How chronic bronchitis affects the lungs

John Bottrell
Chronic bronchitis is a lung disease that causes a cough with increased mucus production for at least three months in two consecutive years.  It generally falls under the category of chronic obstructive pulmonary disease, or COPD.   
The most common cause is cigarette smoking, although the inhalation of irritants at work, air pollution and lung infections may also cause it.  Considering most people develop this disease due to exposure to cigarette smoke, one might wonder: Why does smoking cause chronic bronchitis?  
To best answer this question it’s helpful to understand the basics of airway anatomy, which is covered in the pithy post “Your Journey Down the Respiratory Tract.” Knowledge of lung anatomy is helpful because long-term exposure to inhaled cigarette smoke may cause changes inside the airways.  These changes may include:
1.  Bronchial mucous glands become bigger:  This causes increased mucus or secretion production inside the lungs.
2.  Goblet cells increase in number:  This also causes increased mucus production.
3.  Bronchial walls become inflamed:  This is due to repeated exposure to the harmful chemicals of cigarette smoke.  These chemicals injure the walls, and the body's attempt to fix them causes them to become inflamed or swollen.  Common treatments for this are inhaled corticosteroids such as Qvar, Pulmicort, Advair, and Symbicort. Systemic corticosteroids are also sometimes needed.
4.  Bronchial walls become thick and scarred:  This is often referred to as airway remodeling.  It occurs when inflammation lasts for such a long time that the body tries to fix it.  This results in scar tissue, causing the airways to become fibrotic, or stiff. This damage is permanent and there is no treatment for it.
5.  Cilia lining bronchial walls disappear: Cilia are fine, hair-like structures that act as an escalator to bring mucus to the upper airway where it may either be swallowed, coughed up, or spit up.  Lacking cilia, the airway has a tough time moving mucus to the upper airway, causing mucus buildup in the lungs.  
6.  Mucus plugging in the smaller airways: This means that dried up secretions block air passages.  
7.  Bronchospasm:  Inflamed airways are extra sensitive to certain triggers (such as inhaled irritants, allergens, and strong smells) that may cause flare-ups.  This may cause the muscles wrapping around the airways to spasm.  Flare-ups are discussed in my recent post “COPD flare-up causes.”  Treatment for this includes albuterol (ventolin), levalbuterol (xopenex), ipatropium bromide (Atrovent), Duoneb, Combivent, theophylline, serevent, formoterol, Advair, and Symbicort.
8.  Airway obstruction/ narrowing: The combination of increased mucus, mucus plugging, scarring, inflammation, and bronchospasm cause air passages to become permanently narrowed and frequently obstructed.  Air traveling through narrowed or obstructed airways may cause a wheeze.
9.  Air Trapping:  Air can get past an obstruction in the airway, but has a hard time getting out.  In other words, people suffering from this may feel like they can’t get air in, but the truth is they can’t get air out. This results in a prolonged exhalation.  A good treatment technique for this is to exhale through pursed lips, thus allowing more time for trapped air to get out.
10.  Emphysema: Most people with chronic bronchitis also suffer from emphysema, which is the breakdown or destruction of lung tissue, which is probably also caused by inflammation. More specifically, it is the breakdown of the walls of the air sacs, or alveoli. This makes it so the lungs lose their ability to expand.  Due to breakdown, alveolar sacs also may become detached from the small air passages, decreasing areas available for gas exchange to occur.  The treatment for emphysema is usually supportive, and often includes wearing oxygen.
11.  Airflow limitation:  Narrowed and obstructed airways cause increased resistance to air flowing through them, thus slowing down the flow of this air. This may lead to a feeling of dyspnea, or shortness of breath.  Airflow limitation is partially reversible in chronic bronchitis, depending on the cause:
Reversible:  Obstruction caused by increased mucus, inflammation and bronchospasm
Irreversible: Obstruction caused by airway remodelling and emphysema
Airflow limitation is best measured during pulmonary function testing, a test that can determine how severe your airflow limitation is, or how severe our COPD is.  
12.  Hypoxemia:  Due to the combination of the disease processes described above, there will be areas of the lungs where oxygen cannot get through to the blood.  
This may result in low oxygen blood levels.  This makes it so the blood has less available oxygen to take to tissues, and so it takes it to vital organs before less vital areas of the body like fingertips and lips.  Common symptoms of this are dyspnea and cyanosis, or a blue tinge around the fingertips and lips. Treatment for this is wearing oxygen.
13.  Hypercapnia:  Along with allowing less oxygen to get to the blood, less carbon dioxide (CO2) will be allowed to leave the blood and enter the lungs to be exhaled. CO2 is a waste product of cellular metabolism that the lungs exhale. If it can’t get to the lungs, CO2 builds up in the blood.  Symptoms of this include feeling sleepy and confusion.  
It’s important to note that not all of the above occur in every person with chronic bronchitis,
which is kind of what makes this disease so complicated for physicians to understand and treat. Also, the progression of these disease processes are often so gradual that a person may not even notice them happening, especially in the early stages of the disease.  
A neat thing about this disease, however, is that, while damage already done cannot be undone, quitting smoking will almost immediately slow down its progression.  It is for this reason most physicians recommend people diagnosed with it quit smoking immediately.   
So, now you should have a general idea how people develop chronic bronchitis, what the symptoms are, and how bronchitis physically affects the lungs.n
Source: healthcentral.com