J Manipulative Physiol Ther. 2016 (Jun); 39 (5): 369–380 ~ FULL TEXT
Christine M. Goertz, DC, PhD, Stacie A. Salsbury, PhD, RN, Robert D. Vining, DC,
Cynthia R. Long, PhD, Katherine A. Pohlman, DC, MS,
William B. Weeks, MD, PhD, MBA, Gervasio A. Lamas, MD
Vice Chancellor for Research & Health Policy,
Palmer Center for Chiropractic Research,
Palmer College of Chiropractic,
OBJECTIVE: The purpose of this pilot sham-controlled clinical trial was to estimate the treatment effect and safety of toggle recoil spinal manipulation for blood pressure management.
METHODS: Fifty-one participants with prehypertension or stage 1 hypertension (systolic blood pressure ranging from 135 to 159 mm Hg or diastolic blood pressure ranging from 85 to 99 mm Hg) were allocated by an adaptive design to 2 treatments: toggle recoil spinal manipulation or a sham procedure. Participants were seen by a doctor of chiropractic twice weekly for 6 weeks and remained on their antihypertensive medications, as prescribed, throughout the trial. Blood pressure was assessed at baseline and after study visits 1, 6 (week 3), and 12 (week 6), with the primary end point at week 6. Analysis of covariance was used to compare mean blood pressure changes from baseline between groups at each end point, controlling for sex, age, body mass index, and baseline blood pressure.
RESULTS: Adjusted mean change from baseline to week 6 was greater in the sham group (systolic, –4.2 mm Hg; diastolic, –1.6 mm Hg) than in the spinal manipulation group (systolic, 0.6 mm Hg; diastolic, 0.7 mm Hg), but the difference was not statistically significant. No serious and few adverse events were noted.
CONCLUSIONS: Six weeks of toggle recoil spinal manipulation did not lower systolic or diastolic blood pressure when compared with a sham procedure. No serious adverse events from either treatment were reported. Our results do not support a larger clinical trial. Further research to understand the potential mechanisms of action involving upper cervical manipulation on blood pressure is warranted before additional clinical investigations are conducted.
KEYWORDS: Cervical Spine; Chiropractic; Complementary Therapies; Controlled Clinical Trial; Hypertension; Spinal Manipulation
From the FULL TEXT Article:
Hypertension, or high blood pressure (BP), affects nearly 30% of US adults, with only 35% of those individuals meeting their treatment goals.  Spinal manipulative therapy (SMT) is a manual therapy used by some doctors of chiropractic (DCs) for the treatment of hypertension. [2–7] Small clinical trials and observational studies of SMT have reported a BP-lowering effect for select patients. [8–13] However, many studies of SMT for BP management demonstrate a high bias risk under systematic review, whereas trials with a lower risk of bias have shown null or inconclusive results. [3, 11, 12] In the largest clinical trial conducted to date on the efficacy of SMT for BP control, Goertz et al  studied 140 patients with high normal BP or stage 1 hypertension and concluded that full-spine SMT delivered with the diversified technique, in conjunction with dietary modification, offered no advantage in lowering systolic (SBP) or diastolic (DBP) blood pressure compared with diet modification alone.
Since then, a pilot study by Bakris and colleagues  of a rarely used form of SMT that targets the C1 (atlas) vertebra demonstrated a substantial decrease in SBP and DBP compared with a sham in 50 unmedicated patients with stage 1 hypertension. The SMT participants sustained a mean drop of 17 mm Hg in SBP and 10 mm Hg in DBP over sham participants. Not surprisingly given these results, the study received national media attention with the implication being that chiropractic SMT may be a viable treatment alternative for persons with hypertension.  However, several methodological issues with the study potentially impact its generalizability to chiropractic practice. These issues include unclear allocation and blinding procedures ; the use of an uncommon chiropractic technique not widely available to patients (ie, practiced by less than 50 practitioners worldwide who have the advanced certification level of the trial provider); and the reliance upon a sole DC for many critical aspects of the trial, including development of the sham, identification of cervical spine misalignments, delivery of the SMT and sham, and evaluation of clinical outcomes.  Furthermore, participants were recruited from one medical practice, and the publication offered an incomplete description of the BP assessment procedures used to determine eligibility and outcomes,  leading a systematic review to rank the trial as having an unclear bias risk. 
However, the striking BP-lowering effects of this previous study  called for a well-designed clinical trial to evaluate further the efficacy and safety of cervical SMT for BP management. [15, 16] Thus, our team conducted a pilot study with a more commonly used form of SMT that also targets the C1/C2 vertebrae, using research methodologies that were more rigorous and generalizable. Toggle recoil SMT involves a nonrotary, high-velocity thrust to the C1/C2 vertebrae.  Although the thrust of toggle recoil SMT differs from the gradual, prolonged force application used in the aforementioned trial,  both techniques embrace the same therapeutic paradigm, that is, the alignment of upper cervical vertebrae with a carefully controlled manual force that may influence BP via relaxation of upper cervical spinal muscles and by affecting autonomic control mechanisms located in the medulla oblongata and cervicocranial region. [18, 19]
The purpose of this pilot sham-controlled clinical trial was to estimate the treatment effect and its variance, as well as the safety of upper cervical spinal manipulation for BP management.  Thus, our primary aim was to evaluate the BP-lowering effects of toggle recoil SMT on SBP and DBP against a control group that received a sham manipulation to the neck in individuals with prehypertension or stage 1 hypertension. Our secondary aim was to evaluate the safety of toggle recoil and the sham manipulation by categorizing adverse events (AEs) reported by study participants.
More than 65 million Americans are diagnosed with hypertension.  Population-based studies estimate that up to 5 million patients may use nonpharmacological or complementary treatments, such as SMT, to help control their BP. [41–43] However, there is limited research to support the use of SMT for patients with high BP. Thus, rigorous studies to evaluate the efficacy and safety of SMT for hypertension are needed to guide chiropractic clinical practice. [15, 16]
Based upon our estimates of treatment effect, the CHiP trial did not indicate any benefit from toggle recoil SMT for lowering BP in patients with SBP of 135 to 159 mm Hg or DBP ranging from 85 to 99 mm Hg. The mean BP decline favored the sham over SMT at all 3 end points. These findings did not replicate the striking results of a previous clinical trial of SMT to the upper cervical vertebrae that showed substantial drops in both systolic and diastolic BP compared with a sham treatment.  However, our findings are consistent with other high-quality clinical trials that have demonstrated limited efficacy of SMT for hypertension. 
Our results are particularly noteworthy when placed within the context of recent research suggesting that BP management should aim for SBP measures less than 120 mm Hg rather than the currently accepted guidelines of 140 mm Hg for SBP to minimize patients’ risk of heart attack and stroke from hypertension.  No clinical trials conducted to date have indicated that any form of SMT, used either as a primary or secondary BP intervention, lowers BP levels to these near-normal readings. Chiropractic patients who are offered treatments that are ineffective at treating specific conditions, such as the toggle recoil SMT for reducing BP as tested in this study, may be at risk for negative sequelae of hypertension and should receive further evaluation and management of their BP.
Although this was a pilot study, the CHiP trial design has several advantages over the methodology used by Bakris et al  in their pilot. First, the CHiP sample was drawn from a self-referred, community-based participant pool rather than from patients carefully selected from a single medical clinic. Second, the CHiP trial design was patient- and BP assessor–blinded and did not rely on a single clinician to conduct all treatments, clinical examinations, and radiography assessments. Our methods were more reflective of clinical practice, as multiple experienced DCs delivered the interventions. Next, our believability measures suggest adequate participant blinding throughout active care. In addition, our use of an active surveillance process identified AEs similar in quality, severity, and duration to symptomatic reactions reported by patients receiving cervical SMT in a multicenter cohort study.  Finally, the CHiP trial followed an established BP measurement protocol and used a rigorous and ongoing BP quality control process throughout the trial to confirm the validity of the primary outcome measures. [24, 46]
The CHiP trial demonstrated that DCs can play an important role in identifying, monitoring, and co-managing patients with high BP. [47, 48] Our BP evaluations identified more than 100 study volunteers, most of whom were currently under the care of a primary care provider for their hypertension, who had not achieved recommended BP target levels of 140/90 mm Hg.  Nearly 20% of these participants had average SBP readings of at least 160 mm Hg or DBP readings of at least 100 mm Hg over repeated assessments, placing them at higher risk for the negative sequelae of hypertension, including heart attack, stroke, and kidney disease.  Our study findings suggest that DCs are in a position to adopt clinical practices that support the identification, monitoring, and referral of patients with high BP while making recommendations consistent with antihypertensive treatment regarding health promotion practices and lifestyle changes. [47–49]
Limitations and Suggestions for Future Studies
This pilot study enrolled participants who were imbalanced across treatment groups in relation to their BP medication regimens, with more participants in the SMT group receiving multiple classes of antihypertensive medication. Those patients may have had somewhat more refractory hypertension that was less amenable to response to the study treatments. 
Second, the sham procedure that we used was designed as a comparison technique for patients with neck pain. [36, 37] Although the sham shared characteristics with toggle recoil SMT that would be obvious to participants (ie, table drop mechanism), it had not been validated as a control for BP studies. Although no active thrust was delivered with the sham, the drop mechanism was engaged, potentially delivering muted force to the cervical vertebrae. This action could conceivably create an effect similar to the active SMT procedure used by Bakris et al. 
The CHiP trial differs from the study of Bakris et al in an important way that may have impacted our findings: The CHiP participants did not have their BP medicine washed out before the start of the trial. Our participants had lower BP readings at baseline than those in the study of Bakris et al, perhaps because of this concurrent treatment. Therefore, it remains unknown whether DCs can influence BP through SMT to the upper cervical vertebrae in the absence of antihypertensive medications.
The primary purpose of this pilot was to estimate treatment effects of toggle recoil SMT vs sham SMT for managing BP. A second aim was to evaluate safety. Our results do not support a larger clinical trial of toggle recoil SMT. No serious AEs from either treatment were reported. We propose that further research is needed to understand the potential mechanisms of action involving upper cervical SMT on BP before additional clinical investigation is warranted. 
Fifty-one participants with SBP ranging from 135 to 159 mm Hg or DBP
ranging from 85 to 99 mm Hg were allocated by an adaptive design
to 2 groups: spinal manipulation using toggle recoil
or sham manipulation.
After 6 weeks, spinal manipulation did not reveal any benefit for
lowering SBP or DBP compared with the sham procedure.
We found no evidence to support using toggle recoil spinal manipulation
to the cervical spine to lower BP.