What Are Pulmonary Diseases?

Pulmonary diseases are pathological conditions affecting the lungs and respiratory tract, impairing the organs' ability to exchange oxygen and carbon dioxide between inhaled air and the bloodstream. The lung performs this gas exchange across an estimated 70 to 100 square meters of alveolar surface area, and diseases that disrupt the structure or function of this tissue have serious systemic consequences. Pulmonary diseases rank among the leading causes of death and disability worldwide: chronic obstructive pulmonary disease, asthma, lung cancer, pulmonary hypertension, idiopathic pulmonary fibrosis, and cystic fibrosis together affect more than 400 million people and account for approximately 3 million deaths annually, according to research summarized in bioengineering studies on lung disease from PMC.

The respiratory system depends on coordinated mechanical and biochemical processes. Air moves through the trachea and bronchi, branching progressively to bronchioles and finally to alveolar sacs where gas diffuses across thin epithelial membranes into pulmonary capillaries. Disease at any point in this pathway, whether in the large airways, small airways, lung parenchyma, pulmonary vasculature, or chest wall, produces distinct clinical syndromes that require different diagnostic and therapeutic approaches.

Types of Pulmonary Disease

Pulmonary diseases are categorized by the physiological pattern of impairment they produce. Obstructive diseases, including chronic obstructive pulmonary disease (COPD) and asthma, reduce airflow by narrowing or blocking the airways. COPD encompasses emphysema, in which alveolar walls are destroyed, and chronic bronchitis, in which airway inflammation persists. Restrictive diseases, such as idiopathic pulmonary fibrosis and pneumoconiosis, reduce the total lung volume that can be inhaled, typically because fibrotic scarring stiffens lung tissue.

Pulmonary vascular diseases affect the blood vessels within the lung. Pulmonary arterial hypertension involves abnormally elevated pressure in the pulmonary arteries, placing progressively greater strain on the right ventricle of the heart. Pulmonary embolism occurs when blood clots obstruct pulmonary arteries, acutely reducing gas exchange. Infectious pulmonary diseases include pneumonia, tuberculosis, and nontuberculous mycobacterial infections. Cystic fibrosis, a genetic disease affecting chloride channel function, leads to abnormally thick mucus that obstructs airways and promotes chronic infection.

Diagnosis and Assessment

Pulmonary function testing is the central diagnostic modality for characterizing the degree and pattern of impairment in pulmonary disease. Spirometry measures the forced expiratory volume in one second and the forced vital capacity, values that allow clinicians to distinguish obstructive from restrictive physiology. More detailed testing includes measurement of lung diffusing capacity for carbon monoxide, body plethysmography to measure total lung volume, and cardiopulmonary exercise testing to assess functional reserve under load.

Imaging plays a complementary role. Chest radiography provides a rapid first assessment; computed tomography offers detailed cross-sectional views of lung parenchyma, airways, and vasculature that are essential for diagnosing fibrosis, tumors, and emphysema. Bronchoscopy, a direct endoscopic examination of the airways, allows both visual inspection and tissue sampling. The NHLBI Critical Care Medicine and Pulmonary Branch at the NIH conducts research on lung disease diagnosis and pathogenesis, ranging from molecular mechanisms to population-level studies.

Treatment and Management

Treatment of pulmonary diseases depends heavily on the underlying pathophysiology. Obstructive diseases are managed with inhaled bronchodilators and corticosteroids; COPD also requires pulmonary rehabilitation programs that improve exercise capacity and quality of life. Pulmonary hypertension is treated with vasodilator medications targeting the endothelin, nitric oxide, and prostacyclin pathways. For end-stage disease, lung transplantation is the definitive intervention, though donor organ availability limits it to roughly 2,000 procedures annually in the United States.

Emerging approaches include bioengineered lung scaffolds, organ-on-a-chip models, and organoid cultures that replicate lung physiology in vitro. The American College of Physicians subspecialty description of pulmonary disease outlines the clinical training pathway for physicians specializing in the diagnosis and management of these conditions.

Applications

Research and technology related to pulmonary diseases have roles across a range of fields, including:

• Biomedical engineering development of ventilators, oxygen delivery systems, and lung-assist devices
• Pharmaceutical development of inhaled drug formulations and targeted pulmonary therapeutics
• Diagnostic imaging and signal processing for computed tomography lung analysis
• Tissue engineering research on decellularized scaffolds and bioreactors for lung repair