Power Tools for Technical Communication:
Extended Definition Formatting

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Asthma is a respiratory syndrome often of allergic origin characterized by a reversible constriction of the airways. Asthma is unlike conditions such as emphysema and chronic bronchitis which are widespread, irreversible obstructions of the airways. The following discussion focuses on these aspects of the condition: incidence and symptoms, causes and triggers, process, and treatment.

Asthma affects 5 to 10 % of the world population. More than 14 million people in the USA are afflicted, including almost 5 million children. In the UK, more than 3 million people are affected, including 1 in 7 children and 1 in 25 adults. Asthma is a problem among all races, but hospitalization and death rates for black Americans are 3 times the rate of whites.

The major symptoms of asthma include shortness of breath accompanied by wheezing—whistling and labored breathing—particularly following exercise or exposure to allergens; coughing that lingers for weeks; nighttime wakening with a cough or shortness of breath; and constriction or a feeling of tightness in the chest.

In any discussion of asthma, a distinction must be made between causes and triggers. The causes of asthma are the underlying factors that predispose you to an attack following a trigger. These factors are likely to be inherited genes as well as environmental allergens such as house dust mites, cats, or dogs. In addition, smoking during pregnancy increases the chance of a child developing asthma. If none of these causes are present, it is unlikely that asthma will ever manifest itself in an individual. In young people, 75% of asthma cases are attributable to allergens. Childhood asthma usually improves with age, but aging often worsens adult-onset asthma.

A trigger is something that is not in itself noxious to a non-asthmatic person, but sets off an asthma attack in an individual with the syndrome. The major triggers of an attack include cold air especially following exercise, repiratory infection such as colds and flu, social allergens such as cigarette smoke, atmospheric pollutants such as sulfur dioxide, indigestion caused by the upward movement of gastric acid, and emotional states such as stress.

Figure 1 Drawings depicting a normal and asthmatic airway passage.

Exposure to an allergen such as pollen causes sensitization of the airways. The tissue lining the airways (airway epithelia) produces signaling factors known as immunoglobulins that bind to platelets and white cells in the blood. Upon second exposure of the allergen, histamine is released by the epithelia and an asthma attack ensues. The latter process, which is called a Type 1 hypersensitivity reaction consists of two phases: immediate response and late-phase response. In the immediate-response phase, white blood cells and platelets release histamine, causing contraction of the smooth muscle surrounding the airways (bronchospasm). The late-phase response phase occurs some time after the immediate response is a delayed and is often nocturnal. Factors produced in the first phase attract more white blood cells, in particular, eosinophils. The result of this cellular infiltration is an inflammatory response and swelling of the airway epithelium. This is followed by excess mucous secretion into the air passages and bronchospasm.

Figure 2 Flow diagram of the late-phase response in an asthma attack.

There is no cure for asthma, but symptoms are manageable with drugs. Two types of drugs, relievers and preventors, can stabilize the condition. Relievers primarily consist of short-term bronchodilators such as Salbutamol. These drugs act during the immediate phase of an asthma attack by relaxing airway smooth muscle and dilating air passages. Preventors are anti-inflammatory agents such as corticosteroids that act in the late phase of an attack. The problems with the chronic use of bronchodilators are that the effects of the drug wear off with time. Airway epithelium becomes hypersensitive, and there is a rebound constriction of the airways. Anti-inflammatory agents cause immunosuppression. In addition, patients cannot make their own steroids which results in muscle wasting and osteoporosis.

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