The pathophysiology of asthma

Asthma is one of the most persistent respiratory diseases, characterised by frequent episodes of cough and breathlessness that may range from mild and tolerable to life threatening in severity. It cannot usually be cured, yet it is possible to live a healthy life by effectively managing it with the help of expert advice, medicines and knowledge.

Knowing about asthma and its pathophysiology, i.e.. how it happens can help patients and their attendants prevent frequent flaring up of asthma

PATHOPHYSIOLOGY OF ASTHMA

Asthma results from a combination of multiple factors. Those which play the most important role in the development of this disease are hypersensitivity or allergy, inflammation of airways, excess secretion of mucus and bronchial spasm.

HYPERSENSITIVITY OF AIRWAYS

Perhaps the most characteristic feature of an asthmatic patient is the hypersensitivity of his smaller airways, also called 'bronchioles' to any irritant. Even in normal people, body has its own ways of responding to an external particle that might reach these airways. However, in case of asthmatics, this reaction of any external particle or irritant is highly exaggerated. So the walls of the bronchioles (airways) respond even to harmless particles in such a way that they lead to cough and suffocation.

On being exposed an irritant, the mucosal surface of the bronchioles reacts very strongly. The 'mast cells' in the epithelium of the mucosa secrete 'lymphokines' and 'cytokines' - substances that attract white blood cells like lymphocytes, eosinophils and macrophages to protect the body from the threat posed by this irritant particle. These cells come and secrete various kinds of enzymes that would usually kill bacteria and protect the body from it. Only in this case, the whole exercise is often futile, as there may not be any threat from this external particle at all.

ALLERGY

Allergy is nothing but the hypersensitivity of the body to certain external material. Many patients of asthma are also allergic to many other things, and this tendency is also seen in their body in other forms. Asthma is often linked with allergy - both having similar pathophysiology.

INFLAMMATION OF AIRWAYS

The response of the airways and attracting lymphocytes and macrophages leads to secretion of digestive enzymes which create 'inflammation' or swelling of the bronchial mucosa. The collection of fluids and enzymes and damaged cells accumulate and are slowly digested by the body with the help of macrophages - all this leads to swelling and thickening of the surface layer of airways.

EXCESS SECRETION OF MUCUS

The excess secretion of mucus results from the irritation caused by the hyper-responsiveness to irritants, and it is the body's attempt to clear the irritant. However, instead of helping in clearing, it actually leads to flooding of airways. Too much of mucus blocks the air passage itself and leads to cough and suffocation.

BRONCHOSPASM

The smaller airways have a thin layer of muscle tissue around them. The irritation of the bronchial mucosa and its hypersensitivity also leads to contraction of this layer of muscles thereby causing a spasm of the airway that makes the blockage of the air passage that much more severe. Bronchospasm makes matters much worse.

PRECIPITATING & TRIGGERING EVENTS

Often an asthmatic attack is triggered by exposure to a substance to which the person is allergic or hypersensitive. Many a times, it may also be triggered off by a respiratory infection or an attack of flu, that leads to bronchial mucosal reaction thereby triggering the whole chain of events that results in blocking of the air passages. Other factors that can contribute include smoking, air pollution and excessive weight.

SUMMARY

Thus, asthma results from a complex mechanism that involves a defect in body's response to external material as well as the presence of a trigger. Genetic factors play an important role, as there is a genetic predisposition for allergies that makes many patients of asthma vulnerable. At the same time, knowing how asthma actually happens can help one deal with it in a more realistic way and also take the necessary precautions like avoiding triggers of allergy and infection that can precipitate asthma.