Objective To determine whether skin blood flow (SBF) and muscle blood volume (MBV) responses differ according to the duration of electroacupuncture (EA) stimulation.
Methods Two experiments were conducted. In Experiment 1, healthy male students (n=20) were randomly divided into two groups (an EA group and a no-stimulation group). In Experiment 2, healthy male students (n=37) were randomly divided into three groups with different stimulation durations of EA (5, 10 and 15 min). EA stimulation on the quadriceps femoris muscle was administered with a frequency of 1 Hz. SBF and MBV were estimated before, during and after stimulation.
Results In Experiment 1 there was a significant difference between the groups (p=0.001). In the EA stimulation group, MBV increased immediately following EA (p=0.045) and 5 min (p=0.005) and 10 min (p=0.002) after EA compared with baseline. No significant change was observed in the no-stimulation group. In Experiment 2 there was no significant difference between the groups. All three stimulation durations (5, 10 and 15 min) yielded increases in MBV after stimulation compared with baseline. SBF following stimulation for 5 and 10 min was increased compared with baseline.
Conclusions Based on these findings, we consider that 10 min EA stimulation could be a sufficient duration to induce a blood flow response in a clinical situation when increasing the blood flow is desirable.
- Vascular Medicine
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Electroacupuncture (EA) has been used to alleviate a variety of pain symptoms. Jubb et al1 reported that manual acupuncture and EA provided symptomatic improvement for patients with osteoarthritis of the knee. Electrical stimulation was administered to both the anterior and the posterior part of the knee for a total of 20 min. Zheng et al2 demonstrated a promising short-term reduction in the need for opioid medications for participants with chronic non-malignant pain after 20 min of EA therapy. Cheing et al3 reported that the addition of EA to exercise alleviated shoulder pain and improved shoulder function for people with frozen shoulder. EA stimulation was administered for 20 min during each treatment session in their study. Ng et al4 reported that 20 min of EA treatment (8 sessions over 2 weeks) was effective in reducing osteoarthritis-induced knee pain.
One of the mechanisms behind the pain reduction effects of EA could be related to post-stimulation augmentation of blood flow. It has been reported that blood flow and skin temperature are increased by EA stimulation. For instance, Loaiza et al5 observed changes in microcirculation in the knee joints of rats after the animals were treated with 30 min of EA stimulation. The researchers claimed that the EA stimulations caused muscular contractions in the rats, which resulted in vasodilation responses. Sato et al6 reported that mechanical stimulation and heat stimulation dilated blood vessels in the musculoskeletal system to increase blood flow. Agarwal-Kozlowski et al7 showed that manual acupuncture stimulations with de qi sensation raised the skin temperature. A significant increase in surface temperature occurred within 2 min after the stimulation.
Although EA stimulation has been widely used in clinical and basic research settings, the methods of delivery such as stimulation duration are not standardised. In an experimental study on rats, Ishikawa et al8 conducted a series of experiments in which they administered acupuncture stimulation on the ST36 point with different electric stimulation frequencies and durations. They concluded that differences in the duration of stimulation (15 and 60 min) do not affect changes in blood flow responses. In clinical practice, 10 or 15 min of EA stimulation is commonly used in Japan. For instance, Mori et al9 conducted experiments examining the effects of EA on 27 healthy human subjects. A significant increase in skin temperature and skin and muscle blood flow was observed after administration of EA for 5 min. Another study by Mori et al10 reported reductions of pain in the shoulder, low back and knees after 10 min of EA stimulation (1 Hz). Donoyama et al11 reported the efficacy of 15 min EA application (50 Hz) in Raynaud's disease.
We were unable to find human studies comparing the therapeutic effects of different stimulation durations. If varying lengths of time of EA stimulation do not result in different skin blood flow (SBF) or muscle blood volumes (MBVs), the treatment time could be shortened, especially in a clinical situation when the increase in blood flow is one of the main therapeutic strategies. We therefore attempted to determine whether blood flow responses differ according to the duration of stimulation in human subjects.
We conducted two experiments. In Experiment 1 we examined changes in SBF and MBV following EA stimulation and compared the changes with those of a no-stimulation group. In Experiment 2, SBF and MBV changes following EA stimulation were compared with those of two different stimulation duration groups.
This study adhered strictly to the principles of the Declaration of Helsinki.
Method of stimulation
Two disposable acupuncture needles (40 mm in length, 0.20 mm in diameter; Seirin, Shizuoka, Japan) were inserted at a depth of 10–15 mm into the quadriceps femoris muscle. The exact stimulation sites were as follows: a point located on the rectus femoris muscle, 2 cm proximal from the superior border of the patella; and a point located at the midpoint between the superior border of the patella and the anterior inferior iliac spine. An Ohm Pulser LFP-4000A (Zen Iryoki, Fukuoka, Japan) was used as the device for EA stimulus. EA stimulation (1 Hz, waveform/square) was then administered for 15 min. The intensity of stimulation was adjusted so that muscle twitching contractions were elicited in the targeted muscles without causing pain or discomfort to the subjects.
The participants were asked to lie on the table in a supine position, then rested for 30 min on the table prior to the measurement. The surface electrodes were placed at the midpoint between the stimulation sites on the quadriceps muscle. The experiments were conducted in a room with the temperature set at 25.0±0.5°C and 50.0±5.0% humidity throughout the experimental sessions.
MBV was estimated using a near-infrared spectroscopy (NIRS) device (Tissue SO2/Hb Monitor, PSA-IIIN; Biomedical Science, Tokyo, Japan).12 NIRS has been used to measure local skeletal muscle deoxygenation and also to estimate regional muscle blood flow.13 The SBF was estimated by using a change in the laser Doppler signal (ALF 21D; Advance Co, Tokyo, Japan).
Twenty healthy male students (mean age 19.60±0.26 years) were divided into two groups (an EA stimulation group (n=10) and a no-stimulation group (n=10)) using the envelope allocation method.
The baseline MBV (Pre) was recorded for 1 min, just prior to the intervention period (EA for 15 min or no stimulation). The MBV was estimated also at the following time periods: 10 min after the initiation of EA (Stim 10), immediately after EA (Post 0) and at 5 (Post 5) and 10 (Post 10) min afterwards.
Thirty-seven healthy male students (mean age 23.18±0.96 years) were randomly divided into three groups: 12 were assigned to receive 5 min EA stimulation, 13 were assigned to receive 10 min EA stimulation and 12 were assigned to receive 15 min EA stimulation.
The baseline SBF and MBV (Pre) were recorded for 1 min, just prior to the intervention period. The SBF and MBV were estimated also for the following time periods: immediately after EA (Post 0) and at 5 (Post 5), 10 (Post 10), 15 (Post 15), 20 (Post 20), 25 (Post 25), and 30 (Post 30) min afterwards.
Serial changes in SBF and MBV between the groups were analysed using the mixed model Fisher's least significant difference multiple comparison test. SPSS Advanced Models V.15 was used as the statistical analysis software. The level of significance was set at p<0.05. The values presented are mean±SE.
The MBV responses in Experiment 1 are summarised in figure 1. There was a significant difference between the groups (p=0.001). In the stimulation group, MBV increased at Post 0 (p=0.045), Post 5 (p=0.005) and Post 10 (p=0.002) compared with baseline. No significant change in MBV was observed in the no-stimulation group.
There was no significant difference between the groups. In the 5 min EA stimulation group MBV increased at Post 5 (p=0.001), Post 10 <0.001), Post 15 (p<0.001), Post 20 (p<0.001), Post 25 (p<0.001) and Post 30 (p<0.001) compared with baseline, in the 10 min EA stimulation group MBV increased at Post 15 (p=0.007), Post 20 (p=0.020), Post 25 (p=0.004) and Post 30 (p<0.001) compared with baseline and, in the 15 min EA stimulation group, MBV increased at Post 5 (p=0.006), Post 10 (p=0.049), Post 15 (p=0.010), Post 25 (p=0.001) and Post 30 (p=0.022) compared with baseline.
There was no significant difference between the groups. In the 5 min EA stimulation group no significant change was observed in the SBF compared with baseline, in the 10 min EA stimulation group SBF increased at Post 30 (p=0.008) compared with baseline and, in the 15 min EA stimulation group, SBF increased at Post 0 (p=0.049) and Post 25 (p=0.028) compared with baseline.
In this study we examined the effect of different durations of EA stimulation on blood flow.
Experiment 1 showed that 15 min of acupuncture stimulation increased the MBV while no significant change was observed in the no-stimulation group. In Experiment 2, MBV showed significant increases in the 5, 10 and 15 min groups compared with baseline and there was no significant difference between the groups. On the other hand, SBF increased in the 5 and 10 min groups compared with baseline but there was no significant difference between the groups.
There are limitations to this study. We only compared the effects on blood flow following 5, 10 and 15 min of EA stimulation. Therefore, potential differences in response with very short (<5 min) or long (>15 min) stimulation durations are unknown. In addition, our study was conducted in healthy volunteers and we did not evaluate the clinical effects of acupuncture in patients who have pain symptoms or compromised blood flow. Further studies are needed to determine the clinical efficacy of EA.
In previous experiments using animals it was demonstrated that acupuncture stimulation alters blood flow in various organs.14 Inoue et al15 demonstrated that 3 min of manual acupuncture influenced sciatic nerve blood flow. In terms of muscle blood flow, Noguchi et al16 observed that the muscle blood flow in the biceps femoris muscles of anesthetised rats produced biphasic responses. It initially increased, then slightly decreased after 30 s of EA to the hind paw. The increase in muscle blood flow during the EA was considered to be due to a reflex mean arterial pressure elevation via the sympathetic splanchnic nerve. Sato et al6 reported that the effects of EA on the muscle blood flow volume in experimental rats were induced by calcitonin gene-related peptide. Their experiments showed that electrical stimulation to the third and fifth lumbar dorsal roots for 30 s produced an increase in blood flow in the biceps femoris muscle.
We consider that the change in blood flow in response to acupuncture stimulation is affected by the duration, intensity and sites of stimulation. In this study, however, MBV showed increases in the 5, 10 and 15 min EA duration groups compared with baseline. On the other hand, SBF yielded increases in the 5 and 10 min groups compared with baseline and there was no significant difference between the groups. Our results in healthy volunteers suggest that prolonging EA stimulation beyond 10 min does not increase the blood flow response. However, evaluation in appropriate clinical conditions is still needed.
Based on these findings, we consider that the EA stimulation for 10 min could be a sufficient duration to induce a blood flow response when increasing the blood flow is clinically desirable.
We explored the relationship between the duration of EA and increased blood flow in healthy volunteers
EA can generate an increase in blood flow
The increase is maximum within 10 min
Contributors HM conceived the study and wrote the first draft. HK conducted the statistical analysis. THT contributed to the literature review. ET participated in data collection. All authors critically edited drafts of this manuscript and approved the final manuscript.
Funding This work was supported by Tsukuba University of Technology, Projects for Advanced Education and Research.
Competing interests None.
Patient consent Obtained.
Ethics approval This study obtained approval from the Research Ethics Committee of the National University Corporation at the Tsukuba University of Technology.
Provenance and peer review Not commissioned; externally peer reviewed.
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