Prevalence of Asthma
Is a very common condition. About 10% of the population has the disease.
57% of people with the disease have it poorly controlled.
Characteristics of Asthma
1. Variable airflow obstruction
2. Airway hyperresponsiveness
3. Chronic airway inflammation
Variable Airway Obstruction
Spirometry is critical in the assessment of respiratory disorders, including asthma.
You should never diagnose asthma without measuring spiromery or lung function. There are many people who have been diagnosed with asthma that do not actually have the disease.
Normal people have a FEV1/FVC volume of >80%, but in asthma this is below 70-75% because of the smaller, constricted airway.
FVC in Asthmatic Patients
Forced vital capacity will be the same (or close to) in asthmatics compared to regular people, but it will take them longer to get there because the airway is smaller.
When you administer a bronchodilator to asthmatic patients, they tend to have a marked improvement in their FEV1/FVC ratio.
Patients suffering form other respiratory diseases such as COPD does not show a marked change.
Risk Factors for Developing Severe Asthma
Genetic factors (not just one gene)
Environmental factors (allergens, infections - Baker's asthma is classic)
Host factors (defect in airway epithelium, obesity, etc.)
Triggers (viral infection, allergen exposure)
Early and Late Response
After early exposure to the allergen or trigger, there is a marked decrease in FEV1 as there is an immediate response from cells in the immune system.
Hours later, the histamine and leukotrienes that were dumped in the area act as chemoattractants and initiate an inflammatory response which causes another marked decrease in FEV1 hours later.
We can measure the amount of methacholine that is required to induce a 20% fall in FEV1. This concentration is known as the PC20.
If the PC20 is 4, you clearly have asthma. If the PC20 is between 4 and 16, you may have mild asthma, and if the PC20 is >16, you are normal.
Asthma Sputum Cell Counts
It is normal to have ~2% eosinophils in the sputum.
In patients with severe asthma this number can rise as high as 50%.
Inhaled Corticosteroids (ICS)
Asthmatic symptoms are sensitive to ICS treatment.
Smoking blunts the effects of ICS.
A treatment for severe asthma approved by the FDA in 2010 involving the delivery of controlled, therapeutic radiofrequency energy to the airway wall, thus heating the tissue and reducing the amount of smooth muscle present in the airway wall. This acts to stop the constriction of the smooth muscle and help alleviate asthmatic symptoms
Appears to be safe in the long term.