Prevalence in Bronchial Asthma

Asthma is common and its prevalence is increasing. Studies using objective measurements of lung function, airway responsiveness and symptoms suggests that 7 percent of the adults and up to 15 percent of children in UK have asthma.

There is considerable interest in the reasons for the increase in the prevalence of asthma, most probably relating to changes in the indoor environment including early exposure to air allergens and cigarette smoke, fewer childhood infections and changes in diet.

There is a wide variability in geographical prevalence of asthma, with the highest rates observed in New Zealand, Australia and the UK and the lowest in countries such as China and Malaysia.

The drugs most commonly associated with the induction of acute episodes of asthma are aspirin, coloring agents such as tartrazine, beta adrenergic antagonists and sulfitting agents.

The typical aspirin sensitive respiratory syndrome primarily affects adults, although the condition may be seen in childhood. This problem usually begins with perennial vasomotor rhinitis that is followed by a hyperplasic rhinosinusitis with nasal polyps.

Progressive asthma then appears. On exposure to even very small quantities of aspirin, affected individuals typically develop ocular and nasal congestion and acute, often severe episodes of airway obstruction.

The prevalence of aspirin sensitivity in asthmatic subjects varies from study to study, but many authorities feel that ten percent is a reasonable figure. There is a great deal of cross reactivity between aspirin and other nonsteroidal anti-inflammatory compounds.

Indomethacin, fenoprofen, naproxen, zomepirac sodium, ibuprofen, mefenamic acide, and hylbutazone are particularly important in this regard. On the other hand, acetaminophen, sodium salicylate, choline salicylate, salicylamide and propoxyphene are well tolerated.

The exact frequency of cross reactivity to tartrazine and other dyes in aspirin sensitive asthmatic subjects is also controversial and again ten percent is the commonly accepted figure.

This perculiar complication of tartrazine and other potentially troublesome dyes are widely present in the environment and may be unknowingly ingested by sensitive patients.

Patients with aspirin sensitivity can be desensitized by daily administration of the drug. Following this form of therapy, cross tolerance also develops to other nonsteroidal anti inflammatory agents.

The mechanism by which aspirin and other such drugs produce bronchospasm in unknown but may be related to aspirin induced preferential generation of leukotrienes. Immediate hypersensitivity does not seem to be involved.

Beta adrenergic antagonists regularly produce airway obstruction in asthmatics as well as in others with heightened airway reactivity and should be avoided in such individuals.

Even the selective beta agents have this propensity particularly at higher doses. In fact, even the local use of beta, blockers in the eye for the treatment of glaucoma has been associated with worsening asthma.

Environmental causes of asthma are usually related to climatic conditions that promote the concentration of atmospheric pollutants and antigens.

These conditions tend to develop in heavy industrial or densely populated urban areas and are frequently associated with thermal inversions or other situations associated with stagnant air masses.

In these circumstances, although the general population can develop respiratory symptoms, patients with asthma and other respiratory diseases tend to be more severely affected.

The air pollutants known to have this effect are ozone, nitrogen dioxide and sulfur dioxide. The last needs to be present in high concentrations and produces its greatest effects during periods of high ventilation.

Occupation related asthma is a significant health problem, and acute and chronic airway obstruction has been reported to follow exposure to a large number of compounds used in many types of industrial processes.

Bronchoconstriction can result from working with or exposure to, metal salts, wood and vegetable dusts. It is important to recognize that exposure to sensitizing chemicals, particularly those used in paints, solvents and plastics also can occur during leisure or non-work related activities.

The underlying mechanisms for this airway obstruction appear to be two in number:

1) In some cases the offending agent results in the formation of a specific IgE and the cause seems immunologic and

2) Materials being employed, in other cases, cause a direct liberation of bronchoconstrictor substance.

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