bronchoconstriction
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Bronchoconstriction is the constriction of the airways in the
lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...
due to the tightening of surrounding
smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
, with consequent coughing,
wheezing A wheeze is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed (for example narrowing of the lower respiratory tract ...
, and
shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing disc ...
.


Causes

The condition has a number of causes, the most common being
emphysema Emphysema, or pulmonary emphysema, is a lower respiratory tract disease, characterised by air-filled spaces ( pneumatoses) in the lungs, that can vary in size and may be very large. The spaces are caused by the breakdown of the walls of the alve ...
as well as
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, cou ...
.
Exercise Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...
and
allergies Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...
can bring on the symptoms in an otherwise asymptomatic individual.


Emphysema

With emphysema the shortness of breath due to effective bronchoconstriction from excessive very thick mucus blockage (it is so thick that great difficulty is encountered in expelling it resulting in near exhaustion at times) can bring on panic attacks unless the individual expects this and has effectively learned
pursed lip breathing Pursed-lip breathing (PLB) is a breathing technique that consists of exhaling through tightly pressed (pursed) lips and inhaling through the nose with the mouth closed. Uses Pursed-lip breathing can help to ease shortness of breath in people w ...
to more quickly transfer oxygen to the blood via the damaged alveoli resulting from the disease. The most common cause of emphysema is smoking and
smoking cessation Smoking cessation, usually called quitting smoking or stopping smoking, is the process of discontinuing tobacco smoking. Tobacco smoke contains nicotine, which is addictive and can cause dependence. As a result, nicotine withdrawal often make ...
is mandatory if this incurable disease is to be treated. Prevention of bronchoconstriction by this pathway is vital for people with emphysema and there are several
anticholinergic Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system. These agents inhibit the parasympathetic nervous system ...
medications that in combination with mucous thinning agents such as
Guaifenesin Guaifenesin, also known as glyceryl guaiacolate, is an expectorant medication that aids in the elimination of sputum from the respiratory tract. Chemically it is an ether of guaiacol and glycerine. It is often used in combination with other me ...
cause significant improvement in breathing.


Exercise-induced bronchoconstriction

More generally termed ''
exercise-induced asthma Exercise-induced asthma, or E.I.A., occurs when the airways narrow as a result of exercise. The preferred term for this condition is exercise-induced bronchoconstriction (EIB). While exercise does not cause asthma, it is frequently an asthma trig ...
'', the preferred and more accurate term ''exercise-induced bronchoconstriction'' better reflects underlying
pathophysiology Pathophysiology ( physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is the ...
. It is also preferred due to the former term giving the false impression that asthma is caused by exercise. In a patient with EIB, exercise initially follows the normal patterns of bronchodilation. However, by three minutes, the constriction sets in, which peaks at around 10–15 minutes, and usually resolves itself by an hour. During an episode of this type of bronchoconstriction, the levels of inflammatory mediators, particularly
leukotrienes Leukotrienes are a family of eicosanoid inflammatory mediators produced in leukocytes by the oxidation of arachidonic acid (AA) and the essential fatty acid eicosapentaenoic acid (EPA) by the enzyme arachidonate 5-lipoxygenase. Leukotrienes ...
,
histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in ...
, and
interleukin Interleukins (ILs) are a group of cytokines (secreted proteins and signal molecules) that are expressed and secreted by white blood cells (leukocytes) as well as some other body cells. The human genome encodes more than 50 interleukins and related ...
, increase. TH2-type
lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s are activated, with an increase in
T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...
s expressing CD25 (IL-2R), and
B cell B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...
s expressing CD 23, causing increased production of
IgE Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isotype") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε c ...
. After exercise, the conditions will fade within one to three minutes. In most people with EIB, this is followed by a ''refractory period'', of generally less than four hours, during which if exercise is repeated, the bronchoconstriction is less emphasised. This is probably caused by the release of
prostaglandins The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derive ...
. The underlying cause of this type of bronchoconstriction appear to be the large volume of cool, dry air inhaled during strenuous exercise. The condition appears to improve when the air inhaled is more fully humidified and closer to
body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
. This specific condition, in the general population, can vary between 7 and 20 percent. This increases to around 80 percent in those with symptomatic asthma. In many cases, however, the constriction, even during or after strenuous exercise, is not clinically significant except in cases of severe to moderate emphysema. In May 2013, the American Thoracic Society issued the first treatment guidelines for EIB.


Allergen-induced bronchoconstriction

While a different cause, this has very similar symptoms, namely the immunological reaction involving release of inflammatory mediators. Inhalation of
allergen An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies. In technical terms ...
s in sensitized subjects develops into bronchoconstriction within 10 minutes, reaches a maximum within 30 minutes, and usually resolves itself within one to three hours. In some subjects, the constriction does not return to normal, and recurs after three to four hours, which may last up to a day or more. The first is named the ''early asthmatic response'', and the latter the ''late asthmatic response''. Bronchioconstriction can occur as a result of
anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
, even when the allergen is not inhaled.


Physiology

Bronchoconstriction is defined as the narrowing of the airways in the lungs (bronchi and bronchioles). Air flow in air passages can get restricted in three ways: # a spasmodic state of the smooth muscles in bronchi and bronchioles # an inflammation in the middle layers of the bronchi and bronchioles # excessive production of mucus. The bronchial spasm is due to the activation of
parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...
.
Postganglionic In the autonomic nervous system, fibers from the ganglion to the wikt:effector, effector organ are called postganglionic fibers. Neurotransmitters The neurotransmitters of postganglionic fibers differ: * In the parasympathetic division, neuro ...
parasympathetic fibers will release
acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...
causing the constriction of the
smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
layer surrounding the bronchi. These smooth muscle cells have muscarinic M3 receptors on their membrane. The activation of these receptors by acetylcholine will activate an intracellular
G protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their act ...
, that in turn will activate the
phospholipase C Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...
pathway, that will end in an increase of intracellular calcium concentrations and therefore contraction of the smooth muscle cell. The muscle contraction will cause the diameter of the bronchus to decrease, therefore increasing its resistance to airflow. Bronchoconstriction is common in people with respiratory problems, such as asthma, COPD, and cystic fibrosis.


Management

Medical management of transient bronchoconstriction or
chronic bronchitis Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...
depends on the severity and etiology of the underlying disease and can be treated with combinations of the following medications: * B-receptor agonists: Medications that stimulate the β2 receptor subtype on pulmonary smooth muscle will result in smooth muscle relaxation, bronchodilation, and increased airflow into the lungs during inhalation. These medications include short-acting beta agonists (SABAs) such as
albuterol Salbutamol, also known as albuterol and sold under the brand name Ventolin among others, is a medication that opens up the medium and large airways in the lungs. It is a short-acting β2 adrenergic receptor agonist which works by causing rel ...
which typically last 4–6 hours, and long-acting beta agonists (LABAs) such as
salmeterol Salmeterol (sold in China as Qitai) is a long-acting β2 adrenergic receptor agonist (LABA) used in the maintenance and prevention of asthma symptoms and maintenance of chronic obstructive pulmonary disease (COPD) symptoms. Symptoms of bronchos ...
which lasts 12 hours. For example, during an acute asthma exacerbation where airway smooth muscle is constricted, inhalation of SABAs provide rapid relief of symptoms—within 5–15 minutes—and are typically called "rescue inhalers". Due to their fast onset of action, they have been selected as first-line therapy for quick relief in persistent and intermittent asthma and bronchospasm. Patients may experience dizziness, heart palpitations, hyperglycemia, diarrhea and muscle cramps when taking these medications. Importantly, medications that antagonize the β2 receptor (β-blockers) may significantly increase the risk of asthma exacerbations, and are generally avoided in asthmatic patients. * Corticosteroids: Inhaled corticosteroids (e.g.
fluticasone Fluticasone is a manufactured glucocorticoid used to treat nasal symptoms. Both the esters, fluticasone propionate (a brand name for which is Flovent) and fluticasone furoate, are also used as topical anti-inflammatories and inhaled corticoste ...
,
budesonide Budesonide, sold under the brand name Pulmicort among others, is a medication of the corticosteroid type. It is available as an inhaler, nebulization solution, pill, nasal spray, and rectal forms. The inhaled form is used in the long-term mana ...
) are typically used when bronchoconstrictive disease has advanced to a persistent inflammatory state, more specifically in persistent or severe asthma and
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
(COPD). These medications decrease immune system activity which in turn will decrease swelling of the airways, decrease airway resistance, and increase delivery of air to the alveoli during respiration. Unlike the SABAs, these medications do not provide relief of acute symptoms or asthmatic attacks, and their benefits are typically only seen after 3–4 weeks of therapy. Due to this delayed therapeutic response, it is essential that patients who are prescribed corticosteroids for respiratory disease are adherent to their medication regimen. In the ISOLDE trial, fluticasone therapy decreased the frequency of COPD exacerbations and the rate of health decline in patients with moderate-to-severe COPD; however, had little effect in decreasing the rate of FEV1 decline. Patients should be counseled to wash their mouth following use of inhaled corticosteroids to decrease the risk of developing
oral thrush Oral candidiasis, also known as oral thrush among other names, is candidiasis that occurs in the mouth. That is, oral candidiasis is a mycosis (yeast/fungal infection) of ''Candida'' species on the mucous membranes of the mouth. ''Candida albica ...
, a common side effect of these medications. * Muscarinic antagonists (anti-cholinergics): Blocking the muscarinic acetylcholine receptors in pulmonary smooth muscle tissue results in a decrease in smooth muscle tone and bronchodilation. These medications include short-acting muscarinic antagonists (SAMAs) such as
ipratropium Ipratropium bromide, sold under the trade name Atrovent among others, is a type of anticholinergic (SAMA: short acting muscarinic antagonist) medication which opens up the medium and large airways in the lungs. It is used to treat the symptoms ...
, and long-acting muscarinic antagonists (LAMA) such as
tiotropium Tiotropium bromide, sold under the brand name Spiriva among others, is a long-acting bronchodilator (LAMA: long acting muscarinic antagonist) used in the management of chronic obstructive pulmonary disease (COPD) and asthma. Specifically it is ...
. Onset of action for SAMAs is typically between 30 and 60 minutes, making these drugs less efficacious in treating acute asthma attacks and bronchospasm. Most common side effects for these drugs may include dry mouth, headache, urinary tract infection, and bronchitis. * Other: Other prescription and over-the-counter medications, such as
theophylline Theophylline, also known as 1,3-dimethylxanthine, is a phosphodiesterase inhibiting drug used in therapy for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma under a variety of brand names. As a member of the ...
,
cromolyn Cromoglicic acid ( INN)—also referred to as cromolyn (USAN), cromoglycate (former BAN), or cromoglicate—is traditionally described as a mast cell stabilizer, and is commonly marketed as the sodium salt sodium cromoglicate or cromolyn sodium. ...
, and
montelukast Montelukast, sold under the brand name Singulair among others, is a medication used in the maintenance treatment of asthma. It is generally less preferred for this use than inhaled corticosteroids. It is not useful for acute asthma attacks. Ot ...
are indicated for specific diseases and may only provide bronchoconstriction relief to these studied populations.


See also

* Bronchodilatation *
Bronchospasm Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release (degranulation) of substances from mast cells or basophils under the influence of anaphylatoxins. It causes di ...


References


External links


Pharmacotherapy of bronchoconstriction in patients with asthma by antiepileptic drugs

Why Do So Many Winter Olympians Have Asthma?

Salt Intake, Asthma, and Exercise-Induced Bronchoconstriction: A Review
{{Respiratory physiology Respiratory physiology Pulmonary function testing