What Causes Asthma?
According to recent estimates, asthma affects 300 million people in the world and more than 22 million in the United States. Although people of all ages suffer from the disease, it most often starts in childhood, currently affecting 6 million children in the US. Asthma kills about 255,000 people worldwide every year.
Children at Risk
Asthma is the most common chronic disease among children - especially children who have low birth weight, are exposed to tobacco smoke, are black, and are raised in a low-income environment. Most children first present symptoms around 5 years of age, generally beginning as frequent episodes of wheezing with respiratory infections. Additional risk factors for children include having allergies, the allergic skin condition eczema, or parents with asthma.
Young boys are more likely to develop asthma than young girls, but this trend reverses during adulthood. Researchers hypothesize that this is due to the smaller size of a young male's airway compared to a young female's airway, leading to a higher risk of wheezing after a viral infection.
Almost all asthma sufferers have allergies. In fact, over 25% of people who have hay fever (allergic rhinitis) also develop asthma. Allergic reactions triggered by antibodies in the blood often lead to the airway inflammation that is associated with asthma.
Common sources of indoor allergens include animal proteins (mostly cat and dog allergens), dust mites, cockroaches, and fungi. It is possible that the push towards energy-efficient homes has increased exposure to these causes of asthma.
Tobacco smoke has been linked to a higher risk of asthma as well as a higher risk of death due to asthma, wheezing, and respiratory infections. In addition, children of mothers who smoke - and other people exposed to second-hand smoke - have a higher risk of asthma prevalence. Adolescent smoking has also been associated with increases in asthma risk.
Allergic reactions and asthma symptoms are often the result of indoor air pollution from mold or noxious fumes from household cleaners and paints. Other indoor environmental factors associated with asthma include nitrogen oxide from gas stoves. In fact, people who cook with gas are more likely to have symptoms such as wheezing, breathlessness, asthma attacks, and hay fever.
Pollution, sulfur dioxide, nitrogen oxide, ozone, cold temperatures, and high humidity have all been shown to trigger asthma in some individuals.
During periods of heavy air pollution, there tend to be increases in asthma symptoms and hospital admissions. Smoggy conditions release the destructive ingredient known as ozone, causing coughing, shortness of breath, and even chest pain. These same conditions emit sulfur dioxide, which also results in asthma attacks by constricting airways.
Weather changes have also been known to stimulate asthma attacks. Cold air can lead to airway congestion, bronchoconstriction (airways constriction), secretions, and decreased mucociliary clearance (another type of airway inefficiency). In some populations, humidity causes breathing difficulties as well.
Overweight adults - those with a body mass index (BMI) between 25 and 30 - are 38% more likely to have asthma compared to adults who are not overweight. Obese adults - those with a BMI of 30 or greater - have twice the risk of asthma. According to some researchers, the risk may be greater for non-allergic asthma than allergic asthma.
The way you enter the world seems to impact your susceptibility to asthma. Babies born by Caesarean sections have a 20% increase in asthma prevalence compared to babies born by vaginal birth. It is possible that immune system-modifying infections from bacterial exposure during Cesarean sections are responsible for this difference.
When mothers smoke during pregnancy, their children have lower pulmonary function. This may pose additional asthma risks. Research has also shown that premature birth is a risk factor for developing asthma.
People who undergo stress have higher asthma rates. Part of this may be explained by increases in asthma-related behaviors such as smoking that are encouraged by stress. However, recent research has suggested that the immune system is modified by stress as well.
It is possible that some 100 genes are linked to asthma - 25 of which have been associated with separate populations as of 2005.
Genes linked to asthma also play roles in managing the immune system and inflammation. There have not, however, been consistent results from genetic studies across populations - so further investigations are required to figure out the complex interactions that cause asthma.
Mom and Dad may be partially to blame for asthma, since three-fifths of all asthma cases are hereditary. The Centers for Disease Control (USA) say that having a parent with asthma increases a person's risk by three to six times.
Genetics may also be interacting with environmental factors. For example, exposure to the bacterial product endotoxin and having the genetic trait CD14 (single nucleotide polymorphism (SNP) C-159T) have remained a well-replicated example of a gene-environment interaction that is associated with asthma.
Researchers are not sure why airway hyper-reactivity is another risk factor for asthma, but allergens or cold air may trigger hyper-reactive airways to become inflamed. Some people do not develop asthma from airway hyper-reactivity, but hyper-reactivity still appears to increase the risk of asthma.
Atopy - such as eczema (atopic dermatitis), allergic rhinitis (hay fever), allergic conjunctivitis (an eye condition) - is a general class of allergic hypersensitivity that affects different parts of the body that do not come in contact with allergens. Atopy is a risk factor for developing asthma.
Some 40% to 50% of children with atopic dermatitis also develop asthma, and it is probable that children with atopic dermatitis have more severe and persistent asthma as adults.
Asthma diagnoses are based on three core components: a medical history, a physical exam, and results from breathing tests. A primary care physician will administer tests and, if you have asthma, determine your level of asthma severity as intermittent, mild, moderate, or severe.
A detailed family history of asthma and allergies can help your doctor make an accurate asthma diagnosis. Your own personal history of allergies is also important as many are closely linked to asthma.
Information about asthma symptoms is also useful. Be prepared to divulge when and how often they occur and what factors seem to exacerbate or worsen symptoms. Common symptoms and signs include:
§ Breathing difficulty
§ Tightness in the chest
§ Worsening symptoms at night
§ Worsening symptoms due to cold air
§ Symptoms while exercising
§ Symptoms after exposure to allergens
It is also wise to make note of health conditions that can interfere with asthma management such as runny nose, sinus infections, acid reflux disease, psychological stress, and sleep apnea.
It is often somewhat harder to diagnose young children who may develop their first asthma symptoms before age 5. Symptoms are likely to be confused with those of other childhood conditions, but young children with wheezing episodes during colds or respiratory infections are likely to develop asthma after 6 years of age.
A physical examination will generally focus on the upper respiratory tract, chest, and skin. A doctor will use a stethoscope to listen for signs of asthma in your lungs as you breathe. The high-pitched whistling sound while you exhale - or wheezing - is a key sign of both an obstructed airway and asthma.
Physicians will also check for a runny nose, swollen nasal passages, and nasal polyps. Skin will be examined for conditions such as eczema and hives, which have been linked to asthma.
Physical symptoms are not always present in asthma sufferers, and it is possible to have asthma without presenting any physical maladies during an examination.
Lung function tests, or pulmonary function tests, are the third component of an asthma diagnosis. To measure how much air you breathe in and out and how fast you can blow air out, physicians administer a spirometry test.
Spirometry is a noninvasive test that requires you to take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. The spirometer then displays two key measurements:
Forced vital capacity (FVC) - the maximum amount of air one can inhale and exhale
Forced expiratory volume (FEV-1) - the maximum amount of air exhaled in one second
The measurements are compared against standards developed for a person's age, and measurements below normal may indicate obstructed airways.
Children younger than 5 years of age are difficult to test using spirometry, so asthma diagnoses will rely mostly on symptoms, medical histories, and other parts of the physical examination. It is common for doctors to prescribe asthma medicines for 4 to 6 weeks to see how a young child responds.
A "Challenge Test" (or bronchoprovocation test) is when a physician administers an airway-constricting substance (or something as simple as cold air) to deliberately trigger airway obstruction and asthma symptoms. Similarly, a challenge test for exercise-induced asthma would consist of vigorous exercise to trigger symptoms. A spirometry test is then administered, and if measurements are still normal, an asthma diagnosis is unlikely.
Physicians use allergy tests to identify substances that may be causing or worsening asthma. These tests cannot be used to diagnose asthma, but they can be used to understand the nature of asthma symptoms.
Doctors may also test for another disease with similar symptoms as asthma, such as reflux disease, heartburn, hay fever, sinusitis, sleep apnea, chronic obstructive pulmonary disease (COPD), airway tumors, airway obstruction, bronchitis, lung infection (pneumonia), blood clot in the lung (pulmonary embolism), congestive heart failure, vocal cord dysfunction, and viral lower respiratory tract infection.
Tests may be administered for these ailments such as chest x-rays, EKGs (electrocardiograms), complete blood counts, CT (computerized tomography) scans of the lungs, gastroesophageal reflux assessment, and sputum induction and examination.
A new test using exhaled nitric oxide is being evaluated since physicians are looking for a test that is more accurate than spirometry. Higher levels of nitric oxide are linked to higher degrees of asthma severity. The current drawback lies in the high cost of the test and the specialized equipment required to measure this chemical marker.
An asthma specialist can usually be avoided, as most primary care physicians are capable of diagnosing asthma. An asthma specialist may be necessary, however, if you need special asthma tests or have had a life-threatening asthma attack in the past. In addition, specialists can be of use if you need more than one kind of medicine or higher doses of medicine in order to control your asthma, if you have overall difficulty controlling asthma, or if you will be receiving allergy treatments.