FEV is decreased during an asthma attack.

I: Lobar bronchus- The lobar (secondary) bronchi branch from the primary bronchi, with one serving each lobe of the lung—three on the right and two on the left. They are supported by cartilage and lined with ciliated epithelium, distributing inhaled air to specific lobes and aiding in filtration and mucus clearance.

K: Left oblique fissure- The left oblique fissure is a deep groove that separates the left lung’s superior and inferior lobes. It provides structural division for the lung lobes, helping compartmentalize airflow and facilitating independent expansion and contraction of each lobe during respiration.

B: Horizontal fissure- The horizontal (minor) fissure is found only in the right lung and separates the superior and middle lobes. Like the oblique fissure, it helps define lung lobes anatomically, directing airflow appropriately and allowing for efficient ventilation and surgical orientation.

A. Diameter of the bronchioles: Airway resistance is most directly influenced by the radius of the airways, particularly the bronchioles. According to Poiseuille’s law, small changes in airway diameter result in exponential changes in resistance, making bronchiole constriction or dilation a primary determinant of airflow in the respiratory system.

B. Volume of alveolar fluid: While excessive alveolar fluid, as seen in pulmonary edema, can interfere with gas exchange, it has minimal direct impact on airway resistance. Resistance is determined by the path through which air flows, rather than the fluid volume within the alveoli themselves.

C. Thoracic wall elasticity: Thoracic wall elasticity affects lung compliance and the ease of lung expansion but does not directly regulate the resistance within the airways. Stiffness of the thoracic cage influences the work of breathing but is not the primary factor controlling airflow resistance.

D. Pulmonary surfactant levels: Surfactant reduces alveolar surface tension, preventing collapse and facilitating ventilation, but it has only an indirect effect on airway resistance. The main influence on resistance remains the bronchiole diameter rather than surfactant concentration.