Pulmonary Gas Exchange and Common Lung Diseases

Pulmonary Gas Exchange Physiology

Gaseous diffusion: Gas exchange is performed in the alveoli across the alveolar–capillary membrane. Oxygen moves from the air inside the alveoli into the pulmonary capillary blood across this membrane; carbon dioxide moves in the opposite direction. This diffusion occurs while oxygenates blood flows through the pulmonary capillaries and air fills the alveolar spaces.

Transport of Gases

Gases exchanged in the circulation are transported either bound to hemoglobin or dissolved in plasma in small quantities. Hemoglobin binding accounts for the majority of oxygen transport in blood.

Cellular Respiration

Oxygen passes from the capillaries into the cells, and carbon dioxide passes from the cells into the capillaries, driven by partial pressure differences of the gases.

Pulmonary Pathology

Pneumonia

Pneumonia is the inflammatory or infective process affecting the lungs caused by a variety of germs, commonly pneumococcus. Symptoms include respiratory disturbance, cough, expectoration, dyspnea and fever, often with general malaise. If treated, the lesion may heal without leaving tissue damage. Pneumonia is an infectious pathology.

Restrictive Pathologies

Restrictive pathologies are conditions that reduce the physical space inside the lungs or limit thoracic expansion and ventilatory capacity; therefore they decrease gas exchange. Examples mentioned include asthma and pulmonary emphysema.

Asthma

Asthma usually courses with bronchoconstriction (bronchospasm) provoked by multiple causes, especially allergic factors. It presents with:

• Dyspnea
• Presence of rhonchi
• Wheezing

Emphysema

Emphysema is a pathology in which lung tissue is destroyed and air becomes trapped in the lungs, thereby reducing their effective capacity. It is commonly related to tobacco consumption.

Chronic Obstructive Pulmonary Disease (COPD)

COPD (EPOC in Spanish: enfermedad pulmonar obstructiva crónica) is a chronic obstructive process that impairs airflow and thus prevents the normal movement of inspired and expired air. Clinically it presents with cough, expectoration, and, depending on severity, abnormalities in gas exchange.

Tuberculosis

Tuberculosis is an infectious disease caused by the bacillus of Koch, Mycobacterium tuberculosis, affecting the lungs, bronchi and pleura. It can affect the general population, although some groups are at higher risk. Transmission is typically by respiratory droplets in the air. The clinical picture often includes cough; it is treated with specific antituberculous therapy and may present with hemoptysis when established.

Lung Tumors and Prognosis

Lung tumors are a leading cause of cancer-related death, especially among men. There are several histological types; the most frequent anatomopathologic type is carcinoma. Prognosis is often poor, and five-year survival remains low for many patients.