Chronic Bronchitis
Bronchitis means inflammation of the bronchiole tubes in the lungs. It said to be chronic because it produces productive cough which means produces mucus, for at least 3 months each year for 2 or more years. Chronic bronchitis is actually lump under the umbrella of chronic obstructive pulmonary disease or COPD, along with emphysema. This two are different in that defined by clinical features like a productive cough while the emphysema is defined by structural changes specifically enlargement of the air spaces. That being said they often coexist probably because they share with the same risk factor like smoking. Other risk factor for chronic bronchitis is exposure to air pollutants like sulphur and nitrogen dioxide, exposure to dust and silica, as well as genetic factors like having a family history of chronic bronchitis.
With COPD the airways becomes obstructive and the lungs don’t empty properly and that lead air trapped inside the lungs, for that reasons the maximum amount of air people with COPD can breathe out in single breath known as the FVC or forced vital capacity is lower. This reduction is especially noticeable in the first second air breath out in the single breath called the FEV1 force expiratory volume in 1 seconds, which typically is reduce even more with FVC.
Chronic bronchitis is a type of COPD that diagnose based on clinical symptoms, specifically coughing of a lot of mucus but why is this happened? Well first of all the lungs the wall of the normal airways have a couple of layers, lying along the lumen of the airways, there is the epithelium composed of ciliated pseudostratified columnar epithelial cells, which are named that because this epithelial cells have hair like projection called cilia, their nuclei don’t align and so it look like more than one layer even though they are not and pseudo stratified and because the cells are mostly tall and narrow or columnar in shape. This layer also has the occasional goblet cell which makes some of the mucus that lines the airway.
Alright so going deeper passed that layer you got the basement membrane and loose connective tissue called the lamina proria, which together with the epithelium makes up the mucosa. Behind the mucosa there’s the smooth muscle followed by more connective tissue and together this two layers makes up the submucosa, and this is where the bronchial mucinous glands lives. This are the glans that secretes the majority of the mucus within the lumen of the bronchi, helping to catch and filter out particles and pathogens.
Finally in the bronchi, but not the bronchioles there is also a layer of cartilage below the submucosa which stiffen the bronchus and helps to keep it open. People who smokes exposes their airways to all sorts of irritants and chemicals. Wherever the irritants are there affected to stimulate in hypertrophy and hyperplasia. The mucinous glands in main bronchi, as well as the goblet cells in the smaller airways the bronchioles, which increases the mucus production in both locations.
Since the bronchioles are smaller even a slight increase in mucus can lead to airways obstruction, so this can contribute to the airway trapping. To make matter even worst though smoking makes the cilia shorts and less mobile, making a harder to move mucus up and out the bronchioles towards the back of the throat to get swallowed. As a result of having too much mucus and poorly functioning cilia, people with chronic bronchitis end up relying on coughing to get rid of their mucus plugs.
Read Index Measurement
One measurement, typically done by post mortem is called the read index which is the ratio of thickness of the bronchioles mucinous glands relative to the total thickness of the airway from the epithelium to the cartilage. Normally this ratio should be less than 40% but it could be over 40% for people with chronic bronchitis because of the hyperplasia and hypertrophy of the glands. Even though an increase read index goes along with chronic bronchitis the diagnostics still done clinically and this measurement is not usually used diagnostically.
Sign and Symptoms
All this mucus in the lungs causes people with chronic bronchitis to wheeze, due to narrowing of the passage way available for the air move in and out, these people have also crackles or rales, cause by the popping open of small airways. People with chronic bronchitis also often present with hypoxemia (low oxygen in the blood) and hypercapnia (increase carbon dioxide in the blood) and this is because the mucus plugs the airways blocks the airflow right? Which causes the partial pressure carbon dioxide to go up in the lungs, increase partial pressure of carbon dioxide means that the partial pressure of oxygen in the lungs goes down and the lower partial pressure of carbon dioxide means less oxygen gets to blood causing hypoxemia, this trap carbon dioxide on the lungs also makes harder for carbon dioxide to get out of the blood stream, which also explain for hypercapnia.
The increase carbon dioxide level in the blood can gets so bad that can some people develop cyanosis, which is the blue discoloration of the skin and this why some patients with chronic bronchitis are sometimes referred to as blue bloaters, and this is the term compared with pink poppers which describe patients with emphysema.
In addition to those things in the area with decrease gas exchange blood vessels undergo vasoconstrictions and in attempt to shunt blood to an area with better blood exchange, which if localize to one area belongs that would work pretty well. But if one of a large proportion of lungs aren’t exchanging oxygen effectively, a large proportion of the blood vessels starts too clamped down. And this has the effective increasing pulmonary vascular resistance and the maintained pulmonary blood flow, the body response by developing pulmonary hypertension.
Overtime, this increases the work needed by the right side of the heart to pump blood to the lungs, and eventually the right side enlarges which leads to a right side heart failure a process called cor pulmonale.
And finally another consequences of mucus plugging in chronic bronchitis is that people can develop lung infection behind the mucus blockages of the airways and this infection can worsen the pulmonary and cardiac symptoms.
Treatment of Chronic Bronchitis
Treatment of chronic bronchitis is largely involve in reducing the risk factors, like for example stopping smoking, but also managing associated illnesses, supplemental oxygen as well as certain medication like bronchodilators, inhaled steroids and antibiotics to control secondary infections might also be used.
Chronic bronchitis is type of chronic obstructive pulmonary disease or COPD where exposure to chemical and irritants like smoking. It also stimulate increase mucus production in the airways which causes a productive cough at that last for atleast 3 months each year for 2 years.
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