Autonomic regulation following concussion. It can be a bit like cooking a soufflé.
The autonomic nervous system can be complicated, which sort of makes sense as it is often responding to the complex challenges of life!
From heart rate to hormone, blood pressure to breathing, this is the part of the nervous system that unconsciously recognizes, reacts and regulates so many systems in our body. A conductor of our physiological orchestra, where the sympathetic nerves are activated at times of stress and demand, and the parasympathetic branches are key drivers for recovery and restoration.
However, for all of its nuances, there is increasing evidence that highlights the importance of understanding the autonomic system and how it can be disrupted following an mTBI. Whether it is due to stretching and shearing of axons, inflammation, a change in the levels of neurotransmitters such as adrenaline, noradrenaline and acetylcholine it is not uncommon for patients, who remain symptomatic at 3 weeks, to be experiencing an autonomic component.
So, what to look out for?
If we think of what the autonomic nervous system controls these are the things that can go out of kilter. And whilst the following symptoms may be triggered from other systems, it is worth considering
Cardiovascular: Changes and fluctuations in blood pressure or heart rate
Gastrointestinal: Nause, vomiting, bowel disturbances, loss of appetite
Sleep: Insomnia, excessive sleep, ineffective, non-restorative, sleep
Thermoregulation: Changes in body temperature and sweat response
Eyes: Unequal pupil size (anisocoria), sensitivity to light
How to assess?
Aside from clinical questioning there are a whole host of tests that can be used to help form judgement. Here are three that you may find useful.
Buffalo Concussion Treadmill Test: This test can also be done on a static bike and looks at how heart rate, perceived exertion and symptoms vary with a graduated increase in physical demand. The outcome is a modified heart rate threshold that is relevant to a patient at that moment in time and this allows for greater accuracy in exercise prescription.
NASA Lean Test: A useful way to evaluate excessive changes in heart rate that can be seen with patients who are experiencing postural orthostatic tachycardia syndrome (POTS). If POTS is detected interventions may include medication, nutritional (fluids), compression garments and graded exercise.
Firstbeat Lifestyle Assessment: This brings together physiology and context. A monitor is used to collect changes in heart rate variability and whilst the monitor is worn the patient will keep a diary of actions / feelings. A report is produced that details intra-individual changes in autonomic response and these are mapped, minute by minute, against a timeline. This data is useful in understanding the demands of daily life and lead to lifestyle interventions.
How to Treat?
I have already touched on some of the possible interventions that could be considered on the road to recovery.
Sometimes the symptoms can be obvious, sometimes subtle but consideration of the autonomic system has a role to play in a multisystemic approach to assessment. As for the treatment here are three things to consider:
Medical – Potentially medication can be used to influence blood pressure and heart rate.
Physical – Graded exercise that respects the current heart rate threshold and any symptom provocation is generally accepted as an appropriate intervention.
Lifestyle – There is often a focus on structuring the loads (physical, mental and emotional) that a patient is placed under. Fatigue management is important and so is recovery optimization.
Autonomic deregulation can be seen in concussion, in particular those with persistent symptoms.
Recognition and a proactive approach to the management of autonomic irregularity is something to be considered by all members of the multi-disciplinary team.
The balancing act between the demands of life and the way we cope and recover from these demands is a skill. A bit like a soufflé – undercook it and no progress is made; overcook and collapse occurs – balance is everything!