What is bronchospasm?
Bronchospasm is the constriction and narrowing of sensitive and/or inflamed bronchioles in response to an asthma trigger. Bronchospasm is triggered by an inhaled allergen, irritant, cold air, exercise, emotions or can be triggered by some medications like aspirin. Narrowing or the airways is the cause of symptoms like tightness of the chest, shortness of breath, wheezing and cough.
All bronchodilators act directly on the bronchioles causing them to dilate or widen, which makes breathing easier. However, there are several different mechanisms by which these medications are effective and some are fast-acting, while others are slower to act but are more long-lasting. Most bronchodilators are taken by inhalation although an oral form is available for taking as tablets.
How do bronchodilators work?
When the bands of smooth muscle surrounding the bronchioles contract and tighten, hey cause the bronchioles to narrow or constrict, which causes difficulty breathing. Bronchodilators act directly on the smooth muscle causing them to relax and this opens up the airways. Two types of bronchodilator are used:
- Beta 2-agonists bind to and stimulate specific beta 2 adrenergic receptors in the smooth muscle and this causes the airways to relax and widen (bronchodilation). Some are fast-acting and can be used for rescue medication, others are slower to act but are longer lasting and are used to relieve or control symptoms.
- Anticholinergics block the cholinergic receptors in the smooth muscles of the bronchioles to inhibit muscle contraction and this allows them to widen. These bronchodilators are used for COPD and chronic severe asthma.
Inhaled beta 2-agonists
Salbutamol is a fast-acting bronchodilator that is used as a rescue medication to relieve symptoms of acute asthma or asthma attack. It is usually effective within 5 minutes, lasts for 4-6 hours, and should only be used when needed and not as a regular medication. An asthma preventer should be used for long-term management of asthma.
Salmeterol and formoterol are long-acting bronchodilators that can be used with or without a preventer asthma medication but cannot be used as a rescue medication because of their slow onset of action (10 to 20 minutes). These long-acting bronchodilators are particularly helpful for managing exercise-induced asthma and nocturnal symptoms in asthma, such as night-time cough.
Nebulised beta 2-agonists
Salbutamol and levosalbutamol can be nebulised into a fine aerosol using a nebuliser that creates a fine mist. The bronchodilator medication is then inhaled through a face mask or mouthpiece which is easier for treating severe asthma attack, particularly in children.
Ipratropium and tiotropium are anticholinergic bronchodilators that are used as long-term treatments for chronic obstructive pulmonary disease (COPD) and other obstructive airways disease, like chronic bronchitis, and emphysema. They are delivered into the airways as a dry powder using a special device.
Salbutamol is available as slow release tablets that are effective within 15 minutes and lasts for up to 8 hours. They are particularly helpful for nocturnal asthma and for severe or unstable asthma, but only in addition to a preventer medication and they are not suitable for asthma attack.