Bronchodilation is the process by which the bronchi (tubes in the lungs made of connective tissue and muscle) are dilated, or opened. There are circumstances and conditions that cause the bronchi of the lungs to become narrow, or constrict, making it difficult to breathe. There are endogenous (inside the body) and exogenous (originating outside the body) factors that can affect bronchodilation.
Bronchoconstriction, or the narrowing of the airways, is caused by the muscles surrounding the lungs becoming tight. A build-up of excess mucous as well as inflammation can also cause constriction. The constriction results in coughing, wheezing and shortness of breath. There are several conditions that cause this and require bronchodilation in reponse. Chronic lung disease (CLD) commonly occurs in infants born earlier than 34 weeks gestation. Because their lungs are not mature and they often develop infections, their small airways can constrict. Emphysema involves bronchoconstriction due to blockage by thick mucous. Exercise-Induced bronchoconstriction is caused by elevated levels of inflammatory mediators, including T-cells, B-cells, leukotrienes and histamines during exercise. This usually occurs when large volumes of cool, dry air are inhaled during strenuous exercise. Allergen-induced bronchoconstriction is similar in response to the above condition, but the stimulator is inhalation of allergens. Asthma is a chronic inflammation of the bronchi causing the airways to narrow. Asthma is caused by a combination of environmental and genetic factors.
Sympathetic Nervous System Response
Bronchodilation can occur as part of the body’s natural response. When the sympathetic nervous system is activated in what is commonly known as the “fight or flight” response, the hormones and neurotransmitters of adrenaline (also called epinephrine) and noradrenaline (also called norepinephrine) are released. This response is triggered by physical or mental stress. Increased adrenaline produces increased heart rate, blood flow is shunted away from the skin and toward the muscles and internal organs, increased blood sugar, increased metabolic rate, dilated pupils and bronchodilation. Although adrenaline is a bronchodilator, it is not ideal as a treatment as it also induces the unwanted side effects of increased heart rate and blood pressure. Therefore medications have been created that are similar to adrenaline in affecting bronchodilation but without the side effects.
There are medications that can cause bronchodilation. These medications are commonly prescribed for patients with asthma or other restrictive lung diseases. There are two types of bronchodilators, short-acting and long-acting. These medications affect bronchodilation by causing the muscles in the walls of the bronchioles to relax, therefore dilating the airways.
The purpose of long-acting bronchodilators is to prevent bronchoconstriction. These medications can either be oral or inhaled, and they are to be taken on a routine basis. They do not provide immediate relief but are effective in inducing bronchodilation for up to 12 hours.
Short-acting medications are also called quick relief or rescue medications. These inhaled medications provide quick, fast relief by causing immediate bronchodilation. They typically take effect within 20 minutes and can last for up to 4 or 6 hours.
For conditions that cause inflammation to restrict the airways, steroids can affect bronchodilation. Steroids suppress the immune response and therefore inflammation that cause bronchoconstriction in the lung passageways.