Distribution of ventilation in normal children

Measurements of closing volume and the distribution of ventilation by both single-breath (SBN ₂) and multiple-breath nitrogen washout methods were obtained in 376 healthy boys and girls, ages 6 to 18 yr. A closing volume could be demonstrated in 39% of the subjects, and closing volume expressed as percentage of vital capacity did not change with height. Closing capacity expressed as percentage of total lung capacity showed a slight decrease with height. The slope of phase III of the SBN ₂ curve decreased with height. Single compartment N ₂ washout curves were observed in 72% of the subjects, and the incidence of single compartment curves increased with age. In those subjects with two compartment N ₂ washout curves, the relative compartmental ventilation became more even with increasing height. Our observations suggest that parallel units among peripheral airways grow at different rates.