The process of sensitisation is very common, contributing to a wide range of painful conditions. In conditions such as carpal tunnel syndrome, for example, up to 85% of cases are attributed to nerve sensitisation.
Typically, postural or degenerative changes within the spine exert physical pressure on adjacent nerves causing continual failed initiations. As a result, normal stimuli become sufficient to generate an action potential, most often perceived as pain.
Within the lung, however, these stimuli are interpreted as irritation, leading to the protective responses we describe as an asthma attack.
Treating postural changes (using primarily upper thoracic spinal manipulation) removes a source of nerve stimulation, thus requiring more stimulation for it to signal again. Decreasing the responsiveness of nerves within the lung means that normal stimuli such as cold air are not perceived as threatening and are less likely to cause an asthma attack.
Chiropractic treatment helps a number of conditions by the same principle, with sciatica and thoracic outlet syndrome obvious examples. Having looked at the comparable anatomy and physiology, it doesn’t seem a vast leap to expect results when treating asthma.
There are, however, some flaws with this theory:
Most significantly, it does not take into account the afferent (sensory) role of the vagus nerve. The vagus nerve is involved in autonomic responses, giving the urge to cough when stimulated. While the importance of afferent vagus nerve activity has not been determined in relation to asthma, it is not affected by chiropractic treatment and so may remain a cause of symptoms.
It is also over simplistic to assume that all asthma cases are due to sensitisation of pulmonary nerves. Asthma is a multi-factorial disorder and the treatment of postural changes may not have any impact at all on symptoms.