Chronic Obstructive Pulmonary Disease (COPD)
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Chronic Obstructive Pulmonary Disease (COPD)
What does COPD refer to?
The term chronic obstructive pulmonary disease (COPD) covers the following diagnoses:
- Emphysema ("pink puffers")
- Chronic bronchitis ("blue bloaters")
- Asthma/COPD overlap syndrome (ACOS)
- Bronchiectasis
Describe the key pathology of COPD
COPD is characterized by chronic, progressive, irreversible air flow obstruction and leads to high lung volumes (functional residual capacity, residual volume, and total lung capacity).
What are key pulmonary function test (PFT) findings in COPD?
As a result of airway obstruction, the Forced Expiratory Reserve Volume in 1 second (FEV1) is severely reduced. As well, to a lesser degree, the Forced Vital Capacity (FVC) is also reduced. Thus, overall, the FEV1/FVC ratio is also reduced.
What are key consequences of COPD?
COPD can lead to V/Q mismatch, hypoxemia, pulmonary hypertension, and right heart failure (cor pulmonale).
How common is COPD?
COPD is a leading cause of death worldwide. In the US, the COPD prevalence is 15.7 million (6.4%). Patients are typically over 65 years of age.
What are key risk factors for COPD?
The number one risk factor is smoking (80 - 90%) of COPD patients are smokers / 10 - 15% of smokers will develop COPD.
Other risk factors include: air pollution (including indoor pollution, such as the smoke from burning organic fuels for heating), and, genetics.
Importantly, alpha-1 anti-trypsin deficiency is a known genetic cause of emphysema; this defect allows excess elastase in the lungs, which degrades alveoli.
What are key treatments for COPD?
COPD is not curable but treatments can help slow progression and alleviate symptoms. They include:
- Smoking cessation (or removal of exacerbating factors)
- Bronchodilators
- Corticosteroids
- Respiratory therapy
- Supplemental oxygen
- Surgical resection may be appropriate for some patients
How do we help prevent COPD exacerbations?
COPD exacerbations can stem from respiratory infections. Flu and pneumococcal vaccines are key for prevention.
COPD Signs & Symptoms
COPD is the result of air trapping in the lungs; two key causes of air trapping are:
- Reduced elastic recoil in the lung parenchyma (which occurs in emphysema).
- Increased airway resistance (which occurs in chronic bronchitis and small airway disease, aka, SAD).
What is meant by pink puffers vs blue bloaters?
Patients are divided into Type A COPD patients (“Pink Puffers”), which are those with emphysema, and Type B COPD patients (“Blue Bloaters”), which are those with chronic bronchitis.
Note that despite this sharp distinction, most patients have a combination of these disorders.
Describe key COPD signs and symptoms
- Cough, sputum production
- Wheezing
- Dyspnea
- Decreased (or distant) breath sounds.
- Rhonchi: low-pitched rattling sounds produced by airway secretions.
- Pursed-lip breathing, which slows down the breathing and increases airway pressure (a key part of respiratory therapy).
- The tripod position: patients brace their upper against their legs or the arms of a chair; this position helps to take some of the work out of breathing.
- Cyanosis of the lips and nail beds (signs of hypoxemia)
Describe key physical manifestations (morphological changes in COPD)
Specific morphological changes are due to high lung volumes and hyperinflation of the chest.
- Chronic hyperinflation leads to flattening of the diaphragm and shortening of its muscle fibers, which renders it less mechanically capable.
- Thus, accessory respiratory muscles must do more work (including the scalenes, sternocleidomastoid, trapezius, abdominal muscles). It may be possible to palpate these hypertrophied muscles.
- Many patients develop a "barrel-shaped" chest, in which the anterior-posterior diameter of the chest becomes larger.
- Hoover's respiratory sign is a pronounced inward movement around the costal margin during inspiration.
- Weight loss and muscle wasting, especially of the lower extremities.
- Peripheral edema
- Edema is a potential manifestation of the systemic effects of COPD, which can result in right heart failure and/or reduced renal flow.
Describe key aspects of chronic bronchitis.
Chronic bronchitis affects the bronchi, which are the larger airways of the lungs. It is clinically defined as a chronic cough with sputum production that lasts for three or more months for two consecutive years.
Pathological changes include:
- Mucosa is characterized by hypertrophy and hyperplasia of mucus glands
- Smooth muscle is also hypertrophied
- Submucosa is infiltrated by inflammatory cells (specifically, CD8+ T-cells, neutrophils, and macrophages)
- Respiratory epithelium has excessive goblet cells and possible squamous cell metaplasia
- Respiratory cilia are impaired
- The mucus, which is normally thin and runny, becomes abundant and viscous, thanks to mucus gland hyperplasia.
Describe key aspects of small airway disease
Small airway disease affects the bronchioles.
Pathological changes include:
- Small changes in bronchiole airflow have influence over total airflow, so this is where the most significant airway obstruction occurs.
- Small airway disease is characterized by mucus plugging, inflammation, and airway remodeling, which comprises fibrosis and thickening; together, these factors narrow the bronchiole lumen.
- Variation in V/Q can result from airway obstruction that leaves some alveoli under-ventilated and other alveoli holding trapped air.
Describe key aspects of emphysema
Emphysema affects the respiratory bronchioles and alveoli. Emphysema is also referred to as: Type A COPD (“Pink Puffers”)
Pathological changes include:
- Inflammatory cells, which are recruited in response to cigarette smoke and other irritants, secrete elastase, which is an enzyme that breaks down alveolar walls.
- Oxidative stress from smoking damages pulmonary collagen and elastin.
- Elastase and oxidative damage break down the walls of the respiratory bronchioles and alveoli.
- Thus, there is less elastic recoil; thus, there is a reduction in the driving force to expel air during expiration.
- There is also loss of structural support, so the alveoli and alveolar ducts are prone to collapse and trap air.
- With the loss of respiratory zone structures, there is less surface area for gas exchange.
- Because of variation in the disease process, emphysema is associated with variation in V/Q.
How are antibiotics used in acute exacerbations of COPD?
In patients with acute exacerbations of chronic bronchitis, antibiotics have been shown to (1) shorten recovery time, (2) reduce the risk of early relapse, (3) reduce treatment failure, and (4) reduce hospitalization duration. They should cover H. influenzae, S. pneumoniae, and M. catarrhalis, and duration of therapy should be 5–7 days.
Resistance has been demonstrated in vivo to ampicillin and other first-line agents.
Appropriate options would include any broad-spectrum antibiotics such as clindamycin, azithromycin, doxycycline, amoxicillin/clavulanate, trimethoprim-sulfamethoxazole, a respiratory fluoroquinolone, or a third-generation cephalosporin.
Established treatment options are:
- Trimethoprim/sulfamethoxazole 160 mg/800 mg orally twice a day
- Amoxicillin 250 to 500 mg orally 3 times a day
- Doxycycline 50 to 100 mg orally twice a day
- Azithromycin 500 mg orally once a day
What are some key consequences of COPD?
Right-sided heart failure and cor pulmonale may result from chronic bronchitis and/or emphysema. Diuretic drugs may theoretically improve respiratory symptoms in COPD through several possible mechanisms. Diuretics may reduce pulmonary hypertension and cor pulmonale by decreasing preload to the heart and they can also reduce pulmonary edema.
It should be noted that with the exception of acetazolamide, all other diuretic drugs (particularly loop diuretics) have the potential to increase serum bicarbonate and arterial pH thereby ultimately causing more harm than good.
Describe key aspects of pulmonary function tests (PFTs) in obstructive and restrictive diseases
Three major patterns of pulmonary diseases can be identified in PFTs: normal, obstructive, and restrictive.
An obstructive pattern is seen with asthma, chronic obstructive pulmonary disease (COPD), chronic bronchitis, and bronchiectasis. In cases of obstruction, on spirometry, there will be a SEVERE REDUCTION in expiratory flow (FEV1) (this is the most notable finding). Additional findings include a less severe REDUCTION in forced vital capacity (FVC) and in the FEV1/FVC ratio (because the FEV1 is decreased more than the FVC) and an INCREASE in residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC).
A restrictive pattern is typically seen in obesity, kyphosis, fibrosing lung disease, and interstitial lung disease. The defining factor for restrictive lung disease is a decrease in Total Lung Capacity (TLC) on spirometry. This patient would be expected to have obstructive patterns on PFTs.
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