How our respiratory system works
To have a better understanding of what happens in your body if you are an asthma sufferer, it is important to learn how our respiratory system works.
Our respiratory system consists of the upper and lower airways. It supplies us with vital oxygen (O2) during inhalation and releases the waste product carbon dioxide (CO2) during exhalation.
The upper airways
The upper airways include the nose, the paranasal sinuses and the throat (pharynx).
Air enters the body through the nose. The mucous membrane of the nose is equipped with fine hairs, the ciliated epithelium. Here our breath is filtered, heated and humidified.
Additionally, the nose is our olfactory organ. Particularly when you have a cold, you quickly notice when your nose cannot perform its usual tasks. The nose is connected to the throat via the paranasal sinuses.
The lower airways
The lower airways include the larynx, trachea, lungs and bronchi. The larynx contains the vocal chords and also connects the upper and lower airways. The trachea is connected to the larynx. It is a flexible tube about 12 cm long that branches into the bronchi. The bronchial tubes are part of the system of tubes in the lungs, which conduct air into and out of the lungs. The bronchial system can be imagined as an upside-down tree. The trachea forms the trunk, from which two thick, short branches, namely the left and the right main bronchus, each branch off into one lung.
These in turn branch into smaller and smaller bronchi that fill the entire lung and evolve into microscopically fine air sacs called alveoli. Here the inhaled oxygen is released into the blood which supplies the organs. This is the site of gas exchange between air and blood. Around 300 million alveoli supply our body with oxygen.
What is asthma actually?
Bronchial asthma is a chronic, i.e. persistent, inflammatory disease of the respiratory tract. The airways (bronchi) react hypersensitively to certain stimuli and are temporarily narrowed. Doctors speak of bronchial hyperresponsiveness. Typical symptoms of asthma are:
- chest tightness
- shortness of breath
- dyspnea, especially at night or early in the morning
Every twentieth adult and every tenth child suffer from asthma. It is the most common chronic disease in childhood. Why some people develop asthma and others do not is not fully understood. It is known that both hereditary and environmental factors play a role. Depending on the trigger, the following forms of asthma can be distinguished:
- Allergic asthma
- Eosinophilic asthma
- Mixed forms
In eosinophilic asthma, immune defense reactions also occur, however these are not caused by allergens, but by other triggers such as viral infections, drugs, chemicals, or pollutants.
Often there are mixed forms between allergic and eosinophilic asthma. A distinction is not always easy, because the affected persons usually react equally to non-specific triggers, such as cold air, fog, cigarette smoke, or strong scents, with asthmatic symptoms. These triggers don’t cause the asthma, they merely set it off.
Facts and figures on asthma
Asthma is a worldwide health problem affecting people in low- and middle-income countries as well as in western high-income countries. According to the Global Asthma Report 2018, asthma is estimated to affect as many as 339 million people worldwide.
This chronic disease tends to affect more women than men. In Europe, there are nearly ten million asthmatics below the age of 45. Around ten percent of adult asthmatics suffer from severe asthma, which is difficult to treat. Asthma can affect people of any age, but occurs predominantly in childhood and is also the most common chronic disease in children.
How is asthma diagnosed?
Doctors usually identify the first indications of asthma from patients’ description of the typical symptoms and their medical history. If the suspicion is confirmed during the physical examination, pulmonary function diagnostics is performed. One of the tests is to ascertain how much air passes through the bronchi. This can be measured using the following methods:
Peak flow meter
Peak flow measurement can be done at home with the so-called peak flow meter. This determines the Peak Expiratory Flow (PEF), i.e. the maximum air flow from the lungs.
Spirometry (“small lung function test”)
Spirometry is used to measure lung or respiratory volume and air flow velocity and can only be performed at the doctor’s practice. During the examination, the patient breathes into the spirometer through a mouthpiece. The nose is closed with a clamp.
Body plethysmography (“large lung function”)
Body plethysmography is usually performed by a specialist. In this lung function test, the patient sits in a special glass cabin. This supplements spirometry by determining the complete lung volume and airway resistance, providing the physician with further diagnostic information especially for patients who have difficulties in performing spirometry.
Stress or provocation test
Patients are often free of symptoms when they visit their doctor. Physicians therefore have the possibility to deliberately trigger the narrowing of the airways through different stimuli, e.g. physical stress or inhalation of histamine, in order to test the level of irritability in the airways (hyperresponsiveness).
In patients with respiratory problems and constricted airways (determined by spirometry or PEF), asthma testing is used to examine whether this constriction can be treated through medication (lysis). The patient is given a bronchodilator medication (e.g. salbutamol) before a new spirometry is performed. The drug typically improves values in asthmatics.
Nitric oxide measurement (FeNO)
Asthma is an inflammation of the respiratory tract. However, pulmonary function measurements allow only few conclusions to be drawn about the extent of the underlying inflammatory reaction.
A measure of respiratory inflammation is the amount of nitric oxide (NO) in the exhaled breath (FeNO). In FeNO testing, the patient breathes into a measuring device through a mouthpiece. The measurement is quick, simple and stress-free. It can be performed in the doctor’s office or at home. Experience has also shown that a worsening of the condition indicated by elevated FeNO values can be detected earlier than with other methods.
How is asthma treated?
Despite intensive research, asthma is not curable. Nevertheless, the disease is now effectively treatable with medication. Preventive measures include not smoking, avoiding allergy triggers and exercising regularly.
The goal of asthma treatment is to achieve the best possible asthma control with the lowest possible dose of medication. If persistent asthma symptoms make regular therapy necessary, inhaled corticosteroids form the basis of long-term therapy. Anti-inflammatory drugs must be taken regularly and for longer periods of time, because the hypersensitivity of the bronchial tubes only abates slowly. The most effective anti-inflammatory agent is cortisone. This is usually inhaled as a spray or powder. In this way, it quickly reaches the desired site of action, i.e. gets directly into the respiratory tract. In the case of severe asthma or asthma attacks, it is sometimes necessary to resort to cortisone tablets.
Rapid-acting beta-sympathomimetics that expand the bronchi quickly and reliably can help as emergency medication for sudden shortness of breath. Biologics can also help in therapy, both for severe allergic asthma and eosinophilic asthma. Biologics are genetically engineered drugs that are produced from or with the help of biological organisms. These include antibodies, for example, that can act against certain inflammatory messengers.
Your doctor will discuss with you which medications are most effective for you. The therapy may have to be adapted and changed depending on the season or your state of health.
How can FeNO measurement help me manage my asthma?
Asthma is a complex disease characterized by chronic inflammation of the airways. Different diagnostic methods can help to diagnose and characterize asthma. A newer method is FeNO measurement. This is particularly useful in the case of allergic asthma and enables the detection of an allergic inflammation of the lower respiratory tract.
Nitric oxide (NO), which is measured in the exhaled breath during this test, is produced when the airways are inflamed. There is a correlation between the concentration of NO in exhaled breath and the extent of respiratory inflammation. The higher the NO content, the more severe the inflammation.
FeNO measurement not only serves the physician as a helpful method to diagnose asthma. It can also help you to manage your disease.