Background Acupuncture treatment frequently evokes both pain and fear, causing patients to be hesitant about undergoing the procedure. This study investigated individual differences in autonomic response to acupuncture stimulation and its relationship to fear of the procedure.
Methods Twenty-seven participants filled out the acupuncture fear scale (AFS) questionnaire and underwent acupuncture stimulation at the LI4 acupuncture point. Autonomic responses were measured by recording the skin conductance response (SCR) throughout acupuncture stimulation. Pearson correlation analysis was performed between the self-reported AFS scores and changes in SCR.
Results After acupuncture stimulation, SCR significantly increased and there were greater individual differences in enhanced sympathetic activations to acupuncture stimulation. Changes in SCR correlated with scores for the painful sensation domain of the AFS.
Conclusions Our results indicate that fear of acupuncture-induced pain is associated with physiological arousal when people receive acupuncture stimulation. Fear of pain is the dominant factor in acupuncture-related fear and it should be considered in practice and in research.
- CLINICAL PHYSIOLOGY
- PAIN RESEARCH
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Fear generated during a dangerous or painful experience is critical for human survival mechanisms such as escape or avoidance behaviour.1–4 Pain is one of the most interesting and frequently discussed topics in medical research, as pain has both sensory and affective dimensions and is strongly associated with emotions such as fear, anxiety and depression.5 ,6 Studies have suggested that fear of pain is driven by the anticipation of pain rather than the pain itself, and patients avoid activities which could increase pain.5 ,7–10 In addition, nociceptive input itself does not fully explain the pain response, which has been categorised as an emotional state as well as a measure of the intensity of sensory pain using a one-dimensional pain rating scale.11 ,12
Studies describing the fear of medical procedures have identified examination and care, injections, dental care and invasive procedures as factors that evoke pain and fear,13 and acupuncture treatment using multiple needles might be another medical procedure that could be added to this list. Acupuncture is an ancient East Asian therapeutic technique that uses needles to penetrate the skin and needle manipulation to stimulate skin tissue.14 The manipulation of needles can generate the traditional de qi sensation. However, needle insertion is thought to be the primary basis of acupuncture stimulation.15–17 In addition to needle-induced pain, viewing a sharp object has been reported to be more likely to induce pain than seeing a blunt object.18 Fear of undergoing acupuncture treatment could be due to the fear of acupuncture needle penetration, pain or adverse events. Even though acupuncture carries a low risk of adverse events, anticipating acupuncture-induced pain and fear makes patients hesitant to receive acupuncture treatment.19 ,20 The acupuncture fear scale (AFS) has been developed to evaluate fear of acupuncture, and its validity and reliability were reported in our previous study.21 The AFS comprises two principal components: factor 1 is related to the sensation of pain and factor 2 is related to possible adverse events.
The skin conductance response (SCR) is an autonomic response measured as eccrine sweat gland activity and is primarily involved in emotional responses and sympathetic arousal.22 ,23 The SCR reacts to emotional changes and threat stimuli. Thus, experiencing fear could increase the SCR. The relationship between emotion and SCR has been investigated in dental research, where a statistically significant correlation was found between SCR and the degree of dental anxiety.24 It was also reported that high-fear participants responded with significantly larger SCRs during threat periods than low-fear participants.25
The goal of the present study was to investigate individual differences in the autonomic response to acupuncture stimulation and its relationship to fear of acupuncture, including possible pain and possible adverse events. We wanted to know which factor of AFS is associated with greater sympathetic activation to acupuncture stimulation. The correlation was analysed between self-reported AFS scores and measured autonomic responses following acupuncture stimulation.
Healthy participants were recruited from Kyung Hee University using an advertisement poster. All participants were prohibited from drinking alcohol or caffeine, or taking any drugs or medications on the day of the experiment. Eighteen participants had previous experience with acupuncture treatment and nine participants did not have any experience. All participants received a detailed explanation of the study and written informed consent was obtained.
Acupuncture fear scale (AFS) questionnaire
Subjective fear of acupuncture was measured using the AFS questionnaire before acupuncture stimulation.21 This questionnaire consisted of 16 questions, each with five possible responses ranging from 1 (not at all) to 5 (extremely). It included two domains, one for painful sensations and one for possible adverse events. The answers to all questions were summed, with a maximum total score of 80.
Sympathetic activation measurements
Skin conductance was recorded from the middle phalanges of the second and third digits of the left hand with an electrolyte paste of 0.05 mol/l NaCl. Skin conductance was digitised and recorded using a Galvanic Skin Response Amplifier (GSR Amp ML116; ADInstruments, Bella Vista, Australia) and a high-performance data acquisition system PowerLab 8/30 (ML870; ADInstruments). For assessing the responses before, during and after acupuncture treatment, the signal deviation from the baseline value at acupuncture needle insertion was determined at each second and averaged across the 15 s of acupuncture stimulation and 25 s after pulling out the acupuncture needle for a total of 40 s, resulting in scores that reflected increases or decreases from the baseline.
The acupuncture needles were 0.25 mm in diameter and 30 mm long (Dongbang Acupuncture, Kyunggi-do, Korea). For the stimulation, acupuncture needles were applied to acupuncture point LI4, on the dorsum of the right hand, radial to the midpoint of the second metacarpal bone. The acupuncture point LI4 was found to increase the SCR in our previous study.26 The needle was inserted to a depth of 10 mm and rotated clockwise and counterclockwise (1 Hz) for 15 s in an attempt to elicit de qi sensation. After the acupuncture needle was removed from the skin, we asked each participant whether they experienced any uncomfortable sensation and adverse events during acupuncture stimulation.
The values are expressed as the median (minimum to maximum). The autonomic responses were analysed by ANOVA with one repeated measures factor for time. Pearson correlation analysis was performed between the AFS scores and the changes in SCR. We did not include values 2 standard deviations (SDs) above or below the mean of the SCR increases; this excluded two participants from the study. The level of significance was set at p<0.05 for all analyses. Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) for Windows V.20.0 (Chicago, Illinois, USA).
Acupuncture fear scale
Twenty-seven healthy participants (12 men; age 18–42 years; mean±SD age 25.04±5.06 years) were included. Table 1 summarises the scores from the AFS questionnaire. The median AFS score was 29 (range 16–66). The median AFS factor 1 measuring the sensation of pain was 16 (range 8–40) and the median AFS factor 2 measuring possible adverse events was 13 (range 8–37). There was no difference in the AFS score between the experienced (n=16) and naïve (n=9) groups (experienced group: median 29 (range 16–66); naïve group: median 30 (range 16–52)).
Skin conductance responses
SCR recordings are represented as the mean change in SCR over time (figure 1). For each recording of SCR during the acupuncture sessions, repeated measures ANOVA was calculated and the results showed a significant time effect (F(1,40)=1.752, p<0.01). After acupuncture stimulation, a significant increase in SCR was observed. There were greater individual differences in SCR increases to acupuncture stimulation. No participant reported severe uncomfortable sensations or any adverse events during acupuncture stimulation in the present study.
The results of this study show that the SCR significantly increased after acupuncture stimulation and that fear of acupuncture-induced pain enhanced physiological arousal to acupuncture stimulation. These findings are consistent with results from a previous study that used SCR changes to measure sympathetic activation following acupuncture stimulation.26 ,27 Fear of pain induced by medical instruments increases the subjective pain rating score and physiological response during treatment. It is known that, in addition to anticipating forthcoming pain,28–30 viewing a needle pricking a hand strengthens the perception of pain.18 The acupuncture needle, a tool specially designed for acupuncture treatment, is able to intensify the fear of pain. For acupuncture procedures, even momentary pain-evoking treatment can be an unpleasant experience for patients and can cause treatment avoidance.
The present study also showed that SCR changes significantly correlated with the sensation of pain domain in the AFS but not with the possible adverse events domain. This indicates that, even with the same stimulation, individuals differ in the degree of autonomic response associated with the fear of pain-evoking stimulation. These findings are consistent with a previous study in which heart rate varied with the same stimulation. Thus, changing the patient's understanding of acupuncture may alter the degree of the autonomic response to acupuncture stimulation.31 We can assume that the difference in autonomic response is associated with differences in a positive or negative understanding of acupuncture, such as fear of pain-evoking stimulation. Although possible adverse events are important factors in the AFS, correlation analysis showed that the effect on increased SCR was very limited. As SCR is a fairly instantaneous response, it is assumed that the fear of pain is related to the moment when the acupuncture needle penetrates the skin rather than the fear of possible adverse events, which is a prolonged response.
It has been suggested that the placebo or nocebo phenomenon of acupuncture practice makes it difficult to evaluate the efficacy of acupuncture in clinical trials.31 In addition to methodological problems, including inadequate research design, lack of blinding and insufficient placebo control,32 it is known that incidental factors such as expectation of a positive outcome affect the clinical response in acupuncture research.33 Thus, fear of acupuncture may produce the nocebo effect in clinical practice, although it has not yet been studied with acupuncture therapy. Measurement of the AFS in clinical trials may help in interpreting the results.
Incidental factors are more important than specific factors in clinical practice.34 Our findings suggest that clinicians should be advised to provide information about reducing fear of pain as well as possible adverse events. In one study, acupuncture-induced pain and physiological responses were altered by cognitive manipulation using acupuncture modalities.31 Furthermore, fear may be more common in women and/or children,35 and other demographic variables may be significant predictors of fear of acupuncture.
The results of this study have further implications. Clinically, AFS could be used to acquire basic data for establishing a treatment strategy and patient management; for example, physical symptoms of needle phobia include syncope, near syncope, lightheadedness and vertigo upon needle exposure. Syncope may be influenced by emotion because fear and anxiety have an overwhelming effect on central cardiovascular control.36 Thus, reducing fear of acupuncture may prevent vasovagal syncope, one of the most common acupuncture-related adverse events.37 Psychological approaches to increase patient confidence in the therapeutic effects and safety may reduce fear of acupuncture in the clinic.
There are several limitations to be considered in this study. The SCR is an immediate physiological response to acupuncture stimulation and thus does not sufficiently explain the long-term therapeutic effects of acupuncture. Moreover, when measuring the SCR, it is important to consider non-specific or spontaneous fluctuations as a possible source of error.38
One may wonder if prior experience would be a confounding factor in the interpretation of our data. Since there was no difference in the AFS score between the experienced and naïve group, it is unlikely that prior experience of acupuncture is associated with a fear of acupuncture and the enhanced sympathetic responses to acupuncture in the present study. Pain perception differs with age, gender and socioeconomic and education status. For example, it is reported that women tend to report more dental fear than men and to show greater pain sensitivity.39–42 It is likely that the AFS score would also vary with respect to these parameters, but subgroup analysis was not performed in this study. Understanding the factors that influence the AFS score would be helpful for the application of AFS in clinical studies.
In conclusion, our findings suggest that fear of acupuncture is associated with the sympathetic response to acupuncture stimulation. As the fear of pain is a dominant factor in the fear of acupuncture, it should be considered in practice and research.
Fear of acupuncture enhances the sympathetic response to acupuncture stimulation.
Fear of pain, the dominant fear in acupuncture, should be considered in practice.
Contributors YC designed the study, monitored data collection and drafted and revised the paper. I-SL, S-HL, H-JJ and HL conducted the experiment and drafted relevant sections of the paper. HL, I-SL and H-JP designed the statistical plan and analysed the data. HL and H-JP co-designed the study, monitored data collection and analysed the data.
Funding This research was supported by the Basic Science Research Program through the National Research Foundation (NRF) of Korea, funded by the Ministry of Education, Science, and Technology (No. 2005-0049404 and No. 2011-0009913).
Competing interests None.
Ethics approval The study was approved by the ethics committee of the Acupuncture and Meridian Science Research Centre of Kyung Hee University, Seoul, Republic of Korea.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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