Respiratory disease

Overview
Respiratory disease is an umbrella term for diseases of the lung, pleural cavity, bronchial tubes, trachea, upper respiratory tract and of the nerves and muscles of breathing. Respiratory diseases range from mild and self-limiting such as the common cold to life-threatening such as bacterial pneumonia or pulmonary embolism.

Respiratory diseases can be classified as either obstructive (i.e. conditions which impede the rate of flow into and out of the lungs, for example asthma) or restrictive (i.e. conditions which cause a reduction in the functional volume of the lungs, for example pulmonary fibrosis).

Respiratory disease can be further classified as either upper or lower respiratory tract (most commonly used in the context of infectious respiratory disease), parenchymal and vascular lung diseases. They are a common and important cause of illness and death. In the US, people suffer 1 billion colds per year. One in seven people in the UK is affected by some form of chronic lung disease, most commonly chronic obstructive pulmonary disease and asthma.

Respiratory disease is responsible for over 10% of hospitalizations and over 16% of deaths in Canada. 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.

Chronic Obstructive Pulmonary Disease
Chronic Obstructive Pulmonary Diseases (COPD) are characterised by an increase in airway resistance, shown by a decrease in Peak Expiratory Flow Rate (PEFR; measured in spirometry) and Forced Expiratory Volume in 1 Second (FEV1). The Residual Volume, the volume of air left in the lungs following full expiration, is greatly increased in COPD, while the total lung volume (TLC)is normal, leading to the clinical sign of chest over-inflation in patients with severe disease. Many individuals with COPD present with "barrel chest" - a deformity of outward rib displacement due to chronic over-inflation of the lungs,also, in severe COPD, a flattening of the diaphragm can be seen on chest radiograph.

Examples of obstructive lung diseases include:


 * Emphysema
 * Acute & Chronic Bronchitis
 * Asthma
 * Bronchiectasis
 * Bronchiolitis

Restrictive Lung Disease
Restrictive Lung Diseases (RLD) are characterized by a loss of airway compliance, causing incomplete lung expansion (i.e. via increased lung 'stiffness'). This change manifests itself in a reduced Total Lung Capacity, Inspiratory Capacity and Vital Capacity.

In contrast to OPD, RLD values for Tidal Volume, Expiratory Reserve Volume, Functional Residual Capacity and Respiratory Volume are unchanged. The FEV1 for a patient with RLD will either be normal or slightly increased, and thus the FEV1/FVC ratio will also be normal or increased for a RLD patient.

Notable restrictive lung diseases include:
 * Fibrosis
 * Sarcoidosis
 * Pleural effusion
 * Hypersensitivity pneumonitis
 * Asbestosis
 * Pleurisy
 * Lung Cancer
 * Infant respiratory distress syndrome (IRDS)
 * Acute respiratory distress syndrome (ARDS)
 * Neurologic diseases affecting the ability of the body to alter respiration rate, including spinal cord injury
 * Mechanical diseases affecting pulmonary musculature, including myasthenia gravis
 * Severe acute respiratory syndrome (SARS)

Parenchymal Lung Disease
The basic functional units of the lung, the alveoli, are referred to as the lung parenchyma. Diseases such as COPD are characterised by destruction of the alveoli and are therefore referred to as parenchymal lung diseases.

Signs of parenchymal lung disease include, but are not limited to, hypoxemia (low oxygen in the blood), hypercapnoea (high carbon dioxide in the blood), and abnormal DLCO tests.

Chronic complications of parenchymal lung disease include reduced respiratory drive, right ventricular hypertrophy, and right heart failure (cor pulmonale).

As can be seen from the overlap in categories, parenchymal diseases can be either restrictive, obstructive or both.

Notable parenchymal diseases include:
 * COPD
 * Sarcoidosis
 * Pulmonary fibrosis
 * Emphysema

Vascular Lung Disease
Vascular lung disease refers to conditions which affect the pulmonary capillary vasculature. Alterations in the vasculature manifest in a general inability to exchange blood gases such as oxygen and carbon dioxide, in the vicinity of the vascular damage (other areas of the lung may be unaffected).

Signs of vascular lung disease include, but are not limited to, hypoxemia (low oxygen in the blood) and hypercapnoea (high carbon dioxide in the blood).

Chronic complications of vascular lung disease include reduced respiratory drive, right ventricular hypertrophy, and right heart failure (cor pulmonale).

Notable vascular lung diseases include:
 * Pulmonary oedema
 * Pulmonary embolism
 * Pulmonary hypertension

Infectious Respiratory Disease
Infectious Respiratory Diseases are, as the name suggests, typically caused by one of many infectious agents able to infect the mammalian respiratory system (for example the bacterium Streptococcus pneumoniae).

The clinical features and treatment options vary greatly between infectious lung disease sub-types as each type may be caused by a different infectious agent, with different pathogenesis and virulence. Features also vary between:


 * Upper respiratory tract infection, including strep throat and the common cold; and
 * Lower respiratory tract infection, including pneumonia and pulmonary tuberculosis

Respiratory Tumor
"Respiratory tumor" can refer to either neoplastic (cancerous) or non-neoplastic masses within the lungs or lung parenchyma.

Neoplastic respiratory tumors : Respiratory neoplasms are abnormal masses of tissue within the lungs or parenchyma whose cell of origin may or may not be lung tissue (many other neoplasms commonly metastasize to lung tissue). Respiratory neoplasms are most often malignant, although there are non-malignant neoplasms which can affect lung tissue.

Non-neoplastic respiratory tumors : Tuberculosis cysts, other non-neoplastic masses.

Following is another classification of respiratory tumors:

Malignant tumors
Malignant tumors, or cancers of the respiratory system, particularly lung cancers, are a major health problem responsible for 15% of all cancer diagnoses and 29% of all cancer deaths. The majority of respiratory system cancers are attributable to smoking tobacco.

The major types of respiratory system cancer are:
 * Small cell lung cancer
 * Non-small cell lung cancer
 * Adenocarcinoma
 * Squamous cell carcinoma
 * Large cell undifferentiated carcinoma
 * Other lung cancers (carcinoid, Kaposi sarcoma, melanoma)
 * Lymphoma
 * Head and neck cancer
 * Mesothelioma, usually caused by exposure to asbestos dust.

In addition, since many cancers spread via the bloodstream and the entire cardiac output passes through the lungs, it common for cancer metastases to occur the lung. Breast cancer may invade directly through local spread, and through lymph node metastases. After metastasis to the liver, colon cancer frequently metastasizes to the lung. Prostate cancer, germ cell cancer and renal cell carcinoma may also metastasize to the lung.

Treatment of respiratory system cancer depends on the type of cancer. Surgery (usually removal of part of the lung, a lobectomy or an entire lung, a pneumonectomy), chemotherapy and radiotherapy are all used. The chance of surviving lung cancer depends on the cancer stage at the time the cancer is diagnosed and is only about 14-17% overall. In the case of metastases to the lung, treatment can occasionally be curative but only in certain, rare circumstances.

Benign tumors
Benign tumours are relatively rare causes of respiratory disease. Examples of benign tumours are:
 * Pulmonary hamartoma
 * Congenital malformations such as pulmonary sequestration and congenital cystic adenomatoid malformation (CCAM).

Disorders of breathing mechanics
The brain co-ordinates breathing and sends messages via nerves to the muscles of respiration. The muscles produce the movements of breathing. Disorders of the brain’s control of breathing, the nerves or the muscles of respiration can affect the respiratory system. Common disorders of breathing mechanics are:
 * Obstructive sleep apnea
 * Central sleep apnea
 * Amyotrophic lateral sclerosis
 * Guillian-Barre syndrome
 * Myasthenia gravis

Obesity is often associated with sleep apnea and can cause either an obstructive or a restrictive pattern on spirometry. Obesity reduces the movement of the chest wall which can, in extreme cases, result in the obesity-hypoventilation syndrome, a cause of respiratory failure.

Pulmonary vascular diseases
Pulmonary vascular diseases are conditions that affect the pulmonary circulation. Examples of these conditions are:


 * Pulmonary embolism, a blood clot that forms in a vein, breaks free, travels through the heart and lodges in the lungs (thromboembolism). Large pulmonary emboli are fatal, causing sudden death. A number of other substances can also embolise to the lungs but they are much more rare: fat embolism (particularly after bony injury), amniotic fluid embolism (with complications of labour and delivery), air embolism (iatrogenic).
 * Pulmonary arterial hypertension, elevated pressure in the pulmonary arteries. It can be idiopathic or due to the effects of another disease, particularly COPD. This can lead to strain on the right side of the heart, a condition known as cor pulmonale.
 * Pulmonary edema, leakage of fluid from capillaries of the lung into the alveoli (or air spaces). It is usually due to congestive heart failure.
 * Pulmonary hemorrhage, inflammation and damage to capillaries in the lung resulting in blood leaking into the alveoli. This may cause blood to be coughed up. Pulmonary hemorrhage can be due to auto-immune disorders such as Wegener's Granulomatosis and Goodpasture's syndrome.

Pleural cavity diseases
Pleural cavity diseases include empyema and mesothelioma which are mentioned above.

A collection of fluid in the pleural cavity is known as a pleural effusion. This may be due to fluid shifting from the bloodstream into the pleural cavity due to conditions such as congestive heart failure and cirrhosis. It may also be due to inflammation of the pleura itself as can occur with infection, pulmonary embolus, tuberculosis, mesothelioma and other conditions.

A pneumothorax is a hole in the pleura covering the lung allowing air in the lung to escape into the pleural cavity. The affected lung “collapses” like a deflated balloon. A tension pneumothorax is a particularly severe form of this condition where the air in the pleural cavity cannot escape, so the pneumothorax keeps getting bigger until it compresses the heart and blood vessels, leading to a life threatening situation.

Other Respiratory diseases
There are many other disorders that affect the lung and respiratory system. Auto-immune disorders such as vasculitis,( Wegener's Granulomatosis, Goodpasture's syndrome, for example) attack the blood vessels in the lung, causing pulmonary hemorrhage. Disorders in swallowing,or gastric refluxing can cause aspiration pneumonia.

Symptoms
The symptoms of respiratory disease differ depending on the disease. Common symptoms are:
 * Shortness of breath or dyspnea which usually occurs with exercise and can interfere with daily activities. In severe cases, shortness of breath can occur while resting.
 * Cough with or without the production of sputum.
 * Coughing blood (haemoptysis).
 * Chest pain. This may or may not be pleuritic chest pain (that is pain that worsens with the movements of breathing).
 * Noisy breathing, either wheeze or stridor.
 * Somnolence.
 * Loss of appetite.
 * Weight loss.
 * Cyanosis, a bluish discoloration of the lips, tongue or fingers.

In some cases respiratory disease is diagnosed without symptoms in the investigation of another disease or through a routine check.

Diagnostic tests
Respiratory diseases may be investigated by performing one or more of the following tests
 * Chest x-ray
 * Pulmonary function test
 * Computed tomography
 * Culture of microorganisms from secretions such as sputum
 * Bronchoscopy
 * Biopsy of the lung or pleura
 * Ventilation - perfusion scan
 * Ultrasound scanning can be useful to detect fluid such as pleural effusion

Differential Diagnosis

 * Asthma
 * Bronchiolitis Obliterans Organizing Pneumonia (BOOP)
 * Chronic Bronchitis
 * Chronic Obstructive Pulmonary Disease
 * Emphysema
 * Interstitial lung disease
 * Obstructive lung disease
 * Oxygenation disorders
 * Pulmonary fibrosis
 * Restrictive lung disease
 * Sarcoidosis

Emphysema


Pulmonary tuberculosis


Bronchiectasis


Lung: Silicosis




Diffuse alveolar damage: Adult respiratory distress syndrome (ARDS)


Lung: Goodpasture syndrome


Lung: Hyaline membrane disease


Lung: Alveolar proteinosis


Lung: Blastomycosis


Lung: Aspergillosis




Lung: Adenocarcinoma


Lung: Squamous cell carcinoma


Lung & Bronchus: Cryptosporidium


Lung & Lymph node: Asthma


Haemophilus influenzae laryngitis
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Treatment
Treatment of respiratory disease depends on the particular disease being treated, the severity of disease and the patient. Lifestyle factors such as regular exercise and healthy nutrition are important in preventing and treating respiratory disease. Vaccination can prevent some respiratory diseases. In addition, the following treatments are often used for respiratory diseases:
 * Medication, often given in an inhaled form
 * Corticosteroids
 * Bronchodilators
 * Antibiotics
 * Anticoagulants
 * Cancer chemotherapy
 * Immune suppressants
 * Physiotherapy
 * Oxygen
 * Mechanical ventilation
 * Liquid ventilation (or Liquid breathing)
 * Surfactant Replacement Therapy
 * Radiotherapy
 * Surgery
 * Removal of a cancer e.g. lobectomy, pneumonectomy
 * Pleurodesis
 * Lung volume reduction surgery
 * Lung transplantation
 * Artificial lung