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Spasmodic Dysphonia
Spasmodic asthma is characterized by contraction of the smooth muscle of the airways and, in severe attacks, by airway obstruction from mucus that has accumulated in the bronchial tree. This results in a greater or lesser degree of difficulty in breathing. One approach to classifying asthma differentiates cases that occur with an identifiable antigen, in which antigens affect tissue cells sensitized by a specific antibody, and cases that occur without an identifiable antigen or specific antibody. The former condition is known as “extrinsic” asthma and the latter as “intrinsic” asthma. Extrinsic asthma commonly manifests in childhood because the subject inherits an “atopic” characteristic: the serum contains specific antigens to pollens, mold spores, animal proteins of different kinds, and proteins from a variety of insects, particularly cockroaches and mites that occur in house dust. Exacerbation of extrinsic asthma is precipitated by contact with any of the proteins to which sensitization has occurred; airway obstruction is often worse in the early hours of the morning, for reasons not yet entirely elucidated. The other form of asthma, intrinsic, may develop at any age, and there may be no evidence of specific antigens. Persons with intrinsic asthma experience attacks of airway obstruction unrelated to seasonal changes, although it seems likely that the airway obstruction may be triggered by infections, which are assumed to be viral in many cases.
Asthma acquired as the result of occupational exposure (a special form of intrinsic asthma) is now recognized to be more common than previously suspected. Exposure to solder resin used in the electronics industry, to toluene diisocyanate (used in many processes as a solvent), to the dust of the western red cedar (in which plicatic acid is the responsible agent), and to many other substances can initiate an asthmatic state, with profound airflow obstruction developing when the subject is challenged by the agent.
characteristic of Asthma
It is a characteristic of all types of asthma that those with the condition may exhibit airflow obstruction when given aerosols of histamine or acetylcholine (both normally occurring smooth muscle constrictors) at much lower concentrations than provoke airflow obstruction in normal people; affected individuals may also develop airflow obstruction while breathing cold air or during exercise. These characteristics are used in the laboratory setting to study the airway status of patients. As a result of much recent work, it is thought that the diagnosis of asthma of any kind is difficult to sustain in the absence of a general increase in airway reactivity.
The acute asthmatic attack is alarming both for the sufferer and for the onlooker. There is acute difficulty in breathing, and the chest assumes a more and more inspiratory position. Despite the severe respiratory difficulty, the patient remains fully conscious. The most dangerous form of the condition is known as status asthmaticus. The bronchial spasm worsens over several hours or a day or so, the bronchi become plugged with thick mucus, and airflow is progressively more obstructed. The affected person becomes fatigued; the arterial oxygen tension falls still further, carbon dioxide accumulates in the blood (leading to drowsiness), and the acidity of the arterial blood increases to dangerous levels and may lead to cardiac arrest. Prompt treatment with intravenous corticosteroids and bronchodilators is usually sufficient to relieve the attack, but in occasional cases ventilatory assistance is required. In a few cases, death from asthma is remarkably rapid—too rapid for this complete sequence of events to have occurred, although at autopsy the lungs are overinflated. The exact mechanism of death in these cases is not completely understood.
Although the state of the airway is influenced by psychogenic factors, asthma is not correctly regarded as a disease commonly caused by psychological factors. It may interrupt normal activities and schooling to such an extent that it casts a shadow over the development of the personality. More commonly, it tends to diminish in severity with age, and people who had quite severe asthma in childhood may lead normal lives after the age of 20. It is now known that asthma attacks may be precipitated by food—in small children, possibly by milk; and some adults are extremely sensitive to sulfite compounds in food or wine. A subgroup of asthmatics are so sensitive to aspirin (acetylsalicylic acid) that ingestion of this chemical may lead to a life-threatening attack.
Changes in mortality from asthma in different countries have been closely studied, but the causes are obscure. It is clear, however, that there has been a considerable increase in the rate of hospital admissions for asthma in children and in adults up to the age of 60. Because there is now more effective treatment for asthma than was available previously, it is not clear why this should be occurring. Unless the asthma is complicated by infection (of which that by the fungus Aspergillus is common in damp climates), the chest radiograph remains normal. Asthma does not lead to the destructive lesions of emphysema (described below), although the physical appearance of the patient and the sounds of airflow obstruction in the lung may be similar in the two conditions.
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