The Palliative Effect of TENS-WAA on 'Capsaicin/Heat' Induced Acute Lower Back Pain: a Self-controlled Clinical Study

Acute lower back pain is a common condition that occurs in all age groups, and most people will experience acute lower back pain at least once in their lives. The use of pharmacological analgesic interventions may result in complications such as gastrointestinal reactions, skin reactions, and renal damage, so there is an urgent need for an analgesic method that is easy to use, relatively safe, and has no significant systemic side effects to alleviate patients' pain.

Wrist and ankle acupuncture is an acupuncture therapy developed by Professor Zhang Xinshu and other professors of the First Affiliated Hospital of the Second Military Medical University of the Chinese People's Liberation Army based on the meridian theory of Chinese medicine, by dividing the human body into two segments and six zones and treating them according to the longitudinal zones in which the illnesses are located or the corresponding points of the areas where the primary lesions are located, in order to achieve the purpose of dredging the meridians and collaterals, regulating qi and blood, balancing the yin and yang, relieving pain and treating the illnesses, and it has been widely used for treating the clinical It is widely used to treat all kinds of pain and neurological diseases.

Transcutaneous Electrical Nerve Stimulation is a non-invasive pain treatment method, which relieves pain by distributing current of specific frequency and intensity to stimulate peripheral nerves. In recent years, our team has combined the wrist and ankle needles with transcutaneous electrical nerve stimulation to develop an analgesic device that can be worn on the human wrist and ankle, which is called transcutaneous electrical nerve stimulation based on the theory of wrist and ankle needles. Transcutaneous Electrical Nerve Stimulation based on Wrist-Ankle Acupuncture theory（TENS-WAA) uses low-frequency electronic pulses to stimulate the entry point of the wrist-ankle acupuncture needle, which has the advantages of easy to wear, concentrated treatment site, safe treatment, and needle-free.

Functional near-infrared spectroscopy is a novel optical technique for non-invasive brain activity measurement by reading cerebral haemodynamics and oxygen saturation. Advantages include portability, non-invasiveness, no ionising radiation or drug injections, and simultaneous measurement of two haemodynamic parameters - deoxyhaemoglobin and oxyhaemoglobin. Several studies have demonstrated the utility and potential of functional NIR spectroscopy for pain assessment.

In medical research, the capsaicin model is widely used to simulate acute pain in humans, and capsaicin-induced pain sensations are produced primarily through binding to capsaicin receptors. Topical application of capsaicin activates TRPV1, located at the end of primary sensory neurons in the trunk and viscera, which, through a series of actions, leads to the release of pro-inflammatory factors, while injury receptors in the skin then generate neural signals that are transferred to the cerebral cortex, resulting in the sensation of pain. The sensation is similar to neuropathic pain, and pro-inflammatory factors also play a key role in the pathophysiological process of acute lower back pain. Therefore, the use of capsaicin is effective in inducing acute lower back pain, while related studies have shown that the combination of heat and capsaicin has a synergistic or additive effect.

The present study was designed as an autocross-control study in which a 'capsaicin-thermal pain' low back model was established in healthy subjects to induce acute lower back pain, and the analgesic efficacy of TENS-WAA was verified by using the fNIRS, VAS, and other assessment methods, with the following main objectives:

1. To repeat the validity of the pre-cortical fNIRS pain assessment paradigm in a controlled study;
2. To validate the efficacy of the Transcutaneous Electrical Nerve Stimulation based on Wrist-Ankle Acupuncture theory intervention in an autocross-control study by using fNIRS to collect data on changes in blood oxygen levels in brain regions involved in pain perception (frontal pole area and dorsolateral prefrontal cortex), as well as the VAS;
3. Explore the specificity of Transcutaneous Electrical Nerve Stimulation based on Wrist-Ankle Acupuncture theory acupoints through the self-randomised crossover control of 'unilateral pain + ipsilateral intervention' and 'unilateral pain + contralateral intervention'.