Tuesday, 14 August 2012

Asthma

Asthma is a common disease effecting the respiratory system, and its prevalence has increased significantly over the last 30 years. It is estimated that as many as 300 million people globally are affected by asthma, and it is responsible for around 250,000 deaths a year.

Asthma is characterized by recurring symptoms including wheezing, coughing, chest tightness, and shortness of breathe. These symptoms are variable, and they may differ from person to person. There are different classifications of asthma, which are intermittent, mild persistent, moderate persistent and severe persistent. Diagnosis and classification is based on the symptoms present and their frequency, as well as the patients response to therapy.

Beyond these classifications there are several different types of asthma:

Brittle asthma is the term used to describe asthma that is distinguishable by recurrent and severe attacks. Brittle asthma is separated into two types. Type 1 brittle asthma is highly recurrent, with wide peak flow variability despite intense medication. Type 2 brittle asthma is well-controlled but with sudden severe attacks and exacerbations.

Status asthmaticus is an excaerbation of asthma that does not respond well to standard medication. In some cases, nonselective beta blockers such as Timolol have reportedly caused fatal status asthmaticus.

Exercised-induced asthma is an exacerbation of asthma directly related to exercise. There is a high incidence of asthma in top athletes in sports such as cycling, mountain biking and long-distance running. Conversely there is a low incidence of asthma in sports such as weightlifting and diving. It is not know why this disparity between sports exists.

Occupational asthma is the result of workplace exposures leading to the development or worsening of asthma. It is the most under-reported and unrecognized type of asthma. The American Thoracic Society estimates that between 15-25% of all new-onset asthma cases are work related. Studies have shown high incidences of occupational asthma in certain careers, with basic laborers accounting for the highest percentage of new-onset occupation asthma cases (33%) and administrative workers, such as secretaries, accounting for the lowest percentage (19%). Occupational asthma can be dealt with on a case-by-case basis, however when a high number of workers from a particular location are diagnosed with occupational asthma, it is possible (and prudent) to assess the work place as this can lead to a dramatic decline in the reported cases.

Asthma can be treated effectively in a large number of cases, to such an extent that many patients diagnosed with asthma will go on to be free of asthma-related symptoms after a course of therapy. Due to this factor asthma is classified as a chronic obstructive condition, but it is not considered a chronic obstructive pulmonary disease as this term refers to combinations of diseases that are irreversible, such as chronic bronchitis and emphysema.

Causes


It is currently believed that asthma is caused by a combination of environmental and genetic factors, and these factors influence how severe asthma is, as well as how well it reacts to medication. The interaction between environmental and genetic factors is not currently fully understood.

There are over 100 genes associated with asthma. Most of these genes are associated with the immune system, as well as modulating inflammation, however varying results have been reported for each gene, and more research is required to discover which genes have the highest incidence of asthma associated with them.

Viral respiratory infections are one of the highest causes of asthma in young children.
It is believed that a history of atopic disease may well increase the risk of developing asthma by as much as 3 to 4 times, in children aged between 3 and 14. This is because asthma is easily triggered by allergens; the more allergens that a person reacts positively to, the higher the chance they will develop asthma.

In addition to allergens and viral infections, it is believed that air pollutants may also have an impact on the risk of developing asthma. Smoking during pregnancy has also been linked to a high incidence of asthma in children.

Diagnosis and Treatment


Current understanding of asthma encourages a "reponse to therapy" approach to diagnosis, where a patient is treated for asthmatic symptoms and monitored over the course of treatment to determine the severity of the asthma.

Once diagnosis is made, a treatment and management plan including lifestyle alterations and medication is created. This can include identifying and reducing exposure to triggers such as allergens, as well as a use of a range of short and long term control medications.

Short term medications include short acting beta2-adrenoceptor antagonists, anticholinergenic medications (such as ipratropium bromide), and various adrenergic agonists (such as inhaled epinephrine). Adrenergic agonists are generally not prescribed today due to concerns regarding cardiac stimulation.

Long term medications include glucocorticoids (which are considered among the most effective medications for long term asthma control), long acting beta-andrenoceptor agonists (although this type of medication has been linked to an increased severe exacerbation of asthma in children and adults, and should not be taken without accompanying steroids), Leukotriene antagonists (such as zafirlukast), and Mast cell stabilizers. 


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