Respiratory disease

Respiratory disease is an umbrella term for diseases of the lung, bronchial tubes, trachea and throat . These diseases range from mild and self-limited(coryza -or common cold) to being life-threatening,(bacterial pneumonia, or pulmonary embolism for example).

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.

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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 characterised 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 Tumour

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

Neoplastic respiratory tumours : 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.

Respiratory neoplasms include the following:

• Mesothelioma, a cancer originating on the mesothelium outside the lung.
• Small cell lung cancer
• Non-small cell lung cancer

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

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.