Asthma is a chronic illness characterized by inflammation of the airways

Asthma is a chronic illness characterized by symptoms such as shortness of breath, wheezing and cough, which vary in intensity over time. The primary pathogenic process driving the manifestations of asthma is airway inflammation which leads to two pathophysiological features of asthma: hyper-responsiveness or twitchiness of the airways in response to stimuli such as exercise or allergen exposure, and airway obstruction.⁵

Airway obstruction in asthma is due to three main factors:

1. Bronchoconstriction, where the smooth muscle surrounding the airways tightens in response to a trigger (e.g. exercise) and narrows the airway
2. Swelling of the airway wall due to inflammation
3. Mucus formation within the airways that obstructs the airflow

Narrower airways obstruct the normal flow of air, making it difficult to breathe and leading to clinical symptoms (like wheezing, coughing, chest tightness and shortness of breath). Worsening symptoms can result in an episode of “asthma attack,” or exacerbation.

The number of people living with asthma in the United States has more than doubled from 1982 to 2002. It is now estimated that over 22 million people live with asthma in the United States including more than 6 million children. Asthma symptoms and exacerbations can severely impact the quality of life and lifestyle of people with asthma, their caregivers, parents, and healthcare professionals. Asthma symptoms and exacerbations can be frightening and can result in visits to the emergency room (about 2 million annual visits), hospitalization (about 500,000 annual visits to the hospital) and in some cases, even death (about 4000 people die annually of asthma).⁶  Asthma ranks in the top conditions that lead to preventable hospitalizations (Prevention Quality Indicator 15).⁷  It is also the leading cause of school absences.⁸  The overall socio-economic burden (estimated to be about $14 billion annually)⁹ of asthma and the impact of asthma on the general population are staggering. Medical advances like accurate, practical and non-invasive measurement of exhaled nitric oxide (eNO) promise to improve the standard of care and quality of life of people with asthma.

The most common type of asthma is allergic-asthma, triggered by allergens such as tree and grass pollen, and animal dander. Asthma can also be triggered by physical exercise and irritants like smoke, air pollutants, changes in weather and cold air.⁵  Currently, there is no cure for asthma. The cornerstone for pharmaceutical treatment of persistent symptoms is the daily use of anti-inflammatory drugs, e.g. inhaled steroids which are the most common controller medications for long-term management of the disease. Inhaled steroids have been shown to reduce asthma exacerbations and reduce asthma mortality. Usually, these are supplemented with a ‘rescue medication’ (e.g. albuterol) for quick relief from severe airway constriction, and work by relaxing the airway smooth muscle. These rescue medications can bring immediate relief in case of an emergency or an acute asthma attack, or prevent symptoms to an expected trigger like exercise. Importantly, eNO levels are high in untreated asthma but after anti-inflammatory medications (e.g. inhaled steroids), eNO levels fall rapidly, indicating reduction of airway inflammation. This change in eNO with reduction in inflammation has led to the application of this unique marker in monitoring asthma to bring about an improvement in disease control.