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ABSTRACT. Functional residual capacity (FRC) was determined in 50 infantsMore recently the He-dilution method has been scaled down and perfected for the use in infants (2) and the classical N2 washout technique has been computerized to allow breath by breath analysis of NZ washed out (3, 4). We have developed a simpler, open circuit N2 washout technique suitable to measure FRC in small animals and neonates (5).FRC or TGV measurements have been reported most frequently in term neonates or infants with respiratory illness (6)(7)(8)(9)(10)(11)(12). Only a few of these studies include preterm infants (7, 1 1, 12), and none of them has been done with the N2 washout method.In the present study FRC measurements were performed in normal infants including preterm and term neonates and infants up to 5 yr of age using the open circuit N2 washout technique (5). MATERIALS AND METHODSin preterm and older infants using a NZ washout technique.Fifty healthy infants, free of any signs of pulmonary disease or (Pediatr Res 20: 668-671, 1986) upper respiratory infection were studied. Their weight ranged from 1.19 to 25.8 kg, and their age from 1 wk to 5 yr. Eighteen Abbreviations infants were studied during the newborn period (first 28 days FRC, functional residual capacity after birth). Their gestational age ranged from 32 wk to term, 14 TGV, thoracic gas volume infants were preterm. Gestational age was determined by Dubowitz examination, and added to postnatal age to obtain postconceptional age. None of the infants had a history of respiratory disease or a need for mechanical ventilation. All were breathing room air. The measurement of FRC is an important component when Newborn infants were studied without sedation while all older evaluating pulmonary function in neonates and infants. FRC infants were sedated with 50 mg/kg chloralhydrate PO. The study needs to be known as reference value when comparing compli-was done during sleep while infants rested in the supine position. ance and conductance of individuals with different size and its The procedure was well tolerated. There were no unsuccessful increase with age provides important information about lung attempts and arousal during the measurement occurred in only growth and development.one of 10 infants. Most of the lung volume determinations in neonates andThe details of the system used to measure FRC were described infants have been done by plethysmography measuring TGV previously (5). Briefly it consists of a blender connected to a rather than the FRC. This technique is difiicult to apply to sick source of oxygen and helium, providing a stable continuous flow or small preterm infants, requires complicated highly sensitive of any helium/oxygen mixture. The gas is warmed and humidiequipment, and bears a high risk of technical error. Airway fied and passed through a breathing circuit. The infants breathe closure at FRC as may occur in the newborn infant and uneven the gas from the circuit through a T tube. The gas leaving the distribution of pleural pressure may also lead to er...

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.

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