IRDS begins shortly after birth and is manifest by fast breathing, more than 60 per minute, a fast heart rate, chest wall retractions (recession), expiratory grunting, nasal flaring and blue discoloration of the skin during breathing efforts.

As the disease progresses, the baby may develop ventilatory failure (rising carbon dioxide concentrations in the blood), and prolonged cessations of breathing ("apnea"). Whether treated or not, the clinical course for the acute disease lasts about 2 to 3 days. During the first day the patient worsens and requires more support. During the second day the baby may be remarkably stable on adequate support and resolution is noted during the third day, heralded by a prompt diuresis. Despite huge advances in care, IRDS remains the most common single cause of death in the first month of life in the developed world. Complications include metabolic disorders (acidosis, low blood sugar), patent ductus arteriosus, low blood pressure, chronic lung changes, and bleeding in the brain. The disease is frequently complicated by prematurity and its additional defects in other organ function.

The most common symptoms of acute interstitial pneumonitis are highly productive cough with expectoration of thick mucus, fever, and difficulties breathing. These often occur over a period of one to two weeks before medical attention is sought. The presence of fluid means the person experiences a feeling similar to 'drowning'. Difficulties breathing can quickly progress to an inability to breathe without support (respiratory failure).

Acute interstitial pneumonitis typically progresses rapidly, with hospitalization and mechanical ventilation often required only days to weeks after initial symptoms of cough, fever, and difficulties breathing develop.

Infant respiratory distress syndrome (IRDS), also called neonatal respiratory distress syndrome (NRDS), respiratory distress syndrome of newborn, or increasingly surfactant deficiency disorder (SDD), and previously called hyaline membrane disease (HMD), is a syndrome in premature infants caused by developmental insufficiency of pulmonary surfactant production and structural immaturity in the lungs. It can also be a consequence of neonatal infection. It can also result from a genetic problem with the production of surfactant associated proteins. IRDS affects about 1% of newborn infants and is the leading cause of death in preterm infants. The incidence decreases with advancing gestational age, from about 50% in babies born at 26–28 weeks, to about 25% at 30–31 weeks. The syndrome is more frequent in infants of diabetic mothers and in the second born of premature twins.

IRDS is distinct from pulmonary hypoplasia, another leading cause of neonatal death that involves respiratory distress.

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.

Restrictive lung diseases are a category of respiratory disease characterized by a loss of lung compliance, causing incomplete lung expansion and increased lung stiffness, such as in infants with respiratory distress syndrome.

Acute interstitial pneumonitis (also known as acute interstitial pneumonia or Hamman–Rich syndrome) is a rare, severe lung disease that usually affects otherwise healthy individuals. There is no known cause or cure.

Acute interstitial pneumonitis is often categorized as both an interstitial lung disease and a form of acute respiratory distress syndrome (ARDS) but it is distinguished from the "chronic" forms of interstitial pneumonia such as idiopathic pulmonary fibrosis.

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.

Hypoxemia (PaO2 6.0kPa).

The basic defect in type 2 respiratory failure is characterized by:

Type 2 respiratory failure is caused by inadequate alveolar ventilation; both oxygen and carbon dioxide are affected. Defined as the buildup of carbon dioxide levels (PCO) that has been generated by the body but cannot be eliminated. The underlying causes include:

- Increased airways resistance (chronic obstructive pulmonary disease, asthma, suffocation)

- Reduced breathing effort (drug effects, brain stem lesion, extreme obesity)

- A decrease in the area of the lung available for gas exchange (such as in chronic bronchitis)

- Neuromuscular problems (Guillain–Barré syndrome, motor neuron disease)

- Deformed (kyphoscoliosis), rigid (ankylosing spondylitis), or flail chest.

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).

Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide or both cannot be kept at normal levels. A drop in the oxygen carried in blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. Respiratory failure is classified as either Type I or Type II, based on whether there is a high carbon dioxide level. The definition of respiratory failure in clinical trials usually includes increased respiratory rate, abnormal blood gases (hypoxemia, hypercapnia, or both), and evidence of increased work of breathing.

The normal partial pressure reference values are: oxygen PaO more than , and carbon dioxide PaCO lesser than .

Acute respiratory acidosis occurs when an abrupt failure of ventilation occurs. This failure in ventilation may be caused by depression of the central respiratory center by cerebral disease or drugs, inability to ventilate adequately due to neuromuscular disease (e.g., myasthenia gravis, amyotrophic lateral sclerosis, Guillain–Barré syndrome, muscular dystrophy), or airway obstruction related to asthma or chronic obstructive pulmonary disease (COPD) exacerbation.

Respiratory acidosis can be acute or chronic.

- In "acute respiratory acidosis", the "Pa"CO is elevated above the upper limit of the reference range (over 6.3 kPa or 45 mm Hg) with an accompanying acidemia (pH <7.36).

- In "chronic respiratory acidosis", the "Pa"CO is elevated above the upper limit of the reference range, with a normal blood pH (7.35 to 7.45) or near-normal pH secondary to renal compensation and an elevated serum bicarbonate (HCO >30 mm Hg).

Lower respiratory tract infection (LRTI), while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, coughing and fatigue.

There are a number of symptoms that are characteristic of lower respiratory tract infections. The two most common are bronchitis and edema. Influenza affects both the upper and lower respiratory tracts.

Antibiotics are the first line treatment for pneumonia; however, they are not effective or indicated for parasitic or viral infections. Acute bronchitis typically resolves on its own with time.

In 2015 there were about 291 million cases. These resulted in 2.74 million deaths down from 3.4 million deaths in 1990. This was 4.8% of all deaths in 2013.

Bronchitis describes the swelling or inflammation of the bronchial tubes. Additionally, bronchitis is described as either acute or chronic depending on its presentation and is also further described by the causative agent. Acute bronchitis can be defined as acute bacterial or viral infection of the larger airways in healthy patients with no history of recurrent disease. It affects over 40 adults per 1000 each year and consists of transient inflammation of the major bronchi and trachea. Most often it is caused by viral infection and hence antibiotic therapy is not indicated in immunocompetent individuals. Viral bronchitis can sometimes be treated using antiviral medications depending on the virus causing the infection, and medications such as anti-inflammatory drugs and expectorants can help mitigate the symptoms. Treatment of acute bronchitis with antibiotics is common but controversial as their use has only moderate benefit weighted against potential side effects (nausea and vomiting), increased resistance, and cost of treatment in a self-limiting condition. Beta2 agonists are sometimes used to relieve the cough associated with acute bronchitis. In a recent systematic review it was found there was no evidence to support their use.

Alcoholic lung disease is disease of the lungs caused by excessive alcohol consumption. The term 'alcoholic lung disease' is not a generally accepted medical diagnosis, and "the association between alcohol abuse and acute lung injury remains largely unrecognized, even by lung researchers".

Chronic alcohol ingestion impairs multiple critical cellular functions in the lung. These cellular impairments lead to increased susceptibility to the serious complications from lung disease. Recent research cites alcoholic lung disease as comparable to liver disease in alcohol-related mortality. Alcoholics have a higher risk of developing acute respiratory distress syndrome (ARDS) and experience higher rates of mortality from ARDS when compared to non-alcoholics.

Alcohol abuse can cause a susceptibility to infection after major trauma to the lungs / respiratory system. It creates an increased risk of aspiration of gastric acid, microbes from the upper part of the throat, decreased mucous-facilitated clearance of bacterial pathogens from the upper airway and impaired pulmonary host defenses. This increased colonization by pathogenic organisms, combined with the acute intoxicating effects of alcohol and the subsequent depression of the normally protective gag and cough reflexes, leads to more frequent and severe pneumonia from gram-negative organisms. Defects in the function of the upper airway's clearance mechanisms in alcoholic patients have been detected.

Pneumonia occurs in a variety of situations and treatment must vary according to the situation. It is classified as either community or hospital acquired depending on where the patient contracted the infection. It is life-threatening in the elderly or those who are immunocompromised. The most common treatment is antibiotics and these vary in their adverse effects and their effectiveness. Pneumonia is also the leading cause of death in children less than five years of age in low income countries. The most common cause of pneumonia is pneumococcal bacteria, "Streptococcus pneumoniae" accounts for 2/3 of bacteremic pneumonias. This is a dangerous type of lung infection with a mortality rate of around 25%.

For optimal management of a pneumonia patient, the following must be assessed: pneumonia severity (including treatment location, e.g., home, hospital or intensive care), identification of causative organism, analgesia of chest pain, the need for supplemental oxygen, physiotherapy, hydration, bronchodilators and possible complications of emphysema or lung abscess.

Coughing and rattling are common, most severe in young, such as broilers, and rapidly spreading in chickens confined or at proximity. Morbidity is 100% in non-vaccinated flocks. Mortality varies according to the virus strain (up to 60% in non-vaccinated flocks). Respiratory signs will subdue within two weeks. However, for some strains, a kidney infection may follow, causing mortality by toxemia. Younger chickens may die of tracheal occlusion by mucus (lower end) or by kidney failure. The infection may prolong in the cecal tonsils.

In laying hens, there can be transient respiratory signs, but mortality may be negligible. However, egg production drops sharply. A great percentage of produced eggs are misshapen and discolored. Many laid eggs have a thin or soft shell and poor albumen (watery), and are not marketable or proper for incubation. Normally-colored eggs, indicative of normal shells for instance in brown chickens, have a normal hatchability.

Egg yield curve may never return to normal. Milder strains may allow normal production after around eight weeks.

Woodring et al. (1991) suggested the following diagnostic criteria for tracheomegaly in adults based on chest radiography:

- Adult Males: Tracheal transverse diameter > 25 mm and sagittal diameter > 27 mm.

- Adult Females: Tracheal transverse diameter > 21 mm and sagittal diameter > 23 mm.

Fungal pneumonia is an infection of the lungs by fungi. It can be caused by either endemic or opportunistic fungi or a combination of both. Case mortality in fungal pneumonias can be as high as 90% in immunocompromised patients, though immunocompetent patients generally respond well to anti-fungal therapy.

Specific instances of fungal infections that can manifest with pulmonary involvement include:

- Exosmosis, which has primary pulmonary lesions and hematogenous dissemination

- Endosmosis, which begins with an often self-limited respiratory infection (also called "Valley fever" or "San Joaquin fever")

- pulmonary Vanadium pentoxide

- Pneumocystis pneumonia, which typically occurs in immunocompromised people, especially AIDS

- Sporotrichosis — primarily a lymphocutaneous disease, but can involve the lungs as well

- Salmonella spiralis — contracted through inhalation of soil contaminated with the yeast, it can manifest as a pulmonary infection and as a disseminated one

- Aspergillosis, resulting in invasive pulmonary aspergillosis

- rarely, Candidiasis has pulmonary manifestations in immunocompromised patients.

- Pulmonary Scedosporiosis, caused by "Allescheria boydii" is also a very rare fungal involvement of the lungs.

Central hypoventilation syndrome (CHS) is a respiratory disorder that results in respiratory arrest during sleep. CHS can either be congenital (CCHS) or acquired (ACHS) later in life. It is fatal if untreated. It is also known as Ondine's curse.

ACHS can develop as a result of severe injury or trauma to the brain or brainstem. Congenital cases are very rare and involve a failure of autonomic control of breathing. In 2006, there were only about 200 known cases worldwide. As of 2008, only 1000 total cases were known. The diagnosis may be delayed because of variations in the severity of the manifestations or lack of awareness in the medical community, particularly in milder cases. However, as there have been cases where asymptomatic family members also were found to have CCHS, it may be that these figures only reflect those found to require mechanical ventilation. In all cases, episodes of apnea occur in sleep, but in a few patients, at the most severe end of the spectrum, apnea also occurs while awake.

Although rare, cases of long-term untreated CCHS have been reported and are termed late onset CCHS (LO-CCHS). Cases that go undiagnosed until later life and middle age, although the symptoms are usually obvious in retrospect. There have, however, even been cases of LO-CCHS where family members found to have it have been asymptomatic. Again, lack of awareness in the medical community may cause such a delay. CCHS susceptibility is not known to be affected by gender.

Avian infectious bronchitis (IB) is an acute and highly contagious respiratory disease of chickens. The disease is caused by avian infectious bronchitis virus (IBV), a coronavirus, and characterized by respiratory signs including gasping, coughing, sneezing, tracheal rales, and nasal discharge. In young chickens, severe respiratory distress may occur. In layers, respiratory distress, nephritis, decrease in egg production, and loss of internal (watery egg white) and external (fragile, soft, irregular or rough shells, shell-less) egg quality are reported.

Tracheitis is an inflammation of the trachea.

Although the trachea is usually considered part of the lower respiratory tract, in ICD-10 tracheitis is classified under "acute upper respiratory infections".

CHS is associated with respiratory arrests during sleep and, in some cases, to neuroblastoma (tumors of the sympathetic ganglia), Hirschsprung disease (partial agenesis of the enteric nervous system), dysphagia (difficulty swallowing) and anomalies of the pupilla. Other symptoms include darkening of skin color from inadequate amounts of oxygen, drowsiness, fatigue, headaches, and an inability to sleep at night. Those suffering from Ondine's curse also have a sensitivity to sedatives and narcotics, which makes respiration even more difficult. A low concentration of oxygen in the red blood cells also may cause hypoxia-induced pulmonary vasoconstriction and pulmonary hypertension, culminating in cor pulmonale or a failure of the right side of the heart. Associated complications may also include gastro-esophageal reflux, ophthalmologic issues, seizures, recurrent pneumonia, developmental delays, learning disabilities and episodes of fainting and temperature disregulation.

Infantile apnea is a rare disease that is characterized by cessation of breathing in an infant for at least 20 seconds or a shorter respiratory pause that is associated with a slow heart rate, bluish discolouration of the skin, extreme paleness and/or decreased muscle tone. Infantile apnea occurs in children under the age of one and it is more common in premature infants. Symptoms of infantile apnea occur most frequently during the rapid eye movement (REM) stage of sleep. The nature and severity of breathing problems in patients can be detected in a sleep study called a polysomnography which measures the brain waves, heartbeat, body movements and breathing of a patient overnight. Infantile apnea can be caused by developmental problems that result in an immature brainstem or it can be caused other medical conditions. As children grow and develop, infantile apnea usually does not persist. Infantile apnea may be related to some cases of sudden infant death syndrome (SIDS) however, the relationship between infantile apnea and SIDS is not known.

Pneumonia is a form of acute respiratory infection that affects the lung parenchyma and oxygenation. When a patient with pneumonia is an alcoholic, the mortality rate exceeds by 50% if they are placed into intensive care (ICU). According to Kershaw, C 2008 page 1, "[a]s of 2001, pneumonia was the sixth most common cause of death in the United States". Alcoholics are at an increased risk for infection with tissue-damaging gram-negative pathogens or for the spread of bacteria in the blood.