ADAPT-ABILITY AND HEART RATE VARIABILITY

from Life West Chiropractic Magazine - Summer 2022 Edition

by Life Chiropractic College West

CHIROPRACTIC CARE MAKES SENSE FOR THE

A complex and constantly changing heart rate (HR) is an indicator of a healthy regulatory nervous system that can effectively adapt to sudden environmental and physiological challenges. Heart rate variability (HRV), the variation in time between successive heart beats, is known to represent a non-invasive index of Autonomic Nervous System (ANS) balance. In fact, because the ANS regulates the heart rate, we now know that HRV summarises complex non-linear cardiovascular accommodative responses to dynamic physiological variations. Moreover, the ANS is pivotal in the regulation of far more than just the cardiovascular system. Recent research has started to show that reduced HRV is connected to poor health outcomes in a range of diseases. Additionally, low HRV correlates with increased mortality from all causes and, based on prior and recent research, it seems that the slope of decline in parasympathetic HRV metrics is inversely related to longevity. Recently the fi rst meta-analysis was conducted of studies in patients with Coronary Vascular Disease with follow-up of at least one year. Although there are some limitations to that meta-analysis, the results suggest that compared to patients with a higher HRV, those with a lower HRV had a 112% higher risk of death from all causes. As a result, HRV analysis is now widely used to characterize the functions of the ANS as it relates to the regulation and adaptive capacity of a multitude of physiological responses. Take for example Systemic Lupus Erythematosus (SLE), which is characterized by chronic, systemic infl ammation, organ damage and dysfunction. ANS dysfunction is highly prevalent in SLE patients (up to 54%) and compared to controls, the prevalence may be up to 12 times greater. These numbers parallel fi ndings in other chronic conditions such as Diabetes and Rheumatoid Arthritis (RA). As mentioned, an imbalance of the ANS has been described in RA, infl ammatory bowel disease (IBD), and others. Generally, this imbalance is interpreted as a consequence of the disease more than a cause. However, research has shown that decreased vagal function precedes the development of a number of risk factors for cardiovascular disease and that modifi cation of risk profi les in the direction of lower risk is associated with increased vagal function. In fact, a recent prospective cohort study by Koopman et al., 2016, showed that autonomic dysfunction precedes the development of RA. The results of the study by Koopman et al. are very important since one can imagine that restoring a normal autonomic balance as reflected by increased HRV, might either prevent the development of inflammatory disorders such as RA, IBD, SLE and others, and/or prevent a flare of the disease in such patients with an imbalance of the ANS. Lifestyle modification (physical exercise, exposure to hot and cold, improved quantity/quality sleep, feeding quantity, quality and timing) and nondrug interventions such as yoga, tai chi, acupuncture, hypnosis, non-invasive vagus nerve stimulation and cognitive behavioral therapies, are all receiving increased research attention.

WHAT ABOUT CHIROPRACTIC ADJUSTMENTS?

Some older and less powerful studies have shown that spinal manipulation and chiropractic adjustments are able to modulate ANS activity. Yates, et al. in 1988 examined the effect of chiropractic adjustments to T1–T5 spine segments in patients with arterial hypertension. Immediately after the intervention, they observed a reduction in systolic and diastolic blood pressure and anxiety level. A separate case study showed the effects of 10 sessions of chiropractic adjustments (2 sessions per week) applied throughout the spine (C3 to L5) for 6 weeks. After the fi rst session, there was a reduction in sympathetic activity. A recent systematic review by Wirth et al., in 2019, which only included controlled studies of at least moderate quality, concluded that we now have clear evidence that the main intervention provided by chiropractors (chiropractic adjustment) affects the ANS, that the nature of those effects depend on the spinal level adjusted, and that response might differ between healthy volunteers and those patients presenting with pain. Wrist-worn tracking devices using photoplethysmography now provide the unique potential of continuously measuring surrogates of sympathetic and parasympathetic nervous system activity through the analysis of interbeat intervals. The neurophysiological mechanism underlying HRV exemplifi es the tight, yet highly complex coupling that exists between the brain and the rest of the body and provides us with a non-invasive dynamic metric of the ANS.