COLUMNIST RESEARCH REVIEW Incomplete answers Joint manipulation on the autonomic nervous system STUDY TITLE: The acute effects of joint manipulative techniques on markers of autonomic nervous system activity: a systematic review and meta-analysis of randomized sham-con-trolled trials AUTHORS: Picchiottino M, Leboeuf-Yde C, Gagey O & Hallman DM PUBLICATION INFORMATION: Chiropractic & Manual Therapies 2019; 27: 17. REVIEWED BY SHAWN THISTLE R esearch into biomechanical and neurophysiological mechanisms have yielded in-complete answers, as has ini-tial research into the effect of joint manipulative therapies (JMT) on the autonomic nervous system (ANS). Effects on the ANS such as somato-au-tonomic reflex modulation have been proposed as potential mechanisms. In-deed, the chiropractic profession initially professed to “normalize” autonomic activity as an explanation for the treat-ment effect of high-velocity spinal ma-nipulation. The true mechanism of effect, however, remains elusive. Several litera-ture reviews have attempted to system-atically review and meta-analyze results from studies investigating the mechanism of JMT, although they are limited by methodological concerns. As such, the goal of this study was review and critique the existing literature and compare the acute changes in ANS markers between patients receiving JMT on spinal or pe-ripheral joints with those undergoing a sham treatment. Pertinent Results Study Characteristics: 29 studies met the inclusion criteria, after initial screening of 2267 studies. Interventions included mobilizations (n = 16 studies), ‘atypi-cal’ mobilization (n = 1), sustained natural apophyseal glides (SNAGs) (n = 5) and high-velocity, low-amplitude thrust manipulation (HVLA) (n = 7). Treatment was generally localized to the spine, with 2 studies additionally including peripheral joint treatment. Risk of Bias Assessment : Risk of bias was unclear in all but 4 eligible studies, based largely on uncertainty regarding blinding of participants, the data ex-traction process and blinding of statis-ticians. With respect to specifics, 2 studies (both on mobilization) were determined to have low risk of bias while 3 (2 of which were on HVLA spinal manipulation) were deemed to have a high risk of bias. Overall Technical Quality : Technical quality was judged to be acceptable in 25/29 studies. The remaining studies (2 on mobilization, 2 on manipulation) were deemed to be technically defi-cient, based on a low technical score. Sham Procedures : 25/29 studies de-fined a sham intervention as an “inac-tive” manual contact (i.e. no move-ment). 2/29 studies used a sham treatment mechanically similar to the intervention; 1/29 used a sham similar to the true intervention with less pres-sure and 1/29 did not describe the sham intervention. • • • Effect of Interventions: 1. Mobilization vs. sham • Outcome – Skin Conductance: • DR. SHAWN THISTLE is a practising chiropractor, educator, international speaker, knowledge-transfer leader, evidence-based health care advocate, entrepreneur and medicolegal consultant. He founded RRS Education in 2006 and currently acts as the company’s CEO. RRS Education helps chiropractors and other manual medicine clinicians around the world integrate research into patient care via weekly Research Reviews, Online Courses and Seminars. rrseducation.com 22 Canadian Chiropractor December 2019 Moderate evidence (10 studies) sug-gests that treatment causes a bilateral increase in skin sympathetic nerve activity. Data pooled from 3 studies indicate significant increases over sham (mean difference 13.75, 95% CI 1.36 to 26.14, I2 = 51%, random effect, p = 0.03; 3 studies, 96 sub-jects) between baseline and interven-tion period and between baseline and the post-intervention period (mean difference 9.34, 95% CI 2.85 to 15.83, I2 = 0%, p = 0.005; 3 stud-ies, 96 subjects). Outcome: Skin Temperature: Very low quality evidence (8 studies) in-dicates no effect on skin sympathetic nerve activity or skin temperature. No pooling of data was possible. Outcome – Skin Blood Flow: Very low quality evidence (2 studies) sug-gest no effect on blood flow (1 study in fact found dual effects in opposite directions [increase and decrease]). Outcome – Heart Rate: Very low quality evidence (5 studies) found no effect on heart rate (beats per min-ute) during the intervention (mean difference −0.83 bpm, 95% CI -5.47 to 3.81, I2 = 0%, p = 0.73; 83 sub-jects, 2 studies) and the immediate post-intervention period (mean dif-ference − 1.23 bpm, 95% CI -4.47 to 2.02, I2 = 0%, p = 0.46, 121 sub-jects). 2 other studies found a signif-icant increase in heart rate between baseline and intervention period, while 1 study reported a significant increase in the post-intervention period. Outcome – Blood Pressure: Very low quality evidence (5 studies) indicates no effect on systolic blood pressure during the intervention period (mean difference − 2.02 mmHg, 95% CI -6.96 to 2.92, I2 = 31%, p = 0.42, 83 subjects) and the post-intervention period (mean difference − 1.02 www.canadianchiropractor.ca
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