Breathing is an automatic process, controlled by the autonomic nervous system (or ANS). The ANS is a division of the nervous system that unconsciously regulates many of the automatic bodily functions that we depend on every second such as our heart rate, digestion or blood circulation to different organs.
In a recent literature review, it was found that there is evidence to suggest that concussion does impact the function of the autonomic nervous system (Pertab et al., 2018). The nature of the symptoms from autonomic dysfunction
confound with those of post-concussion syndrome.
In the study of the relationship between mTBI and the autonomic system, various modalities have been used.
Among the available noninvasive techniques for assessing the autonomic status, measuring heart rate variability (HRV)
has been commonly used (Esterov et al., 2017).
Diaphragmatic breathing is required to effectively train one’s HRV
is frequently impacted in individuals with concussion or mild traumatic brain injury (Thompson et al., 2012).
Moreover, post-concussion syndrome consists of many symptoms (e.g., cognitive dysfunction, emotional regulation, headaches, etc.) for which HRV
has evidence as a useful treatment. An added bonus is that there are relatively no side effects to HRV
training and concussion patients are generally more sensitive to the side effects of medications; and the medications are often less effective than in the non-concussion population (Ashina et al., 2020).
In concussion, some of the adversely affected networks in the brain may participate in the affective network (i.e., anterior cingulate, amygdala, anterior insula, etc.). This is a network of brain structures that are involved in emotional regulation. It is not just involved in the demonstration of emotions, but also memory, pain tolerance and many other functions.
This is intuitive, consider the following examples:
1. A young child really wants earrings and is willing to endure the pain for the same, but when her little sister lightly hits her, she cries.
2. When you are really interested in something, you tend to absorb more of the material.
This affect network is connected to important structures in the brainstem like the locus coeruleus in the pons and the nucleus of the solitary tract (NST) in the medulla. The NST, for example, influences activity in many brain regions like the locus coeruleus, cingulate, amygdala and the hypothalamus that, in turn, influence our sympathetic nervous system’s activity
, our blood pressure and heart rate
, fear behaviours, and the hormone-pituitary-adrenal (HPA) axis (Thompson et al., 2015).
HRV breathing stimulates vagus afferent feedback to the brain stem.
This may theoretically explain why HRV has grade A evidence for the treatment of migraine
. As migraine is a condition of cortical hyperexcitability that involves the brainstem. Inhibiting this excited signal in the brainstem before it goes up to the trigeminal nerve and the cortex with this vagus afferent feedback (from HRV training) may be how HRV works. When one considers that many conditions of cortical hyperexcitability (e.g., tension-type headache [TTH], migraine-like headache, dizziness, anxiety/depression, PTSD
, chronic fatigue syndrome, temporomandibular disorder [TMD], myofascial pain syndrome [e.g., chronic neck pain], chronic pain syndromes) exist in the context of post-concussion syndrome, it is understandable why so many have started studying HRV training and its effects in post-concussion syndrome patients.