PSIO 532 Study Guide - Midterm Guide: Bronchiole, Pulmonary Vein, Circulatory System
PSL – Respiratory Physiology
Airway Velocity
• On the picture above (right), the cross-section area of the airway increases as the airway
generation increase
• Not much cross-sectional area in the conducting zone (0-16th airway generation);
however, due to the branching of the of tracheobronchial tree, you get an exponential
increase of cross-sectional area after 16th generation
• Note the rapid increase in total cross-sectional area of the airways in the respiratory
zone (approximately 70 m2)
• At the top of the tracheobronchial tree, the diameter is very large and that diameter
decreases as you go down the generations
• Area is low at the top of the tracheobronchial tree and high area at the bottom → this
results in a higher velocity at the top of the tracheobronchial tree and lower velocity at
the bottom
• Due to the high velocity, we get turbulent flow at the top and laminar flow (slow
velocity) at the bottom
• Resistance tends to be higher at the top and lower at the bottom; the resistance is lower
at the bottom because of the large cross-sectional area at the bottom
• Forward velocity of gas during inspiration is very slow in the respiratory zone and
diffusion is the chief mode of ventilation
• Airflow in the respiratory zone is laminar; this is important because it is due to the lower
velocity
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