Chronic Obstructive Pulmonary Disease
Respiratory scientist Peter Barnes on the risk factors of COPD, the ways to diagnose it and how is it different from asthma
videos | July 2, 2020
Chronic obstructive pulmonary disease, or COPD, is a major global epidemic. It’s one of the most common killers in the world and yet has been greatly neglected. What it involves is a progressive narrowing of the airways due to a combination of small airway obstruction and emphysema or destruction of the lung parenchyma. This leads to progressive narrowing of the airways with increasing shortness of breath and periods of exacerbation or worsening of the disease. This is a very common disease and is now affecting over 10% of people aged over 45 and is seen throughout the world.
The most common risk factor is cigarette smoking: this accounts for something like 80% of COPD cases in the Western world. But in developing countries, COPD is also seen very commonly in non-smokers, and it’s thought that this is due to exposure to wood smoke from cooking in poorly ventilated houses. These are the two most common risk factors, but in addition, there’s increasing evidence that passive smoking and exposure to air pollution may also be contributory. If you look at smoking as a risk factor, only about 20-30% of people who smoke develop COPD, so there are obviously some additional risk factors that may be genetic or may be due to some early life event that makes people more susceptible.
You can see that it’s a major clinical problem, but it’s still very poorly diagnosed. Many people who have COPD are undiagnosed: they may not be diagnosed at all, or they may be misdiagnosed as asthma, which means they may not be treated with the currently available therapies. So this has a very big impact on society. Also, because it is common, chronic and involves frequent hospitalization in many patients, it’s a very expensive disease. Yet, the general public knows very little about COPD; they’re not even aware of the term ‘COPD’ although they may know ‘chronic bronchitis’ and ‘emphysema’, which were previous terms that we used for this disease.
We know that the pathology of the disease involves obstruction of small airways, which is due to progressive scarring and constriction of the airways but also due to emphysema with destruction of the lung parenchyma. This means that when people with COPD breathe out, the air in the lungs gets trapped, and this leads to air trapping or hyperinflation. So, patients with COPD have large lung volumes, and this is something that gets worse with exercise. This results in progressive air trapping, which leads to progressive shortness of breath on exertion and reduced exercise tolerance. These are the main clinical features of COPD.
We normally diagnose COPD by spirometry which means blowing into a machine that measures the flow of air coming out of the lung. This shows a typical obstructive pattern that does not improve significantly with bronchodilators, so it’s differentiated from asthma which is another obstructive airways disease where you normally see large improvements in airway function, so this is largely fixed obstruction of the airways.
It’s a progressive disease: it means that patients get progressively worse over the years, and eventually, they develop respiratory failure. In fact, very few patients ever reach the point of developing respiratory failure because they die of other diseases. One of the characteristics of COPD is that they suffer from other chronic diseases such as ischemic heart disease, heart failure, type-2 diabetes, osteoporosis, metabolic syndrome and lung cancer. Indeed, the most common causes of death in COPD patients are cardiovascular diseases such as heart attacks and lung cancer, which commonly occur in COPD patients. This is a very complicated disease because it involves more than airway obstruction and lung disease: it involves comorbid diseases that occur together and, of course, complicate the management.
The mainstay of our current management of COPD is to give long-lasting bronchodilators which reduce air trapping and, in that way, are able to reduce symptoms and improve exercise tolerance. The two main classes of long-acting bronchodilators that we use are long-acting muscarinic antagonists and long-acting beta-agonists. These drugs are equally effective, but fortunately, they have additive effects, so for patients especially with severe disease, we usually give both drugs together. Recently, combination inhalers that contain both treatments have become available, which makes the management of COPD much easier.
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