Asthma

Name	Asthma
Diseasesdb	1006
Caption	Peak flow meters are used to measure one's peak expiratory flow rate
Icd10
Icd9
Omim	600807
Medlineplus	000141
Emedicinesubj	article
Emedicinetopic	806890
Emedicine mult
Meshname	Asthma allergy
Meshnumber	C08.127.108

Asthma (from the Greek άσθμα, ásthma, "panting") is a 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.

Treatment of acute symptoms is usually with an inhaled short-acting beta-2 agonist (such as salbutamol). Symptoms can be prevented by avoiding triggers, such as allergens and irritants, and by inhaling corticosteroids. Leukotriene antagonists are less effective than corticosteroids and thus less preferred. In 2009 asthma caused 250,000 deaths globally. Despite this, with proper control of asthma with step down therapy, prognosis is generally good.

Classification

Asthma is clinically classified according to the frequency of symptoms, forced expiratory volume in 1 second (FEV₁), and peak expiratory flow rate. Asthma may also be classified as atopic (extrinsic) or non-atopic (intrinsic), based on whether symptoms are precipitated by allergens (atopic) or not (non-atopic).

While asthma is classified based on severity, at the moment there is no clear method for classifying different subgroups of asthma beyond this system. Within the classifications described above, although the cases of asthma respond to the same treatment differs, thus it is clear that the cases within a classification have significant differences. Finding ways to identify subgroups that respond well to different types of treatments is a current critical goal of asthma research.

Although asthma is a chronic obstructive condition, it is not considered as a part of chronic obstructive pulmonary disease as this term refers specifically to combinations of disease that are irreversible such as bronchiectasis, chronic bronchitis, and emphysema. Unlike these diseases, the airway obstruction in asthma is usually reversible; however, if left untreated, the chronic inflammation of the lungs during asthma can become irreversible obstruction due to airway remodeling. In contrast to emphysema, asthma affects the bronchi, not the alveoli.

Brittle asthma

Brittle asthma is a term used to describe two types of asthma, distinguishable by recurrent, severe attacks. Type 1 brittle asthma refers to disease with wide peak flow variability, despite intense medication. Type 2 brittle asthma describes background well-controlled asthma, with sudden severe exacerbations.

Asthma attack

An acute asthma exacerbation is commonly referred to as an asthma attack. The classic symptoms are shortness of breath, wheezing, and chest tightness. While these are the primary symptoms of asthma, some people present primarily with coughing, and in severe cases, air motion may be significantly impaired such that no wheezing is heard.

Signs which occur during an asthma attack include the use of accessory muscles of respiration (sternocleidomastoid and scalene muscles of the neck), there may be a paradoxical pulse (a pulse that is weaker during inhalation and stronger during exhalation), and over-inflation of the chest., a blue color of the skin and nails may occur from lack of oxygen.

In a mild exacerbation the peak expiratory flow rate (PEFR) is ≥200 L/min or ≥50% of the predicted best.

Insufficient levels of vitamin D are linked with severe asthma attacks.

Occupational

Asthma as a result of (or worsened by) workplace exposures is a commonly reported occupational respiratory disease. Still most cases of occupational asthma are not reported or are not recognized as such. Estimates by the American Thoracic Society (2004) suggest that 15–23% of new-onset asthma cases in adults are work related. Animal proteins, enzymes, flour, natural rubber latex, and certain reactive chemicals are commonly associated with work-related asthma. When recognized, these hazards can be mitigated, dropping the risk of disease. Some people with asthma only rarely experience symptoms, usually in response to triggers, whereas other may have marked persistent airflow obstruction.

Gastro-esophageal reflux disease

Gastro-esophageal reflux disease coexists with asthma in 80% of people with asthma, with similar symptoms. This is due to increased lung pressures, promoting bronchoconstriction, and through chronic aspiration. this increases one's risk of hay fever by up to 5x and the risk of asthma by 3-4x.

GSTM1

IL10

CTLA-4

SPINK5

LTC4S

LTA

GRPA

NOD1

CC16

GSTP1

STAT6

NOS1

CCL5

TBXA2R

TGFB1

IL4

IL13

CD14

ADRB2 (β-2 adrenergic receptor)

HLA-DRB1

HLA-DQB1

TNF

FCER1B

IL4R

ADAM33

Many of these genes are related to the immune system or to modulating inflammation. However, even among this list of highly replicated genes associated with asthma, the results have not been consistent among all of the populations that have been tested. This indicates that these genes are not associated with asthma under every condition, and that researchers need to do further investigation to figure out the complex interactions that cause asthma. One theory is that asthma is a collection of several diseases, and that genes might have a role in only subsets of asthma. For example, one group of genetic differences (single nucleotide polymorphisms in 17q21) was associated with asthma that develops in childhood. |- ! Endotoxin levels !! CC genotype !! TT genotype |- ! High exposure | Low risk || High risk |- ! Low exposure |High risk || Low risk |}

Research suggests that some genetic variants may only cause asthma when they are combined with specific environmental exposures, and otherwise may not be risk factors for asthma.

The genetic trait, CD14 single nucleotide polymorphism (SNP) C-159T and exposure to endotoxin (a bacterial product) are a well-replicated example of a gene-environment interaction that is associated with asthma. Endotoxin exposure varies from person to person and can come from several environmental sources, including environmental tobacco smoke, dogs, and farms. Researchers have found that risk for asthma changes based on a person's genotype at CD14 C-159T and level of endotoxin exposure. Perfumes are a common cause of acute attacks in females and children. Both virus and bacterial infections of the upper respiratory tract infection can worsen asthma.

Hygiene hypothesis

One theory for the cause of the increase in asthma prevalence worldwide is the "hygiene hypothesis" —that the rise in the prevalence of allergies and asthma is a direct and unintended result of reduced exposure to a wide variety of different bacteria and virus types in modern societies, or modern hygienic practices preventing childhood infections. The prevalence of "severe persistent" asthma is also greater in low-income communities than those with better access to treatment. |- ! style="border-top: 3px solid darkgray;" | Near-fatal asthma | colspan="2" style="border-top: 3px solid darkgray;" | High PaCO₂ and/or requiring mechanical ventilation |- ! rowspan="9" style="border-top: 3px solid darkgray;" | Life threatening asthma | colspan="2" style="border-top: 3px solid darkgray;" | Any one of the following in a person with severe asthma:- |- ! Clinical signs ! Measurements |- | Altered level of consciousness | Peak flow < 33% |- | Exhaustion | Oxygen saturation < 92% |- | Arrhythmia | PaO₂ < 8 kPa |- | Low blood pressure | "Normal" PaCO₂ |- | Cyanosis |- | Silent chest |- | Poor respiratory effort |- ! rowspan="5" style="border-top: 3px solid darkgray;" | Acute severe asthma | colspan="2" style="border-top: 3px solid darkgray;" | Any one of:- |- | colspan="2" | Peak flow 33-50% |- | colspan="2" | Respiratory rate ≥ 25 breaths per minute |- | colspan="2" | Heart rate ≥ 110 beats per minute |- | colspan="2" | Unable to complete sentences in one breath |- ! rowspan="3" style="border-top: 3px solid darkgray; border-bottom: 3 px solid darkgray;" | Moderate asthma exacerbation | colspan="2" style="border-top: 3px solid darkgray;" | Worsening symptoms |- | colspan="2" | Peak flow 80%-50% best or predicted |- | colspan="2" style="border-bottom: 3 px solid darkgray;" | No features of acute severe asthma |} There is currently not a precise physiologic, immunologic, or histologic test for diagnosing asthma. The diagnosis is usually made based on the pattern of symptoms (airways obstruction and hyperresponsiveness) and/or response to therapy (partial or complete reversibility) over time. Spirometry is needed to establish a diagnosis of asthma.

Wheezing—high-pitched whistling sounds when breathing out—especially in children. (Lack of wheezing and a normal chest examination do not exclude asthma.)

history of any of the following:

*Cough, worse particularly at night

*Recurrent wheeze

*Recurrent difficulty in breathing

*Recurrent chest tightness

Symptoms occur or worsen in the presence of:

*Exercise

*Viral infection

*Animals with fur or hair

*House-dust mites (in mattresses, pillows, upholstered furniture, carpets)

*Mold

*Smoke (tobacco, wood)

*Pollen

*Changes in weather

*Strong emotional expression (laughing or crying hard)

*Airborne chemicals or dusts

*Menstrual cycles

Symptoms occur or worsen at night, awakening the patient

The latest guidelines from the U.S. National Asthma Education and Prevention Program (NAEPP) recommend spirometry at the time of initial diagnosis, after treatment is initiated and symptoms are stabilized, whenever control of symptoms deteriorates, and every 1 or 2 years on a regular basis. Peak flow readings can be charted together with a record of symptoms or use peak flow charting software. This allows patients to track their peak flow readings and pass information back to their doctor or nurse.

Infants and Children

*Upper airway diseases

**Allergic rhinitis and sinusitis

*Obstructions involving large airways

** Foreign body in trachea or bronchus

** Vocal cord dysfunction

**Vascular rings or laryngeal webs

**Laryngotracheomalacia, tracheal stenosis, or bronchostenosis

**Enlarged lymph nodes or tumor

*Obstructions involving small airways

**Viral bronchiolitis or obliterative bronchiolitis

**Cystic fibrosis

** Bronchopulmonary dysplasia

** Heart disease

*Other causes

**Recurrent cough not due to asthma

**Aspiration from swallowing mechanism dysfunction or gastroesophageal reflux

**Medication induced

Adults

*COPD (e.g., chronic bronchitis or emphysema)

* Congestive heart failure

*Pulmonary embolism

* Mechanical obstruction of the airways (benign and malignant tumors)

*Pulmonary infiltration with eosinophilia

* Cough secondary to drugs (e.g., angiotensin-converting enzyme (ACE) inhibitors)

*Vocal cord dysfunction

Before diagnosing asthma, alternative possibilities should be considered such as the use of known bronchoconstrictors (substances that cause narrowing of the airways, e.g. certain anti-inflammatory agents or beta-blockers). Among elderly people, the presenting symptom may be fatigue, cough, or difficulty breathing, all of which may be erroneously attributed to Chronic obstructive pulmonary disease(COPD), congestive heart failure, or simple aging.

Pulmonary aspiration, whether direct due to dysphagia (swallowing disorder) or indirect (due to acid reflux), can show similar symptoms to asthma. However, with aspiration, fevers might also indicate aspiration pneumonia. Direct aspiration (dysphagia) can be diagnosed by performing a modified barium swallow test. If the aspiration is indirect (from acid reflux), then treatment is directed at this is indicated.

Prevention

The evidence for the effectiveness of measures to prevent the development of asthma is weak. Ones which show some promise include: limiting smoke exposure both in utero and after delivery, breastfeeding, increased exposure to respiratory infection per the hygiene hypothesis (such as in those who attend daycare or are from large families).

Management

A specific, customized plan for proactively monitoring and managing symptoms should be created. Someone who has asthma should understand the importance of reducing exposure to allergens, testing to assess the severity of symptoms, and the usage of medications. The treatment plan should be written down and adjusted according to changes in symptoms.

Lifestyle modification

Avoidance of triggers is a key component of improving control and preventing attacks. The most common triggers include: allergens, smoke (tobacco and other), air pollution, non selective beta-blockers, and sulfite-containing foods. Anticholinergic medications, such as ipratropium bromide provide addition benefit when used in combination with SABA in those with moderate or severe symptoms. Anticholinergic bronchodilators can also be used if a person cannot tolerate a SABA. Older, less selective adrenergic agonists, such as inhaled epinephrine, have similar efficacy to SABAs. Inhaled forms are usually used except in the case of severe persistent disease, in which oral steroids may be needed. Inhaled formulations may be used once or twice daily, depending on the severity of symptoms.

Long acting beta-adrenoceptor agonists (LABA) have at least a 12-hour effect. They are however not to be used without a steroid due to an increased risk of severe symptoms. Mast cell stabilizers (such as cromolyn sodium) are another non-preferred alternative to glucocorticoids.

;Delivery methods Medications are typically provided as metered-dose inhalers (MDIs) in combination with an asthma spacer or as a dry powder inhaler. The spacer is a plastic cylinder that mixes the medication with air, making it easier to receive a full dose of the drug. A nebulizer may also be used. Nebulizers and spacers are equally effective in those with mild to moderate symptoms however insufficient evidence is available to determine whether or not a difference exist in those severe symptomatology. Heliox, a mixture of helium and oxygen, may also be considered in severe unresponsive cases. Intravenous salbutamol is not supported by available evidence and is thus used only in extreme cases. Methylxanthines (such as theophylline) were once widely used, but do not add significantly to the effects of inhaled beta-agonists. The dissociative anesthetic ketamine is theoretically useful if intubation and mechanical ventilation is needed in people who are approaching respiratory arrest; however, there is no evidence from clinical trials to support this.

Complementary medicine

Many asthma patients, like those who suffer from other chronic disorders, use alternative treatments; surveys show that roughly 50% of asthma patients use some form of unconventional therapy.

A study of "manual therapies" for asthma, including osteopathic, chiropractic, physiotherapeutic and respiratory therapeutic manoeuvres, found there is insufficient evidence to support or refute their use in treating.

Prognosis

The prognosis for asthma is good, especially for children with mild disease. Of asthma diagnosed during childhood, 54% of cases will no longer carry the diagnosis after a decade. The extent of permanent lung damage in people with asthma is unclear. Airway remodeling is observed, but it is unknown whether these represent harmful or beneficial changes. As of 1998, there was a great disparity in prevalence worldwide across the world (as high as a 20 to 60-fold difference), with a trend toward more developed and westernized countries having higher rates of asthma. Mortality however is most common in low to middle income countries,

While asthma is more common in affluent countries, it is by no means a restricted problem; the WHO estimate that there are between 15 and 20 million people with asthma in India. In the U.S., urban residents, Hispanics, and African Americans are affected more than the population as a whole. Striking increases in asthma prevalence have been observed in populations migrating from a rural environment to an urban one, and 5% of people in the United Kingdom. Asthma causes 4,210 deaths per year in the United States. In 2005 in the United States asthma affected more than 22 million people including 6 million children.. More boys have asthma than girls, but more women have it than men.

Increasing frequency

Rates of asthma have increased significantly between the 1960s and 2008. In the US, asthma prevalence is highest in Puerto Ricans, African Americans, Filipinos, Irish Americans, and Native Hawaiians, and lowest in Mexicans and Koreans. As these psychoanalysts interpreted the asthmatic wheeze as the suppressed cry of the child for its mother, so they considered that the treatment of depression was especially important for individuals with asthma.

Research

The University of Maryland School of Medicine announced in 2010 that bitter taste receptors had been discovered on smooth muscle in human lung bronchi. These smooth muscles control airway contraction and dilation - contrary to expectation, bitter substances such as quinine or chloroquine opened contracted airways, offering new insight into asthma.

References

;Bibliography

External links

World Health Organization site on asthma

National Heart, Lung, and Blood Institute — Asthma – U.S. NHLBI Information for Patients and the Public page.

MedLinePlus: Asthma – a U.S. National Library of Medicine page

Asthma Management Handbook 2006 National Asthma Council Australia

the Global Initiative for Asthma (GINA)

NHS Guidance for the management of Asthma

Types of Asthma by NHS

Childhood Asthma

Category:Chronic lower respiratory diseases