Asthma/COPD – Causes, Symptoms, Treatments

What are Asthma and COPD? 

Asthma is a chronic respiratory condition characterized by inflammation and narrowing of the airways, which makes breathing difficult. It is a common condition that affects people of all ages, from children to the elderly. 

The prevalence of asthma varies across different regions and populations. According to the World Health Organization (WHO), as of recent statistics, estimates suggest over 262 million people globally had asthma in 2019, with millions more likely undiagnosed. In the US alone, over 25 million people, including more than 5 million children, are currently diagnosed with asthma.

Chronic obstructive pulmonary disease (COPD) on the other hand is an umbrella term for progressive lung diseases that obstruct airflow from the lungs. This includes emphysema; a condition that involves damage to the air sacs in the lungs, which are responsible for gas exchange. Damaged air sacs become less elastic and lose their ability to efficiently transfer oxygen into the bloodstream and remove carbon dioxide. 

Another condition included under COPD is chronic bronchitis. This is a long-term inflammation of the airways in the lungs. The inflamed airways produce excess mucus (phlegm), which can narrow the airways and make breathing difficult.

Symptoms of Asthma and COPD

While both asthma and COPD cause difficulty breathing, their symptoms differ in their characteristics and progression. 

Asthma

In the case of Asthma, wheezing occurs due to narrowed airways in the lungs. When you breathe, air struggles to pass through the constricted airways, causing a whistling sound. Wheezing can be high-pitched or low-pitched, and it may occur during inhalation (breathing in) or exhalation (breathing out). In asthma, wheezing is often worse at night or early morning, during exercise, or after exposure to triggers.

Asthmatic coughs, another prominent symptom, can vary depending on the severity of the condition. It’s often a dry, hacking cough that worsens at night or after exercise. This cough is the body’s attempt to clear mucus and irritants from the airways.

One of the characteristic symptoms of asthma is shortness of breath (dyspnea). This is a feeling of not being able to get enough air. In asthma, shortness of breath can come on suddenly and may be triggered by allergens, exercise, or emotional stress. It can be a scary experience, but proper treatment can help manage it.

Chest tightness is reported to feel like a band is squeezing your chest, making it difficult to breathe deeply. It can be a very uncomfortable sensation and often accompanies wheezing and shortness of breath during an asthma attack.

A key characteristic of asthma is that symptoms tend to fluctuate. You might experience long periods without any symptoms (remission) followed by flare-ups (exacerbations) triggered by specific factors. Triggers can be allergens (dust mites, pollen, pet dander), irritants (smoke, air pollution), respiratory infections, or even strong emotions.

COPD

The most prominent symptom of COPD is shortness of breath (dyspnea) and progressively worsens over time. It’s initially noticeable during physical activity, but as the disease progresses, it can occur even at rest. People with COPD often describe a constant feeling of air hunger.

Chronic cough is a persistent cough that produces mucus (phlegm), and is a hallmark symptom, particularly in chronic bronchitis, a subtype of COPD. This cough is often worse in the morning and can loosen mucus that has accumulated in the airways overnight.

While less common than in asthma, COPD can also cause wheezing, especially in later stages when airflow becomes significantly obstructed. The wheezing sound may be constant or intermittent. A feeling of tightness or constriction in the chest is another common symptom of COPD. It can be a constant sensation or worsen with activity.

People with COPD often experience fatigue and shortness of breath that significantly limits their ability to exercise or engage in physical activities. Even simple tasks like climbing stairs can become difficult.

Additional Points:

• Progression of symptoms: A crucial distinction between asthma and COPD is the progression of symptoms. Asthma symptoms tend to be variable, while COPD symptoms characteristically worsen steadily over time.
• Mucus production: Persistent cough with phlegm production is more indicative of COPD, whereas asthma typically presents with a dry cough.
• Nighttime symptoms: While both conditions can disrupt sleep, asthma symptoms often worsen at night, whereas COPD can cause daytime sleepiness due to labored breathing.

Causes and Triggers of Asthma and COPD

Asthma

Asthma is a complex condition influenced by various factors, and its exact cause is not fully understood. However, several common triggers and risk factors are associated with the development and exacerbation of asthma symptoms.

Asthma tends to run in families, suggesting a genetic predisposition to the condition. Specific genetic variations may increase the likelihood of developing asthma or contribute to its severity. Allergic asthma on the other hand is triggered by exposure to allergens such as pollen, dust mites, pet dander, mold spores, and cockroach droppings. When individuals with allergic asthma come into contact with these allergens, their immune system reacts, leading to airway inflammation and asthma symptoms.

Viral respiratory infections, particularly during childhood, can exacerbate asthma symptoms and increase the risk of developing asthma in susceptible individuals. Common viruses associated with asthma exacerbations include rhinovirus, respiratory syncytial virus (RSV), and influenza virus.

Exposure to environmental pollutants and irritants can trigger asthma symptoms or exacerbate existing asthma. Some individuals may develop asthma or experience worsening symptoms due to exposure to workplace irritants or allergens. This condition, known as occupational asthma, can be caused by various substances encountered in certain occupations. These may include tobacco smoke, air pollution (such as vehicle emissions and industrial pollutants), strong odors, chemical fumes, dust, animal dander and indoor pollutants (e.g., from cooking or cleaning products). 

Emotional stress and strong emotions, such as anxiety and laughter, can sometimes trigger asthma symptoms or exacerbate existing asthma. While the exact mechanisms are not fully understood, stress may influence the immune system and airway function, contributing to asthma symptoms. Certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), beta-blockers, and some pain relievers, can trigger asthma symptoms or worsen existing asthma in susceptible individuals. 

Other factors that may contribute to asthma include obesity, gastroesophageal reflux disease (GERD), hormonal changes (such as during pregnancy), and exposure to secondhand smoke during early childhood. Cold, dry air can also irritate the airways and trigger asthma symptoms in some individuals. Additionally, changes in weather, such as temperature fluctuations, humidity levels, and thunderstorms, have been associated with asthma exacerbations.

COPD

• Cigarette smoking is by far the leading cause of COPD. The harmful chemicals in cigarette smoke damage the delicate structures of the lungs over time, leading to emphysema and chronic bronchitis.

Other Contributing Factors:

While smoking is the main culprit, other factors can contribute to the development of COPD, especially when combined with smoking:

• Long-term exposure to air pollution: Exposure to air pollution from traffic fumes, industrial emissions, or even secondhand smoke can irritate the airways and accelerate lung damage. This can be a significant risk factor for people who live in highly polluted areas or work in environments with air contaminants.
• Occupational exposures: Certain occupations that involve long-term inhalation of dusts, fumes, and chemicals can increase the risk of COPD. 
• Genetics: In rare cases, genetics can play a role in the development of COPD. A specific genetic condition called alpha-1 antitrypsin deficiency can cause COPD at a younger age. Alpha-1 antitrypsin deficiency (AATD) is a genetic disorder that can affect the lungs and liver. It results in a shortage of a protein called alpha-1 antitrypsin (AAT), which plays a critical role in protecting the lungs from damage. However, it’s important to note that genetics alone rarely cause COPD; it usually occurs in combination with other risk factors, especially smoking.

Understanding How Smoking Causes COPD:

Cigarette smoke contains thousands of harmful chemicals that irritate and damage the lungs. Here’s how smoking contributes to the development of the two main COPD conditions:

• Emphysema: The chemicals in cigarette smoke damage the air sacs (alveoli) in the lungs. These air sacs are responsible for gas exchange, where oxygen from inhaled air enters the bloodstream and carbon dioxide is removed from the blood to be exhaled. Over time, the damaged air sacs lose their elasticity and rupture, reducing the surface area available for gas exchange. This makes it difficult to breathe.
• Chronic Bronchitis: Smoking irritates the lining of the airways (bronchi) in the lungs, causing them to become inflamed and produce excess mucus (phlegm). This chronic inflammation narrows the airways, further obstructing airflow and making breathing difficult.

Long Term Complications of Asthma and COPD

Asthma

Fortunately, with proper treatment and management, most people with asthma can lead active and fulfilling lives. However, uncontrolled or poorly managed asthma can lead to long-term complications.

One complication is airway remodeling. This is a process where chronic inflammation in the airways leads to permanent structural changes. The airways become thickened, scarred, and narrowed, making it even harder to breathe. This can happen due to repeated asthma attacks or ongoing inflammation, even if symptoms aren’t severe.

Over time, uncontrolled asthma can damage the lungs, leading to reduced lung function. This means the lungs become less efficient at absorbing oxygen and releasing carbon dioxide. People with asthma are more susceptible to respiratory infections like pneumonia and bronchitis. This is because the inflamed airways are more vulnerable to viruses and bacteria.

Asthma symptoms like coughing, wheezing, and shortness of breath can significantly disrupt sleep. This can lead to daytime fatigue, impacting daily activities and overall well-being.

In children, uncontrolled asthma can affect growth and development. Poor sleep and difficulty breathing can hinder the production of growth hormone, leading to stunted growth.

The chronic nature of asthma and the limitations it can impose can sometimes lead to anxiety and depression. Severe asthma attacks can also require emergency medical attention and hospitalization.

COPD

Chronic obstructive pulmonary disease (COPD) has a progressive nature, meaning it worsens over time. This ongoing decline in lung function can lead to various long-term complications that significantly impact a person’s health and quality of life. 

Shortness of breath, the hallmark symptom of COPD, steadily worsens over time. Even simple activities like walking or climbing stairs can become increasingly difficult. This can lead to social isolation and decreased physical activity, further impacting overall health.

COPD flare-ups, also known as exacerbations, are episodes where symptoms worsen significantly. These can be triggered by respiratory infections, air pollution, or other factors. In severe cases, exacerbations may require hospitalization and intensive treatment with oxygen therapy or even mechanical ventilation. Frequent exacerbations can accelerate lung function decline and worsen the overall prognosis.

People with COPD also have weakened respiratory defenses, making them more susceptible to respiratory infections like pneumonia and bronchitis. These infections can further damage the lungs and exacerbate COPD symptoms.

The heart has to work harder to pump blood through narrowed airways in COPD. This strain can lead to cor pulmonale, a condition where the right side of the heart weakens and enlarges due to high blood pressure in the lungs. Other potential heart complications include arrhythmias (irregular heartbeats) and heart failure.

COPD makes breathing difficult during physical activity, leading to reduced physical activity levels and muscle wasting. Additionally, breathing difficulties can increase energy expenditure, making it challenging to maintain a healthy weight. Muscle weakness and weight loss can further limit mobility and decrease quality of life. An increased risk of osteoporosis, a condition that weakens bones and makes them more prone to fractures, is another complication of COPD. This is partly due to decreased physical activity and inflammation associated with COPD.

Similar to asthma, sleep disturbances are common in COPD. Shortness of breath, coughing, and difficulty getting enough oxygen can significantly disrupt sleep patterns, leading to daytime fatigue and impacting overall well-being. The chronic nature of COPD, its limitations on daily activities, and the constant struggle to breathe can contribute to anxiety and depression. Severe COPD can significantly increase the risk of death, particularly from respiratory failure or complications arising from heart problems.

How are COPD and Asthma diagnosed?

Asthma

Diagnosing asthma often involves a multi-step approach, as there’s no single definitive test. Doctors typically rely on a combination of factors, including your medical history, a physical examination, and various lung function tests, to arrive at an accurate diagnosis.

Your doctor will likely begin by asking you detailed questions about your symptoms, such as:

• When did you first experience symptoms like wheezing, coughing, shortness of breath, or chest tightness?
• How often do you experience these symptoms?
• What seems to worsen your symptoms (e.g., exercise, allergens, cold air)?
• Do you have any allergies or a family history of asthma or allergies?
• Do you smoke or have exposure to secondhand smoke?

This information helps the doctor understand the nature of your symptoms, their frequency, and potential triggers. They may also conduct these physical tests: 

1. Physical Examination:
   • The doctor will listen to your chest using a stethoscope. In some cases of asthma, wheezing or other abnormal breath sounds may be detectable during an asthma attack or even when your breathing seems normal.
   • Your doctor may also check your nose and sinuses for signs of allergies or infections that could be contributing to your symptoms.
2. Lung Function Tests:
   • These tests measure how well your lungs are working and can help assess airflow obstruction, a hallmark of asthma. Here are some common lung function tests used for asthma diagnosis:
     • Spirometry: This is the most common and informative test. It involves blowing maximally into a mouthpiece connected to a machine called a spirometer. The spirometer measures the amount and speed of air you can forcefully exhale after taking a deep breath. People with asthma often have lower than normal airflow rates.
       • Sometimes, a bronchodilator medication may be given before a repeat spirometry test. If your lung function improves significantly after taking the medication, it suggests that reversible airway obstruction is present, which is characteristic of asthma.
     • Peak flow monitoring: This test uses a handheld device called a peak flow meter to measure the maximum speed at which you can forcefully exhale. You may be asked to take peak flow readings at home several times a day over a period of time. Monitoring peak flow variations can help identify asthma patterns and track treatment effectiveness.
3. Allergy Testing (Optional):
   • While not essential for diagnosing asthma, allergy testing can be helpful in identifying specific allergens that may be triggering your symptoms. This can be done through skin prick tests or blood tests.
   • Knowing your triggers can help you develop strategies to avoid them and potentially reduce asthma flare-ups.

Additional Considerations:

• Age: Diagnosing asthma in young children can be challenging, as lung function tests may not be reliable until around age 5. Doctors may rely more heavily on symptoms and parental observations in these cases.
• Other Conditions: Some other medical conditions can mimic asthma symptoms. Your doctor may order additional tests to rule out other possibilities before diagnosing asthma.

COPD

Your doctor will start by gathering information about your symptoms, risk factors, and overall health. Here are some questions they might ask:

• Symptoms: When did you first experience shortness of breath, coughing (especially with mucus), wheezing, or chest tightness? How often do these symptoms occur, and are they worse with exertion?
• Smoking history: Smoking is the leading cause of COPD. The doctor will inquire about your smoking history, including the number of years smoked, the amount you smoked daily, and if you’ve quit.
• Occupational exposures: Long-term exposure to air pollution, dust, or chemicals at work can contribute to COPD. The doctor will ask about your current and past occupations.
• Family history: While less common, genetics can play a role in some cases of COPD, particularly alpha-1 antitrypsin deficiency. Knowing your family history can be helpful.

Some physical tests they might have you do include: 

1. Physical Examination:
   • The doctor will perform a physical examination, focusing on your lungs. They will listen to your chest with a stethoscope to detect any abnormal breath sounds like wheezing. They may also check your fingers and nails for signs of clubbing, which can sometimes occur in advanced COPD.
2. Lung Function Tests:
   • These tests are the cornerstone of COPD diagnosis, as they measure how well your lungs are working and identify airflow obstruction. Here are the key tests used:
   • Spirometry: This is the most important test. You’ll forcefully exhale into a mouthpiece connected to a spirometer, which measures the amount and speed of air you can expel. In COPD, airflow is typically reduced, particularly during forced exhalation.
   • Sometimes, a bronchodilator medication might be administered before a repeat spirometry test. If your lung function improves significantly after taking the medication, it suggests reversible airway obstruction, which is not characteristic of COPD. However, some people with COPD may still show improvement with bronchodilators.
3. Chest X-Ray (Optional):
   • While not definitive for COPD diagnosis, a chest X-ray can provide additional information about your lungs. It can help identify other conditions that might mimic COPD symptoms, such as pneumonia, heart failure, or lung cancer.
4. Alpha-1 Antitrypsin Deficiency Testing (Optional):
   • In rare cases, a blood test may be done to check for alpha-1 antitrypsin deficiency, a genetic condition that can contribute to COPD development at a younger age. This test is usually only considered if you have a strong family history of COPD or if your symptoms started earlier than usual.

How are Asthma and COPD treated?

Asthma

There is no cure for asthma, but there are effective treatments that can help control symptoms and allow you to live a normal, active life. Here’s a breakdown of the different approaches used in asthma management:

1. Identifying and Avoiding Triggers:
   • The first line of defense is to identify and avoid your asthma triggers whenever possible. Common triggers include:
     • Allergens: Dust mites, pet dander, pollen, mold spores, and cockroaches are frequent culprits.
     • Irritants: Smoke (cigarette smoke, secondhand smoke, air pollution), strong chemical fumes, and cold, dry air can irritate airways and trigger symptoms.
     • Respiratory infections: The common cold, flu, and other respiratory illnesses can worsen asthma symptoms.
     • Medications: Certain medications like aspirin and beta-blockers (except those specifically designed for asthma) can trigger asthma symptoms in some people.
     • Exercise-induced bronchoconstriction (EIB): Physical activity can trigger symptoms, especially in cold, dry air.
     • Emotional stress: Strong emotions like anxiety or anger can worsen symptoms in some people.
   • By working with your doctor, you can develop strategies to minimize exposure to your triggers and reduce the frequency of asthma attacks.
2. Medications:
   • There are two main categories of medications used to control asthma:
     • Controller medications which are taken daily, even when you don’t have symptoms. These include: 
       • Inhaled corticosteroids (ICS), Long-acting bronchodilators (LABAs) and Leukotriene modifiers. 
       • Reliever medications are quick-relief medications used to treat sudden asthma symptoms during an attack. The most common type of reliever medication is a short-acting bronchodilator, usually delivered through an MDI.
3. Proper Inhaler Technique:
   • Getting the most out of your asthma medications relies heavily on proper inhaler technique. Here are some key points:
     • Use the specific inhaler device prescribed by your doctor and follow the instructions carefully.
     • Coordinate inhaling with actuation to ensure medication reaches your airways effectively.
     • Rinse your mouth with water after using an inhaler to minimize medication buildup in your mouth and throat.
   • Your doctor or pharmacist can demonstrate the proper technique for your specific inhaler and answer any questions you may have.
4. Monitoring and Action Plans:
   • Symptom monitoring: Keeping a track of your asthma symptoms, including their frequency and severity, can help you and your doctor assess your asthma control and adjust your treatment plan if needed.
   • Peak flow monitoring: In some cases, your doctor may recommend using a peak flow meter to measure your peak expiratory flow (PEF), which is the maximum speed at which you can forcefully exhale. Regular PEF monitoring can help identify early signs of worsening asthma and prompt adjustments in your medication regimen.
   • Asthma action plan: Developing an asthma action plan with your doctor is crucial for managing your condition effectively. This plan outlines how to manage your asthma on a daily basis, including proper medication use, and specific steps to take during an asthma attack.
5. Additional Management Strategies:
   • Allergy shots (immunotherapy): If allergies are a significant trigger for your asthma, allergy shots may be an option. These injections gradually expose you to increasing amounts of allergens, aiming to build up your tolerance and reduce allergy symptoms, including those that worsen asthma.
   • Pulmonary rehabilitation: These programs combine exercise training, education, and support to help manage symptoms, improve exercise tolerance, and maintain daily activities.
   • Maintaining a healthy weight: Obesity can worsen asthma symptoms. Losing weight can improve lung function and overall health in people with asthma.

COPD

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease with no cure. However, there are effective treatment strategies that can help manage symptoms, slow disease progression, and improve quality of life for people with COPD. Here’s a breakdown of the key approaches used in COPD management:

1. Smoking Cessation:
   • The single most important step in managing COPD is quitting smoking. Smoking is the leading cause of COPD, and continued smoking significantly accelerates lung damage and worsens symptoms. Quitting smoking helps slow disease progression, improve lung function, and reduce the risk of complications like heart disease and lung cancer.
2. Medications:
   • Several medications can help manage COPD symptoms and improve breathing difficulties. These typically include Bronchodilators, Inhaled corticosteroids (ICS) and Mucolytics.
3. Pulmonary Rehabilitation:
   • Pulmonary rehabilitation programs play a crucial role in COPD management. These programs typically include:
     • Exercise training: Supervised exercise training helps improve lung function, increase exercise tolerance, and reduce shortness of breath during daily activities.
     • Education: Educational sessions provide patients with information about COPD, its management, medication use, and breathing techniques.
     • Nutritional counseling: Maintaining a healthy weight can improve overall health and well-being in people with COPD. A nutritionist can provide guidance on proper nutrition to support lung health.
     • Psychological support: Living with a chronic illness like COPD can be challenging. These programs may offer psychological support to help patients cope with the emotional aspects of the condition.
4. Oxygen Therapy:
   • In severe COPD cases where blood oxygen levels are consistently low, supplemental oxygen therapy may be necessary. Oxygen is delivered through nasal cannulas or masks to increase the amount of oxygen reaching the bloodstream and improve symptoms like shortness of breath and fatigue.
5. Vaccination:
   • Staying up-to-date on vaccinations for influenza and pneumonia is crucial for people with COPD.  Respiratory infections can worsen COPD symptoms and lead to complications. Vaccinations help protect against these illnesses and reduce the risk of hospitalization.
6. Surgical Interventions (In rare cases):
   • In some rare and severe cases of COPD, surgery may be an option. Two potential procedures are:
     • Lung volume reduction surgery (LVRS): This surgery removes a small portion of diseased lung tissue to improve lung elasticity and breathing capacity. It’s typically considered for patients with a specific type of emphysema (upper-lobe predominant).
     • Lung transplant: In very severe cases where other treatment options have failed, a lung transplant may be a lifesaving option. However, due to the scarcity of donor lungs and the complexity of the procedure, lung transplants are only offered to a select group of patients who meet specific criteria.
7. Lifestyle Modifications:
   • Avoiding secondhand smoke and air pollution: Exposure to these irritants can further worsen COPD symptoms. It’s essential to avoid secondhand smoke exposure and minimize time spent outdoors when air quality is poor.
   • Managing stress: Stress can worsen COPD symptoms for some people. Finding healthy ways to manage stress, such as relaxation techniques or exercise, can be beneficial.

What medications are most often prescribed for Asthma and COPD?

Asthma

There are two main categories of medications used to treat asthma:

1. Controller medications:  These are taken daily, even when you don’t have symptoms, to prevent inflammation and airway narrowing. Inhaled corticosteroids (ICS) are the most effective controller medications, ICS reduce airway inflammation, the underlying cause of asthma symptoms. They come in various forms, including metered-dose inhalers (MDIs) and dry powder inhalers (DPIs).
   • Long-acting bronchodilators (LABAs): These medications relax the muscles around the airways, allowing them to stay open and improve airflow. They are often combined with ICS in a single inhaler for better adherence.
   • Leukotriene modifiers:  These medications work by blocking the action of leukotrienes, inflammatory chemicals released by the body during an asthma attack. They may be an option for people who cannot tolerate ICS or who have exercise-induced asthma.
2. Reliever medications: These quick-relief medications are used to treat sudden asthma symptoms during an attack. They act rapidly to relax the airways and ease breathing difficulties. The most common type of reliever medication is a short-acting bronchodilator, usually delivered through an MDI.

COPD

In COPD (chronic obstructive pulmonary disease), medications are primarily aimed at managing symptoms and slowing disease progression. There isn’t a cure, but several medication classes can significantly improve quality of life for people with COPD. Here’s a breakdown of the most commonly prescribed medications for COPD:

1. Bronchodilators:
   • Bronchodilators are the mainstay of COPD treatment. They work by relaxing the muscles surrounding the airways, allowing them to stay open and improve airflow. This helps reduce shortness of breath, a hallmark symptom of COPD.
     • Short-acting bronchodilators (SABAs):  These medications provide quick relief for sudden breathing difficulties and are typically used with a metered-dose inhaler (MDI) or nebulizer. Examples include albuterol (ProAir, Ventolin HFA) and levalbuterol (Xopenex HFA).
     • Long-acting bronchodilators (LABAs): These medications provide sustained relief for a longer duration (usually 12 hours or more) and are often the preferred option for long-term COPD management. They come in various forms, including inhalers and nebulizer solutions. Common LABAs include:
       • Beta2-agonists: Salmeterol (Serevent) and formoterol (Foradil, Perforomist) are some examples.
       • Anticholinergics: Tiotropium (Spiriva) is a long-acting medication that works by blocking a different mechanism compared to beta2-agonists.
     • Combination inhalers:  Many COPD medications combine a LABA with an inhaled corticosteroid (ICS) in a single inhaler for better adherence and improved control. Examples include budesonide/formoterol (Symbicort) and fluticasone/salmeterol (Advair).
2. Inhaled Corticosteroids (ICS):
   • While not as effective in COPD as in asthma, ICS can help reduce airway inflammation in some people with COPD, particularly those with a significant eosinophilic component (a type of white blood cell). ICS are typically used in combination with LABAs in a single inhaler. Examples include budesonide (Pulmicort), fluticasone (Flovent), and beclomethasone (Qvar).
3. Mucolytics:
   • These medications help thin and loosen mucus secretions in the airways, making them easier to cough up and improving airflow. Mucolytics are particularly beneficial for people with COPD who experience chronic mucus production (chronic bronchitis). A common example is N-acetylcysteine (Mucomyst).