Bronchoconstriction
Encyclopedia
Bronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle
, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus
.
as well as asthma
. Exercise and allergies can bring on the symptoms in an otherwise non-symptomic individual.
is mandatory if this incurable disease is to be treated. Prevention of bronchoconstriction by this pathway is vital for emphysema sufferers and there are several anticholinergic
medications that can greatly improve the quality of life for these individuals. In combination with mucous thinning agents such as Guaifenesin
significant improvement in breathing can be accomplished.
, the preferred and more accurate term exercise-induced bronchoconstriction better reflects underlying pathophysiology
. 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 bronchorestriction, the levels of inflammatory mediators, particularly leukotrienes, histamine
, and interleukin
, increase. TH2-type lymphocyte
s are activated, with an increase in T cell
s expressing CD25 (IL-2R), and B cell
s expressing CD 23, causing increased production of IgE
. After exercise, the conditions will fade within one to three minutes. In most sufferers of EIB, this is followed by a refractory period, of generally less than four hours, during which if exercise is repeated, the bronchorestriction is less emphasised. This is probably caused by the release of prostaglandins.
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.
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.
Inhalation of allergen
s in sensitized subjects develops into bronchorestriction 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
, even when the allergen is not inhaled.
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
.
Physiology
Bronchoconstriction is due to an activation of the parasympathetic nervous system. Postganglionic parasympathetic fibers will release acetylcholine next to the Reissessen muscle, a smooth muscle layer surrounding the bronchi. These smooth muscle cells have M3 type muscarinic receptors on their membrane. The activation of these receptors by ACh will activate an intracellular Gq protein, that in turn will activate the PLC 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.Causes
The condition has a number of causes, the most common being emphysemaEmphysema
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary...
as well as asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
. Exercise and allergies can bring on the symptoms in an otherwise non-symptomic individual.
Emphysema
With emphysema the shortness of breath due to effective bronchoconstriction from excessive very thick mucous 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 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 cessationSmoking cessation
Smoking cessation is the process of discontinuing the practice of inhaling a smoked substance. This article focuses exclusively on cessation of tobacco smoking; however, the methods described may apply to cessation of smoking other substances that can be difficult to stop using due to the...
is mandatory if this incurable disease is to be treated. Prevention of bronchoconstriction by this pathway is vital for emphysema sufferers and there are several anticholinergic
Anticholinergic
An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central and the peripheral nervous system. An example of an anticholinergic is dicycloverine, and the classic example is atropine....
medications that can greatly improve the quality of life for these individuals. In combination with mucous thinning agents such as Guaifenesin
Guaifenesin
Guaifenesin INN or guaiphenesin , also glyceryl guaiacolate, is an expectorant drug sold over the counter and usually taken by mouth to assist the bringing up of phlegm from the airways in acute respiratory tract infections.-History:Similar medicines derived from the guaiac tree were in use as a...
significant improvement in breathing can be accomplished.
Exercise-induced bronchoconstriction
More generally termed exercise-induced asthmaExercise-induced asthma
Exercise-induced asthma, or E.I.A., is a medical condition characterized by shortness of breath induced by sustained aerobic exercise. It shares many features with other types of asthma, and responds to some typical asthma medications, but does not appear to be caused by the same inflammatory...
, the preferred and more accurate term exercise-induced bronchoconstriction better reflects underlying pathophysiology
Pathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
. 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 bronchorestriction, the levels of inflammatory mediators, particularly leukotrienes, histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
, and interleukin
Interleukin
Interleukins are a group of cytokines that were first seen to be expressed by white blood cells . The term interleukin derives from "as a means of communication", and "deriving from the fact that many of these proteins are produced by leukocytes and act on leukocytes"...
, increase. TH2-type lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s are activated, with an increase in T cell
T cell
T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...
s expressing CD25 (IL-2R), and B cell
B cell
B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...
s expressing CD 23, causing increased production of IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...
. After exercise, the conditions will fade within one to three minutes. In most sufferers of EIB, this is followed by a refractory period, of generally less than four hours, during which if exercise is repeated, the bronchorestriction is less emphasised. This is probably caused by the release of prostaglandins.
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.
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.
Allergen-induced bronchoconstriction
While a different cause, this has very similar symptoms, namely the immunological reaction involving release of inflammatory mediators.Inhalation of allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
s in sensitized subjects develops into bronchorestriction 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
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...
, even when the allergen is not inhaled.