HEART RATE VARIABILITY AS AN OUTCOME MEASURE IN CLINICAL TRIALS OF ACUPUNCTURE AGAINST PAIN:A SYSTEMATIC REVIEW

Randomized controlled trials(RCTs) have demonstrated the efficacy of acupuncture treatment against chronic pain and other ailments.In the present contribution, we are interested in two topics of current research in acupuncture:(1) a possible working mechanism of acupuncture, and(2) why the placebo control of sham acupuncture(SA) seems to achieve similar effects as verum acupuncture(VA).As a working mechanism, it has been proposed that acupuncture can modulate the autonomous nervous system(ANS) to restore homeostatic equilibrium.The ANS is responsible for the adaptation of the heartbeat rhythm and other physiological processes to the external and internal environment.Heart rate variability(HRV) is an objective and non-invasive biomarker that quantifies the state of the ANS, and estimates the contributions of the antagonistic orthosympathetic(ONS) and parasympathetic(PNS) nervous system components.It has been suggested that an imbalance between ONS and PNS may be at the origin of many symptoms of chronic pain.We realized a systematic revision of the medical literature, and localized six RCTs where a total of 203 chronic pain patients were treated with acupuncture, and where HRV was used to evaluate the outcome of the treatment.We found evidence that(1) VA is able to modulate the ANS as seen by significant changes in HRV, and(2) HRV seems to discriminate between VA and SA, whereas clinical and quality-of-life parameters tend to fail to do so.However,(3) most of the included RCTs failed to interpret HRV at the baseline, so that it is not clear whether the ANS is imbalanced at the pre-treatment stage, and which antagonistic component(ONS or PNS) is responsible for the imbalance.As a consequence of this methodological flaw, at present, it is not clear whether the observed ANS modulation by VA corresponds to a restoration of the homeostasis.