeptide release. Heart rate variability (HRV) analysis is considered a valuable method to assess autonomic function, and includes sympathetic and parasympathetic activities in normal healthy, diabetic, and cardiovascular patients (Malik, 1996a; 1996b; van Ravenswaaij-Arts et al., 1993). Time and frequency domain methods may be used to measure HRV, and these methods are divided into short- (5 min) and long-term (24 hr) recordings (Malik, 1996a; 1996b). The high-frequency (HF) power (0.15-0.4 Hz) of HRV may represent vagal activity, while low frequency (LF) power (0.04-0.15) may reflect both sympathetic and vagal activities, or a sympathetic modulations (Guzzetti et al., 1998; Malliani et al., 1991; Yamasaki et al., 1991). The HF% of HRV represents an indicator of parasympathetic activity, and the LF/HF ratio may reflect the modulation of sympathovagal activity, or sympathetic nerve activity (Malik, 1996a;1996b). Acupuncture at Cleft Gate (郄門 xī mén, PC-4) may cause a reciprocal modulation by reducing cardiac sympathetic and increasing cardiac parasympathetic activities, resulting in a decrease in heart rate (Nishijo et al., 1997). Acupuncture at Inner Pass (內關 nèi guān, PC-6) may increase the normalized HF power of HRV (Huang et al., 2005). Williams et al. (1991) reported that acupuncture may reduce diastolic blood pressure in patients with diastolic hypertension (Williams et al., 1991), and Li et al. (2004) found that 2 Hz EA applied to Inner Pass (內關 nèi guān, PC-6) and Intermediary Courier (間使 jiān shǐ, PC-5) may reduce the increase in mean artery pressure induced by exercise (Li et al., 2004), but Lee et al. (2009) concluded that no evidence supported a reduction in blood pressure by acupuncture (Lee et al., 2009). Therefore, the purpose of the present study was to investigate the effect of EA at different frequencies in specific sites on HRV and blood pressure. We used 2 Hz, 15 Hz and 50 Hz EA, respectively, applied to bilateral Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37) acupoints, and HRV and blood pressure simultaneously recorded.

Materials and methods

Subjects

Twenty-two healthy adults were recruited between August 2008 and January 2009. The experiments were approved by the Institutional Review Board of China Medical University Hospital (IRB, DMR97-IRB-046). Signed informed consent was obtained from every subject after the experimental purpose and procedure was explained in detail prior to the experiments. The experiment was performed at 8:30-12:00, and 13:30-17:00 in a quiet room with the temperature maintained at 24±1°C by an air conditioner. The subjects were placed in the experimental bed in a supine position. Medications, coffee, and tea were prohibited 24 hr prior to the experiments. Acupuncture was performed by an experienced Chinese physician. The inclusion criteria were as follows: 1) 20-40 years of age; 2) female or male; and 3) physical examination within normal limits. The exclusion criteria were as follows: (1) hypertension (systolic pressure ≧ 140 mmHg and diastolic pressure ≧ 90 mmHg); 2) severe medical disease, including congestive heart failure, myocardial infarction, arrhythmia, chronic obstructive pulmonary disease, renal failure, cancer, and pregnancy; and 3) psychiatric disorders.

Study design

The experiment was designed as a randomized complete block design according to the number of lots from a hard paper box. The sample size was calculated according to Dupont and Plummer (Dupont and Plummer, 1990); 20 subjects were required to obtain statistical significance.

Experimental procedure

Each subject completed 4 sessions (sham, 2 Hz, 15 Hz, and 50 Hz); each interval between sessions was at least 1 week to prevent residual effect. Each session was divided into the pre-EA period (baseline period (BLP)), EA period (EAP), and post-EA period (PEP); each period was 20 min in length. Both HRV and blood pressure were recorded simultaneously in each period (Figure 1).

Figure 1

Experimental procedure. Baseline: before electroacupuncture period (baseline period); EA: electroacupuncture period; Post-EA: post electroacupuncture period; HRV: heart rate variability recordings; BP: blood pressure recordings

During the sham sessions, both the baseline HRV and blood pressure were recorded after the subjects had rested in a relaxed state as BLP recordings. The BLP recordings were followed by placement of the electrodes of the EA apparatus (HANS LY257; Healthronics, Singapore) were placed on the surface of the Leg Three Li (足三里 zú sān lǐ, ST-36; 3 cun below the knee and one finger lateral to the anterior crest of the tibia) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37; 3 cun below Leg Three Li), bilaterally, and these electrodes were connected to the EA apparatus, but no electrical stimulation was delivered. The electrodes were taken off immediately after the EAP recordings were completed; both HRV and blood pressure were then recorded as PEP recordings.

During the 2 Hz, 15 Hz, and 50 Hz sessions, the procedure was similar to the sham session, except the stainless acupuncture needles (7.5 cm in length, gauge #30; Yu Kuang, Taiwan) were inserted into Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37) acupoints bilaterally and were twisted manually to elicit qi (the acupuncturist experiences a feeling like a fish biting on bait; the subject experienced a sensation of soreness, numbness, swelling, and heaviness around the inserting area). The cathode of the EA apparatus was connected to the Leg Three Li (足三里 zú sān lǐ, ST-36) needles, whereas the anion was connected to the Upper Great Hollow (上巨 虛 shàng jù xū, ST-37) needles. Electrical stimulation of 2 Hz, 15 Hz, and 50 Hz EA was then delivered after BLP recordings. The intensity of electrical stimulation was adjusted to obtain visible twitching of the anterior tibial muscle about 2.0-2.5 mA.

HRV Analysis Recordings

A HRV analyzer (WG-MD-ANSA01 HRV analyzer; WeGene Technologies Inc., Jonghe City, Taiwan) was used to record the HRV. The electrodes were placed on the subject’s right and left forearms and right lower leg. The HRV analyzer converted time domain signals into frequency domain signals by fast fourier transformation (FFT), and the present study used frequency domain analysis with 5 min of short-term recording. The data of HRV recordings was storage and analysis in a personal computer. The individual component of HRV was definite according to the guidelines for HRV (Malik, 1996a;1996b). Frequencies between 0.15 and 0.40 Hz were high frequency (HF), and frequencies between 0.04 and 0.15 Hz were low frequency (LF).

Blood pressure recordings

The blood pressure was measured using a blood pressure apparatus (Spectrumpulse TM Heart Monitor, OSTAR Model: A2; Ostar Meditech Corp., Taiwan). The sensor of the blood pressure apparatus was placed at the elbow just below the brachial artery of the left arm, and the blood pressure was measured automatically. The blood pressure recording data were stored and analyzed in a personal computer.

Statistical analysis

The data are presented as the mean ± standard deviation (SD) and analyzed by SPSS 18.0 software. One-way analysis of variance (ANOVA) with LSD post hoc test was used to assess the differences among the periods. The significance level was set at α= 0.05.

Results

Basic data analysis

Twenty-two healthy adults were recruited in the present study, and 2 subjects were excluded due to arrhythmias, therefore there were 20 subjects (males, 15; females, 5) who finished the study. The ages ranged between 21 and 36 years (mean ± SD, 28.8 ± 4.3 years).

Effect of EA at different frequencies on HRV

The natural logarithmic HF power (lnHF) of HRV was greater during the PEP than during the BLP in the 2 Hz EA sessions (p < 0.05; Table 1), whereas the lnHF was not significantly difference between the EAP and BLP, and between PEP and EAP (both P > 0.05; Table 1). The lnHF in the sham, 15 Hz and 50 Hz EA sessions were not significantly different between the EAP and BLP, between PEP and BLP, and between PEP and EAP (all p > 0.05; Table 1).

Table 1

Effect of electroacupuncture at different frequencies on heart rate viability

The natural logarithm LF power (lnLF) of HRV was greater during the PEP than during the BLP in 15 Hz EA sessions (p < 0.05; Table 1), whereas the lnLF was not significantly different between the EAP and BLP, and between the PEP and EAP (both P > 0.05; Table 1). The lnLF in the sham, 2 Hz and 50 Hz sessions were not significantly different between EAP and BLP, between PEP and BLP, and between PEP and EAP (all p > 0.05; Table 1).

The HF%, LF% and lnLF/HF ratio of the HRV in the sham, 2 Hz, 15 Hz, and 50 Hz sessions were not significantly different between PAP and BLP, between PEP and EAP, and between PEP and BLP (all p > 0.05; Table 1).

With regard to the natural logarithm very low frequency power (lnVLF), total power (lnTP), variance power (lnVAR), and R-R interval components of HRV, BLP EAP PEP their results of the present study were summarized in Table 1.

Effect of EA at different frequencies on blood pressure

The systolic, diastolic and mean blood pressure in the sham, 2 Hz, 15 Hz, and 50 Hz sessions was not significantly different between PAP and BLP, between PEP and EAP, and between PEP and BLP (all p > 0.05; Table 2).

Table 2

Effect of electroacupuncture at different frequencies on blood pressure

Discussion

The 2 Hz increase vagal activity, whereas 15 Hz EA enhanced sympathetic activity

The results of the present study indicated that the lnHF was greater during the PEP than during the BLP in the 2 Hz EA sessions, whereas no similar results occurred in the sham, 15 Hz and 50 Hz sessions, suggesting that 2 Hz EA applied to the Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨 虛 shàng jù xū, ST-37) acupoints increase vagal activity due to lnHF can represent vagal activity (Imai et al., 2008; Malik, 1996a; 1996b); our results also indicated that lnLF was greater during PEP than during BLP in 15Hz EA sessions, but no similar results were noted in the sham, 2 Hz and 50 Hz sessions, suggesting that 15 Hz EA applied to Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37) acupoints can enhances sympathetic activity. LnLF is a parameter of both sympathetic and vagal activities, a sympathetic modulations (Malik, 1996a; 1996b), and an index of sympathovagal balance (Goldberger, 1999). Our results were consistent with other studies that EA applied to bilateral Leg Three Li (足三里 zú sān lǐ, ST-36) acupoints can enhance gastric motility and increased vagal activity (Imai et al., 2008; Ouyang et al., 2002), and also similar to the results of our previous studies that 2 Hz EA at Leg Three Li (足 三里 zú sān lǐ, ST-36) and Union Valley (合谷 hé gǔ, LI-4) may reduce gastric half-emptying time in diabetic patients with gastroparesis (Wang et al., 2008). In addition, the effect of EA is partially mediated via the opoid pathway to enhance vagal activity (Chen et al., 2008).

EA cannot change blood pressure

Our results indicate that blood pressure includes systolic, diastolic and mean arterial pressures were similar between EAP and BLP, between PEP and BLP, and between PEP and EAP in the 2 Hz, 15 Hz and 50 Hz EA sessions, these results indicated that 2 Hz, 15 Hz and 50 Hz EA applied to bilateral Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37) acupoints cannot affect blood pressure. Iwa et al., (2005) report that EA delivered to Leg Three Li (足三里 zú sān lǐ, ST-36) may reduce the increase in mean arterial pressure induced by rectal distension in conscious dogs, and suggest this effect of EA results from the opioid release of EA, and opioid reduces visceral pain (Iwa et al., 2005). Chen and Ma (2003) found that EA of 30 Hz applied to bilateral Leg Three Li (足三里 zú sān lǐ, ST-36) can reduce mean arterial pressure and heart rate in rats, and these effects of EA can be enhanced by L-arginine derived nitric oxide (NO) administration of the gracile nucleus, suggesting that EA at the Leg Three Li (足三里 zú sān lǐ, ST-36) acupoint induces a hypotensive effect has a close relationship to NO (Chen and Ma, 2003). The hypotensive effect of EA at Leg Three Li (足三里 zú sān lǐ, ST-36) is partly mediated via the arterial baroreflex reflex due to endogenous opioids may modulate the arterial baroreflex (Michikami et al., 2006). The 2 Hz or 20 Hz EA at the Leg Three Li (足三里 zú sān lǐ, ST-36) acupoints do not affect blood pressure, while 2 Hz EA at Union Valley (合谷 hé gǔ, LI-4) may induce a tonic effect to increase blood pressure, and 20 Hz EA at Union Valley (合谷 hé gǔ, LI-4) may elicit a phasic effect to increase blood pressure in normal and acute hemorrhage rat (Liao et al., 2006; Ting et al., 2002). The 2 Hz EA at Union Valley (合谷 hé gǔ, LI-4) may induce vasodilation and may reduce blood pressure in healthy young adults (Lin et al., 2003), therefore, the effect of EA on blood pressure in human needs further study.

Limitation

Although our results indicated that both 15 Hz and 50 Hz EA can increase lnVLF and lnTP components of HRV, and 50 Hz EA also can increase lnVar component. The lnVLF is defined from 0.003-0.04 Hz, and its physiologic significance is less clear (Kuo et al., 1999; Malik, 1996a; 1996b). The lnTP influence LF and HF power and relate to the fractional distribution of the energy (Malik, 1996a;1996b). The lnVar of HRV is the variance of R-R intervals (Kuo et al., 1999).

Conclusion

Based on the results, 2 Hz and 15 Hz applied to Leg Three Li (足三里 zú sān lǐ, ST-36) and Upper Great Hollow (上巨虛 shàng jù xū, ST-37) acupoints, may induce reverse effect on autonomic function. 2 Hz EA increases vagal activity, where 15 Hz EA enhances sympathetic activity. These results may provide scientific evidence for the selection of clinical treatment of disease.