It might seem that Heart Rate Variability (HRV) a bit of a hot topic in chiropractic circles right now, as practitioners and researchers alike begin to understand the many potential applications of this tool. We know that it is non-invasive in its nature, and an easy way to measure autonomic function and adaptability. But it isn’t just chiropractic science that is harnessing the insight HRV has on offer. A recent study published in the Journal of Manipulative and Physiological Therapeutics has shown that HRV indices are significantly associated with neck pain.
It is a noteworthy study, given there is only a limited number of HRV and neck pain studies currently in circulation. Interestingly, one such study observed “an abnormal sympathetic baroreceptor response to daily physical activity” in chronic neck pain patients [2, in 1] and another observed “an association between HRV reduction and the subjective perception of disability” in patients with chronic neck pain [3, in 1].
All in all, they are interesting observations given they pertain to the sympathetic nervous system which governs the response to the literal or metaphorical “bear in the room” (in the words of Dr. Otto Janke from last months blog video).
In this most recent piece of research, a blind, cross-sectional study design was used on a sample of thirty participants. The participants were divided into chronic neck pain (CNP) and healthy groups. They were between 18 and 45 years old (regardless of sex), and had sedentary lifestyles. They were included in the first group if they had chronic neck pain with a duration greater than 90 days, and a neck disability index (NDI) score greater than 5 or a numerical rating scale score greater than 3/10.
Measurements included in the study were the “Catastrophic Thoughts about Pain” scale, which is composed of 9 items on a Likert scale, and the Tampa Scale for Kinesiophobia, which is used to evaluate fear of movement and recurrence of the lesion. Prior to the test, participants were not to consume caffeine or alcohol, or engage in moderate up to heavy physical exertion. They did not sleep or talk during the measurement procedure, and the test took place over a period of ten minutes, in a quiet room after 10 minutes rest.
At this point, HRV measures were taken while in supine, sitting and standing positions.
The authors remarked that:
“In the present study, neck pain was correlated with worse linear and nonlinear HRV indices. To our knowledge, this is the first study to address these relationships. The results, therefore, reinforce the clinical importance of the early evaluation of the cardiac nervous system function and its association with chronic neck pain, even if mild, given the implication that this pain already causes autonomic issues.”
They went on to state that the association between chronic pain conditions and altered nervous system function is robust, and that this present study indicated “a significant correlation between pain and an increase of sympathetic activity in patients with chronic neck pain.” Their analysis lead them to comment on the negative effects of sedentarism on autonomic function, and the implications of HRV on pain medicine (given the increase in pain catastrophization in chronic neck pain patients with decreased HRV in the study). On the latter, they remarked, “the analysis of HRV becomes of extreme importance once the chronic pain may lead directly to dysregulation in both the sympathetic and parasympathetic nervous systems, further diminishing the capacity to respond adaptively to threats .”
While the study was not without its limitations and was not a chiropractic specific study, it is certainly an interesting one, especially in light of autonomic dysregulation and adaptation. It is these two issues that speak to the heart of chiropractic. While there is a mountain of literature out there that indicates chiropractic can help with neck pain, it is in the area of chiropractic, adaptation and sympathetic regulation that may prove most enlightening in the future.
Science is beginning to reveal just how far the effects of chronic neck pain reach. But it is the insight into the autonomic effects that prove most interesting, and most relevant to the everyday experience of chiropractors and chiropractic patients alike.
As always, more research is required. Until then, we keep on doing what we do best: removing subluxations and letting the body do the rest.