Which pulmonary function parameter represents the average flow during the middle half of expiration and is more sensitive to airway obstruction than FEV1?

Which pulmonary function parameter represents the average flow during the middle half of expiration and is more sensitive to airway obstruction than FEV1?

• A. FEV1
• B. FEF25-75%
• C. PEFR
• D. DLCO

Answer: (B)

The key idea is that mid-expiratory flow reflects how quickly air moves through the smaller airways during the middle portion of a forced breath. FEF25-75% represents the average flow between about 25% and 75% of the vital capacity, so it taps into the flow available when the larger, more central airways have already released air but before the end of expiration. In obstructive disease, these smaller airways tend to narrow early, causing a drop in this middle-flow value even when the overall FEV1 is still relatively preserved. That makes FEF25-75% more sensitive to early or mild airway obstruction than FEV1. The other measures don’t fit this specific role: FEV1 is the maximal flow in the first second and reflects overall obstruction but isn’t as sensitive to early small-airway changes; peak expiratory flow is the highest initial flow and is highly effort-dependent and more influenced by large airways; DLCO gauges gas transfer across the lung membrane, not airway flow.

The key idea is that mid-expiratory flow reflects how quickly air moves through the smaller airways during the middle portion of a forced breath. FEF25-75% represents the average flow between about 25% and 75% of the vital capacity, so it taps into the flow available when the larger, more central airways have already released air but before the end of expiration. In obstructive disease, these smaller airways tend to narrow early, causing a drop in this middle-flow value even when the overall FEV1 is still relatively preserved. That makes FEF25-75% more sensitive to early or mild airway obstruction than FEV1.

The other measures don’t fit this specific role: FEV1 is the maximal flow in the first second and reflects overall obstruction but isn’t as sensitive to early small-airway changes; peak expiratory flow is the highest initial flow and is highly effort-dependent and more influenced by large airways; DLCO gauges gas transfer across the lung membrane, not airway flow.