Pulmonary mechanics in normal infants and young children during first 5 years of life

Abstract

To characterize lung function in young children we measured lung compliance and pulmonary conductance in 40 normal infants and children ranging in age from the newborn period to 5 years. Inspiratory and expiratory flow was measured by a pneumotachograph, esophageal pressure through a water-filled feeding tube, and functional residual capacity (FRC) by a N2 washout technique. The esophageal pressure change per breath [(mean +/- SD) 7.3 +/- 1.4 cm H2O] and specific compliance (75 +/- 13 ml/cm H2O/L-FRC) did not change with growth. Specific conductance was high (0.60 L/s/cm H2O/L-FRC) in preterm infants, decreasing rapidly with initial growth but minimally beyond 10 kg of body weight, and stabilizing at 0.10 L/s/cm H2O/L-FRC. During the age period studied, compliance increased approximately x 25 whereas conductance only rose five-fold. The changes in compliance and conductance were well correlated to FRC, body weight, and length. These findings suggest that in the last trimester of pregnancy the airways are already well developed and postnatal lung growth occurs mainly by formation of new alveoli, leading to a proportional increase in FRC and lung compliance. Postnatally, conductance increases much more slowly than FRC, resulting in a rapid drop in specific conductance.

Infant Pulmonary Function in a Randomized Trial of Fetal Tracheal Occlusion for Severe Congenital Diaphragmatic Hernia

“…We corrected these measurements to the patients' weight to standardize the measurements for size. However, previous investigators have demonstrated that airway conductance does not have a linear relationship to size in healthy newborns, with the airways relatively more developed in small infants (44). Therefore, the greater PEF that we observed in the TO group may be secondary to prematurity rather than an effect of TO itself.…”

“…We did not perform lung volume measurements by gas dilution or lung morphologic examinations. However, the modest increases in Crs in this study could be secondary to increased fetal lung growth in the TO group (44). Although V E had a wide range, the values were in the normal range (47) and were highly associated with PaCO 2 (higher V E associated with lower PaCO 2 ), which was tightly controlled throughout the perioperative period.…”

“…Measurements were subsequently exported to a spreadsheet (Excel; Microsoft, Redmond, WA), where 8 -20 uniform, representative breaths (selected from tracings) were used for analysis. A summary measurement was obtained for the variables of interest from each study [respiratory system compliance (Crs), minute ventilation (V E ), and peak expiratory flow (PEF)] by calculating a mean value and then dividing by the patient's weight to normalize the measurements for body size (44).…”

Multiple-breath nitrogen washout techniques: including measurements with patients on ventilators

“…SIVAN and co-workers [4] have published data on six children with normal lungs at the (usual) 2-4 cmH 2 O PEEP chosen by clinicians in these circumstances. Two children were close to the predicted values of GERHARDT et al [61] (18-22 mL·kg -1 ; mean= 20.4 mL·kg -1 ) and the other four were 39-52% higher. They came back into the ''normal" range only when PEEP was removed.…”

Evaluation of predictors of weaning from mechanical ventilation in pediatric patients

“…The decision to normalize each patient's VT and dynamic compliance to their body weight was based on two factors: First, before any weight correction, the range of values obtained was much wider for both the modified RSB and modified CROP indices. As a result, it was difficult to identify a cutoff value that clearly differentiated between the successful and unsuccessful weaning groups (data not shown); Second, it is common practice to report the VT in cc/kg and clinical investigation 7 has shown that changes in dynamic compliance are highly correlated with the patient's body weight. It follows, therefore, that the VT and the dynamic compliance should be normalized for the patient's weight in kilograms.…”