Acute v Chronic Pain – what is the difference or are they just the same thing?

by | Aug 12, 2016 | Pain | 0 comments

Pain is something we have all experienced but we may not give much thought as to how or why we feel pain until it happens to us.

Most people have heard of acute and chronic pain. Acute pain may seem obvious, as it sounds urgent and is the immediate pain we feel when we hurt ourselves. Chronic pain is generally less understood, other than it can last for a long time for no apparent reason.

What is perhaps not well known is that all pain develops from the same biological response. How our bodies and minds deal with that pain determines whether we just experience short-term acute pain or it develops into long-term chronic pain.

To explain the biology of pain, our bodies contain millions of tiny nerve endings, or sensors, which are embedded in all of our tissues. They detect heat, cold, different types of pressure from very light touch to deep sustained pressure, our sense of spatial awareness or proprioception and, most relevant for pain, potential danger.

Our danger sensors are called nociceptors, ‘noci’ meaning harmful. Contrary to popular belief, these are not actually pain sensors, instead they signal the presence of tissue damaging conditions which can include chemicals, heat, pressure, injury or irritation and even excessive overstretching of muscles and joints, such as in a sprained ankle.

Despite being everywhere in our tissues, nociceptors do not respond to the normal day to day activities such as moving and exercising. Instead they only react to abnormal situations when the tissues they are sitting in are ‘under threat’, for example they are being squashed, stretched, or poisoned. In anatomical terms, the nociceptors change from a dormant state to being excited. And once excited, they start to send messages.

These messages are sent from the area under threat to the spinal cord where they are prioritised to the high speed route, the super highway to the brain, because they are signalling dangerous or even life threatening conditions.

The nociceptive messages continue their journey to an area of the brain called the cortex which is responsible for interpreting the incoming messages and assigning appropriate responses. This is the first time that the brain interprets the sensation as pain. Until then, it has just been a danger signal.

The cortex will also assign an emotion to the pain, as a way of identifying it for future reference, but at first pain will be the predominant sensation. And initially this will be acute, an intense sensation of excruciating pain designed to make you stop doing whatever is causing the pain (such as stop walking on that leg if you have sprained your ankle). This protects the body from further harm and allows it time to repair.

Nociceptor messages also trigger the release of large amounts of a chemical called substance P which acts to enhance their messages. Why do they do this? By turning up the volume on their messages, the nociceptors ensure they get top priority as they travel up the spinal cord.

To counter this, the cortex triggers the release of natural chemical painkillers to help reduce the pain, which are 200 times more powerful than morphine. These flood back down the spinal cord and effectively alter the perception of the messages. This response was coined the ‘gate control theory’ in the 1960s as it seemed that the natural chemicals were effectively closing the gate on the pain response. This is also how most painkillers work, by effectively closing the gate on nociceptor messages to the brain.

In many cases of tissue damage, the body is able to make a full repair and the tissues can return to their normal state within a few days. Medically the ‘normal’ healing time is regarded as anything up to three months.

However, in some cases even though the tissues appear to have healed, the pain continues well beyond this medical time limit, at which point it is called chronic pain. Why does this happen?

Initially tissue damage causes inflammation as part of the repair process. This causes an increase in pressure in the area which continues to trigger the local nociceptors. Inflammation also causes the body to grow extra nociceptors in the area and these can double in number within 12 days if the inflammation lasts that long.

This creates what is known as sensitisation as there are now many more local nociceptors which are all more alert to the possibility of further damage and need less of a trigger to respond. In fact, they can also respond to nothing, because they are on such high alert that they can spontaneously trigger.

This increased sensitivity creates unconscious changes in your body. You use a painful area less or differently, maybe favouring the other leg when walking. Your posture changes as a result and this can cause other areas to tighten and also become painful, creating referred pain. Sometimes the pain can become systemic, affecting your whole body, as in conditions like fibromyalgia.

Nociceptor messages continue to be sent to the cortex, but they are now predictable and are downgraded to the slower paths which are the B roads in the spinal cord. They are routed through the areas of the brain responsible for emotions and the release of stress hormones, which explains the strong link between chronic pain and negative emotions such as stress, anxiety and depression.

By now there are also biological changes in the spinal cord which mean that the painkiller chemicals are no longer produced to block the pain messages and instead they are magnified, as if the pain gates have been wedged open.

These significant biological changes can start to happen within only a few minutes of the original damage and, if they persist for more than a few days, they cause your cortex to create a new, yet unwanted learned behaviour which becomes chronic pain.

However, just as the body and brain can learn this behaviour, with the right signals they can also un-learn it and replace it with something more positive and pain-free. Body interventions such as myofascial release and mind interventions such as cognitive hypnotherapy are powerful ways in which we can ‘reset’ ourselves by interrupting the old messages and replacing them with something positive.

Myofascial release works by releasing fascial (connective tissue) restrictions that form as a result of tissue damage and the subsequent spreading of further restrictions throughout the body. In doing so it takes the pressure off the nociceptors, allowing them to switch off. In releasing fascial restrictions it also helps to rebalance and restore better posture and movement throughout the body.

Cognitive hypnotherapy works by changing the emotional links to pain created by the cortex. Instead of the limiting beliefs associated with chronic pain that hold the mind and body in restriction, the unconscious mind can be reprogrammed to restore pain-free movement to the body.

Just as chronic pain behaviours can start within a few minutes or days of the original tissue damage, so can these therapies work just as fast to start the gradual process of rehabilitation, cumulatively re-building the good and natural behaviours of a normal pain-free life.

At the Pain Care Clinic we specialise in both myofascial release and cognitive hypnotherapy for the effective treatment of chronic pain conditions.


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