Which factor increases as airway resistance rises during breathing?

Which factor increases as airway resistance rises during breathing?

• A. Tidal volume
• B. Work of breathing
• C. Heart rate
• D. Oxygen saturation

Answer: (B)

When airway resistance increases, the muscles have to generate a larger pressure difference to move the same amount of air. Air flow is driven by pressure and opposed by resistance, so to keep breathing effective you must do more work—the energy expended to inhale and exhale rises. That increased effort is the work of breathing. Tidal volume isn’t automatically increased by more resistance; it often stays the same or may decrease if fatigue sets in. Oxygen saturation depends on how well air reaches the alveoli and how efficiently gas exchange occurs, which isn’t a direct, immediate result of increased resistance. Heart rate may rise due to stress or hypoxia, but the primary, direct change with rising resistance is the higher work of breathing.

When airway resistance increases, the muscles have to generate a larger pressure difference to move the same amount of air. Air flow is driven by pressure and opposed by resistance, so to keep breathing effective you must do more work—the energy expended to inhale and exhale rises. That increased effort is the work of breathing.

Tidal volume isn’t automatically increased by more resistance; it often stays the same or may decrease if fatigue sets in. Oxygen saturation depends on how well air reaches the alveoli and how efficiently gas exchange occurs, which isn’t a direct, immediate result of increased resistance. Heart rate may rise due to stress or hypoxia, but the primary, direct change with rising resistance is the higher work of breathing.