Moment Ratio Analysis of Multiple Breath Nitrogen Washout in Infants with Lung Disease

Measurement of lung volumes at end expiratory level and assessment of ventilation inhomogeneity is important for respiratory management in infants with lung disease. This study compared multiple breath nitrogen washout was compared with body plethysmography to measure functional residual capacity in infants and assessed ventilation inhomogeneity using mean dilution numbers and alveolar based gas dilution numbers. Measurements were performed in 23 infants with lung disorders, eleven had wheezing bronchitis, four bronchopulmonary disease, and eight cystic fibrosis. Mean age was 11.2+/-5.8 months. Functional residual capacity of nitrogen washout (29.8+/-11.4 mL x kg(-1)) was significantly (p<0.05) lower than the plethysmographically measured functional residual capacity (40.3+/-11.4 mL x kg(-1)). Tidal volumes before nitrogen washout (90.4+/-35.1 mL) were significantly larger than at the end of the washout (72.2+/-26.9 mL). Alveolar based gas dilution numbers (6.7+/-2.3) were significantly lower (p<0.001) than mean dilution numbers (10+/-5.7). Functional residual capacity determination by nitrogen washout and plethysmography in infants with lung disease showed evidence of air trapping and ventilation inhomogeneity. Ventilation inhomogeneities are best described by alveolar based dilution numbers, since rebreathing of 100% oxygen changes ventilation pattern.