- A new theory of allergic asthma in Chinese medicine.
Pathology and Aetiology of Allergic Asthma in Western
Medicine
Pathology
The pathology of asthma is characterized by a partial obstruction of airflow in the airways. This
is caused by a temporary narrowing of the bronchi by muscle spasm followed by mucosal
swelling. The bronchial narrowing interferes with ventilation and raises the resistance to airflow
in the bronchi. This is more marked on exhalation and it causes air to be trapped in the lungs.
The narrowed bronchi can no longer be effectively cleared of mucus by coughing.
In allergic asthma, the bronchospasm is caused by an allergic reaction due to immune
hypersensitivity. This is also called anaphylactic or Type-I reaction. Only IgE (reaginic)
antibodies produce Type-I reactions. As these antibodies adhere strongly to tissues (and
particularly to mast cells in the tissues), they are often called tissue-sensitizing antibodies.
Anaphylactic crises in asthma are caused by an antigen-antibody reaction on the surface of the
mast cells in the bronchi. This activates a series of enzymes which leads to the release of certain
chemical substances from the mast cells, such as histamine, serotonin, bradykinin and
prostaglandins. The IgE-dependent release of mast-cell products not only provokes acute
bronchospasm but also contributes to the development of the late-phase asthmatic reaction
(Figure 5.1(107)).
IgG antibodies account for 73% of Ig antibodies in serum and they can prevent IgE-mediated
allergic reactions. They are the only antibodies that are transported across the placenta to reach
the foetal circulation. This factor is quite significant in explaining the aetiology of allergic
asthma from a Chinese medical perspective, as will be discussed later.
Bronchospasm from an allergic reaction, however, is only one aspect of the pathology of asthma,
chronic inflammation of the bronchial mucosa being another. The mucosa is inflamed and
oedematous, and there are infiltrating inflammatory cells. There is an excess of eosinophils
which lead to destruction of epithelial cells with consequent exposure of irritant receptors on the
basement membrane. This, in turn, leads to an increase in bronchial responsiveness from allergic
stimulation.1(108)
Aetiology
There are two types of asthma: the early-onset type which is also called extrinsic or atopic
asthma, and the late-onset type which is also called intrinsic asthma. As the names imply, the
early-onset one usually starts during childhood while the late-onset one starts later on in life. Our