Shortness of breath is often the symptom that most bothers people. It is commonly described as: "my breathing requires effort," "I feel out of breath," or "I can't get enough air in". Different terms, however, may be used in different cultures. Typically the shortness of breath is worse on exertion of a prolonged duration and worsens over time. In the advanced stages, or end stage pulmonary disease it occurs during rest and may be always present. It is a source of both anxiety and a poor quality of life in those with COPD. Many people with more advanced COPD breathe through pursed lips and this action can improve shortness of breath in some.

A chronic cough is often the first symptom to develop. When it persists for more than three months each year for at least two years, in combination with sputum production and without another explanation, it is by definition chronic bronchitis. This condition can occur before COPD fully develops. The amount of sputum produced can change over hours to days. In some cases, the cough may not be present or may only occur occasionally and may not be productive. Some people with COPD attribute the symptoms to a "smoker's cough". Sputum may be swallowed or spat out, depending often on social and cultural factors. Vigorous coughing may lead to rib fractures or a brief loss of consciousness. Those with COPD often have a history of "common colds" that last a long time.

Asthma is an obstructive lung disease where the bronchial tubes (airways) are extra sensitive (hyperresponsive). The airways become inflamed and produce excess mucus and the muscles around the airways tighten making the airways narrower. Asthma is usually triggered by breathing in things in the air such as dust or pollen that produce an allergic reaction. It may be triggered by other things such as an upper respiratory tract infection, cold air, exercise or smoke. Asthma is a common condition and affects over 300 million people around the world.

Asthma causes recurring episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning.

- Exercise-Induced Asthma — is common in asthmatics, especially after participation in outdoor activities in cold weather.

- Occupational Asthma — An estimated 2% to 5% of all asthma episodes may be caused by exposure to a specific sensitizing agent in the workplace.

- Nocturnal Asthma — is a characteristic problem in poorly controlled asthma and is reported by more than two thirds of sub-optimally treated patients.

A peak flow meter can record variations in the severity of asthma over time. Spirometry, a measurement of lung function, can provide an assessment of the severity, reversibility, and variability of airflow limitation, and help confirm the diagnosis of asthma.

Diagnosis of obstructive disease requires several factors depending on the exact disease being diagnosed. However one commonalty between them is an FEV1/FVC ratio less than 0.7, i.e. the inability to exhale 70% of their breath within one second.

Following is an overview of the main obstructive lung diseases. "Chronic obstructive pulmonary disease" is mainly a combination of chronic bronchitis and emphysema, but may be more or less overlapping with all conditions.

Bronchiolitis obliterans is a lung disease characterized by fixed airway obstruction. Inflammation and scarring occur in the airways of the lung, resulting in severe shortness of breath and dry cough.

FEV1 (forced expiratory volume in 1 second) should be above 80% of predicted values to be considered normal. Bronchiolitis obliterans reduces this to between 16% and 21%.

Symptoms include dry cough, shortness of breath and wheezing.

The symptoms can start gradually, or severe symptoms can occur suddenly.

The major signs of indium lung are pulmonary alveolar proteinosis and pulmonary fibrosis. Symptoms include dyspnea (shortness of breath), cough, and increased sputum production. Hemoptysis has also been seen in people with indium lung. Other symptoms seen in some but not all cases include digital clubbing, low DLCO (capacity to move oxygen from the alveoli into the blood), and lowered forced expiratory volume. Emphysema has been associated with indium lung, but may not be part of the syndrome.

Bronchiolitis obliterans (BO), informally known as popcorn lung, is a disease that results in obstruction of the smallest airways of the lungs (bronchioles) due to inflammation. Symptoms include a dry cough, shortness of breath, wheezing, and feeling tired. These symptoms generally get worse over weeks to months. It is not related to organizing pneumonia.

Causes include breathing in toxic fumes, respiratory infections, connective tissue disorder, or following a bone marrow or heart-lung transplant. Symptoms may not occur until two to eight weeks following toxic exposure or infection. The underlying mechanism involves inflammation that results in scar tissue formation. Diagnosis is by CT scan, pulmonary function tests, or lung biopsy. A chest X-ray is often normal.

While the disease is not reversible treatments can slow further worsening. This may include the use of corticosteroids or immunosuppressive medication. A lung transplant may be tried. Outcomes are often poor with most people dying in months to years.

Bronchiolitis obliterans is rare in the general population. It affects about 75% of people by ten years following a lung transplant and up to 10% of people who have received a bone marrow transplant from someone else. The condition was first clearly described in 1981. Prior descriptions occurred as early as 1956.

Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the nerves and muscles of breathing. Respiratory diseases range from mild and self-limiting, such as the common cold, to life-threatening entities like bacterial pneumonia, pulmonary embolism, acute asthma and lung cancer.

The study of respiratory disease is known as pulmonology. A doctor who specializes in respiratory disease is known as a pulmonologist, a chest medicine specialist, a respiratory medicine specialist, a respirologist or a thoracic medicine specialist.

Respiratory diseases can be classified in many different ways, including by the organ or tissue involved, by the type and pattern of associated signs and symptoms, or by the cause of the disease.

Chronic respiratory diseases (CRDs) are diseases of the airways and other structures of the lung. This disease could be characterized by a high inflammatory cells recruitment (neutrophil) and/or destructive cycle of infection, (e.g. mediated by "Pseudomonas aeruginosa"). Some of the most common are asthma, chronic obstructive pulmonary disease, or acute respiratory distress syndrome . CRDs are not curable, however, various forms of treatment that help dilate major air passages and improve shortness of breath can help control symptoms and increase the quality of life for people with the disease.

it usually lasts for three months to two years

Pulmonary interstitial emphysema is a concern in any of the following diagnosis:

- Prematurity

- Respiratory distress syndrome (RDS)

- Meconium aspiration syndrome (MAS)

- Amniotic fluid aspiration

- Sepsis, or other infections

- Mechanical ventilation

Pulmonary interstitial emphysema (PIE) is a collection of air outside of the normal air space of the pulmonary alveoli, found instead inside the connective tissue of the peribronchovascular sheaths, interlobular septa, and visceral pleura. (This supportive tissue is called the pulmonary interstitium.) This collection of air develops as a result of alveolar and terminal bronchiolar rupture. Pulmonary interstitial emphysema is more frequent in premature infants who require mechanical ventilation for severe lung disease. Infants suffering from pulmonary interstitial emphysema are typically recommended for admission to a neonatal intensive care unit.

Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs. Symptoms include coughing up mucus, wheezing, shortness of breath, and chest discomfort. Bronchitis is divided into two types: acute and chronic. Acute bronchitis is also known as a chest cold.

Acute bronchitis usually has a cough that lasts around three weeks. In more than 90% of cases the cause is a viral infection. These viruses may be spread through the air when people cough or by direct contact. Risk factors include exposure to tobacco smoke, dust, and other air pollution. A small number of cases are due to high levels of air pollution or bacteria such as "Mycoplasma pneumoniae" or "Bordetella pertussis". Treatment of acute bronchitis typically involves rest, paracetamol (acetaminophen), and NSAIDs to help with the fever.

Chronic bronchitis is defined as a productive cough that lasts for three months or more per year for at least two years. Most people with chronic bronchitis have chronic obstructive pulmonary disease (COPD). Tobacco smoking is the most common cause, with a number of other factors such as air pollution and genetics playing a smaller role. Treatments include quitting smoking, vaccinations, rehabilitation, and often inhaled bronchodilators and steroids. Some people may benefit from long-term oxygen therapy or lung transplantation.

Acute bronchitis is one of the most common diseases. About 5% of adults are affected and about 6% of children have at least one episode a year. In 2010, COPD affects 329 million people or nearly 5% of the global population. In 2013, it resulted in 2.9 million deaths, a change from 2.4 million deaths in 1990.

Acute bronchitis, also known as a chest cold, is short term inflammation of the bronchi of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortness of breath, fever, and chest discomfort. The infection may last from a few to ten days. The cough may persist for several weeks afterwards with the total duration of symptoms usually around three weeks. Some have symptoms for up to six weeks.

Indium lung is a rare occupational lung disease caused by exposure to respirable indium in the form of indium tin oxide. It is classified as an interstitial lung disease (diffuse parenchymal lung disease).

Signs and symptoms of spontaneous subcutaneous emphysema vary based on the cause, but it is often associated with swelling of the neck and chest pain, and may also involve sore throat, neck pain, difficulty swallowing, wheezing and difficulty breathing. Chest X-rays may show air in the mediastinum, the middle of the chest cavity. A significant case of subcutaneous emphysema is easy to detect by touching the overlying skin; it feels like tissue paper or Rice Krispies. Touching the bubbles causes them to move and sometimes make a crackling noise. The air bubbles, which are painless and feel like small nodules to the touch, may burst when the skin above them is palpated. The tissues surrounding SCE are usually swollen. When large amounts of air leak into the tissues, the face can swell considerably. In cases of subcutaneous emphysema around the neck, there may be a feeling of fullness in the neck, and the sound of the voice may change. If SCE is particularly extreme around the neck and chest, the swelling can interfere with breathing. The air can travel to many parts of the body, including the abdomen and limbs, because there are no separations in the fatty tissue in the skin to prevent the air from moving.

According to the International Labour Office (ILO), PMF requires the presence of large opacity exceeding 1 cm (by x-ray). By pathology standards, the lesion in histologic section must exceed 2 cm to meet the definition of PMF. In PMF, lesions most commonly occupy the upper lung zone, and are usually bilateral. The development of PMF is usually associated with a restrictive ventilatory defect on pulmonary function testing. PMF can be mistaken for bronchogenic carcinoma and vice versa. PMF lesions tend to grow very slowly, so any rapid changes in size, or development of cavitation, should prompt a search for either alternative cause or secondary disease.

Patients with subacute HP gradually develop a productive cough, dyspnea, fatigue, anorexia, weight loss, and pleurisy. Symptoms are similar to the acute form of the disease, but are less severe and last longer. On chest radiographs, micronodular or reticular opacities are most prominent in mid-to-lower lung zones. Findings may be present in patients who have experienced repeated acute attacks.

The subacute, or intermittent, form produces more well-formed noncaseating granulomas, bronchiolitis with or without organizing pneumonia, and interstitial fibrosis.

Subcutaneous emphysema is when gas or air is in the layer under the skin. "Subcutaneous" refers to the tissue beneath the skin, and "emphysema" refers to trapped air. It is sometimes abbreviated SCE or SE and also called tissue emphysema, or Sub Q air. Since the air generally comes from the chest cavity, subcutaneous emphysema usually occurs on the chest, neck and face, where it is able to travel from the chest cavity along the fascia. Subcutaneous emphysema has a characteristic crackling feel to the touch, a sensation that has been described as similar to touching Rice Krispies; this sensation of air under the skin is known as "subcutaneous crepitation".

Numerous etiologies of subcutaneous emphysema have been described. Pneumomediastinum was first recognized as a medical entity by Laennec, who reported it as a consequence of trauma in 1819. Later, in 1939, at The Johns Hopkins Hospital, Dr. Louis Hamman described it in postpartum woman; indeed, subcutaneous emphysema is sometimes known as Hamman's syndrome. However, in some medical circles, it can instead be more commonly known as Macklin's Syndrome after L. Macklin, in 1939, and M.T. and C.C. Macklin, in 1944, who cumulatively went on to describe the pathophysiology in more detail.

Subcutaneous emphysema can result from puncture of parts of the respiratory or gastrointestinal systems. Particularly in the chest and neck, air may become trapped as a result of penetrating trauma (e.g., gunshot wounds or stab wounds) or blunt trauma. Infection (e.g., gas gangrene) can cause gas to be trapped in the subcutaneous tissues. Subcutaneous emphysema can be caused by medical procedures and medical conditions that cause the pressure in the alveoli of the lung to be higher than that in the tissues outside of them. Its most common causes are pneumothorax and a chest tube that has become occluded by a blood clot or fibrinous material. It can also occur spontaneously due to rupture of the alveoli with dramatic presentation. When the condition is caused by surgery it is called "surgical emphysema". The term "spontaneous subcutaneous emphysema" is used when the cause is not clear.

Subcutaneous emphysema is not typically dangerous in and of itself, however it can be a symptom of very dangerous underlying conditions, such as pneumothorax. Although the underlying conditions require treatment, subcutaneous emphysema usually does not; small amounts of air are reabsorbed by the body. However, subcutaneous emphysema can be uncomfortable and may interfere with breathing, and is often treated by removing air from the tissues, for example by using large bore needles, skin incisions or subcutaneous catheterization.

Occupational lung diseases are occupational diseases affecting the respiratory system, including occupational asthma, black lung disease (coalworker's pneumoconiosis), chronic obstructive pulmonary disease (COPD), mesothelioma, and silicosis. Infectious lung diseases can also be acquired in an occupational context. Exposure to substances like flock and silica can cause fibrosing lung disease, whereas exposure to carcinogens like asbestos and beryllium can cause lung cancer. Occupational cases of interstitial lung disease may be misdiagnosed as COPD, idiopathic pulmonary fibrosis, or a myriad of other diseases; leading to a delay in identification of the causative agent.

The main symptom is usually severe central chest pain. Other symptoms include laboured breathing, voice distortion (as with helium) and subcutaneous emphysema, specifically affecting the face, neck, and chest. Pneumomediastinum can also be characterized by the shortness of breath that is typical of a respiratory system problem. It is often recognized on auscultation by a "crunching" sound timed with the cardiac cycle (Hamman's crunch).

Pnemomediastinum may also present with symptoms mimicking cardiac tamponade as a result of the increased intrapulmonary pressure on venous flow to the heart.

The symptoms of pulmonary hypertension include the following:

Less common signs/symptoms include non-productive cough and exercise-induced nausea and vomiting. Coughing up of blood may occur in some patients, particularly those with specific subtypes of pulmonary hypertension such as heritable pulmonary arterial hypertension, Eisenmenger syndrome and chronic thromboembolic pulmonary hypertension. Pulmonary venous hypertension typically presents with shortness of breath while lying flat or sleeping (orthopnea or paroxysmal nocturnal dyspnea), while pulmonary arterial hypertension (PAH) typically does not.

Other typical signs of pulmonary hypertension include an accentuated pulmonary component of the second heart sound, a right ventricular third heart sound, and parasternal heave indicating a hypertrophied right atrium. Signs of systemic congestion resulting from right-sided heart failure include jugular venous distension, ascites, and hepatojugular reflux. Evidence of tricuspid insufficiency and pulmonic regurgitation is also sought and, if present, is consistent with the presence of pulmonary hypertension.

Pulmonary embolism classically presents with an acute onset of shortness of breath. Other presenting symptoms include pleuritic chest pain, cough, hemoptysis, and fever. Risk factors include deep vein thrombosis, recent surgery, cancer, and previous thromboembolism. It must always be considered in those with acute onset of shortness of breath owing to its high risk of mortality. Diagnosis however may be difficult and Wells Score is often used to assess the clinical probability. Treatment, depending on severity of symptoms typically start with anticoagulants, presence of ominous signs (low blood pressure), may warrant the use of thrombolytic drugs.

The symptoms of pneumonia are fever, productive cough, shortness of breath, and pleuritic chest pain. Inspiratory crackles may be heard on exam. A chest x-ray can be useful to differentiate pneumonia from congestive heart failure. As the cause is usually a bacterial infection, antibiotics are typically used for treatment.

Severity and prognosis of pneumonia can be estimated from CURB65, where C=Confusion, U= Uremia (>7), R=Respiratory rate >30, B= BP65.

In the acute form of HP, symptoms may develop 4–6 hours following heavy exposure to the provoking antigen. Symptoms include fever, chills, malaise, cough, chest tightness, dyspnea, rash, swelling and headache. Symptoms resolve within 12 hours to several days upon cessation of exposure.

Acute HP is characterized by poorly formed noncaseating interstitial granulomas and mononuclear cell infiltration in a peribronchial distribution with prominent giant cells.

On chest radiographs, a diffuse micronodular interstitial pattern (at times with ground-glass density in the lower and middle lung zones) may be observed. Findings are normal in approximately 10% of patients." In high-resolution CT scans, ground-glass opacities or diffusely increased radiodensities are present. Pulmonary function tests show reduced diffusion capacity of lungs for carbon monoxide (DLCO). Many patients have hypoxemia at rest, and all patients desaturate with exercise. Extrinsic allergic alveolitis may eventually lead to Interstitial lung disease.

Progressive Massive Fibrosis (PMF), characterized by the development of large conglomerate masses of dense fibrosis (usually in the upper lung zones), can complicate silicosis and coal worker's pneumoconiosis. Conglomerate masses may also occur in other pneumoconioses, such as talcosis, berylliosis (CBD), kaolin pneumoconiosis, and pneumoconiosis from carbon compounds, such as carbon black, graphite, and oil shale. Conglomerate masses can also develop in sarcoidosis, but usually near the hilae and with surrounding paracitricial emphysema.

The disease arises firstly through the deposition of silica or coal dust (or other dust) within the lung, and then through the body's immunological reactions to the dust.