Respiratory disease

Respiratory diseases are pathological conditions that affect the organs and tissues used for gas exchange. In air-breathing animals, these diseases make it difficult to move oxygen into the body and remove carbon dioxide. The respiratory tract includes several vital structures. These include the trachea, the bronchi, and the smaller bronchioles. The process also involves the alveoli, which are tiny air sacs. Other parts include the pleurae, the pleural cavity, and the muscles and nerves used for breathing. The medical study of these conditions is known as pulmonology. Doctors who specialize in this field are called pulmonologists. They may also be called thoracic medicine specialists or respirologists.

Doctors often classify these diseases by how they affect the mechanics of breathing. One major category is obstructive lung disease. In these conditions, the airways become obstructed or narrowed. This obstruction limits the amount of air that can reach the alveoli. This often happens because of inflammation that constricts the bronchial tree. Common examples include asthma, chronic bronchitis, and chronic obstructive pulmonary disease, or COPD. Asthma is a common obstructive disease, though its definitive cause is not yet known. COPD is often caused by tobacco smoking. Other conditions like bronchiectasis can be caused by cystic fibrosis or severe infections. Doctors use pulmonary function tests, such as spirometry, to diagnose these issues. Management often involves avoiding triggers like dust mites or smoking. Patients may also use bronchodilators to open airways or corticosteroids to suppress inflammation.

Another category is restrictive lung disease. These diseases cause a loss of lung compliance, which means the lungs become stiff. This stiffness makes it difficult for the lungs to expand fully. Restrictive diseases are divided into intrinsic and extrinsic types. Intrinsic factors occur within the lung tissue itself. This might happen due to toxins or tissue death from inflammation. Extrinsic factors originate from outside the lungs. These can include neuromuscular dysfunction or irregular movements of the chest wall. An example of a restrictive condition is respiratory distress syndrome in infants.

Infections are a very common cause of respiratory issues. These are divided into upper and lower respiratory tract infections. The upper respiratory tract includes all structures from the mouth and nose to the glottis. Common upper infections include the common cold, sinusitis, and tonsillitis. Some infections are very serious. Epiglottitis is a bacterial infection of the larynx that causes swelling of the epiglottis. It can be life-threatening, with a mortality rate of 7% in adults and 1% in children. Croup is a viral infection of the vocal cords that causes a barking cough. In children aged 3 months to 5 years, croup may show a "steeple sign" on an X-ray. This sign indicates a narrowing of the trachea.

Lower respiratory tract infections affect the deeper parts of the lungs. Pneumonia is the most common lower infection. It is usually caused by bacteria, such as Streptococcus pneumoniae, in Western countries. However, viruses and fungi can also cause it. For example, COVID-19 and severe acute respiratory syndrome are viral causes. Tuberculosis is another important cause of pneumonia worldwide. Infections can lead to complications like a lung abscess. This is a round cavity caused by the infection. Poor oral care can even contribute to these infections. Bacteria from gum disease can travel through the airways into the lungs.

Tumors also represent a major respiratory health challenge. Malignant tumors, or cancers, are responsible for 15% of all cancer diagnoses. They also account for 30% of all cancer deaths. Most respiratory cancers are linked to smoking tobacco. There are several histological types, such as small cell lung cancer and non-small cell lung cancer. Other types include adenocarcinoma and squamous cell carcinoma. Some cancers, like pleural mesothelioma, are almost always caused by asbestos exposure. Because the entire cardiac output passes through the lungs, cancer often spreads there. This is called metastasis. Cancers from the breast, colon, or prostate can all metastasize to the lungs.

Finally, diseases can affect the pulmonary circulation or the pleural cavity. Pulmonary vascular diseases affect blood flow. A pulmonary embolism occurs when a blood clot travels through the heart and lodges in the lungs. Large emboli can cause sudden death. Another condition is pulmonary edema, where fluid leaks from capillaries into the alveoli. This is often due to congestive heart failure. In the pleural cavity, a pneumothorax can occur. This is a hole in the pleura that allows air to escape into the pleural cavity. This causes the lung to collapse like a deflated balloon. A tension pneumothorax is a severe version that can compress the heart and blood vessels.

Even newborns face unique respiratory challenges. Infant respiratory distress syndrome occurs in about 1% of births in the United States. This most often happens to premature infants. The risk is much higher for infants under 750g. This condition is caused by a lack of surfactant. Surfactant is a substance that helps the lungs stay open. Without enough surfactant, the lungs become atelectatic. This leads to a mismatch in how air and blood interact in the lungs.