Chronic obstructive pulmonary disease is a category of lung conditions, that is characterised by airway obstruction due to inflammation of the small airways. COPD is subdivided into two main diseases; chronic bronchitis and emphysema.
A major cause of COPD is the inhalation of toxins, most commonly cigarette smoke. However, some people are predisposed to COPD due to a genetic mutation such as alpha-1-antitrypsin deficiency. An obstructive condition means that the airways are obstructed therefore air can get trapped inside an area of the lung. This area is therefore not involved in gas exchange as the oxygen has already been used and is full of waste products that cannot escape that area. Lung conditions can either be obstructive or restricted and this depends on two values; how much air the lungs can exhale in one breath (vital capacity - FVC) and the amount of air that can be exhaled in 1 second (FEV1). Both of these would be lower than normal in COPD and other obstruction conditions. Whereas restrictive conditions the FEV1 would be reduced but the FVC would remain the same, as restrictive is a problem with the speed at which air can be inhaled and exhaled not a decrease in the volume of air the lung can contain.
Chronic Bronchitis
Chronic bronchitis is inflammation of the bronchial tubes within the lungs. It is defined clinically by a productive cough for at least 3 months a year for at least 2 years. Exposure to irritants and chemicals such as cigarette smoke causes hypertrophy and hyperplasia of the bronchial mucinous glands (in the main bronchi) and the goblet cells (in the bronchioles) who’s function is to produce mucus, therefore more mucus is secreted. In the smaller airways of the bronchioles this can be enough to obstruct the lumen of the airway causing air trapping. To add to this smoking causes the cilia in the airway (hair like projections that waft the mucus out of the airways) to shorten causing them to be less mobile and therefore less effective in their job of clearing the airways of mucus. Therefore, people with chronic bronchitis have to cough to clear the mucus rather than the cilia wafting it up the airway to the throat to be swallowed.
Chronic bronchitis patients are often described as blue bloaters due to the signs and symptoms they present with. This is due to the poorly ventilated lung where oxygen cannot be delivered, and carbon dioxide removed effectively. This leads to cyanosis (bluish discolouration) especially of the lips. The increased carbon dioxide (hypercapnia) within the blood also leads to oedema due to the acidosis that is caused by the increased carbon dioxide.
When an area of lung is not functioning for gas exchange, vasoconstriction occurs in this area in order to divert the blood to an area of the lung where gas exchange can occur. Whereas when a large proportion of the lung is not effective as gas exchange this increased vasoconstriction causing pulmonary hypertension as vascular resistance is increased. This pulmonary hypertension puts increase strain on the right side of the heart, leading to right sided heart failure.
Emphysema
Emphysema is defined by structural changes, involving enlargement of the air spaces. Toxins such as cigarette smoke cause the destruction on elastin and collagen within the alveoli walls. This lack of elastin gives weak walls of the alveoli, therefore when breathing out the alveoli walls are not strong enough to withstand the change in pressure so collapse trapping air distally. The break down of the elastin also causing the septa between alveoli to be destroyed making an increased volume, this however leaves to a reduction in surface area for gas exchange to occur. This process happens in the acinus, the respiratory end of the airways. Centriacinar emphysema is the most common form and only affects the most proximal alveoli of the acinar. This is due to less cigarette smoke making it to the distal alveoli of the acinar. Most commonly affecting the upper lobes of the lungs.
Patient with emphysema are known as pink puffers. Initially these patients are well oxygenated however they strain to expire as the loss of elastic recoil in the lungs means that expiring quickly can cause areas of the lungs to collapse. This leads to the pursed lips with prolonged exhalation. Polycythaemia occurs in emphysema (increase in the number of red blood cells) as the body tries to increase it’s capacity to carry oxygen from the lungs to the tissues. This polycythaemia gives patients a pink appearance. Due to all the air trapping and hyperinflation patients can develop a barrel shaped chest.
As cigarette smoke is a major cause of both chronic bronchitis and emphysema these two conditions can co-exist resulting in different presentations from this typical pink puffer or blue bloater phenotypes.
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