Acupuncture has been practiced in China for over 2000 years to treat a variety of diseases based on the “meridian theory,” as described in the “Yellow Emperor's Classics of Internal Medicine.” Deqi refers to the excitation of qi or vital energy inside meridians by acupuncture needle stimulation. Patients often experience multidimensional and intense needling sensations such as numbness, soreness, distention, heaviness, dull pain, and sharp pain during acupuncture stimulation. Deqi is considered as an important parameter in the process of achieving therapeutic effectiveness in acupuncture treatment. Understanding this phenomenon from neurophysiological aspects is important for clinical practice and enables practitioners to perform quantitative acupuncture evaluation to obtain a reliable prognosis of acupuncture treatment. This review paper describes our current knowledge and understanding of Deqi from a physiological aspect.

Theuse of acupuncture in theUSAand otherWestern counties has increased, and is now being utilized as an adjunct in treatment of many illnesses [1]. Manual acupuncture and more recently electroacupuncture have been used to treat ailments in the Far East for decades. However, because the efficacy of acupuncture remains controversial and because the physiological mechanisms determining its actions are largely unknown, Western medicine has not adapted acupuncture readily. Some of the controversy surrounding the success of acupuncture can be attributed to its method of delivery and the subjective nature of efficacy. A likely important component of the acupuncture response is known as Deqi, the excitation of qi or vital energy inside meridians. Deqi is considered an important parameter in the process of achieving therapeutic effectiveness in acupuncture treatment. In the ensuing review,we will attempt to address some of the neurophysiological aspects of Deqi and try to shed light on its utility in measuring the response to acupuncture.

In addition to the sharp needling sensation, patients undergoing acupuncture treatment often report a host of sensations such as numbness, soreness, and dull pain. Hui et al [2] performed an elegant study to characterize the Deqi response to acupuncture stimulation at different acupoints using functional magnetic resonance imaging (MRI). They demonstrated that, among the sensations typically associated with Deqi, aching, soreness, and pressure were most common, followed by tingling, numbness, dull pain, heaviness, warmth, fullness, and coolness. Clinical practitioners of acupuncture believe Deqi to be a necessary component of analgesia. Curiously, intramuscular injection of local anesthetics, prior to acupuncture in the laboratory, eliminates Deqi and analgesia alike [3]. Japanese researchers reported that type II afferent nerves were sufficient for acupuncture analgesia in rats [4]. Pomeranz and Paley [5] recorded the afferent nerves of mice from Hegu acupoints, and also found that type II afferent nerves were enough to produce acupuncture analgesia.

Characterization of the pain response following acupuncture has been proved to be crucial to the understanding of Deqi. While in typical noxious simulation, individuals feel a sharp followed by a dull sensation, in the Deqi response, the dull component precedes the sharp pain. In the former case, the dull component, also described as the “second pain,” typically follows the sharp pain [6], whereas in case of acupuncture, they may occur independently. Functional MRI studies of the limbic system have demonstrated that Deqi may deactivate this region, whereas noxious stimuli activate this system [7,8]. Such distinct differences can, in part, be explained by a variety of nerves that transmit such impulses to the central nervous system. In contrast to the superficial nerve fibers that carry commonly utilized painful stimuli such as heat, acupuncture needles deliver stimulation to deeper nerve bundles.

Given the broad nature of perceived sensations in acupuncture and Deqi, many investigators have attempted to scientifically identify individual nerve fiber types involved in this response. It is now generally accepted that Deqi involves a multitude of fiber types, ranging from the fast-conducting myelinated Aβ fibers with higher thresholds to the slow-conducting unmyelinated C fibers with lower thresholds (Table 1). Yet the exact fiber types involved in the analgesic response to acupuncture remain unclear [9,10,11]. Experiments by Lu [9,10] have identified the slower conducting Aẟ and C fibers to be involved in the dull component of Deqi sensation. Numbness and tingling may involve the Aβ fibers, but are not specific.

Note. From “Characterization of the ‘deqi’ response in acupuncture,” by K.K. Hui, E.E. Nixon, M.G. Vangel, J. Liu, O. Marina, V. Napadow, et al, 2007, BMC Complementary and Alternative Medicine, 7, p. 33. Copyright 2007, 2007 Hui et al; licensee Biomed Central Ltd. Adapted with permission..

&md=tbl&idx=1' data-target="#file-modal"">Table 1

Relations of acupuncture sensations to functions of afferent nerve fibers..

Afferent nerve fibers	Diameter	Velocity	Functions	Acupuncture sensations
Type	(µm)	(m/s)
β II myelinated	8-13	40-70	Touch, vibration	Numbness
Aγ III	4-8	15-40	Touch, pressure	Heaviness, pressure, fullness
Aẟ III	1-4	5-15	Pain, warmth, cold, pressure	Soreness, pressure, pain, warmth, cold
C IV unmyelinated	0.2-1	0.2-2	Pain, warmth, cold, pressure autonomic	Pain, soreness, warmth, cold, pressure
			Postsynaptic, olfactory

Note. From “Characterization of the ‘deqi’ response in acupuncture,” by K.K. Hui, E.E. Nixon, M.G. Vangel, J. Liu, O. Marina, V. Napadow, et al, 2007, BMC Complementary and Alternative Medicine, 7, p. 33. Copyright 2007, 2007 Hui et al; licensee Biomed Central Ltd. Adapted with permission..

The spatial distribution of nerves has led scientists to study the depth dependence of the acupuncture response. Researchers have confirmed that, in humans, penetration of muscle layer coincides with the sensation of Deqi [9,10,12]. When transcutaneous electrical stimulation was used, deep tissue but not cutaneous afferents mitigated the pain response [13]. On the contrary, however, others have suggested that superficial nerves may also be important to the Deqi response, given the significant internetwork connections and cross-talk that exists between the superficial and deep systems [14,15].

A number of investigators have used other means of stimulation in controlled studies to evaluate acupuncture, Deqi, and sensation by individuals. When tactile stimulation was used in place of acupuncture, many of the sensations associated with Deqi were reported, albeit with different patterns and frequency. Although tingling and numbness were reported in the tactile stimulation group, dull aching and soreness were almost exclusively seen in the acupuncture group [2,7,8]. The presence of Aγ and ẟ fibers in deeper tissue layers may account for such differences and explain why Deqi was reported in 98% of individuals undergoing treatment with acupuncture and in only 27% experiencing tactile stimulation [11].

Taken together, experimental evidence suggests that although all nerve fibers at all levels are involved, the intramuscular neuronal network likely plays a major role.

Many historical and contemporary sources have suggested that Deqi is necessary for attaining the therapeutic effects of acupuncture. A study by Chiang et al [3] showed the correlation between analgesia and Deqi. A series of studies of acupuncture anesthesia and analgesia conducted in the 1950-1980s in China also corroborate the significance of Deqi [16].

More recently, Takeda and Wessel [17] found that Deqi can be used to predict significant improvement in the pain of osteoarthritis. This study suffered from the limitation of a small sample size and was therefore not fully conclusive. Others investigating osteoarthritis have reached conflicting conclusions, and some have questioned the need for deep stimulation and Deqi in achieving analgesia [18,19,20,21].

Clinical and experimental data indicate a disparity among individuals in achieving Deqi and benefiting from acupuncture. The ratio of responders to nonresponders is estimated to be 8:2 or 7:3 [2]. Interestingly, this is congruent with the approximately 70% Deqi frequency when all acupoints are combined. Such a variation may stem from a true lack of efficacy, variable endogenous opioids, and an inability to measure accurately the delivery and results of acupuncture.

Indeed, one of the main criticisms of acupuncture remains the lack scientifically acceptable data and quantifiable efficacy. Because the perception of acupuncture appears to vary considerably among individuals, a number of tools have been developed to quantify the sensations elicited by acupuncture.

A number of groups have developed questionnaire-based forms that assess the quality and quantity of pain and other sensations [16,22,23,24]. Descriptors may not be part of the assessment as in the Acupuncture Sensation Scale for use on Korean healthy. Given the complexity of such sensations, an international panel of experts concluded that all sensations may be assigned to either of two categories: A study where an international group of acupuncture experts rated the importance of descriptors on an established needle sensation scale found two clusters of sensations: (1) Deqi, including sensations such as aching, dull, heavy, numb, radiating, spreading, and tingling and (2) acute pain at the site of needling, including sensations such as burning, hot, hurting, pinching, pricking, sharp, shocking, stinging, and tender [25].

Recently, “Southampton Needle Sensation Questionnaire” has been used in assessing acupuncture [24]. Development of this form pointed to two clusters of sensations, known as “aching Deqi” (7 items with a close relationship to painful needle sensations) and “tingling Deqi” (7 items unrelated to painful sensations). All such questionnaires aim at quantifying the utility and efficacy of acupuncture in a more scientific manner. What currently stands is the need for more basic research that would mechanistically relate Deqi to analgesia and other beneficial effects of acupuncture.

Herein, we have presented a brief overview of Deqi and the current body of knowledge surrounding its relation to the analgesic and other salutary effects of acupuncture. Defined as the dull component of pain that ensures acupuncture, Deqi is likely driven by slow conducting pain fibers. Integration of such signals in the central nervous system leads to modulation of other sensory inputs and comprises at least part of the acupuncture effect.

Measurement of Deqi and effects of acupuncture in a uniform and scientific manner has been proved difficult. A number of questionnaires have been developed to address this issue, but few are utilized outside of small studies. One of the major future challenges for investigators in the field of acupuncture remains to understand the actual mechanism of Deqi as it relates to analgesia. Elegant studies using state-of-the-art techniques such as functional MRI are being performed to answer such questions. Although we are aware of the correlation between Deqi and analgesia, large-scale trials with uniformity and scientific validity are needed to convincingly demonstrate the need for achieving Deqi.

The author affirms there are no conflicts of interest and the author has no financial interest related to the material of this manuscript.