The autonomic nervous system (ANS) is the part of our nervous system that controls functions of the body which are not consciously controlled, such as heart rate, breathing and digestion. The sympathetic nervous system (SNS) is part of the ANS and its main function is to activate the changes necessary for a perceived harmful event, commonly referred to as our ‘fight or flight’ response.
This hardwired fight or flight response was arguably more important to our survival back in the days when our ancient ancestors were a much favoured meal for apex carnivores. When the response is triggered, certain hormones are released which make rapid changes to our bodies preparing us to fight or flee. These include increasing our heart rate, increasing blood flow to major muscle groups and slowing our digestion, ready to give the body a sudden burst of strength and energy.
These days it’s unlikely that we would need to run from a lion, but the response is still very much there and often triggered when we least need it, perhaps as we stand to give a presentation at work or if somebody is driving aggressively behind us. Our heart rate increases, our breathing becomes shallower and our palms sweat.
‘Fight or flight’ and CRPS
Whilst the link is not entirely understood, it is thought that the SNS plays a role in the development and maintenance of CRPS. Indeed, in an earlier article we considered how nerve blocks into the SNS are sometimes used as a diagnostic tool for CRPS.
One theory suggests that following physical trauma, CRPS may develop as a result of the SNS triggering the release of certain ‘fight-or-flight’ hormones known as catecholamines. Of course, these hormones are released by everybody in a traumatic situation, but the theory goes that in some people an as yet unknown susceptibility may cause these hormones to over activate pain receptors. This would explain why the symptoms of CRPS are out of all proportion to the precipitating injury; it is not the injury itself causing the extreme pain but rather the way the body has responded to the injury.
Other symptoms of CRPS include skin colour and temperature changes. As the SNS is responsible for regulating the blood vessels of the skin, could a problem with the SNS also be responsible for those changes?
Clearly, the balance of available evidence points to some link between the SNS and CRPS. Undoubtedly, medical science will eventually uncover the nature and extent of that link and, crucially, whether that link moves us any closer to a cure for CRPS.